Preparatory Guide on Biochemistry, Molecular Biology, Physiology, Microbiology, Immunology, Pharmacology & Drug Discovery

Medical Microbiology: Enteric Bacteria MCQ

October 09, 2018
Multiple Choice Question on Enteric Bacteria (E. coli, Salmonella spp and Shigella spp)


1) Intestines of human and other mammals are the natural habitat of enteric organisms, a large family of bacteria is present as a normal flora, which of the following is not the normal flora of intestine?
a) Escherichia spp
b) Salmonella spp
c) Staphylococcus spp
d) Proteus spp

2) Some enteric bacteria are part of normal inhabitants and incidentally cause disease but others such as.........are regularly pathogenic for humans.
a) Pseudomonas spp
b) Streptococcus spp
c) Salmonella spp
d) Proteus spp

3) All are the general characteristics of enteric bacteria, EXCEPT?
a) Catalase positive
b) Non-spore forming
c) Grow in media with bile salts
d) Nitrate negative

4) Enteric bacteria are mainly classified based on their ability to ferment various sugars including lactose. Which of the following bacteria is a non-lactose fermenter?
a) Klebsiella spp
b) Salmonella spp
c) Enterobacter spp
d) Citrobacter spp

5) Escherichia coli is one of the major enteric bacteria that causes diarrhea and is characterized according to its virulence properties. All are the types of E. coli, EXCEPT?
a) Enterohemorrhagic E. coli
b) Enteropathogenic E. coli
c) Enterotoxigenic E. coli
d) Enterolysogenic E. coli

6) After the bacteria is ingested, enteropathogenic E. coli (EPEC) attaches to the mucosal cells of the small intestine which results in malabsorption and diarrhea, mostly infecting infants in developing countries. Symptoms include watery diarrhea, vomiting, non-bloody stools which lasts for short duration mostly 1-3 days. What are the two important factors of pathogenesis?
a) The chromosomal locus of enterocyte effacement (LEE)
b) The bundle-forming pilus encoded by a plasmid adherence factor (EAF)
c) Both of the above
d) None of the above

7) Enteroinvasive E. coli (EIEC) are nonmotile, non-lactose or late lactose fermenters which are predominantly found in developing countries infecting children and travelers. Which of the following infection is similar to EIEC infection?
a) Bacillary dysentery
b) Shigellosis
c) Traveler’s diarrhea
d) Enteric fever

8) Enterobacteriaceae expresses a variety of virulent antigens, all of the following are the antigens, EXCEPT?
a) O antigen
b) K and Vi antigen
c) H antigen
d) D antigen

9) E. coli is one of the most common enteric bacteria in urinary tract infection (UTI) followed by Proteus mirabilis. All of the followings are the characteristic feature Proteus mirabilis, EXCEPT?
a) Facultative aerobes
b) Urease positive
c) Motile
d) Citrate positive

10) Shigellosis is caused by Shigella dysenteriae in humans causing fever, abdominal cramps, diarrhea sometimes with blood. The infection is attributed to the …........ activity of Shiga toxin which increases the severity by tissue invasion of the large intestine.
a) Exotoxic
b) Enterotoxic
c) Cytotoxic
d) Neurotoxic

11) Enterotoxigenic E. coli (ETEC) produces two major types of toxins, heat labile (LT) and heat stable (ST) toxins. LT or cholera-like toxin activates adenylate cyclase (cAMP) whereas ST activates.............causing Travelers’ diarrhea.
a) Ribosomal dysfunction
b) Decarboxylase reaction
c) Guanylate cyclase
d) Fermentation of sugars

12) Which of the following is a rapid lactose fermenter, motile enteric bacteria and is the major cause of a broad range of hospital-acquired infections such as pneumonia, urinary tract infections, and wound and device infections?
a) Streptococcus pyogenes
b) Pseudomonas aeruginosa
c) Mycobacterium tuberculosis
d) Enterobacter aerogenes

13) Salmonella typhi enter the human body through oral route penetrating into the intestine and reaching the lymphatics and the bloodstream ultimately causing the infection "Typhoid".Which of the following are most correct examples of the region of infection caused by the S. typhi?
a) Mononuclear phagocytic cells in the liver and Peyer’s patches of the small intestine
b) Liver, spleen, lymph nodes and large intestine
c) Isolated follicles and Peyer’s patches of a large intestine
d) None of the above

14) Which type of salmonellae is primarily infectious for humans?
a) Salmonella typhi A
b) Salmonella paratyphi A, B, and C
c) Salmonella paratyphi A and B
d) Salmonella paratyphi A
15) The symptoms of typhoid fever develop in one to three weeks after exposure to S. typhi, all of the given below are the major symptoms, EXCEPT?
a) Weight gain
b) Headache
c) High-grade fever
d) Rashes

16) Which of the following Shigella spp produces a heat labile exotoxin that affects both the gut and central nervous system resulting in diarrhea and meningismus?
a) Shigella sonnie
b) Shigella dysenteriae type 1
c) Shigella dysenteriae type 2
d) Shigella dysenteriae type 3

17) S. enteritidis and S. typhimurium causes enterocolitis and gastroenteritis in humans. What is the most common food for the transmission of this infection?
a) Raw meat
b) Eggs
c) Canned beans
d) Yogurt

18) The biochemical test used to identify and determine the ability of a bacteria to convert tryptophan into indole is?
a) IMViC test
b) MRVP test
c) TSI test
d) Citrate test

19) Which one is not the selective culture media for salmonellae and shigellae?
a) Deoxycholate citrate agar
b) Xylose-lysine decarboxylase agar
c) Salmonella –shigella agar
d) Blood agar

20) The Widal test is used for the detection of Salmonella typhi and other subspecies. This test is based on the principle where?
a) the antigens are detected using the neutralization assay
b) the antigen combines with its soluble antibody and form a lattice and develops a visible precipitate
c) the antigens bind to RBCs and form the agglutination
d) None of the above
Multiple Choice Answers
1)-c,
2)-c,
3)-d,
4)-b,
5)-d,
6)-c,
7)-b,
8)-d,
9)-a,
10)-b
11)-c,
12)-d,
13)-a,
14)-c,
15)-a,
16)-b,
17)-b,
18)-a,
19)-d,
20)-b

Medical Microbiology: Enteric Bacteria MCQ Medical Microbiology: Enteric Bacteria MCQ Reviewed by Biotechnology on October 09, 2018 Rating: 5

Medical Microbiology: Gram Positive Rods MCQs

September 26, 2018
Multiple Choice Questions on Gram Positive Rods

1) All are general characteristics of Bacilli, except
a) Anaerobes
b) Gram-positive
c) Spore-forming
d) Ubiquitous

