Glycolysis Shorteut Suppose you discovered a mutant yeast whose glycolytic pathw

Question

Glycolysis Shorteut Suppose you discovered a mutant yeast whose glycolytic pathway was shorter because of the presence of a new enzyme catalyzing the reaction NAD+ NADH +H Glyceraldehyde 3-phosphate +IH2 3-phosphoglycerate Would shortening the glycolytic pathway in this way benefit the cell? Explain. What is net energy production in yeast mutant? 4 points Will this mutant yeast will be able to survive/grow under 6 points a) Aerobic conditions b) Anaerobic conditions Glycogen is used as fuel source for energy, What is the net production of ATP at the end of glycolysis by breaking one molecule of glucose? 5 points

Explanation / Answer

Ans. #1. Glycolysis consists of 10 reaction steps, each step occurring at its own rate. Each reaction step, thus, consumes a fraction of the total time taken to convert a glucose into two pyruvates.

In normal glycolysis, conversion of G-3-P in 3-PGA via 1,3-bisPGA produces 1 ATP.

The glycolysis in presence of new enzyme does not produces any ATP during the conversion of G-3-P in 3-PGA. Thus, the new pathway causes loss of 1 ATP, while the overall reaction remains the same.

# The shortening of glycolytic pathway may is most likely to give following benefits-

I. The overall time required to convert glucose into pyruvate is reduced because the lost required for the intermediate reaction is eliminated. So, overall speed (rate) of glycolysis is increased.

II. Increase in speed of glycolysis increases the rate of pyruvate production. So, the cell will have relatively higher concertation of pyruvate as substrate for tricarboxylic acid cycle (TCA). Higher [pyruvate] as substrate shifts the overall equilibrium for TCA to the right. So, more ATP will be produced per unit time through TCA and ETC.

By doing so the squirrel may generate metabolic energy more rapidly and carryout faster movements for prolonged time.

III. Cell has limited pool of NAD+/NADH. During glycolysis NAD+ is reduced to NADH. So, [NAD+] gradually decreases as glycolysis continues. If not regenerated, the unavailability of NAD+ will cause glycolysis to shut down.    

Increase in speed of TCA also increases the speed of regeneration of cytoplasmic NAD+. Increased rate of NAD+ regeneration also ensures that glycolysis does not face the limited availability of NAD+, so glycolysis is also less likely to be stopped due to limited NAD+.

#1.B. Net energy production: The net ATP gain of glycolysis is reduced by 1 ATP per glucose. The ATP production through citric acid cycle and ETC remains unaffected.

So,

Net energy gain per glucose in mutant yeast =

Normal ATP gain per glucose – Loss of 1 ATP per glucose

                                    = 30 ATP – 1 ATP

                                    = 29 ATP

#1. C Survival/ Growth-

#A. Under aerobic condition: The total ATP gain from complete oxidation of 1 glucose is 29 ATP. The ATP gain is nearly the same as the normal condition (30 ATP). So, the mutant yeast grows almost normal.

#B. Anaerobic condition: The ATP gain is reduced by 50% as ATP gain is reduced by 1 ATP out of total 2 ATP gain during glycolysis. So, the cell is most likely to go deprived of energy due to 50% reduction in net ATP gain, and may even die due to it.

#2. Net ATP gain from 1 glucose molecule = 29 ATP    (See #1.B)   

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