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Gas exchange and respiration
triose phosphate produced in the lysis of
Fructose-1, 6-biphosphate. But the two Exercise 6.2
ATP formed are used to pay back the 1. Discuss the role of enzymes in a
initial ATP used during the first process glycolytic pathway.
of glycolysis (phosphorylation of glucose 2. What would happen if the first
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stage). enzyme in glycolysis is irreversibly
inhibited by a toxic substance?
The formed 3-PGA is converted into
2-phosphoglycerate or 2-phosphoglyceric 3. Starting with glucose, write
the overall reaction for aerobic
acid (2-PGA) by phosphoglyceromutase respiration.
(phosphoglycerate mutase) enzyme.
This enzyme rearranges the phosphate 4. What are the main stages of aerobic
group from the third carbon of 3-PGA respiration? List down the important
to the second carbon, hence forming materials that are involved in each
stage.
2-PGA. The 2-phosphoglycerate is then
converted into phosphoenol pyruvate 5. The initial stages of glycolysis
(PEP) under the influence of enolase involve the use of ATP. Explain.
enzyme, in this reaction water molecule is 6. Explain the mechanism of gas
removed from 2-phosphoglycerate. Then exchange in plants.
the phosphoenol pyruvate is converted
into pyruvate (pyruvic acid) by pyruvate 6.3.3 The fate of pyruvic acid
kinase enzyme, where by the phosphate The pyruvate produced during glycolysis
group (Pi) from PEP is transferred to has two possible fates, depending on the
ADP molecule and combine to form availability of oxygen in the cell. In the
ATP molecule. Again two molecules of presence of oxygen, the pyruvate will
ATP and two pyruvate are formed as enter Kreb’s cycle in which they will be
explained earlier. This is because the completely oxidised into carbon dioxide
triose phosphate has to enter twice in the and water. Alternatively, in the absence
glycolysis process that is; when 3-PGAL of oxygen (in anaerobic condition) the
is used, the dihydroxyacetone phosphate pyruvate will undergo fermentation.
is converted into 3-PGAL and enters the
cycle. The formation of pyruvate ends the
glycolysis process (Figure 6.9).
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