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

Fatty acid synthesis: MCQ of the day

November 26, 2017

Q) In what compartment does the de novo fatty acid synthesis occurs?

a) Mitochondria
b) Perioxosome
c) Endoplasmic reticulum
d) Cytosol

Explanation
Fatty acid biosynthesis takes place in the cytosol
Intermediates covalently linked to an acyl carrier protein
The acetyl CoA is activated to malonyl CoA
Four steps repeating cycle are condensation, reduction, dehydration, and reduction. One cycle leads to extension by 2-carbons

Comparison of Fatty acid synthesis and oxidation

Characteristics
Synthesis
Degradation
Location
Cytosol
Mitochondrial Matrix
Activated Intermediates
Bound to ACP
Thioester of CoA
Enzymes
FAS is a multienzyme complex
4 distinct enzymes
Substrate
Acetly CoA
Fatty Acids
Direction
Starts at methyl end
Starts at the carboxyl end
Cofactors
NADPH
FADH/NADH
Major sites
Liver
Muscle and Liver
Hormonal Regulation
High Insulin/Glucagon ratio
Low Insulin/Glucagon ratio
Activator
Citrate
Free fatty acids
Inhibitor
Fatty acyl CoA
Malonyl CoA




Fatty acid synthesis: MCQ of the day Fatty acid synthesis: MCQ of the day Reviewed by Biotechnology on November 26, 2017 Rating: 5

Lipid Metabolism: MCQ on Lipid Transport, Lipoproteins and related disorders

November 12, 2017
Multiple Choice Question on Lipid and Lipoprotein Metabolism

1) Which of the following molecule is not a gluconeogenic substrate?
a) alanine
b) oxaloacetate
c) glycerol
d) acetyl-CoA

2) Obesity has been considered as an excess accumulation of body fat, and what is the cut-off value of BMI to consider as obese?
a) 25 to 30
b) 30.5 to 34.9
c) >35
d) >40

3) The highest phospholipids content is found in …
a) Chylomicrons
b) VLDL
c) LDL
d) HDL

4) The class of lipoproteins that is beneficial to atherosclerosis is …
a) Low density of lipoproteins
b) Very low density lipoproteins
c) High density lipoproteins
d) Chylomicrons

5. Genetic deficiency of lipoprotein lipase cause hyperlipoproteinemia of the following type:
a) Type I
b) Type IIa
c) Type IIb
d) Type V

6) Activated lecithin cholesterol acyl transferase is essential for the conversion of ...
a) VLDL remnants into LDL
b) Nascent HDL into HDL
c) HDL2 into HDL3
d) HDL3 into HDL2

7) Zellweger’s syndrome is associated with abnormality of
a) Non essential fatty acid metabolism
b) Essential fatty acid metabolism
c) cholesterol metabolism
d) Lipoprotein metabolism

8) Tangier disease is a disorder of lipoprotein metabolism. The phenotype corresponds to
a) Low level of VLDL
b) Low level of LDL
c) Low level of IDL
d) Low level of HDL

9) Although ketogenesis occurs in hepatocytes it cannot utilize ketone bodies. It is due to deficiency of the enzyme
a) Thiokinase
b) Thiophorase
c) Thiolase
d) Thiolyase

10) Fatty acid oxidation is regulated by malonyl CoA. The malonyl CoA inhibits
a) Entry of fatty acid into the cell
b) Activation of fatty acid to fatty acyl CoA
c) Shuttling of fatty acyl CoA to mitochondria
d) Dehydrogenation of fatty acyl CoA to enoyl CoA


Multiple Choice Answers
1-d) Acetyl-CoA
2-c) 35
3-d) HDL
4-c) High density lipoproteins
5- b) Type IIa
6-d) HDL3 into HDL2
7-b) Essential fatty acid metabolism
8-d) Low level of HDL
9-b) Thiophorase
10-c) Shuttling of fatty acyl CoA to mitochondria
Answer (Click Here)

