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Biochemistry > Chapter 13 > Flashcards

Chapter 13 Flashcards

1
Q

Catabolism

A

the degradative phase of metabolism - releases energy

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2
Q

Anabolism

A

the building phase of metabolism, requires energy

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3
Q

What is free energy?

A

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

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4
Q

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

A

oxidation-reduction reactions

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5
Q

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

A

free energy is released and the reaction is exergonic

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6
Q

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

A

free energy is gained and the reaction is endergonic

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7
Q

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

A

reaction releases heat and is exothermic

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8
Q

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

A

the reaction takes up heat and is endothermic

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9
Q

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

A

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

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10
Q

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

A

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

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11
Q

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

A

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

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12
Q

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

A

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

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13
Q

Can enzymes change equilibrium constants?

A

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

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14
Q

Are endergonic reactions favorable or unfavorable?

A

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

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15
Q

What types of reactions are favorable? Example?

A

Exergonic, such as hydrolysis b/c spontaneous

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16
Q

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

A

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

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17
Q

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

A

complete oxidation of reduced compounds

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18
Q

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

A

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

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19
Q

The carbon of the ________ group is an electrophilic carbon

A

carbonyl

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20
Q

What molecules can enhance the electrophilicity of carbonyl groups?

A

General acid catalysts or metal ions

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21
Q

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

A

by delocalizing electrons

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22
Q

Substitution on an sp3 carbon occurs via what reaction types

A

SN1 OR SN2

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23
Q

Substitution on an sp2 carbon occurs via what reaction types?

A

addition-elimination mechanism

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24
Q

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

A

Synthases

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25
Q

These enzymes catalyze condensation reactions that require a nucleotide triphosphate

A

Synthetases
(think T for ATP)

26
Q

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

A

Ligases

27
Q

These enzymes catalyze cleavages or additions in which electronic rearrangements occur

A

Lyases

28
Q

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

A

Kinases

29
Q

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

A

Oxidases
- mixed function oxidases oxidize two different substrates simultaneously

30
Q

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

A

Oxygenases

31
Q

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

A

Dehydrogenases

32
Q

What makes ATP hydrolysis favorable?

A
  • better charge separation in products
  • better solvation of products
  • more favorable resonance stabilization of products
33
Q

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

A

Phosphorylases

34
Q

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

A

Phosphatases

35
Q

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

A

exceeds

36
Q

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

A

Cellular ATP concentrations are usually far above the equilibrium concentration

37
Q

When are reactions favorable?

A

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

38
Q

Biochemical phosphoryl transfer reactions are favorable when?

A
  • the phosphate donors are destabilized by electrostatic repulsion
  • the reaction products are stabilized by resonance
39
Q

Most organic molecules are in what spin state?

A

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

40
Q

What spin state is molecular oxygen in?

A

The triplet spin state = 2 electrons are unpaired

41
Q

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?

A

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

42
Q

Measurements of NADH are taken at what absorbance?

A

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

43
Q

What are cofactors/pyridine nucleotides

A

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

44
Q

What is Reduction potential (E) ?

A

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

45
Q

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

A

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

46
Q

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

A

Alkanes (CH2-CH3) are most reduced
CO2 least

47
Q

Why do thioesters undergo less resonance stabilization than oxygen esters ?

A

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

48
Q

Homolytic cleavage

A

each atom leaves the bond as a radical

49
Q

Heterolytic cleavage

A

one atom retains both bonding electrons

50
Q

Nucleophiles vs Electrophiles

A

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

51
Q

What are considered “high energy” bonds?

A

Exergonic hydrolyses or group transfer reactions

52
Q

Is negative delta S (entropy) favorable?

A

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

53
Q

What does a positive delta G value indicate?

A

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

54
Q

What does a negative delta G value indicate?

A

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

55
Q

What two forces are all chemical reactions influenced by?

A
  • 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.
56
Q

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

A

In aldol condensation, claisen condensation and decarboxylation

57
Q

Dehydrogenases catalyze which types of reactions?

A

Oxidation - reduction

58
Q

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

A

Thioesters and ATP

59
Q

What is an important thioester in metabolism?

A

acetyl-coA

60
Q

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

A

oxidized

61
Q

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

A

reduced

Biochemistry (10 decks)

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