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Chem 301 Study questions for Unit 6 -10 GRADED A 2024 Athabasca University

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Chem 301

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Athabasca University (AU )

1. For metabolism in multicellular organisms to proceed efficiently, it is important that the final products be gases, water, or both. Why? To maintain metabolism in a steady state, there must be no possibility of a build–up of final products. The easiest disposal products are the multicellula...

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Chem 301 Study questions for Unit 6 -10
GRADED A 2024

Introduction to Biochemistry (Athabasca University)

,Chem 301 Study questions Unit 6-10:

UNIT 6: - Metabolism I

Lesson 1: Overview of Metabolism Concepts

1. For metabolism in multicellular organisms to proceed efficiently, it is
important that the final products be gases, water, or both. Why?

To maintain metabolism in a steady state, there must be no possibility of a
build–up of final products. The easiest disposal products are the
multicellular organism’s universal solvent, gases, or both.

2. Look at the two starred reactions in the lesson just covered (the
redox reactions involving NADH and O2). Compare the tendency of
NADH to donate electrons and the tendency of oxygen to accept
them. If NADH and oxygen are mixed, will the electrons stay with
NADH or go to oxygen? Explain.

If NADH and oxygen are mixed, electrons will be transferred from NADH to
oxygen with the release of considerable energy:

NADH + ADH + ½ O2 + H+ ↔ NAD+ + H2O εo′ = 1.13 V

3. What structural feature do the “high-energy” compounds ATP, FADH2,
and NADH share with acetyl-CoA?

The “high-energy” compounds share an ADP unit or, in the case of
acetyl-CoA, a closely related derivative.

Lesson 2: Glycolysis, Fermentation, and Gluconeogensis

1. Add up the ten physiological free energy values for the ten glycolysis
reactions in erythrocytes (see the table in the commentary above).
What is the overall ΔG for glycolysis? Why can the reaction never
come to equilibrium in vivo?

ΔG = −74.0 kJ/mol for the overall glycolytic process. This large negative
value indicates that the overall reaction is spontaneous (i.e., the final
product, pyruvate, is being removed fast enough, and glucose is being added
constantly enough), so that there is no back reaction:

Pyruvate → Glucose

, 2. Glycolysis is inhibited by iodoacetic acid through inactivation of the
enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). As a
result, there is an accumulation of fructose-1,6-biphosphate. Why is
this product more prevalent than glyceraldehyde-3-phosphate and
dihydroxyacetone phosphate, the products that form immediately
preceding GAPDH?

The reaction that converts fructose 1,6-bisphosphate to
glyceraldehyde-3-phosphate and dihydroxyacetone phosphate is near
equilibrium in vivo (i.e., ΔG near zero), while the preceding reaction
producing fructose 1,6-bisphosphate is not. Therefore it is F1,6BP that will
accumulate, not glyceraldehyde-3-phosphate and dihydroxyacetone
phosphate.

3. The “Pasteur effect” is the dramatic decrease in glucose consumption
when oxygen is introduced to an anaerobic fermentation broth. Why
do the yeast cells use less glucose after oxygen is introduced? How
much less glucose do they use after oxygen is introduced?

The introduction of oxygen allows yeast to convert from anaerobic to
aerobic metabolism. Since aerobic metabolism provides more ATP, the
amount of glucose that must be used to nourish the yeast is much less.
Approximately 6% of the glucose metabolized anaerobically is needed to
provide the same amount of energy under aerobic conditions.

4. Why do you get hot when you exercise?

PEP is a very high-energy compound. The reaction that converts PEP to
pyruvate is so highly energetically favourable (very negative ΔG) that there
is almost enough energy in PEP to stimulate production of a second ATP
through substrate level phosphorylation, but it is not used. The excess
energy is lost as heat.

5. What are the three enzymes that are regulated in glycolysis? How
does AMP affect glycolysis?

The three enzymes that are regulated in glycolysis are: hexokinase,
phosphofructokinase (PFK), and pyruvate kinase. High amounts of AMP

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Chem 301 Study questions for Unit 6 -10 GRADED A 2024 Athabasca University

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