Lipid Metabolism: MCQ on Lipid Transport, Lipoproteins and related disorders Lipid Metabolism: MCQ on Lipid Transport, Lipoproteins and related disorders Reviewed by Biotechnology on November 12, 2017 Rating: 5

Carbohydrate Metabolism: MCQ on Glycogen Synthesis and Breakdown

November 06, 2017
Multiple Choice Question on Glycogen Synthesis and Breakdown

1) Which of the following is false about glycogen molecules?
a) Glycogen is polysaccharide
b) Glycogen is a polymer of beta-D-Glucose
c) Glycogen consists of α(1-4) and α (1-6) glycosidic linkage
d) Glycogen have are a helical structure with branching.

2) Which of the following organs do not have glycogen storage?
a) Liver
b) Muscle
c) Erythrocytes
d) All of the above

3) Which of the following enzyme is responsible for glycogen breakdown?
a) Glycogen phosphorylase
b) Glycogen phosphatase
c) Glycogen hydrolase
d) Glycogen phosphoglycosidase

4) Liver glycogen contributes to the maintenance of glucose but not muscle glycogen. Which of the following enzyme is absent in muscle?
a) Glycogen phosphorylase
b) Hexokinase
c) Glucose-6-phosphatase
d) Debranching enzyme

5) Which of the enzyme is responsible for hydrolysis of α (1-6) glycosidic bond present at a branching point of glycogen molecules?
a) β-Glucosidase
b) α- Glucosidase
c) Glycosidase
d) Phosphorylase

6) Glycogen phosphorylase is responsible for the breakdown of glycogen to
a) Glucose
b) Glucose-1-phosphate
c) Glucose-6-phosphate
d) Maltose

7) Which of the following is false about enzyme glycogen phosphorylase of glycogen breakdown?
a) Glycogen phosphorylase is active as homodimer.
b) Glycogen phosphorylase is present in two conformation state
c) Glycogen phosphorylase possess high-affinity binding to glycogen in T conformational state
d) Glycogen phosphorylase high-affinity binding to glycogen in R conformation state

8) Which of the following metabolite allosterically activate glycogen phosphorylase?
a) ATP
b) AMP
c) Glucose-6-P
d) Glucose-1-P

9) In response to glucagon and epinephrine, cells undergo a series of changes in signal transducing molecules that phosphorylates and activates glycogen phosphorylase. Which of the following enzyme is responsible for covalent modification of glycogen phosphorylase?
a) Protein kinase A
b) Phosphorylase kinase
c) Protein kinase C
d) Protein kinase B

10) Which of the following is not the direct/ indirect activator of glycogen phosphorylase in muscle?
a) AMP
b) Ca++
c) Epinephrine
d) Insulin

11) Which of the following protein is required for de novo synthesis of glycogen?
a) Glycoprotein
b) Glycogenin
c) Proteoglycan
d) Glucogenin

12) Which of the following enzyme is responsible for the addition of UDP-Glucose to the existing chain?
a) Glycogen synthase
b) Glycogen polymerase
c) Glycogen synthetase
d) Glycogen lyase

13) All the following enzymes are involved in glycogen synthesis except
a) Hexokinase
b) Phosphoglucomutase
c) Glucose-1-P uridylyltransferase
d) Glycogen synthetase

14) Which of the following statement is false regarding glycogenesis?
a) Glycogen synthase is activated in the phosphorylated state.
b) Glycogen synthase enzyme is inhibited by glucagon and epinephrine action.
c) Protein phosphatase removes the phosphate group and activates the enzyme
d) Insulin promotes glycogen synthesis in liver and skeletal muscles

15) The iodine test is used to differentiate glycogen from starch. On iodine test glycogen gives
a) Blue color
b) Green color
c) Yellow color
d) Violet color