2) Which one of the following Bacillus spp is NOT a medically important pathogenic bacteria?
a) Bacillus cereus
b) Bacillus thuringiensis
c) Bacillus thermophilus
d) Bacillus anthracis

3) Bacillus.............is commonly found in soil and is an insect pathogen which can infect humans also. This organism is often used as pest control in insecticidal products.
a) thuringiensis
b) subtilis
c) anthracis
d) cereus
4) Most of the species of Bacilli and Clostridia are.............., which means they obtain their nutrients from dead or organic matter.
a) Parasites
b) Saprophytes
c) Symbiotic
d) Mutualistic

5) Bacillus anthracis is a principle pathogen of a disease known as "anthrax" which primarily infects animals like goats and cattle and is transmitted to humans through ingestion or inhalation of spores. What are the two important virulence factors of this organism?
a) Capsule and enterotoxins
b) Exotoxins and enterotoxins
c) Endotoxins and capsule
d) Capsule and exotoxins

6) Bacillus cereus causes two types of foodborne intoxications, known as the emetic type and diarrheal type. What is the incubation period for the onset of symptoms ingestion in the emetic type of food intoxication?
a) 1-12 hours
b) 1-2 days
c) 1-5 hours
d) 1-24 hours

7) Bacillus….......is a common laboratory contaminant and is used as sterility testing. It is an endospore-forming bacteria and resistant to an extreme environmental condition.
a) subtilis
b) thermophilus
c) cereus
d) agalactiae

8) Which of the following species of Clostridia do not have flagella, but rapidly grows on nutrient media and mimics the growth of motile organisms?
a) Clostridium botulinum
b) Clostridium perfringens
c) Clostridium tetani
d) Clostridium difficile

9) All of the following is the type of infections caused by Clostridium perfringens, EXCEPT?
a) Gas gangrene
b) Food poisoning
c) Cellulitis
d) None of the above

10) The AVA BioThrax is the FDA approved vaccines for
a) Bacillus cereus
b) Clostridium tetani
c) Bacillus anthrax
d) Bacillus substilis

11) The shape and position of spores vary in different types of species and is useful in identification of Clostridia. Clostridium perfringens forms subterminal spores whereas Clostridium....... forms terminal spores.
a) tetani
b) botulinum
c) cereus
d) sordellii

12) The bacterial spore of..............can invade human body through a puncture wound and ultimately enter the central nervous system by releasing a potent toxin known as neurotoxins, thus blocking the release of neurotransmitters and resulting in cramping of muscles, causing loc jaw and other muscle related spasms.
a) Bacillus anthracis
b) Clostridium botulinum
c) Clostridium tetani
d) Bacillus subtilis

13) Which is the most common food associated with infant botulism?
a) Maple syrup
b) Honey
c) Canned baby food
d) Corn syrup

14) All of the given species of Clostridia produces botulinum toxins, except
a) Clostridium botulinum
b) Clostridium butyricum
c) Clostridium baratii
d) Clostridium difficile
15) The toxin responsible for food poisoning by Bacillus cereus is
a) Cytotoxins
b) Neurotoxins
c) Enterotoxins
d) None of the above

16) All of the statements given below for Bacillus anthracis are true, EXCEPT
a) Hemolytic colonies on Blood agar
b) Large gram-positive rods
c) Non-motile
d) Capsulated

17) Colony characteristics/characteristic of Clostridia
a) Grow well in Nutrient agar
b) Produce alpha hemolytic colonies
c) Grow under aerobic conditions
d) None of the above

18) Clostridium botulinum associated foodborne illness can occur within 18-24 hours of ingestion of a toxin produced by the bacteria in food. Which of the following is NOT the symptoms associated with C.botulinum toxin?
a) Poor vision
b) Fever
c) Difficulty swallowing
d) Bulbar paralysis

19) All of the following are the preventive measures for Tetanus, EXCEPT
a) Active immunization of toxoids
b) Prophylactic use of antitoxin
c) Administration of Bacitracin
d) None of the above

20) Clostridium perfringens toxins are released only after entering the host cell through wounds or from the intestinal tract, which of the following also known as alpha toxin can damage the cell membranes ultimately resulting in hemolysis and tissue destruction?
a) Lecithinase
b) Enterotoxin
c) Alpha
d) Beta
Multiple Choice Answers
1)- a,
2)-c,
3)-a,
4)-b,
5)-d,
6)-c,
7)-a,
8)-b,
9)-d,
10)-c
11)- a,
12)- c,
13)-b,
14)-d,
15)-c,
16)-a,
17)-d,
18)-b,
19)-c,
20)-a
Medical Microbiology: Gram Positive Rods MCQs Medical Microbiology: Gram Positive Rods MCQs Reviewed by Biotechnology on September 26, 2018 Rating: 5

Medical Microbiology- Microbial Culture and Identification: MCQ

September 18, 2018
Multiple Choice Questions on Microbial Culture and Identification

1) A bacteriological stain also known as Differential stain is used to identify acid-fast organisms, what is the name of the stain?
a)Negative stain
b) Gram stain
c) Ziehl-Neelsen stain
d) Schaeffer stain- Fulton stain

2) A Capsule is a.........layer lying outside the bacterial cell and can be found both gram positive and gram negative bacteria
a) Lipopolysaccharide layer
b) Polysaccharide
c) Phospholipid
d) None of the Above

3) Negative staining is the technique where the background of a specimen is stained whereas positive staining stains the whole specimen. Which dye is required for the negative staining technique?
a) Crystal violet
b) India ink
c) Methylene blue
d) Iodine

4) All of the following are common bacteriological stains, Except:
a) Bismarck brown
b) Methylene blue
c) Eosin
d) Crystal violet

5) Gram staining technique is used for the differentiation of gram-positive and gram-negative bacteria. What color do gram-negative bacteria show when observed under the microscope after the staining procedure?
a) Blue
b) Pink
c) Purple
d)Violet

6) MacConkey’s agar is both Selective and Differential media used primarily for the isolation of gram-negative bacteria. It consists of ...........which inhibits the growth of gram-positive bacteria.
a) Blood
b) Peptone
c) Bile salts
d) Tryptophan

7) All of the following are lactose fermenting bacteria, except
a) Klebsiella pneumoniae
b) Escherichia coli
c) Enterobacter aerogenes
d) Pseudomonas aeruginosa

8) Which of the given bacteria has flagella and shows positive motility test?
a) Staphylococcus aureus
b) Yersinia pestis
c) Klebsiella pneumoniae
d) Proteus vulgaris

