Chapter 15: Metabolism Basic Concepts and Design

Question 1

The third state of digestion involves:

Answer 1

acetyl CoA

Question 2

The reaction pathways that transform fuels into cellular energy are:

Answer 2

catabolic

Question 3

The metabolic pathways that require energy and are often biosynthetic processes are:

Answer 3

anabolic

Question 4

What is the standard-state free energy (ΔG°′) for the hydrolysis of ATP to ADP?

Answer 4

−30.5 kJ/mol

Question 5

Which energy source is used to regenerate ATP from ADP and Pi?

Answer 5

oxidation of carbon to CO2

Question 6

Which is the correct coenzyme–carrier pair?

Answer 6

coenzyme A: acyl.

Question 7

Which of the following molecules has a higher phosphoryl-transfer potential than ATP?

Answer 7

phosphoenolpyruvate, creatine phosphate, and 1,3-bisphosphoglycerate

Question 8

Metabolic processes are regulated by:

Answer 8

transcriptional regulation of the amount of enzyme, allosteric control of enzyme activity, and the accessibility of substrates by compartmentalization.

Question 9

Some of the mechanisms by which enzyme catalytic activity is controlled are:

Answer 9

allosteric control, feedback inhibition, and covalent modification.

Question 10

What is meant by intermediary metabolism?

Answer 10

The highly integrated biochemical reactions that take place inside the cell.

Question 11

Differentiate between anabolism and catabolism.

Answer 11

Anabolism is the set of biochemical reactions that use energy to build new molecules and, ultimately, new cells.

Catabolism is the set of biochemical reactions that extract energy from fuel sources or breakdown molecules.

Question 12

What are the three primary uses for cellular energy?

Answer 12

1. Cellular Movements and the performance of mechanical work
2. Active transport
3. Biosynthetic reactions

Question 13

Define: Cellular Energy Currency

Answer 13

ATP

Question 14

Define: Anabolic Electron Carrier

Answer 14

NADP+

Question 15

Define: Phototroph

Answer 15

Converts light energy into chemical energy

Question 16

Define: Catabolic Electron Carrier

Answer 16

NAD+

Question 17

Define: Oxidation-Reduction Reaction

Answer 17

Transfers electrons

Question 18

Define: Activated carrier of two-carbon fragments

Answer 18

Coenzyme A

Question 19

Define: Vitamin

Answer 19

Precursor to coenzymes

Question 20

Define: Anabolism

Answer 20

Requires energy

Question 21

Define: Amphibolic Reaction

Answer 21

Used in anabolism and catabolism

Question 22

Define: Catabolism

Answer 22

Yields energy

Question 23

What factors account for the high phosphoryl-transfer potential of nucleoside triphosphates?

Answer 23

Charge repulsion, resonance stabilization, increase in entropy, and stabilization by hydration.

Question 24

Why does it make good sense to have a single nucleotide, ATP, function as the cellular energy currency?

Answer 24

Having only one nucleotide function as the energy currency of the cell enables the cell to monitor its energy status.

Question 25

Why is ATP usually associated with magnesium or manganese ions?

Answer 25

These divalent ions bind to the negatively charged oxygen atoms found on the phosphoryl groups and help stabilize the charges on ATP.

Question 26

What is the direction of each of the following reactions when the reactants are initially present in equimolar amounts?

ATP + H2O ADP + Pi

Answer 26

To the left

Question 27

What is the direction of each of the following reactions when the reactants are initially present in equimolar amounts?

ATP + glycerol glycerol 3-phosphate + ADP

Answer 27

To the right

Question 28

What is the direction of each of the following reactions when the reactants are initially present in equimolar amounts?

ATP + pyruvate phosphoenolpyruvate +ADP

Answer 28

To the left

Question 29

What is the direction of each of the following reactions when the reactants are initially present in equimolar amounts?

ATP + glucose glucose-6-phosphate + ADP

Answer 29

To the right

Question 30

Metabolic pathways frequently contain reactions with positive standard free-energy values, yet the reactions still take place. How is it possible?

Answer 30

The free-energy changes of the individual steps in a pathway are summed to determine the overall free-energy change of the entire pathway. Consequently, a reaction with a positive free-energy value can be powered to take place if coupled to a sufficiently exergonic reaction.

Question 31

What is the structural feature common to ATP, FAD, NAD+, and CoA?

Answer 31

An ADP unit

Question 32

Thioesters, common in biochemistry, are more unstable (energy rich) than oxygen esters. Explain.

Answer 32

The electrons of the C=O bond cannot form resonance structures with the C-S bond that are as stable as those that they can form with the C-O bond. Thus, the thioester is not stabilized by resonance to the same degree as is an oxygen ester.

Question 33

What are the three principle means of controlling metabolic reactions?

Answer 33

1. Control of the amount of enzymes
2. Control of enzyme activity
3. Control of the availability of substrates

Question 34

The muscles of some invertebrates are rich in arginine phosphate (phosphoarginine). Propose a function for this amino acid derivative.

Answer 34

Arginine phosphate in invertebrate muscle, like creatine phosphate in vertebrate muscle, serves as a reservoir of high potential phosphoryl groups. Arginine phosphate maintains a high level of ATP in muscular exertion.

Question 35

Creatine is a popular, but untested, dietary supplement.

What is the biochemical rationale for the use of creatine?

Answer 35

The rationale behind creatine supplementation is that it would be converted into creatine phosphate and thus serve as a rapid means of replenishing ATP after muscle contraction.

Question 36

Creatine is a popular, but untested, dietary supplement.

What type of exercise would most benefit from creatine supplementation?

Answer 36

If creatine supplementation were beneficial, it would affect acitivities that depend on short bursts of activity; any sustained activity would require ATP generation by fuel metabolism, which requires more time.