Multiple Choice Answers
1-b) Glycogen is a polymer of beta-D-Glucose
2-c) Erythrocytes
3- a) Glycogen phosphorylase
4-c) Glucose-6-phosphatase
5-b) α- Glucosidase
6-c) Glucose-6-phosphate
7-c) Glycogen phosphorylase possess high-affinity binding to glycogen in T conformational state
8-b) AMP
9-b) Phosphorylase kinase
10-d) Insulin
11-b) Glycogenin
12-a) Glycogen synthase
13-d) Glycogen synthetase
14-a) Glycogen synthase is activated in the phosphorylated state
15-d) Violet color


Carbohydrate Metabolism: MCQ on Glycogen Synthesis and Breakdown Carbohydrate Metabolism: MCQ on Glycogen Synthesis and Breakdown Reviewed by Biotechnology on November 06, 2017 Rating: 5

PHOSPHATIDYL CHOLINE AS LUNGS SURFACTANT

November 05, 2017

The surfactants are the chemical substance that is capable of lowering surface tension. The lung surfactants contain a complex mixture of phospholipids, neutral lipids, and specific proteins. The lung surfactants are essential for normal lung function as it reduces surface tension at the air-liquid interface of alveolar spaces. Phosphatidylcholine is the major component of the surfactant comprising 90% of the lipids. Four specific surfactant proteins SP-A, SP-B, SP-C, SP-D. The synthesis and secretion of functional surfactants are confined to type II cells of the alveolar epithelium.

The fundamental pathway for lung surfactant phospholipid synthesis, it's packaging into storage lamellar bodies (LB), secretion into the alveolar lining fluid and recycling back into ATII cells are well known. Bulk surfactant phospholipid synthesized at the ER is transported to LBs by a mechanism that may employ specific carrier proteins and/or traffic through the Golgi. During the processes of synthesis, transport, and selection, the PC components are enriched saturated species that involves
a) the combination of acyl remodeling of unsaturated species,
b) selective transport of saturated species or selective exclusion of unsaturated species.

Newly synthesized surfactant, in the apical membrane (LBs), then adsorbs to the air-liquid interface where saturated PC contributes to surface activity.

Infant respiratory distress syndrome:
The developmental insufficiency of these surfactants production and immature structural immaturity of lungs in neonates leads to a pathological condition known as Infant respiratory distress syndrome. For the prenatal diagnosis, the fetal lung maturity may be tested by sampling the amount of surfactant in the amniotic fluid by amniocentesis. Several tests are available that correlate with the production of surfactant.
Example- Lecithin-sphingomyelin ratio ("L/S ratio"): If the result is less than 2:1, the fetal lungs may be surfactant deficient. The presence of PG usually indicates fetal lung maturity.

History on the identification of Lungs surfactant
Van Neegard first hypothesized that lungs consist of an active substance that exerts and maintain a low alveolar surface tension, allows adequate ventilation of the peripheral airways for normal lungs function, and prevent end-expiratory alveolar collapse. It was strongly believed that these surfactants are lipoproteins- a mixture of phospholipids and proteins. Based on the results obtained from centrifugations and recovery of phospholipids and proteins from lungs washing and homogenates, the composition of lipids and protein were not uniform across the experiments. There was certainly two possibilities:
a) Lung surfactant constitutes large lipoproteins component,
b) Phospholipids are the major lung surfactant and proteins are only artifacts.

Because of uncertainty that if phospholipids are the integral component of large lipoprotein complex or entirely independent entity that function as lung surfactant, researchers have used analysis of protein and lipid mixture obtained from the lung sample, ultracentrifugation to find the fraction of lipoproteins. The research findings concluded that phospholipids are a major component of lung surfactant and a small fraction of proteins function to reduce surface tension in the lungs.
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ACETYL COA CARBOXYLASE: ISOFORMS AND REGULATION

November 05, 2017

Malonyl-CoA is the C2 donor in the de novo synthesis of fatty acids, and it plays an important role as an inhibitor of the carnitine palmitoyl shuttle system for fatty acid oxidation. Acetyl CoA carboxylase is the enzyme that is responsible for carboxylation of acetyl CoA to malonyl CoA. 

