What are the precursors of gluconeogenesis?: Biochemistry

Gluconeogenesis is the metabolic pathway through which glucose is synthesized from a non-glucose (carbohydrate) precursors including pyruvate, lactate, and amino acids.

Pyruvate and Lactate:
The precursor of gluconeogenesis is primarily pyruvate.
Pyruvate is the end product of glycolysis which can be further metabolized to either acetyl CoA or lactate. The conversion of pyruvate to these products depends on tissue type, ATP status, and regulatory effector molecules. The conversion of pyruvate to acetyl CoA is an irreversible step that is catalyzed by the enzyme pyruvate dehydrogenase that occurs mainly in oxidative tissues such as the liver, cardiac muscle. 
In contrast, the conversion of pyruvate to lactate is a reversible step catalyzed by lactate dehydrogenase that occurs mainly in non-oxidative tissues such as red blood cells. The lactate dehydrogenase is also present in skeletal muscle that converts pyruvate to lactate during vigorous exercise.

Figure 1: Fates of Pyruvate PDH- Pyruvate dehydrogenase, LDH- Lactate dehydrogenase

Pyruvate and Lactate formed in peripheral tissues are transported into the liver for gluconeogenesis.
The lactate formed during anaerobic glycolysis can directly be shuttled into the liver, there the lactate dehydrogenase isoenzyme converts lactate and pyruvate. 
Alternately, the lactate formed during anaerobic glycolysis is reconverted into pyruvate and subsequently converted to alanine by the enzyme alanine transaminase. The lactate or alanine diffuse into the bloodstream that is taken up by the liver and alanine is converted by liver alanine transaminase to convert into pyruvate.

Figure 2: Glucose-alanine cycle

Figure 3: Cori cycle or lactic acid cycle in Erythrocytes

Amino acids
Glucogenic amino acids are a group of amino acids whose metabolic intermediates can enter the gluconeogenic pathway and form glucose. Examples include alanine, aspartate, glutamate, etc.

Propionyl CoA
Propionyl CoA an intermediate of odd-chain fatty acids is also the precursor for the gluconeogenic pathway. Propionyl CoA is converted into methyl malonyl CoA by the enzyme propionyl CoA carboxylase ( a biotin-containing enzyme). The methyl malonyl CoA is converted into succinyl CoA by the enzyme methyl malonyl CoA mutase and the succinyl CoA enters the TCA cycle to form oxaloacetate. The oxaloacetate thus formed enters the gluconeogenic pathway to form glucose.