Biochemistry question. After a person has a typical meal with plenty of starch,
ID: 163702 • Letter: B
Question
Biochemistry question.
After a person has a typical meal with plenty of starch, blood glucose levels go up and are above normal for at least 75-90 minutes. During this period consider what is happening to the pathways of glucose metabolism we have been studying, and answer the questions about this listed below, for liver and muscle tissues.
(a) List all the pathways that are “turned on”, and which are turned off (Glycolysis, Gluconeogenesis, TCA Cycle, Glycogenesis, Pentose Phosphate Pathway). Also, for the “turned-on” pathways describe what each is contributing to the needs of the cells and whole organism in this situation (high blood glucose). (Consider what each is producing and what that provides the cells in these organs directly and/or indirectly.)
(b) For each “turned-on” pathway, describe in detail what has caused this pathway to be “on”. (Consider all forms of regulation we have covered, as appropriate.) This question is about what makes each pathway go forward, faster or slower; the main things involved in affecting the flow of each pathway in this particular state (high blood glucose).
Explanation / Answer
a) High blood glucose level will turn on turn on the glucose metabolism pathway to obtain energy for the growing cells and tissues. The metabolism of glucose is inevitable as it is the energy source for muscle cells, brain cells, red blood cells etc.
Breakdown of one molecule of glucose by aerobic respiration involving both glycolysis and Krebs cycle yields about 33-35 ATP.
The pathways for aerobic respiration to yield ATP from the substrate glucose will turn on:
1. Glycolysis – In this pathway there is oxidation of glucose molecules to obtain ATP and Pyruvate.
2. TCA Cycle- Pyruvate obtained from glycolysis enters the TCA cycle or the Krebs cycle which is also known as the citric acid cycle after oxidative decarboxylation of Pyruvate into Acetyl CoA.
3. PPP or Pentose Phosphate Pathway is an alternative pathway in cellular respiration parallel to glycolysis during which there is regeneration of NADPH and conversion of hexoses into pentoses.
4. Glycogenesis or the conversion of excess glucose into glycogen for cellular storage. Glycogenesis prevents excessive osmotic pressure to build up inside the cell due to accumulation of glucose molecules.
Gluconeogenesis will turn ‘off’ as the glucose level is already high. Gluconeogenesis is the de novo synthesis of glucose from simple organic compounds like some amino acids in cellular protein converting into glucose.
b) The turned on pathway in this particular state will be as under:-
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