Question

4)   In the absence of O2 fermentation will occur, why?.....what does it yield that the organism needs from these reactions? Why?

5)   Gluconeogenesis is the production of glucose from non-carbohydrate precursors.
a.   What distinguishes glycolysis from gluconeogenesis? (hints: substrates, energetics of reactions, where do they occur)
b.   What molecule is a key regulator of glycolysis and gluconeogenesis? What does it do? (p. 245)

Answer 1

Ans) fermentation reactions do not require oxygen it is an anaerobic reaction when cells need energy in lack of oxygen conditions they switch to fermentation . The substrate i. E, glucose is converted to ethanol or lactic acid producing energy in the form on ATP. This ATP is required by organisms for cellular metabolism and respiration.

Glycolysis	gluconeogenesis
Substrate is glucose or glycogen	substrates are lactate, pyruvate, glucogenic amino acids, propionate and glycerol
Glycolysis Net ATP synthesis is 8 or say 7 as one ATP is utilised in step one with hexokinase. Summary Glucose + 2ADP +2 Pi ====> 2 lactate +2 ATP.	No Net ATP synthesised in this process but 4ATP and and 2 GTP molecules are utilised. Summary 2 pyruvate + 4ATP +2 GTP +2NADH + 2H+ +6H2O ====> glucose + 2NAD++ 4ADP + 2GDP +6 Pi + 6H+.
Occurs in cells lacking mitochondria this is in the cytosol of RBCs, lens, cornea.	in cytosol. Mostly takes place in liver and in kidney matrix also.

Key regulator in gluconeogenesis is hormone Glucagon.

It stimulates gluconeogenesis in 2 ways.

Pyruvate kinase is converted to inactive form, reduced pyruvate kinase concentration leads to decrease in conversion of phosphoenol pyruvate to pyruvate and phosphoenol pyruvate gets diverted to form glucose.

It reduces the concentration of 2,6 bisphosphate, it causes allosteric inhibition of fructose 1,6 bisphosphate which favours gluconeogenesis.

Key regulator in glycolysis is hwxokinase and phosphofructokinase.

Hexokinase is inhibited by glucose - 6- phosphate. So it will prevent accumulation of glucose - 6 phosphate due to product inhibition.

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