Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

BIOCHEM 2700/2710 > Enzymes > Flashcards

Enzymes Flashcards

1
Q

What is a catalyst?

A

Substance that speeds up the rate of a chemical reaction without being consumed. Includes enzymes, RNA.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the difference between an apoenzyme and a holoenzyme?

A

Apoenzyme: Protein enzyme
Holoenzyme: Protein + coenzyme

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What do oxidoreductases, transferases, hydrolases, lyases, isomerases and ligases do?

A

Oxidoreductase: transfer e- as H or H+

Transferase: transfer groups between molecules

Hydrolases: Add functional groups to water which assists in cleaving covalent bonds

Lyases: Form or add double bonds which assist in cleaving covalent bonds

Isomerases: isomerize by group transfer

Ligase: form bonds from C to C, S, O, and N coupled with ATP cleavage for energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Why are enzymes necessary?

A
  1. Catalyze chemical reactions by accelerating bond formation and breakdown
  2. Responsible for the majority of all reactions in living systems
  3. Highly specific
  4. Able to be regulated
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the difference in the progression of uncatalyzed and catalyzed reactions?

A

Uncatalyzed: S to S++ to P

Catalyzed: S + E to ES to ES++ to EP to E + P

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the transition state theory?

A

Rate of chemical reaction depends on how much energy the reactant acquire in order to reach the transition state

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the direction of free energy in the reaction coordinate of a catalyzed reaction?

A
  1. G increases because S requires energy to remove water shell and fit in enzyme active site
  2. G decreases because ES creates favourable non-covalent interactions
  3. G reaches transition state energy for the enzyme destabilize the substrate
  4. G decreases as energetically favourable product is formed from destabilized substrate as well as product interactions with enzyme
  5. G increases because energy is required to cleave E and P from its stabilized EP form
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is binding energy used for?

A
  1. Decrease in entropy to hold substrates close together in proper orientation for reaction
  2. Desolvation (removal of water shell)
  3. Accommodation for steric/electronic strain
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How does the enzyme recognize and bind a substrate?

A
  1. substrate must fit the enzyme
  2. Correct matching of ionic and H bonds within the active site
  3. Protein must be able to flex to adopt a substrate, and a substrate must be able to flex to fid into the active site.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the two types of enzyme specificity?

A
  1. Optical specificity: Enzyme recognizes certain chiral conformations over others
  2. Geometric specificity: Enzyme converts certain isomers over others
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is a “pro-“ or “-ogen” enzyme?

A

Enzymes in their inactive form; e.g. fibrinogen and trypsinogen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the purpose of metal cofactors in enzyme catalysis?

A
  1. Weak interactions between metals and substrate stabilize charged transition states and may help orienting and binding the substrate
  2. Metals accept and donate electrons in redox reactions
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What does the coenzyme in carboxypeptidase do?

A

Zinc is used instead of an amino acid to form an oxyanion hole.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the relationship between velocity and [substrate] in an enzyme that exhibits michaelis menten kinetics?

A

hyperbolic: as [S] increases, v increases but eventually levels off at Vmax

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

When given the rates of each step in a catalyzed reaction, how is the overall velocity defined?

A

v = k3 [ES]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is [E total]

A

The total concentration of enzyme, bound and unbound.

[E total] = [E] + [ES]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How is the overall velocity defined compared to the maximum velocity?

A

overall velocity (v) = k3*[ES]

Maximum velocity (Vmax) = k3*[E total]

18
Q

What is the michaelis constant?

A

Km = { Rate of formation of ES (k2) * Rate of formation of E+P (K3) } / Rate of breakdown of ES (k1)

19
Q

What is Vmax proportional to, and what is Km proportional to? Which inhibitors affect them?

A

V max is proportional to the number of enzymes available (non/un-competitive inihibitors)

Km is inversely proportional to the affinity of the enzymes to substrate (competitive inhibitors)

20
Q

What is the Michaelis mentent equation?

A

V = Vmax [S] /Km + [S]

21
Q

What does a high and low Km mean?

A

High = Low rate of formation of ES (large k1) = low affinity = unfavourable

Low = High rate of formation of ES (small k1) = high affinity = need for low [S] = favourable

22
Q

What happens at 1/2 Vmax?

