生化作业1. Pathway of Atoms in Fermentation A “pulse-chase” experiment using 14C-labeled carbon sources is carried out on a yeast extract maintained under strictly anaerobic conditions to produce ethanol. The experiment consists of incubating

生化作业1. Pathway of Atoms in Fermentation A “pulse-chase” experiment using 14C-labeled carbon sources is carried out on a yeast extract maintained under strictly anaerobic conditions to produce ethanol. The experiment consists of incubating
生化作业
1. Pathway of Atoms in Fermentation
A “pulse-chase” experiment using 14C-labeled carbon sources is carried out on a yeast extract maintained under strictly anaerobic conditions to produce ethanol. The experiment consists of incubating a small amount of 14C -labeled substrate (the pulse)with the yeast extract just long enough for each intermediate in the fermentation pathway to become labeled. The label is then “chased” through the pathway by the addition of excess unlabeled glucose. The chase effectively prevents any further entry of labeled glucose into the pathway.
(a) If [1-14C]glucose (glucose labeled at C-1 with 14C) is used as a substrate, what is the location of 14C in the product ethanol? Explain.
(b) Where would 14C have to be located in the starting glucose to ensure that all the14C activity is liberated as 14CO2during fermentation to ethanol? Explain
2. Blood Lactate Levels during Vigorous Exercise
The concentrations of lactate in blood plasma before, during, and after a 400 m sprint are shown in the graph.
(a) What causes the rapid rise in lactate concentration?
(b) What causes the decline in lactate concentration after completion of the sprint? Why does the decline occur more slowly than the increase?
(c) Why is the concentration of lactate not zero during the resting state?
3. Respiration Studies in Isolated Mitochondria
Cellular respiration can be studied in isolated mitochondria by measuring oxygen consumption under different conditions. If 0.01 M sodium malonate is added to actively respiring mitochondria that are using pyruvate as fuel source, respiration soon stops and a metabolic intermediate accumulates.
(a) What is the structure of this intermediate?
(b) Explain why it accumulates.
(c) Explain why oxygen consumption stops.
(d) Aside from removal of the malonate, how can this inhibition of respiration be overcome? Explain.
4. Keeping the Sweet Taste of Corn
The sweet taste of freshly picked corn (maize) is due to the high level of sugar in the kernels. Store-bought corn (several days after picking) is not as sweet, because about 50% of the free sugar is converted to starch within one day of picking. To preserve the sweetness of fresh corn, the husked ears can be immersed in boiling water for a few minutes (“blanched”) then cooled in cold water. Corn processed in this way and stored in a freezer maintains its sweetness. What is the biochemical basis for this procedure?
5.Estimation of Vmax and Km by Inspection

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生化作业1. Pathway of Atoms in Fermentation A “pulse-chase” experiment using 14C-labeled carbon sources is carried out on a yeast extract maintained under strictly anaerobic conditions to produce ethanol. The experiment consists of incubating
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