2016_FRQ_by_topics_Core_topics_Respiration_and_Photosynthesis_ANS

Respiration 1. [Tutorial 9286/08/2/7a] Outline the main stages of glycolysis. [8] Glycolysis occurs in the cytoplasm and does not require the presence of oxygen. It involves the oxidation / breakdown of glucose to yield two molecules of pyruvate; Glycolysis can be divided into two phases: energy investment phase and energy pay-off phase; During the energy investment phase , energy in the form of 2 ATP is used per glucose molecule; Activation of glucose occurs to make it more chemically reactive with the phosphorylation of glucose using ATP to produce glucose-6-phosphate. This reaction is catalysed by hexokinase; Glucose-6-phosphate is then isomerised to fructose-6-phosphate by isomerase; Phosphorylation of fructose-6-phosphate using ATP produces fructose-1,6-bisphosphate. This reaction is catalysed by phosphofructokinase; Cleavage / Splitting of fructose-1,6-bisphosphate produces 2 molecules of glyceraldehyde- 3-phosphate (GALP); During the energy payoff phase, energy in the form of 4 ATP is produced via substrate level phosphorylation; Each GALP is subsequently converted to pyruvate via multiple steps where 2 ATP are generated via substrate level phosphorylation and protons and e lectrons released via dehydrogenation are transferred to 1 oxidised NAD to form 1 reduced NAD; Since 2 molecules of GALP is formed from 1 glucose molecule, therefore 2 pyruvate , 4 ATP and 2 reduced NAD are produced per glucose molecule; Or Breakdown down 1 molecule of glucose to 2 pyruvate, 2 reduced NAD, with net gain of 2 ATP; [AJC 2013] Explain the significance of the steps in glycolysis. [5]  Glycolysis is a common step in both anaerobic and aerobic respiration;  Phosphorylation of glucose (by 2 ATP) is to activate it;  Phosphorylation of glucose (by 2 ATP) / glucose -6-phosphate results in glucose being trapped in the cytosol/ unable to leave the cell through the same glucose carrier protein/ committed to the end of glycolysis;  PFK which catalyse the phosphorylation of fructose phosphate also control rate of glycolysis/ high rate of ATP act as allosteric inhibitor to PFK;  ATP synthesis by substrate level phosphorylation;  Forms two glyceraldehyde-3-phosphate/ triose phosphate from one glucose;  Forms two reduced NAD (NADH) (by dehydrogenation);  Which later give 6 ATP by oxidative phosphorylation;  Pyruvate can enter into link reaction/ mitochondria or be converted to lactate (in mammals) or ethanol and carbon dioxide (in yeast);  Pyruvate is small enough to enter mitochondrion for aerobic respiration; [ACJC 2010 H1 P2] Describe the role of glycolysis in respiration. [7] 1. glycolysis - oxidation of glucose to pyruvate; 2. phosphorylation of glucose; 3. add (2) phosphate groups to glucose; 4. from (2 molecules of) ATP;

5. to produce (1 molecule of) fructose-1,6-bisphosphate; 6. to raise the energy level of glucose; 7. so that useful energy can be harvested in later steps in the pathway; 8. oxidation