A
  1. Km = [S]
  2. 50% [E], 50% [ES]
23
Q

What is the Lineweaver-Burk Plot?

A

Visual that determines Km and Vmax through the use of linear equations on a 1/vº vs 1/[S] plot.

1/vº = Km/Vmax[S] + 1/Vmax

24
Q

What is the catalytic rate constant (kcat)?

A

Reflects the slow step rate of the enzyme; how many times per second does a reaction take place with units 1/time.

kcat = Vmax/[E total]

25
Q

What is the specificity constant?

A

A measure of how efficiently an enzyme converts substrates into products.

kcat/Km

26
Q

What are enzyme inhibitors?

A

Compounds that reduces the rate of conversion of S to P. Includes, competitive, noncompetitive, uncompetitive.

27
Q

What are competitive inhibitors?

A

Resemble substrate and bind in active site, blocking access of the natural substrate until displaced at high [S].

28
Q

What are competitive inhibitors’ effect on the rate of catalysis?

A

Competetive inhibitors decrease affinity for [S] and the reaction require higher [S] to reach Vmax. This low affinity means Km is larger, which is further on the M-M plot, and closer to 0 on the lineweaver burk plot.

29
Q

What are non competitive inhibitors?

A

inhibitors that bind to a site distinct from the substrate site (allosteric) on EITHER E or ES and prevent P formation.

30
Q

What are non-competitive inhibitors’ effect on the rate of catalysis?

A

Since the affinities of I to E and ES are the same, Km will not decrease.

However, binding of I on E and ES prevents the formation of product, binding to E or ES reduces [Etotal] which reduces V max. (Lower Vmax on M-M, higher y-intercept on LW-B plot)

31
Q

What are uncompetitive inhibitors?

A

inhibitors that bind to the allosteric site of the ES complex, preventing them from detatchment.

32
Q

What are uncompetitive inhibitors’ effect on the rate of catalysis?

A

Binding to [ES] prevents detachment which promotes high affinty for S to E. This decreases Km. As binding prevents production of product, Vmax decreases.

On a MM plot, the curve is flattened and 0.5Vmax is reached earlier. On a LWB plot, the line is parallel to control except further to the left.

33
Q

What is the difference between allosteric enzyme plots vs MM plots?

A

MM plots are hyperbolic and normal v0 vs [S] plots are sigmoidal

34
Q

What is allosteric cooperativity?

A

Occupancy of an active site on one subunit of an enzyme has an effect on other subunits. Binding of S stabilizes R state by pulling equilibrium to high affinity and creates a sigmoidal curve.

35
Q

What is the difference between R state and T state?

A

R: relaxed, high affinity

T: taut, low affinity

36
Q

What are activators and inhibitors?

A

Allosteric enzymes that displace equilibrium and affect the kinetic curve.

Activators: bind to R state and pulls equilibrium to R state

Inhibitors: bind to T state and pulls equilibrium to T state.

37
Q

What are the inhibitors and activators of phosphofructokinase?

A

Activator: AMP
Inhibitor: ATP

38
Q

How is hemoglobin affected by allostery?

A

BPG inhibits binding of O2 to hemoglobin by promoting T-state, while binding of O2 itself promotes allosteric cooperativity.

39
Q

What role do allosteric enzymes play in feedback inhibition?

A

After production of sufficient end products after a long pathway, one of the end products will bind to allosteric sites, preventing the production of any more enzymes.

40
Q

What are examples of covalent regulation?

A

Protein kinase: phosphorylation induces allosteric conformational change

Phosphatase: dephosphorylation induces allosteric conformational change

Ubiquitination: ubiquitin reversibly added to modulate function

41
Q

What are zymogens?

A

Enzymes activated by protyolitic cleavage. Includes trypsinogen, chymotrypsinogen, proelastase, procarboxy-peptidase.

42
Q

What are irresversible enzmye inhibitors?

A

inhibitors that form covalent bonds with active site amino acids, fully preventing the functions of the enzyme.

penicillin: inhibits transpaptidase

Aspirin: inhibits COX-2

Diisopropylfluorophosphate: inhibits chymotrypsin

BIOCHEM 2700/2710 (8 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions