Chapter 13

Question 1

Catabolism

Answer 1

the degradative phase of metabolism - releases energy

Question 2

Anabolism

Answer 2

the building phase of metabolism, requires energy

Question 3

What is free energy?

Answer 3

The maximum energy made available to do work when a chemical reaction occurs

The amount of energy capable of doing work during a reaction at constant temp and pressure

Question 4

What type of reactions indirectly provide much of the energy required to make ATP?

Answer 4

oxidation-reduction reactions

Question 5

When delta G is negative, free E is ______ and the reaction is _______

Answer 5

free energy is released and the reaction is exergonic

Question 6

When delta G is positive, free E is _____ and the reaction is ______

Answer 6

free energy is gained and the reaction is endergonic

Question 7

When enthalpy, H, is negative, the reaction _______ heat and is _______

Answer 7

reaction releases heat and is exothermic

Question 8

When enthalpy, H, is positive, the reaction _______ heat and is ________

Answer 8

the reaction takes up heat and is endothermic

Question 9

When Keq is > 1, delta G is (+/-) and the direction of the chemical reaction goes…

Answer 9

Keq > 1 = delta G is negative and the reaction proceeds forward, more products than reactants

Question 10

When Keq is = 1, delta G is ? and the direction of the chemical reaction goes..

Answer 10

Delta G is zero, reaction is at equilibrium and products = reactants

Question 11

When Keq is < 1, delta G is (+/-) and the direction of the chemical reaction goes..

Answer 11

Delta G is positive when Keq < 1, the reaction proceeds in the reverse direction, there are more reactants than products

Question 12

What does the actual free-energy change of a reaction in the cell depend on?

Answer 12

The standard change in free E and the actual concentration of products and reactants

Question 13

Can enzymes change equilibrium constants?

Answer 13

No, the ratio of products to reactants is the same regardless of enzymes present

Enzymes can only increase the rate at which a reaction proceeds

Question 14

Are endergonic reactions favorable or unfavorable?

Answer 14

Unfavorable b/c delta G is + and therefore the reaction is NOT spontaneous
But endergonic reactions can be driven In the forward direction by coupling them with an exergonic reaction

Question 15

What types of reactions are favorable? Example?

Answer 15

Exergonic, such as hydrolysis b/c spontaneous

Question 16

What is the delta G of isomerization reactions b/w enantiomers?

Answer 16

Delta g = O b/c they are not different energetically, just changing arrangement

Question 17

What is a favorable reaction by which cells obtain most of their energy?

Answer 17

complete oxidation of reduced compounds

Question 18

What are the two ways in which covalent bonds can be broken ?

Answer 18

Homolytic cleavage (rare in biochem)
Heterolytic cleavage (common, but the products are highly unstable)

Question 19

The carbon of the ________ group is an electrophilic carbon

Answer 19

carbonyl

Question 20

What molecules can enhance the electrophilicity of carbonyl groups?

Answer 20

General acid catalysts or metal ions

Question 21

How do carbonyl and imine groups form carbanions on adjacent carbons?

Answer 21

by delocalizing electrons

Question 22

Substitution on an sp3 carbon occurs via what reaction types

Answer 22

SN1 OR SN2

Question 23

Substitution on an sp2 carbon occurs via what reaction types?

Answer 23

addition-elimination mechanism

Question 24

These enzymes catalyze condensation reactions in which no nucleotide triphosphate is required (no ATP/GTP) needed just the enzyme itself

Answer 24

Synthases

Question 25

These enzymes catalyze condensation reactions that require a nucleotide triphosphate

Answer 25

Synthetases (think T for ATP)

Question 26

These enzymes catalyze condensation reactions in which two smaller molecules are joined using ATP or another energy source

Answer 26

Ligases

Question 27

These enzymes catalyze cleavages or additions in which electronic rearrangements occur

Answer 27

Lyases

Question 28

These enzymes catalyze the transfer of a phosphoryl group from ATP to an acceptor molecule (phosphorylation reaction)

Answer 28

Kinases

Question 29

These enzymes catalyze biological oxidation reactions in which oxygen is the electron acceptor but oxygen DOES NOT appear in the oxidized product

Answer 29

Oxidases - mixed function oxidases oxidize two different substrates simultaneously

Question 30

These enzymes catalyze oxidation reactions in which oxygen is the electron acceptor but Oxygen APPEARS in the oxidized product

Answer 30

Oxygenases

Question 31

These enzymes catalyze oxidation-reductase in which NAD+ is the electron acceptor and molecular oxygen is not involved

Answer 31

Dehydrogenases

Question 32

What makes ATP hydrolysis favorable?