9) The biochemical test helps in identification and classification of microorganisms, there are many different types of this test, which of the following tests show a negative result for Escherichia Coli?
a) Lactose
b) Indole
c) Citrate
d) Glucose

10)The cultural characteristics of Clostridium perfringens, when grown on Blood agar, are all of the given below, Except?
a) Microaerophilic
b) Spore-forming
c) Lecithinase positive
d) Stormy fermentation

11) …................is a rod-shaped gram-positive, a non-spore forming organism that can cause foodborne illness in human and animals. It can grow at very low temperature on a wide variety of food including raw meat, raw vegetables, unpasteurized milk, cheese, etc., and is considered one of the most virulent foodborne pathogenic bacteria.
a) Bacillus cereus
b) Listeria monocytogens
c) Clostridium botulinum
d) Lactobacillus acidophilus

12)Which of the given organism when grown in blood agar media is classified according to its hemolytic properties?
a) Bacillus anthracis
b) Proteus vulgaris
c) Streptococcus pyogens
d) Staphylococcus epidermidis

13) All of the statements for Bacillus anthracis are true except
a) Grows aerobically as well as anaerobically
b) Nonhemolytic colonies on Blood agar
c) Major foodborne pathogen
d) Endospore-forming bacteria

14) Which of the following bacteria is a part of human gut and mouth flora and is also used in making some fermented dairy products?
a) Candida albicans
b) Lactobacillus acidophilus
c) Staphylococcus aureus
d) Micrococcus luteus

15) …............is part of human normal gut flora and also a clinically important pathogen, it's infection can lead to symptoms such as itchy skin, itchy genital area, white coat on the tongue and mouth ulcers, constipation. When grown in the lab, the organism produces green pigmented colonies on CHROMagar.
a) Streptococcus mutans
b) Mycobacterium tuberculosis
c) Proteus mirabilis
d) Candida albicans

16) Which of the following organism of the Enterobacteriaceae family have the characteristics of swarming growth on culture media, produces urease enzyme, do not usually ferment lactose and is mainly the cause of urinary tract infections and nosocomial infections?
a) Proteus spp
b) Salmonella spp
c) Lactobacillus spp
d) Klebsiella spp

17) ................is a gram-negative bacillus, encapsulated, lactose fermenter and show mucoid colonies on media. It is also a part of the normal flora of the oral cavity, skin, and intestine.
a) Pseudomonas aeruginosa
b) Staphylococcus aureus
c) Streptococcus pneumoniae
d) Klebsiella pneumoniae

18) …......... is a blood agar media prepared by slowly heating the media at 80 degree Celsius until it becomes brown, it is used for the isolation of some important pathogenic organisms such as Haemophilus spp and Neisseria gonorrhoea.
a) Potato dextrose agar
b) Chocolate agar
c) Nutrient agar
d) Mac Conkey agar

19) All of the statements are true for Corynebacterium spp, except
a) Requires selective media containing tellurite
b) Gram-positive
c) Colonies appear black or gray
d) Motile

20. Mannitol Salt agar is both selective and differential media, it is used for the isolation of ................, the high salt concentration inhibits the growth of gram-negative bacteria.
a) Micrococcus spp
b) Streptococcus spp
c) Staphylococcus spp
d) Corynebacterium spp

Multiple Choice Answers
1(c), 2(b), 3(b), 4(a), 5(b), 6(c), 7(d), 8(d), 9(c), 10(a),
11(b), 12(c), 13(c), 14(b), 15(d), 16(a), 17(d), 18(b), 19(d), 20(c)
Medical Microbiology- Microbial Culture and Identification: MCQ Medical Microbiology- Microbial Culture and Identification: MCQ Reviewed by Biotechnology on September 18, 2018 Rating: 5

Immunology: Immunoglobulin Structure, Function: MCQ

September 15, 2018
Multiple Choice Question on Immunoglobulin Structure, Function

1) Immunoglobulin is the plasma protein that specifically binds to antigens. Identify the region of electrophoresis that consists of these major immunoglobulins.

a) Alpha region
b) Beta region
c) Gamma region
d) None of the above

2) The five classes of immunoglobulin include the following except
a) IgA
b) IgD
c) IgE
d) IgH

3) Which of the following class of immunoglobulin is pentameric structure?
a) IgA
b) IgD
c) IgH
d) IgM

4) Which of the following class of immunoglobulin is dimeric structure?
a) IgA
b) IgD
c) IgH
d) IgM

5) The IgA and IgMs consist of the following chain that allows its polymerization.
a) H chain
b) L chain
c) J chain
d) V chain

6) The monomeric immunoglobulin consists of heterodimers of heavy (H) and light (L) chain bound together by non-covalent interaction and disulfide bonds. Which of the following is the antigen binding site?
a) Fab
b) Fc
c) Hinge region
d) None of the above

7) The hinge region of the immunoglobulin consists of the disulfide bond that held the heterotetramer together. Also, it contributes to the flexibility of the antibody chain. Which of the following antibody class do not have a hinge region?
a) IgA
b) IgD
c) IgE
d) IgG

8) The hypervariable complementarity determining region is responsible for which of the following function
a) binding to antigen
b) binding to FcR
c) binding to complement
d) None of the above

9) Identify the protease that results in two different fragments of antibodies namely Fab and Fc fragments as shown in the figure below:

a) Pepsin
b) Trypsin
c) Papain
d) Fucin

10) Identify the protease that results in two different fragments of antibodies namely Fab and Fc fragments as shown in the figure below:

a) Pepsin
b) Trypsin
c) Papain
d) Fucin

11) The variable heavy and light chain make up the antigen recognition region which consists of six complementarity determining regions (CDRs) (three from each heavy and light chain). In addition, a stretch of amino acid sequence also known as framework region
a) assist in the recognition of antigen
b) act as a scaffold to support CDR
c) are highly variable
d) None of the above

12) The variable heavy and light chain make up the antigen recognition region. Which of the following is mostly involved in antigen binding?
a) Variable light chain
b) Variable heavy chain
c) Both of the above
d) None of the above

13) The contact area of the antigen binding area may consist of the protrusion or depression that complementarity matches the antigen. This contact area span approximately ................... based on well-studied Lysozyme/anti-Lysozyme interaction.
a) 5-12 amino acids
b) 15-22 amino acids
c) 25-60 amino acids
d) None of the above

14) The antigen-antibody interactions are considered inducible which means
a) The antigen binding site performed site that exactly fits the antigen.
d) The antigen binding site is rigid
c) The antigen binding site undergo confirmation changes after contact with the antigen
d) None of the above

