The V max values for certain enzymes can be used as an indication of the relativ
ID: 176466 • Letter: T
Question
The Vmax values for certain enzymes can be used as an indication of the relative importance of various ATP-producing pathways. The Vmax values (in mmol substrate/min/g tissue) for several enzymes from the pectoral muscles (chest muscles used for flying) of pigeon and pheasant are listed below:
Enzyme
Pigeon
Pheasant
Hexokinase
3.0
2.3
Glycogen phosphorylase
18.0
120.0
Phosphofructokinase-1
24.0
143.0
Citrate synthase
100.0
15.0
Triacylglycerol synthase
0.07
0.01
Discuss the relative importance of the various ATP-producing pathways in the pectoral muscles of these birds.
Predict oxygen consumption in the two muscles.
Judging solely from the data in the table, predict which bird is a long-distance flyer and justify your answer.
Why were these enzymes selected for comparison? Would the activities of triose phosphate isomerase and malate dehydrogenase be equally good basis for comparison? Explain.
Enzyme
Pigeon
Pheasant
Hexokinase
3.0
2.3
Glycogen phosphorylase
18.0
120.0
Phosphofructokinase-1
24.0
143.0
Citrate synthase
100.0
15.0
Triacylglycerol synthase
0.07
0.01
Explanation / Answer
The various ATP-producing pathways in the pectoral muscles of these birds are:
1. Glycolysis--It is the 1st pathway for metabolizing sugar which breaks sugar into 3C compounds viz.pyruvate and lactate. These occur in cytoplasm with the formation ofATP. The final products of glycolysis are lactate/pyruvate and ATP. For each glucose molecule that is metabolized to two pyruvate or lactate molecules, two ATP molecules are formed.
2. Pathway 2- In this pathway, the mitochondria pyruvate dehydrogenase converts 3C compound to 2C compound acetyl CoA and CO2 is released. The extra H's are stored in NADH temporarily. The final products of pyruvate dehydrogenase are ATP, NADH, acetylCoA and CO2.
2.Beta-oxidation --It is the pathway in which fatty acids are converted into 2C compound viz.acetyl CoA and H's are temporarily stored in NADH and FADH.
3. Kreb's Cycle- In this pathway foodis metabolized into CO2 and H2O and H's are temporarily stored in NADH and FADH.
4. Oxidative phosphorylation- This pathway takes H from NADH and FADH adds it to oxygen from breathing and converts it to water along with formation of many ATP.
Beta oxidation is observed to be predominant in the pigeon and anaerobic glycolysis in case of pheasant.
Relatively more oxygen is consumed by the pigeon muscle as compared to the pheasant.
More energy per gram is produced from fat as compared to glycogen. During anaerobic glycolysis formation of lactate creates fatigue and limits tissue tolerance. Thus, pigeon is a long distance flyer.
These enzymes are considered to be regulatory enzymes in their respective pathways which thereby limit ATP production rates.
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