Answer 32

- better charge separation in products - better solvation of products - more favorable resonance stabilization of products

Question 33

These enzymes catalyze a displacement reaction in which phosphate attacks and becomes covalently attached at the point of bond breakage (phosphorolysis reaction)

Answer 33

Phosphorylases

Question 34

These enzymes catalyze the removal of a phosphoryl group from a phosphate ester (dephosphorylation reactions)

Answer 34

Phosphatases

Question 35

Free energy change is more favorable if the reactant concentration _________ its equilibrium concentration

Answer 35

exceeds

Question 36

What is one reason ATP is such a potent source of chemical energy?

Answer 36

Cellular ATP concentrations are usually far above the equilibrium concentration

Question 37

When are reactions favorable?

Answer 37

When the free energy of products is much lower than the free energy of the reactants

Question 38

Biochemical phosphoryl transfer reactions are favorable when?

Answer 38

- the phosphate donors are destabilized by electrostatic repulsion - the reaction products are stabilized by resonance

Question 39

Most organic molecules are in what spin state?

Answer 39

The singlet spin state - all electrons are paired in electron pairs

Question 40

What spin state is molecular oxygen in?

Answer 40

The triplet spin state = 2 electrons are unpaired

Question 41

Direct electron transfer from a singlet reduced species to a triplet oxidizing species is quantum mechanically unfavorable, however, there are molecules that are able to catalyze consecutive single electron transfers needed for the utilization of O2. What are these?

Answer 41

COFACTORS aka PYRIDINE NUCLEOTIDES - such as transition metal ions and flavin adenine dinucleotide (FAD)

Question 42

Measurements of NADH are taken at what absorbance?

Answer 42

Measure the change of absorbance at 340nm NADH has two bands at 340nm that NAD+ does not

Question 43

What are cofactors/pyridine nucleotides

Answer 43

NAD+ and NADP+ serve as cofactors/pyridine nucleotides meaning they can dissociate from the enzyme after a reaction

Question 44

What is Reduction potential (E) ?

Answer 44

Reduction potential is a molecule's ability to accept electrons - electrons are transferred from lower to higher E - higher E = higher affinity (+) is favorable reduction, easier to give electrons (-) is harder to give electrons

Question 45

What type of reaction is the conversion of an alcohol to a ketone

Answer 45

oxidation reaction (number of C-O bonds is increased)

Question 46

What is the most reduced organic molecule? The least reduced?

Answer 46

Alkanes (CH2-CH3) are most reduced CO2 least

Question 47

Why do thioesters undergo less resonance stabilization than oxygen esters ?

Answer 47

B/c the difference in free E b/w reactants and products is greater for thioesters (greater Delta G for thioester hydrolysis) Oxygen in oxygen ester is more willing to donate electrons than the sulfur in thioesters

Question 48

Homolytic cleavage

Answer 48

each atom leaves the bond as a radical

Question 49

Heterolytic cleavage

Answer 49

one atom retains both bonding electrons

Question 50

Nucleophiles vs Electrophiles

Answer 50

Nucleophiles - electron rich, capable of donating electrons Electrophiles - electron poor, accept electrons

Question 51

What are considered "high energy" bonds?

Answer 51

Exergonic hydrolyses or group transfer reactions

Question 52

Is negative delta S (entropy) favorable?

Answer 52

No, a negative entropy change is not favorable, it is bad since reactants are less complex and more disordered than products

Question 53

What does a positive delta G value indicate?

Answer 53

that the products of the reaction contain more free energy than the reactants (bad)

Question 54

What does a negative delta G value indicate?

Answer 54

that the products of the reaction contain Less free E than the reactants (good, reaction occurs spontaneously)

Question 55

What two forces are all chemical reactions influenced by?

Answer 55

- the tendency to achieve the most stable bonding state (for which enthalpy, H, is a useful expression) - the tendency to achieve the highest degree of randomness, expressed as entropy, S.

Question 56

In what 3 reaction types is a carbanion intermediate stabilized by or reacted with a carbonyl group?

Answer 56

In aldol condensation, claisen condensation and decarboxylation

Question 57

Dehydrogenases catalyze which types of reactions?

Answer 57

Oxidation - reduction

Question 58

What two molecules have large, negative, standard free energies of hydrolysis

Answer 58

Thioesters and ATP

Question 59

What is an important thioester in metabolism?

Answer 59

acetyl-coA

Question 60

What is the term for a loss of electrons by a chemical species

Answer 60

oxidized

Question 61

What is the term for a gain of electrons by a chemical species

Answer 61

reduced