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Biochemistry I > Chapter 7 > Flashcards

Chapter 7 Flashcards

1
Q

Apoenzyme

A

The protein portion, without its cofactors

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2
Q

Holoenzyme

A

An enzyme containing all its cofactors

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3
Q

Cofactors

A

Metal ions - inorganic

Coenzymes - organic

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4
Q

Prosthetic group

A

A cofactor which is covalently bound to the enzyme

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5
Q

Active site micro-environment contribution to catalysis:

A

Exclude excess water

Provide optimal orientation

Binding interactions between the substrate and the enzyme to create a transition state

Presence of catalytic functional groups

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6
Q

Michaelis-Menten assumptions

A

The concentration of ES is relatively constant after the initial reaction time.

The reaction must be considered early, before any appreciable amount of product has been generated.

The product release is a rapid step in the process.

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7
Q

Velocity of a rxn in relation to the rate constant

A

v = k[S]

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8
Q

What AA’s are phosphorylated by kinases?

A

Serine, Threonine, and Tyrosine

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9
Q

For competitive inhibitors

A

vmax remains the same, but Km increases

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10
Q

For uncompetitive inhibitors

A

vmax and Km decrease

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11
Q

For mixed inhibitors

A

decrease vmax, but can increase or decrease Km

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12
Q

For noncompetitive inhibitors

A

decrease vmax, but has no effect on Km

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13
Q

How to determine equation for no inhibition

A

It will have the lowest slope and y-intercept

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14
Q

Turn over number

A

Kcat.. Use this EQ to solve for it

Vmax = Kcat [E]t

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15
Q

Catalytic efficiency

A

aka specificity constant

Kcat/Km

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16
Q

High Km

A

Low affinity

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17
Q

Low Km

A

High affinity

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18
Q

two models to explain how the binding of

enzyme and substrate occurs

A

Lock and Key

Induced Fit

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19
Q

Substrate AKA

A

Reactant

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20
Q

Lock and Key Model

A

Substrate fits perfectly with the enzyme

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21
Q

Induced Fit Model

A

Enzyme is flexible to accommodate the ill fitting
substrate

Permits a much larger number of weaker
interactions between the substrate and enzyme

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22
Q

EX of an induced fit mechanism

A

Hexokinase

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23
Q

Critical Aspects of Enzyme Structure and Function

A

Enzymes bind to substrates with high affinity and
specificity

Substrate binding to the active site induces
changes in the enzyme

Enzyme activity is highly regulated in cells

24
Q

Active sites AKA

A

Binding pockets

25
Q

Modes of enzyme regulation

A

Bioavailability: Amount of enzyme
present in the cell

Catalytic efficiency: Quantitative measure of
enzyme activity

26
Q

Organic catalysts vs enzymes

A

catalysts speed up reactions but not as fast as enzymes

Enzymes are highly specific where as catalysts are not

27
Q

Enzymes alter the rates of reaction without changing

the ratio of:

A

substrates and products at equilibrium

28
Q

6 Major groups of enzymes:

A 
Oxidoreducatase
Transferase
Hydrolase
Lyase
Isomerase
Ligase
29
Q

Oxidoreducatase

A

Oxidation/reduction, Transfer of H or O atoms

30
Q

Transferase

A

Transfer of functional group

31
Q

Hydrolase

A

Formation of two products by hydrolyzing the substrate

32
Q

Lyase

A

Cleavage of C-C, C-O and C-N and other bonds by means other than hydrolysis or oxidation

33
Q

Isomerase

A

Intramolecular rearrangements, transfer of groups with in a molecule

34
Q

Ligase

A

Formation on C-C, C-O, C-S and C-N bonds using ATP cleavage

35
Q

3 ways enzymes increase the rate of a reaction:

A

They lower the activation energy by stabilizing the
transition state

They provide an alternate path for product
formation

They reduce entropy by orienting the substrates
appropriately for the reaction to occur

36
Q

Physical and Chemical Properties of Active Sites

A

Hydrophobic regions and charged regions

37
Q

Enzymes decrease the ____ of the reaction

A

Δ𝐺‡

38
Q

Michaelis-Menten constant

A

Km = (k-1 + k2) / k1

Describes rates of breakdown and formation of ES

39
Q

Catalytic efficiency of an enzyme is regulated by:

A

reversible and irreversible inhibition, allosteric
control, covalent modification, and proteolytic
processing

40
Q

Reversible inhibition

A

Noncovalent bonding

Includes: Competitive, uncompetitive and mixed

Can be decreased by diluting the enzyme reaction

41
Q

Irreversible inhibition

A

forms a covalent bond or very strong non-covalent bond

“suicide inhibitors” kill the enzyme

Not affected by enzyme dilution

42
Q

Diisopropylfluorophosphate an example of:

A

Irreversible Inhibitor

Blocks protease and phospholipase enzymes

43
Q

A Reversible Inhibitor ex

A

Malonate

Competes with succinate to bind to the active
site of succinate dehydrogenase

44
Q

Type of inhibition that can be overcome by increasing [S]

A

Competitive

45
Q

Competitive inhibition:

A

E + S –> E S –> E +P
II
EI

46
Q

Uncompetitive inhibition:

A

E + S –> E S –> E +P
……………..II
……………..ESI

47
Q

Mixed inhibition:

How do you know is it is noncompetitive or not?

A

E + S –> E S –> E +P
II…………..II
EI………….ESI

Ki = Ki’

Ki = K-i / Ki
Ki' = K-i' = Ki'
48
Q

EX of competitive inhibition:

A

Saquinavir

An HIV protease inhibitor

Mimics the natural Phe-Pro dipeptide substrate

49
Q

Fxn of Saquinavir

A

HIV protease essential for processing of proteins in virus.

Without these proteins, viable viruses can not be released to cause further infection

50
Q

Uncompetitive inhibitors bind to the:

A

enzyme-substrate complex and alters the active site conformation

51
Q

Mixed inhibitors bind to sites unique from the _____

A

active site

52
Q

Kcat =

A

K2

53
Q

How do enzymes fxn so efficiently?

A

When S binds to active site on E they make and ES complex, While in the transition state, binding occurs which allows S to interacting with different AA’s in the active site, during these small weak interactions, energy is released, and it accumulates to make “binding energy” which is used to lower Ea

54
Q

K(t)

A

Ae^(-Ea/Rt)

If Ea goes down, K(t) goes up which means Rate goes up!

55
Q

Ea is the same as

A

Δ𝐺‡

Biochemistry I (13 decks)

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