Concept 9.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways

Question 1

We obtain most of our calories in the form of fats, proteins, and carbohydrates such as .

Answer 1

sucrose and other disaccharides, and starch, a polysaccharide

Question 2

Glycolysis can accept a wide range of carbohydrates for

Answer 2

catabolism.

Question 3

In the digestive tract, starch is hydrolyzed to glucose, which can then be broken down in the cells by

Answer 3

glycolysis and the citric acid cycle

Question 4

The digestion of disaccharides, including

Answer 4

sucrose, provides glucose and other monosaccharides as fuel for respiration.

Question 5

Many of the amino acids are used by the organism to build

Answer 5

new proteins.

Question 6

Amino acids present in excess are converted by enzymes to intermediates of

Answer 6

glycolysis and the citric acid cycle

Question 7

Before amino acids can feed into glycolysis or the citric acid cycle, their amino groups must be removed, a process called

Answer 7

deamination.

Question 8

The nitrogenous waste is excreted from the animal in the form of

Answer 8

ammonia (NH3), urea, or other waste products.

Question 9

can also harvest energy stored in fats obtained either from food or from fat cells in the body.

Answer 9

Catabolism

Question 10

After fats are digested to glycerol and fatty acids, the glycerol is converted to

Answer 10

glyceraldehyde 3-phosphate, an intermediate of glycolysis.

Question 11

breaks the fatty acids down to two-carbon fragments, which enter the citric acid cycle as acetyl CoA.

Answer 11

beta oxidation

Question 12

NADH and FADH2 are also generated during beta oxidation; they can enter the electron transport chain, leading to further

Answer 12

ATP production.

Question 13

Not all the organic molecules of food are destined to be oxidized as fuel to make

Answer 13

ATP.

Question 14

Compounds formed as intermediates of glycolysis and the citric acid cycle can be diverted into anabolic pathways as precursors from which the cell can synthesize the

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molecules it requires.

Question 15

humans can make about half of the 20amino acids in proteins by modifying compounds siphoned away from the citric acid cycle; the rest are .

Answer 15

“essential amino acids” that must be obtained in the diet

Question 16

these anabolic, or biosynthetic, pathways do not generate ATP, but instead

Answer 16

consume it.

Question 17

Basic principles of supply and demand regulate the

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metabolic economy.

Question 18

If there is a surplus of a certain amino acid, for example, the anabolic pathway that synthesizes that amino acid from an intermediate of the citric acid cycle is

Answer 18

switched off.

Question 19

The most common mechanism for this control is feedback inhibition:

Answer 19

The end product of the anabolic pathway inhibits the enzyme that catalyzes an early step of the pathway

Question 20

The cell also controls its

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catabolism

Question 21

f the cell is working hard and its ATP concentration begins to drop, respiration

Answer 21

speeds up.

Question 22

When there is plenty of ATP to meet demand, respiration

Answer 22

slows down

Question 23

Phosphofructokinase is an allosteric enzyme with receptor sites for specific

Answer 23

inhibitors and activators

Question 24

It is inhibited by

Answer 24

ATP and stimulated by AMP (adenosine monophosphate)

Question 25

As ATP accumulates, inhibition of the enzyme slows down

Answer 25

glycolysis.

Question 26

The enzyme becomes active again as cellular work converts ATP to ADP (and AMP) faster than .

Answer 26

ATP is being regenerated

Question 27

is also sensitive to citrate, the first product of the citric acid cycle.

Answer 27

Phosphofructokinase

Question 28

If citrate accumulates in mitochondria, some of it passes into the cytosol and inhibits

Answer 28

phosphofructokinase.

Question 29

As citrate accumulates, glycolysis slows down, and the supply of pyruvate and thus acetyl groups to the citric acid cycle

Answer 29

decreases

Question 30

f citrate consumption increases, either because of a demand for more ATP or because anabolic pathways are draining off intermediates of the citric acid cycle,

Answer 30

glycolysis accelerates and meets the demand.

Question 31

The energy that keeps us alive is released, not _____________, by cellular respiration.

Answer 31

produced