Two different isoforms of acetyl CoA carboxylase exists, i.e. ACC1 and ACC2. ACC1 and ACC2 are encoded by two separate genes localized at chromosome 17q12 and 12q23, respectively. The amino acid sequences of ACC1 and ACC2 are approximately 80% identical.

 ACC1 is a multifunctional enzyme encoded by a single gene. ACC1 is composed of three distinct functional units: biotin carboxylase, biotin carboxyl carrier protein, transcarboxylase. In presence of ATP, biotin carboxylase transfers CO2 from bicarbonate to the biotin carboxyl carrier protein, forming the carboxybiotin derivative. The transcarboxylase catalyzes the transfer of the carboxylase group to acetyl CoA forming Malonyl CoA. ACC1 is generally expressed in all tissues, it is expressed in more lipogenic tissues such as liver, adipose, and lactating mammary gland.

 In contrast, ACC2 is highly expressed in heart, muscle and to a lesser extent in the liver. ACC1 derived malonyl-CoA is utilized by FAS for the synthesis of fatty acids in the cytosol. In contrast, the ACC2-generated malonyl CoA functions as an inhibitor of the carnitine/palmityl transferase 1 activity and the transfer of the fatty acyl group through CPT shuttle to inside the mitochondria for beta-oxidation. 


ACETYL COA CARBOXYLASE: ISOFORMS AND REGULATION ACETYL COA CARBOXYLASE: ISOFORMS AND REGULATION Reviewed by Biotechnology on November 05, 2017 Rating: 5

Carbohydrate Metabolism: MCQ on Pentose Phosphate Pathway

November 05, 2017
Multiple Choice Question on the Pentose Phosphate Pathway

1) Which of the following step is common in glycolysis and pentose phosphate pathway?
a) Conversion of glucose to glucose-6-P
b) Conversion of glucose-6-P to ribose-5-P
c) Conversion of glucose-6-P- to fructose-6-P
d) Conversion of glucose to glucose-1-P

2) Pentose phosphate pathway is responsible for generating NADPH (reducing equivalents in the cell) in the cell. Which of the following enzyme is involved in generating NADPH?
a) Glucose-6-P oxidase
b) Glucose-6-P dehydrogenase
c) Glucose-6-P reductase
d) Glucose-6-P synthetase

3) Which of the following step is the rate-limiting step of the pentose phosphate pathway?
a) Transketolase
b) Glucose-6-P dehydrogenase
c) Transaldolase
d) Phosphogluconate dehydrogenase

4) Insulin activates the pentose phosphate pathway. Which of the following enzyme is activated by insulin action?
a) Transketolase
b) Glucose-6-P dehydrogenase
c) Transaldolase
d) Phosphogluconate dehydrogenase

5) Which of the following enzyme is used for diagnosis of thiamine deficiency?
a) Transketolase
b) Glucose-6-P dehydrogenase
c) Transaldolase
d) Phosphogluconate dehydrogenase

6) Glucose -6-Phosphate dehydrogenase is allosterically activated by
a) NADPH
b) NADH
c) NAD +
d) NADP +

7) Glucose-6-Phosphate dehydrogenase is allosterically inhibited by
a) Acetyl CoA
b) Citrate
c) Glucose
d) Fructose

8) In some individuals, ingesting fava beans leads to hemolytic anemia. Which of the following enzyme may be deficient in these individuals?
a) Glucose-6-Phosphatase
b) Glucose-6-P- dehydrogenase
c) Glucose -6-Phosphate Isomerase
d) Glycogen phosphorylase

9) What is the cause of hemolytic anemia in Glucose-6-phosphate deficiency?
a) Decreased ATP in erythrocytes
b) Decreased free radicals in erythrocytes
c) Increased sodium concentration in erythrocytes
d) Increased free radicals in erythrocytes