15) Which of the following antibody have four constant regions (CH1, CH2, CH3, CH4)?
a) IgA
b) IgD
c) IgM
d) IgG

16) The effector function of the antibody requires its Fc region. The Fc region binds to cells or proteins to mediate its function. Which of the following is the effector function of the antibody?
a) Antigen binding to antibody promotes opsonization
b) Antigen binding to antibody activates complement
c) Antigen binding to antibody activates cell cytotoxicity
d) All of the above

17) Which of the following immunoglobulins are secretory and present in the milk?
a) IgG
b) IgM
c) IgE
d) IgA

18) The receptor that is responsible for transport of IgAs across the epithelial barriers:
a) Poly Fc receptor
b) Poly Ig receptor
c) Poly Fab receptor
d) All of the above

19) Which of the following antibody is produced as a primary immune response and have higher valency to remove clear antigens?
a) IgA
b) IgG
c) IgM
d) IgE

20) Which of the following is the passive immunity transferred from mother to its offspring?
a) Transplacental transfer of IgGs
b) Transfer of IgAs in the milk
c) Both a & b
d) None of the above

21) Which of the following antigen-bound antibodies bind to the Fc receptor present on the basophils and tissue mast cells, and releases various pharmacoactive mediators involved in anaphylaxis?
a) IgA
b) IgD
c) IgE
d) IgM

22) The Fc receptor is a plasma membrane glycoprotein that binds to different immunoglobulin and triggers effective functions. Which of the following Fc receptor is involved in the transfer of IgG from mother to fetus
a) Fc€R
b) FcRN
c) FcµR
d) FcγR

23) The immunoglobulin superfamily is the group of membrane proteins that possess one or more homologous immunoglobulin domain. Which of the following is NOT immunoglobulin superfamily?
a) T cell receptor
b) beta2 microglobulin
c) Insulin receptor
d) Platelet-derived growth factor

24) B-cell receptor consist of membrane-bound immunoglobulin and a small heterodimer protein required for signaling. Which of the following is the heterodimer protein?
a) Igα & Igβ
b) Igµ & Igγ
c) Igα & Igγ
d) None of Above

25) Multiple Myeloma is characterized by excessive production of immunoglobulin and presence of light chain in urine. Which of the following cells are responsible for the production of immunoglobulin
a) T cells
b) B-cells
c) Plasma cells
d) Dendritic cells

26) Which of the following complement is bound by IgG?
a) C2a
b) C2b
c) C3a
d) C3b

27) Which of the following subclass of IgG molecule is the most potent activator of complement pathway?
a) IgG1
b) IgG2
c) IgG3
d) IgG4

28) Which of the following subclass of IgG does not readily cross the placental barriers?
a) IgG1
b) IgG2
c) IgG3
d) IgG4

29) Which of the immunoglobulin isotype have the shortest half-life?
a) IgG
b) IgM
c) IgA
d) IgE

30) Which of the immunoglobulin isotype have the longest half-life?
a) IgG
b) IgM
c) IgA
d) IgE


Multiple Choice Answers

1)-c, 2)-d, 3)-d, 4)-a, 5)-c, 6)-a, 7)-c, 8)-a, 9)-c, 10)-a

11)-b, 12)-b, 13)-b, 14)-c, 15)-c, 16)-d, 17)-d, 18)- b, 19)-c, 20)-b

21)-c, 22)-b, 23)-c, 24)-a, 25)-c, 26)-d, 27)-c, 28)-b, 29)-d, 30)-a

Immunology: Immunoglobulin Structure, Function: MCQ Immunology: Immunoglobulin Structure, Function: MCQ Reviewed by Biotechnology on September 15, 2018 Rating: 5

Immunology: Host Defense Mechanism: MCQs

September 12, 2018
Multiple Choice Questions  on Host Defense Mechanism

1) According to ........................ theory, an individual lymphocyte expresses a membrane receptor that is unique to each antigen. The binding of the antigen to specific receptor provoke an immune response against that specific antigen.
a) Selective theory
b) Instructional theory
c) Clonal selection theory
d) None of Above

2) Immunity is the defense mechanism of the body that protect against foreign pathogens. The immunity can be classified into innate immunity and acquired immunity. Which the following is NOT true regarding innate immunity?
a) Broadly specific against the foreign antigen
b) Exist prior to the exposure o the antigens
c) Have memory cells
d) All of the above

3) Which of the following are the characteristics of acquired immunity?
a) Diversity
b) Memory
c) Specific
d) All of the above

4) Which of the following is not an example of innate immunity?
a) Phagocytosis
b) Antibodies
c) Interferon
d) Mucus membrane

5) Lysozyme is an enzyme present in the tears and mucous secretion that cleaves
a) Lipopolysaccharides
b) Cellulose
c) Peptidoglycan
d) None of the above

6) Lipopolysaccharides present in the cell membrane of gram-negative bacteria are recognized by .................... and elicit an inflammatory immune response
a) Phagocytosis
b) Antibodies
c) Mucus lining
d) Toll-Like receptors (TLR-2)

7) The cardinal signs of inflammation are rubor (redness), tumor (swelling), calor (heat) and dolor (pain). Which of the following is the characteristic feature of inflammation response?
a) Vasodilation
b) Increased capillary permeability
c) Recruitment of phagocytosis
d) All of the above

8) The adaptive immunity that involves the production of antibodies for the clearance of antigen is called
a) Cell-mediated cytotoxicity
b) Cell-mediated immunity
c) Humoral Immunity
d) None of the above


9) The antigen presenting cells (APCs) plays a crucial role in antibody-mediated and cell-mediated immune response. Which of the following is not the characteristic feature of APCs?
a) APCs internalize and degrade antigens
b) APCs present antigens to the T-cells via MHC-II molecules
c) APCs provide a co-stimulatory signal for T-cell activation
d) Excess co-stimulatory signals from APCs lead to hyperactivation of an immune response.


