Chapter 3 Study Questions (Part 2)

Question 1

many enzymatically catalyzed reactions are reversible, except for… (2)

Answer 1

1. reactions that have very large negative Gibbs free energy values
2. reactions that involve ATP

Question 2

all steps in glycolysis that do not involve ATP are…

Answer 2

reversible

Question 3

which steps in glycolysis are reversible? why?

Answer 3

those that don’t involve ATP. because of where phosphate is located on ATP.

Question 4

what are three reasons that cells do not store ATP?

Answer 4

1. not stable (doesn’t last long)
2. less energy dense than glucose (1:1 vs. 1:32)
3. absorbs a ton of water, cell swells to unhealthy size.

Question 5

what are the different energy sources used by the cell to produce ATP?

Answer 5

carbohydrate
fatty acids
proteins

Question 6

what do we store carbohydrates as?

Answer 6

glycogen

Question 7

what do we store fatty acids as?

Answer 7

triglycerides

Question 8

what do we store proteins as?

Answer 8

we don’t store it

Question 9

which energy source provides the most energy?

Answer 9

lipids, because they are the most energy dense.

Question 10

what are the two models of enzyme catalysis?

Answer 10

lock and key (we don’t use)

induced fit

Question 11

what is the induced fit model of enzyme catalysis? why do we use it?

Answer 11

not fit exactly, induced fit. explains how the reaction can keep going.

Question 12

what is the lock and key model of enzyme catalysis?

Answer 12

doesn’t explain how the reaction can keep going

Question 13

how can an enzyme break a chemical bond without requiring an input of energy?

Answer 13

charges pull in different directions, changes the bond angles.

thus the enzyme falls out because there is no longer complementarity.

charged attractions distort conformation, so no ATP is used.

Question 14

what is the difference between a substrate and a ligand?

Answer 14

just as a ligand reacts with a receptor, a substrate bonds with an enzyme.

they bind to cause a change, change shape, and pop out when we want it to stop

Question 15

compare and contrast allosteric and covalent regulation of enzyme activity

Answer 15

A: - 1 catalytic/active site, substrate binds and is modified
- 1+ regulatory site: anything else can bind there and it changes the catalytic site

C: attach phosphate group by covalent bond

Question 16

name an example of an allosteric enzyme

Answer 16

glycogen phosphorylase

Question 17

which effector molecules modulate glycogen phosphorylase activity?

Answer 17

AMP and ATP

Question 18

how does AMP affect glycogen phosphorylase enzyme activity? ATP?

Answer 18

AMP: increased AMP means we want more ATP, increases enzyme activity

ATP: increased ATP means we want less enzyme activity, less AMP

Question 19

which enzyme regulates glycolysis?

Answer 19

phosphofructokinase (PFK)

Question 20

what is the role of PFK? how is it regulated?

Answer 20

regulate glycolysis. allosterically regulated.

Question 21

effect of AMP on PFK activity

Answer 21

enhances

Question 22

effect of ATP on PFK activity

Answer 22

inhibits

Question 23

PFK: if ATP levels are high…

how does that affect the catalytic site?

Answer 23

the energy level is good, so the cell doesn’t need to run glycolysis as much.

promote access to catalytic site

Question 24

PFK: if AMP is high…

how does that affect the catalytic site?

Answer 24

energy level is low so the cell wants to speed up the rate of glycolysis.

discourage access to catalytic site.

Question 25

in glycolysis, why is glucose phosphorylated? (2)

Answer 25

1. keeps it in the cell. by adding phosphate, glucose is no longer recognized by the glucose transporter.
2. maintains concentration gradient. by adding phosphate, there is still more glucose outside the cell than inside, because what’s inside isn’t glucose.

Question 26

why is glucose-6-phosphate isomerized to fructose-6-P?

Answer 26

fructose-6-P is more symmetrical. 2 3C molecules.