10) The glutathione cycle is the conversion of oxidized glutathione to reduced glutathione in the presence of NADPH. Which of the following enzyme catalyzes this reaction
a) Glutathione peroxidase
b) Glutathione dehydrogenase
c) Glutathione reductase
d) Glutathione synthetase

Multiple Choice Answers
1-a) Conversion of glucose to glucose-6-P
2-b) Glucose-6-P dehydrogenase
3-b) Glucose-6-P dehydrogenase
4-b) Glucose-6-P dehydrogenase
5-a) Transketolase
6-d) NADP +
7-b) Citrate
8-b) Glucose-6-P- dehydrogenase
9-d) Increased free radicals in erythrocytes
10-c) Glutathione reductase



Carbohydrate Metabolism: MCQ on Pentose Phosphate Pathway Carbohydrate Metabolism: MCQ on Pentose Phosphate Pathway Reviewed by Biotechnology on November 05, 2017 Rating: 5

Lipid Metabolism: MCQ on Fatty acid metabolism synthesis and breakdown

November 01, 2017
Multiple Choice Question on 
Fatty Acid Synthesis and Breakdown

1) Free fatty acids in the plasma

a) Circulate in the unbound state
b) Bind to lipoproteins and circulated
c) Bind to albumin and circulated
d) Bind to a fatty acid binding protein and circulated
Answer (Click Here)


2) In what compartment does the de novo fatty acid synthesis occur?
a) Mitochondria
b) Peroxiosome
c) Endoplasmic reticulum
d) Cytosol
Answer (Click Here)


3) What is the precursor for fatty acid synthesis?
a) Acetyl CoA
b) Propionyl CoA
c) Succinyl CoA
d) Acetoacetyl CoA
Answer (Click Here)


4) The conversion of acetyl CoA to malonyl CoA is the rate-limiting step in the fatty acid synthesis. Which of the following enzyme catalyzes the above-mentioned reaction?
a) Acetyl CoA carboxylase
b) Malonyl CoA synthetase
c) Acetyl CoA decarboxylase
d) Malonyl CoA synthase
Answer (Click Here)

5) The acetyl CoA is produced in the mitochondria and must be transported into the cytosol for synthesis of fatty acid.  Which of the following is true regarding its transport?
a) Acetyl CoA is diffused from the mitochondrial membrane
b) Acetyl CoA is transported by its specific transporter protein
c) Acetyl CoA is converted into pyruvate, enters into the cytosol and acetyl CoA is regenerated
d) Acetyl CoA is converted into citrate, enters into the cytosol and acetyl CoA is regenerated.
Answer (Click Here)


6) What is the allosteric regulator of acetyl CoA carboxylase?
a) Fatty acid
b) ATP
c) Citrate
d) Acetyl CoA
Answer (Click Here)


7) Which of the following event inactivates acetyl CoA carboxylase?
a) ADP-Ribosylation
b) Glycosylation
c) Phosphorylation
d) Farnesylation
Answer (Click Here)




8) Which of the following is not a positive regulator of acetyl CoA carboxylase
a) Excess calories
b) Insulin
c) Citrate
d) Long chain fatty acid
Answer (Click Here)


9) Which of the following enzyme statement is not true regarding fatty acid synthase?
a) Fatty acid synthase is a multifunctional enzyme
b) Fatty acid synthase is active as a dimer
c) Fatty acid synthase is activated by high-calorie food
d) Fatty acid synthase complex is inhibited by its phosphorylation
Answer (Click Here)


10) What form of energy is required for fatty acid biosynthesis?
a) ATP
b) NADH
c) NADPH
d) FADH2
Answer (Click Here)


11) What is the source of NADPH required for fatty acid synthesis?
a) Pentose phosphate pathway
b) Malic enzyme
c) Both
d) None
Answer (Click Here)




Lipid Metabolism: MCQ on Fatty acid metabolism synthesis and breakdown Lipid Metabolism: MCQ on Fatty acid metabolism synthesis and breakdown Reviewed by Biotechnology on November 01, 2017 Rating: 5
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