10) Which of the following is not the class of T cells?
a) T-helper cells
b) T-cytotoxic cells
c) T-suppressor cells
d) T-activator cells

11) Which of the following cells produces antibodies?
a) T-cells
b) Plasma cells
c) B cells
d) Memory cells

12) Which of the following is expressed in T cells that interact with antigen epitope?
a) T-cell receptor
b) T-cell antibodies
c) B-cell receptor
d) B-cell antibodies


13) Antibody functions as the effector of the humoral response by antigen binding and neutralizing it. The antigen can be eliminated by
a) Facilitating the antibodies update by phagocytes
b) Activating complements and inducing cell lysis
c) Preventing the binding and host cell attachment
d) All of the above

14) Which of the following immune cells are not derived from lymphoid progenitor cells?
a) B-cells
b) T-cells
c) Natural Killer cells
d) Neutrophils

15) The development of pluripotent hematopoietic stem cells into different cell types requires the expression of a different set of genes for lineage determination at appropriate time and order. The various transcription factor is required for the expression of these genes. Which of the following statement is TRUE
a) GATA-1 is required for myeloid lineage
b) Oct-2 is required for B cell differentiation to plasma cells
c) Ikaros is required for erythroid lineage
d) None of the above

16) The different lineage of the lymphocytes can be distinguished by characterizing the expression of their membrane molecules called the cluster of differentiation (CD). Which of the following CD is only found in B-cells?
a) CD-4
b) CD-8
c) CD-32
d) CD-45

17) Which of the following CD molecule is present in both cell types of T cells (Th and Tc) and acts as a receptor for the co-stimulatory signal from APCs?
a) CD2
b) CD4
c) CD28
d) CD45

18) Which of the following CD molecule is a signaling transduction molecule present in lymphoid lineage cells such as T-cell, B-cells, and NK
a) CD2
b) CD4
c) CD28
d) CD45

19) Which of the following cell plays a crucial role in antibody-dependent cell cytotoxicity
a) Macrophage
b) Natural Killer cells
c) B-cells
d) Dendritic cells

20) The tissue-specific macrophage-like tissues are essential for phagocytosis of the antigens. Which of the following cells are present in the kidney?
a) Alveolar macrophages
b) Kuffer cells
c) Histiocytes
d) Mesangial cells
21) Immunogens are the antigens that can evoke an immune response. Which of the following is not an immunogen?
a) Protein
b) Lipopolysaccharides
c) Polysaccharides
d) Hapten

22) The degree of immunogenicity generally depends on the degree of foreignness. Which of the following protein are highly conserved among species and have little immunogenicity when injected to cross-species?
a) Bovine Serum Albumin
b) Thyroglobulin
c) Insulin
d) Collagen

23) Although the degree of immunogenicity generally depends on the degree of foreignness, certain antigens/tissues are immunogenic against self-antigens. The example includes
a) Kidney
b) Cornea
c) Heart
d) Collagen

24) Which of the properties of an antigen makes it poorly immunogenic?
a) Distant species origin
b) High molecular weight proteins
c) Heteropolymers
d) Homopolymers

25) B-cells have cell surface antibodies that serve as the recognition molecule, and T cell recognizes when these antigens are presented via MHC molecules. Some glycolipids are also recognized by T-cell when presented by a non-MHC molecule known as
a) CD1
b) CD2
c) CD4
d) CD8

26) The discrete sites on the are recognized by antibody or T cells are called epitopes. Which of the following is TRUE regarding epitopes
a) B cell and T cells recognize the same epitopes
b) B cell and T cells recognize different epitopes
c) Epitope contains only sequential amino acids.
d) Epitopes bind to the antibody with covalent bonding

27) The epitopes that are recognized by B-cells are known as B-cell epitopes. The following is a true statement regarding B-cell epitope
a) they are generally hydrophilic amino acids present on the surface
b) they contain both sequential and conformational epitopes
c) they tend to present on the flexible region of the antigens
d) All of the above

28) The epitopes that are recognized by T-cells are known as T-cell epitopes. The following is a true statement regarding T-cell epitope:
a) the epitopes are recognized by T-cell as a trimeric complex of TCR, antigen and MHC molecule.
b) antigen processing is required for its presentation by APC
c) amino acid sequences of T-cell epitopes are generally internal of a protein molecule
d) All of the above

29) The following congenital defect of thymus development lead to T-cell deficiency:
a) Graves disease
b) DeGeorge's syndrome
c) Anaphylaxis
d) All of the above

30) Severe Combined immunodeficiency disorder (SCID) is a genetic disorder caused by a defective enzyme
a) Xanthine oxidase
b) Adenosine deaminase
c) Anaphyloticase
d) Lysozyme




Multiple Choice Questions Answer review
1)- c,
2)- c,
3)-d,
4)- b,
5)- c,
6)- d,
7)- d,
8)- c,
9)- d,
10)- d
11)-b,
12)-a,
13)-d,
14)-d,
15)-b,
16)-c,
17)-c,
18)-d,
19-b),
20)-d
21)-d,
22)-d,
23)-c,
24)-d,
25)-a,
26)-b,
27)-d,
28)-d,
29)-b,
30)-b
Immunology: Host Defense Mechanism: MCQs Immunology: Host Defense Mechanism: MCQs Reviewed by Biotechnology on September 12, 2018 Rating: 5

Medical Microbiology- Bacterial Pathogenesis: MCQ

September 09, 2018
Multiple Choice Question on Bacterial Pathogenesis

1) Which of the following microorganism is the major inhabitant of the skin?
a) Escherichia coli
b) Staphylococcus epidermidis
c) Staphylococcus aureus
d) Streptococcus pyogens

2) Which one of the following is not the normal flora of the skin?
a) Diptheriods
b) Staphylococci
c) Helicobacter
d) Micrococci

3) All of the following are gram-negative bacilli EXCEPT
a) Proteus spp
b) Pseudomonas spp
c) Neisseria spp
d) Klebsiella spp

4) Which of the following cocci shaped bacteria is usually seen in pairs?
a) Klebsiella spp
b) Neisseria spp
c) Pseudomonas spp
d) Clostridium spp

5) Which one of the following pathogenic organism is capable of living inside the living cell only(obligate intracellular pathogen)?
a) Salmonella
b) Mycobacterium
c) Rickettsia
d) Vibrio

6) ...................is the common normal flora of upper respiratory tract
a) Lactobacillus spp
b) Staphylococcus spp
c) Vibrio spp
d) None of the above

7) Which of the following organism releases endotoxin that causes muscular paralysis?
a) Clostridium botulism
b) Bacillus cereus
c) Streptococcus pyogens
d) Salmonella typhi

8) Which of the following enzyme is used to distinguish between different types of Staphylococcus isolates?
a) Proteases
b) Lipase
c) Hyaluronidase
d) Coagulase

9) Which of the following is the predominant urogenital flora present during newborn female infants?
a) Candida albicans
b) Lactobacillus acidophilus
c) Escherichia coli
d) Neisseria gonorrohea

10) All of the given organisms are the predominant normal flora of human feces EXCEPT
a) Pseudomonas sps
b) Bacteroides sps
c) Enterococcus sps
d) Bacillus sps

11) Vector-borne bacterial pathogenesis is caused only when bacteria are transmitted into a host cell through a vector. Among these ................ is a vector-borne pathogen.
a) Salmonella typhi
b) Yersinia pestis
c) Shigella dysenteriae
d) Escherichia coli

