Exam 3: Energy of Phosphorylation and Redox Reactions

Question 1

The actual free-energy change in a reaction depends on standard free energy and which other factor?

Answer 1

The actual concentrations of the products and reactants.

Question 2

What is the standard free-energy change for the hydrolysis of ATP?

Answer 2

-30.5 kJ/mol.

Question 3

The free-energy change is _____ favorable if the [ATP]_reactants:[ATP]_products exceeds that of the standard [ATP] ratio.

a. more
b. less

Answer 3

a. more

Question 4

What makes the free-energy change less favorable when [ATP] is low?

Answer 4

There are fewer molecules to drive the reaction and ΔG also becomes less negative.

Question 5

Cellular ATP is typically kept ______ than equilibrium concentration.

a. higher
b. lower

Answer 5

a. higher

Question 6

The hydrolysis of a phosphate generates more or less free energy than phosphorylating a molecule?

Answer 6

The hydrolysis of a phosphate generates more free energy.

Question 7

What are the two steps of the activation process?

Answer 7

1st. A phosphate is bound to a substrate or enzyme.

2nd. The phosphate is displaced.

Question 8

_TP and _TP can be hydrolyzed directly to provide energy for movement.

Answer 8

ATP and GTP.

Question 9

True or false, proteins can undergo conformational changes when they are phosphorylated.

Answer 9

True.

Question 10

True or false, proteins can undergo a change in activity when they are phosphorylated.

Answer 10

True.

Question 11

What is required in order for two ADP to react to produce an ATP and AMP ?

Answer 11

[ATP] must be low.

Question 12

Why will the cell react two ADP to create an ATP and AMP?

Answer 12

Because in order for ATP reactions to move forward with a complimentary free-energy change, [ATP] must be kept high.

Question 13

What are the four main types of Redox Reactions?

Answer 13

1. Where a single electron is transferred with or without stimulus from proton transfer.
2. Where there is a transfer of a hydride ion (H^2-).
3. Where electrons transfer to a molecular oxygen.
4. Where both molecular oxygens from an O_2 are incorporated into a substrate.

Question 14

In the transferring of a single electron, name 4 cofactors that are often required for the redox reaction to occur.

Answer 14

1. Hemes
2. Iron-sulfur proteins
3. Copper ions
4. Flavin nucleotides (FMN or FAD)

Question 15

In reactions with a transfer of a hydride ion, which two positively charged molecules are usually involved? What do they become with the donation of the electron from the hydride ion?

Answer 15

NAD+ and NADP+ become NADH and NADPH.

Question 16

In reactions that transfer electrons to a molecular oxygen, the reactions are catalyzed by enzymes called ________.

Answer 16

oxidases.

Question 17

In reactions where both molecular oxygen atoms of an O_2 are incorporated into a substrate, the reactions are catalyzed by enzymes called ________.

Answer 17

oxygenases.

Question 18

_______ organic molecules serve as fuels.

a. Reduced
b. Oxidized

Answer 18

a. Reduced

This is because the stripping of their electrons can be used to continue or initiate a reaction.

Question 19

True or false, the exchange of electrons or pairs of electron are typically partnered with the exchanging of protons. Why or why not?

Answer 19

True, as this helps maintain a balance of charge.

Question 20

In reactions with dehydrogenases, the reactions proceed with the transfer of a ______ and then a ______.

Answer 20

…a proton and then a hydride.

Question 21

The combination of the oxidized and reduced forms of a molecule is called a __________________.

Answer 21

…conjugate redox pair.

Question 22

Define the standard reduction potential of a chemical species and which units it is defined in.

Answer 22

The standard reduction potential is the tendency for the chemical species to be reduced at standard conditions and is measured in volts.

Question 23

Does a more positive value or a more negative value in a reduction potential indicate that a chemical species is more likely to be reduced?

Answer 23

A more positive reduction potential indicates that a species is more likely to be reduced.

Question 24

What does the variable E represent?

What conditions does ∆E*’ assume?

Answer 24

E represents the reduction potential of a chemical species.

∆E*’ assume a pH of 7 and concentrations of 1M.

Question 25

True or false: coenzymes can dissociate from the enzyme after the reaction and react somewhere else.

Answer 25

True.

Question 26

NADPH is usually used to ______ other molecules.

a. reduce
b. oxidize

Answer 26

a. reduce

Question 27

True or false: flavin cofactors (FAD+) only allows for single electron transfers.

Answer 27

False, flavin cofactors allow for both single and double electron transfers.