12) Some bacteria and fungi need an iron receptors molecule for their growth, what is it called?
a) Siderophores
b) Ionophores
c) Siderocytes
d) None of the above

13) Which toxin is produced by Streptococcus pyogens?
a) Shiga like toxin
b) Alpha toxin
c) Erythrogenic toxin
d) Cyanotoxin

14) Which bacteria causes toxic shock syndrome
a) Staphylococcus epidermidis
b) Staphylococcus aureus
c) Staphylococcus intermedius
d) None of the above

15) Catalase test is the biochemical test used for identification of various bacteria. Which of the following bacteria is negative to this test?
a) Enterobacter
b) Pseudomonas
c) Corynebacterium
d) Streptococci

16) Staphylococcus aureus releases a various toxin that is important for their pathogenesis. Following are toxin released by S aureus EXCEPT:
a) Botulinum
b) Alpha
c) Leucocidin
d) Enterotoxin

17) Which pathogen is a major cause of dental disease?
a) Staphylococcus epidermidis
b) Streptococcus mutans
c) Staphylococcus aureus
d) Streptococcus agalactiae

18) The microorganism that commonly causes an eye infection is
a) Chlamydia trachomatis
b) Staphylococcus aureus
c) Streptococcus pneumoniae
d) Streptococcus sanguinis

19) The most significant bacteria found in acne is ........ acnes.
a) Staphylococcus
b) Streptococcus
c) Propionibacterium
d) Bacillus

20) Which of the following bacteria is predominantly present in normal urine?
a) Escherichia coli
b) Staphylococcus epidermidis
c) Staphylococcus aureus
d) Streptococcus pyogens

Multiple Choice Answer Review
1- b) Staphylococcus epidermidis
2-c) Helicobacter
3- c) Neisseria spp
4-b) Neisseria spp
5-c) Rickettsia
6- b) Staphylococcus spp
7-a) Clostridium botulism
8-d) Coagulase
9- b) Lactobacillus acidophilus
10-a) Pseudomonas sps
11-b) Yersinia pestis
12-a) Siderophores
13-b) Alpha toxin
14-b) Staphylococcus aureus
15-d) Streptococci
16-a) Botulinum
17-b) Streptococcus mutans
18-a) Chlamydia trachomatis
19-c) Propionibacterium
20-a) Escherichia coli

Medical Microbiology- Bacterial Pathogenesis: MCQ Medical Microbiology- Bacterial Pathogenesis: MCQ Reviewed by Biotechnology on September 09, 2018 Rating: 5

Molecular Biology: MCQ on RNA Synthesis (Translation) & Maturation

September 05, 2018
Multiple Choice Question on
Transcription (RNA synthesis) and RNA processing 

1) Transcription of DNA results RNA that have multiple functions including
a) messenger RNA serves as a template for synthesis of proteins
b) tRNA serves as the adapter molecule for the addition of amino acids and elongation of the peptide chain
c) ribosomal RNA serves as machinery for protein synthesis
d) All of the above

2) Which of the following RNA serves the regulatory functions including splicing, gene silencing?
a) mRNA
b) tRNA
c) rRNA
d) small RNA

3) Which of the following statement is NOT true regarding transcription/RNA synthesis?
a) RNA synthesis occurs in the nucleus
b) Unlike DNA synthesis, the only selective sequence of DNA is transcribed to RNA
c) RNA synthesis requires a short stretch of RNA primers
d) DNA sequences, specific proteins, and small RNAs regulate RNA synthesis.

4) The pentose sugar moieties are the primary structural difference between DNA and RNA. In addition which of the following is primarily associated with RNA molecule?
a) RNA consist of thymine instead of uracil
b) RNA molecules are highly branched structure
c) RNA molecules have higher structural complexities
d) RNA molecules are anti-parallel and double-stranded


5) In prokaryotes, RNA polymerase catalyzes the synthesis of:
a) mRNA
b) rRNA
c) tRNA
d) All of the above

6) The RNA polymerase is a multi-subunit enzyme that recognizes a consensus nucleotide sequence (promoter region) upstream of the transcription start site. In prokaryotes, the consensus promoter sequence consists of 5-TATAAT-3' also known as
a) Enhancer box
b) Pribnow box
c) Transcription unit
d) None of the above

7) RNA polymerase catalyzes the synthesis of RNA by addition nucleotide monophosphate and release of pyrophosphate for nucleotide triphosphate. RNA polymerase
a) consists of 5'-3' exonuclease activity
b) lacks 3'-5' endonuclease activity
c) is a high fidelity enzyme
d) All of the above

8) In prokaryotes, a holoenzyme RNA polymerase consists of four core subunits namely 2α, 1β, 1β' and a promoter recognizing σ subunit. It may also require a termination factor for termination of the transcription factor. Which of the following is a transcription factor?
a) gamma factor
b) delta factor
c) epsilon factor
d) rho factor

9) In prokaryotes, TTGACA is an upstream consensus nucleotide sequence that is required for transcription ....... step
a) Initiation
b) Elongation
c) Termination
d) Capping

10) The termination of transcription occurs in both rho-dependent and rho-independent manner. Which of the following is NOT true regarding the termination of transcription
a) rho proteins recognize C-rich region near 3'end of the newly synthesized RNA
b) rho-independent termination occurs when the transcription reaches the palindromic structure leading to the formation of hairpins
c) rho protein competes with RNA polymerase for binding to nucleotides
d) None of the above

11) Rifamycin is an antibiotic used for the treatment of tuberculosis. It binds to .... subunit of RNA polymerase and inhibits the initiation of transcription.
a) α,
b) β
c) σ
d) ζ

12) In eukaryotes, the RNA synthesis process is more complex than prokaryotes. The RNA synthesis process is regulated by chromatin structure, upstream and downstream sequences, binding partners, etc. Which of the following is TRUE regarding the transcription process in eukaryotes:
a) Most actively transcribed genes are found in a loosely relaxed form of chromatin called euchromatin
b) The most inactive segment of DNA is found in compact chromatin structure called heterochromatin
c) Histone modification such as methylation, acetylation regulate the RNA transcription by modulating chromatin structure
d) All of the above

13) In eukaryotes, three different RNA polymerases are involved in the synthesis of a different class of RNAs namely: rRNA, tRNA, and mRNA. The RNA polymerase that is required for the synthesis of mRNA is
a) RNA polymerase I
b) RNA polymerase II
c) RNA polymerase III
d) None of the above

14) In eukaryotes, the consensus promoter sequences (TATA box) that are required for initiation of transcription is generally present
a) 10 nucleotide upstream of transcription start site (TSS)
b) 25 nucleotide upstream of TSS
c) 10 nucleotide downstream of TSS
d) 25 nucleotide downstream of TSS

15) Enhancers are special cis-acting DNA sequences that increase the rate of transcription by RNA polymerase. Which of the following is true regarding enhancers?
a) 10 nucleotide upstream elements
b) 25 nucleotide downstream elements
c) present closer or 1000s nucleotide upstream or downstream of TSS
d) All of the above

16) The capping of nucleotide prevents the rapid cleavage of mRNA and catalyzed by guanylyltransferase. Identify the nucleotide cap that is attached at the 5'end of mRNA.
a) 5-methyl guanosine
b) 7- methyl guanosine
c) 5- acetyl guanosine
d) 7- acetyl guanosine

17) The polyadenylation is a post transcription modification that stabilizes the mRNA and prevent from the cleavage. The consensus PolyA sequence is
a) (AAGAAA)n
b) (AACAAA)n
c) (AATAAA)n
d) (AAUAAA)n

18) In eukaryotes, the primary transcripts are processed to remove intervening sequence resulting in mRNA and the process is known as splicing. The complex of RNA, nucleoproteins that execute splicing process is called:
a) Primosome
b) Splicing fork
c) Spliceosome
d) None of the above

19) The role of small nuclear ribonucleoprotein particles (snRNPs) is
a) to bind intronic sites and exon segments
b) facilitate the looping of the two exons into the correct alignment for splicing
c) All of the above
d) None of the above

20) The auto-antibodies against the small nucleoproteins are present in
a) beta thalassemia
b) systemic lupus erythematosus
c) Phenylketonuria
d) None of the above

21) The antibody binding diversity is a result of a type splicing that produces mRNA variants and protein variants by processing different segment of exons. The process is known as
a) Diversity splicing
b) Alternative splicing
c) Conservative splicing
d) None of the above

22) CAAT box is present in many
a) Prokaryotic promoters upstream of TATA box
b) Prokaryotic promoters are downstream of TATA box
c) Eukaryotic promoters are upstream of TATA box
d) Eukaryotic promoters are downstream of TATA box


Multiple Choice Answers
1-d) All of the above
2-d) small RNA
3- c) RNA synthesis requires a short stretch of RNA primers
4- a) RNA consist of thymine instead of uracil
5- d) All of the above
6-b) Pribnow box
7-b) lacks 3'-5' endonuclease activity
8- d) rho factor
9-a) Initiation
10)-c) rho protein competes with RNA polymerase for binding to nucleotides
11- b) β
12- d) All of the above
13-b) RNA polymerase II
14-b) 25 nucleotide upstream of TSS,
15-c) present closer or 1000s nucleotide upstream or downstream of TSS,
16-b) 7- methyl guanosine
17-d) (AAUAAA)n
18-c) Spliceosome
19-c) All of the above
20-b) systemic lupus erythematosus,
21- b) Alternative splicing
22-a)Prokaryotic promoters upstream of TATA box



Molecular Biology: MCQ on RNA Synthesis (Translation) & Maturation Molecular Biology: MCQ on RNA Synthesis (Translation) & Maturation Reviewed by Biotechnology on September 05, 2018 Rating: 5

Homocystinuria & Homocysteinemia: Clinical Condition and Biochemical Interpretation

August 29, 2018
Homocystinuria is an inherited disorder primarily caused by a deficiency of enzymes of methionine metabolism which lead to accumulation and excretion of homocystine in the urine. Cysteine is a non-essential amino acid that is synthesized from methionine and involves four steps catalyzed by four different enzymes as shown in figure 1. Defective enzymes of this pathway or deficiency of co-factors or enzymes that are involved in the recycling of the co-factors lead to elevated blood homocysteine and homocystinuria. The increased blood homocysteine is also known as homocysteinemia are associated with various cardiovascular diseases and stroke but the mechanism is not unknown.





Metabolism of Methionine and Cysteine 



Homocystinuria can be classified into three different categories based on the defective enzymes and symptoms:
Homocystinuria type I
Homocystinuria type II
Homocystinuria type III

Homocystinuria type I:
The classical homocystinuria is an autosomal recessive disorder that involves multiple organ involvement including the eye, skeletal system, thromboembolism, delayed development, and intellectual disability. The CBS enzyme is located on the long arm of chromosome 21 (21q22.3) and the mutation of the CBS gene may result in reduced activity of cystathionine beta-synthase resulting in classical homocystinuria. The confirmatory diagnosis includes increased plasma methionine, homocysteinemia, and presence of homocystine in the urine.

Homocystinuria type II & II
Methylcobalamin is required for the reconversion of homocysteine to methionine and the defect in the formation of methylcobalamin or methylation pathway results in type II & III homocystinuria. The type II & III homocystinuria is characterized by megaloblastic anemia, homocystinuria and low levels of methionine with mild clinical severity.







Possible Causes of Homocystinuria and Homocysteinemia
Biochemical Diagnosis:
-Nitroprusside test
-Amino Acid Chromatography in Urine
-Enzyme activity in fibroblast and Mutation analysis


Treatment:
The treatment of homocystinuria may include dietary control of proteins and amino acids, supplementation of cyanocobalamin, folic acid and pyridoxine may alleviate the symptoms.
Homocystinuria & Homocysteinemia: Clinical Condition and Biochemical Interpretation  Homocystinuria & Homocysteinemia: Clinical Condition and Biochemical Interpretation Reviewed by Biotechnology on August 29, 2018 Rating: 5

Glycogen synthesis and Breakdown Pathway

August 22, 2018
Introduction
Glycogen is a polysaccharide consist of glucose linked together by glycosidic linkage. In animal and humans; glucose is stored in the form of glycogen in liver (~10%) and muscles (~2%). These stored glycogen molecules can readily be degraded into glucose molecules and enter into the glycolytic pathway for energy. The liver glycogen can also contribute to the maintenance of normal blood glucose.  The glycogen synthesis and breakdown pathway are highly regulated and, the synthesis and breakdown do not occur at the same time. 

Glycogenesis

Figure 1: Overview of Glycogen synthesis (Glycogenesis)


Synthesis of Glycogen
The addition of glucose to form a glycogen requires a primer molecule where the glucose can be added to the non-reducing ends. During de novo synthesis, glucose molecules are added to tyrosine residues of primer protein glycogenin. The enzyme Glycogen synthase catalyzes the addition of glucose molecules at the nonreducing end of core glycogen molecule  In this reaction, a activated UDP-glucose molecule forms 1-4 glycosidic linkage with existing glucose moiety of glycogen molecule and free UDP is liberated. This result in the elongation of glycogen molecule with addition of one glucose moiety in each reaction. 

Figure 2: Glycogen Synthase-addition of glucose from UDP-glucose to core glycogen molecules.


Glycogenolysis

Figure 3: Overview of Glycogen Breakdown(Glycogenolysis)


Figure 4: Glycogen phosphorylase-removal of glucose from glycogen molecules.




Regulation of Glycogen Metabolism



-Glycogen synthesis occurs when the glucose and ATP are abundant in the cells. In contrary, glycogen breakdown release glucose for muscle contraction and regulation of blood glucose. 

-Glycogen metabolism is regulated by allosteric modification and covalent modifications. 

-The glycogen synthesis and breakdown are reciprocally regulated to ensure that both pathways do not occur at the same time in the cell.

Glycogen phosphorylase regulation

Allosteric modification: 

-The glycogen phosphorylase exists in two different conformations. T-state or inactive state and R-state or active state. 
-In muscle, the binding of an AMP molecule to glycogen phosphorylase enzyme shifts the T-state glycogen phosphorylase to R-state. 
-ATP and Glucose-6-phosphate exert an inhibitory effect by favoring T-state of glycogen phosphorylase (inactive form).
-In liver, the presence of glucose shifts the R-state glycogen phosphorylase to T-state (inactive). 


Allosteric Modification of glycogen phosphorylase in muscle 

Allosteric Modification of glycogen phosphorylase in liver

Covalent modification:
-Insulin and glucagon reciprocally regulate glycogen phosphorylase by adding/removing phosphate group to the enzyme glycogen phosphorylase. 
- During muscle contraction, in addition to low glucose and ATP, the release of calcium from sarcoplasmic reticulum activates calcium-dependent protein kinase that inturns phosphorylate and activate glycogen phosphorylase. 
- Calcium ions partially activate calcium-dependent protein kinase that requires phosphorylation by protein kinase A for full activity. Epinephrine binding to its receptor induces the signaling cascade to activate protein kinase A. 
- In liver, glucagon and epinephrine induce the signaling cascade to phosphorylate activate phosphorylase kinase and activate downstream protein glycogen phosphorylase.
-In response to high blood glucose concentration, insulin is released from beta cells of the pancreas.
-Insulin binds to tyrosine kinase receptor and induces signaling pathway to activate protein phosphatase 1. The protein phosphatase 1 catalyzes the removal of the phosphate group from glycogen phosphorylase and deactivates it. 

 

Phosphorylation activates glycogen phosphorylase enzyme and increases glycogen breakdown in exercising muscle and liver when blood glucose is low. 


 

Dephosphorylation inactivates glycogen phosphorylase enzyme and decreases glycogen breakdown in resting muscle and liver when blood glucose is abundant. 


Glycogen synthase regulation
Covalent Modification:
-The glycogen synthase is the regulatory enzyme of glycogen synthesis.
-Insulin induces glycogen synthesis by activating the enzyme glycogen synthase (in a dephosphorylated state).
- In contrast, glucagon and epinephrine deactivate the enzyme (increasing phosphorylation) thereby reducing glycogen synthesis. 

 

Dephosphorylation activates glycogen synthase enzyme and increases glycogen synthesis in resting muscle and liver when blood glucose is abundant. 

 

Phosphorylation inactivates glycogen synthase enzyme and decreases glycogen synthesis in exercising muscle and liver when blood glucose is low. 




Glycogenesis is the biosynthetic pathway for synthesis of glycogen from glucose molecules.  This biosynthetic pathway can be divided into two stage i.e activation of glucose and addition of glucose to core glycogen molecules at a nonreducing end.

Activation of glucose molecules: 
The precursor glucose molecules are first activated by an enzyme hexokinase/glucokinase to form glucose-6-phosphate. The next step is the conversion of glucose-6-phosphate to glucose-1-phosphate which is catalyzed by enzyme phosphoglucomutase. This enzyme catalyzes the transfer of phosphate group 6-carbon group to 1- carbon resulting in glucose-1-phosphate. 

The second reaction is the formation high energy UDP-glucose catalyzed by an enzyme UDP-Glucose pyrophosphorylase. In this reaction, the uridine monophosphate group from UTP to form UDP-glucose and pyrophosphate. The pyrophosphate formed is subsequently hydrolyzed to inorganic phosphates to release energy. 

The glycogen molecule is highly branched. The branching glycogen molecule is introduced by branching enzyme that transfers the oligopeptide glucose moieties from 1-4 glycosidic linkage to form 1-6 glycosidic linkage with the interior glucose moiety of glycogen molecule. This results in branching of glycogen molecule at every 8-10 residues and compact helical structure.

Glycogenolysis is the breakdown of glycogen to glucose-6-phosphate and involve a series of enzyme catalyzed reactions.

Phosphorolysis of Glycogen to glucose-1-phosphate
The first reaction of glycogen breakdown is the phosphorolysis of glycogen molecule to liberate one glucose-1-phosphate. This phosphorolysis reaction is catalyzed by a pyridoxal-5-phosphate requiring enzyme Glycogen phosphorylase. During this reaction, the inorganic phosphate is incorporated to the glucose molecules allowing the intermediates to directly enter other metabolic pathways (glycolysis and pentose phosphate pathway)

Conversion to Glucose-6-phosphate
Glucose-1-phosphate is converted into glucose-6-phosphate catalyzed by an enzyme phosphoglucomutatse as described above. In liver, glucose-6-phosphate formed are converted into free glucose by enzyme glucose-6-phosphatase and contributes to blood glucose maintenance. In contrast, muscle tissue lacks an enzyme glucose-6-phosphatase and glucose-6-phosphate produced in the muscle tissues do not contribute to the blood glucose maintenance. The function of glycogen in muscle is to feed glucose-6-phosphate into glycolytic pathway for ATP required for muscle contraction during exercise. 

(Note: The hydrolysis to glucose during this step would have required ATP for the activation. Therefore, the phosphorolysis captures the inorganic phosphate and conserve one ATP in energy-deprived cells.  that may would have required if the hydrolysis of glycogen to glucose.)

Removal of glucose by debrancing enzyme
As the glycogen are highly branched, and glycogen phosphorylase only removes glucose from nonreducing end of 1-4 glycosidic linkage; an additional enzyme 1,6-glucosidase  (debranching enzyme) hydrolyzes the 1-6 glycosidic linkage at branch site release free glucose. 

Glycogen synthesis and Breakdown Pathway Glycogen synthesis and Breakdown Pathway Reviewed by Biotechnology on August 22, 2018 Rating: 5
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