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Lecture 7 Information Flashcards

1
Q

How do enzymes with more than 1 substrate bind them?

A

Can form a tertiary complex to bind both at the same time

Can interact with multiple substrates in an ordered manner (interact with one substrate before the other)

Can interact with multiple substrates in a ping pong manner (one is converted to product then the other is converted to product)

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2
Q

Binding affinity for more than 1 substrate

A

Enzymes will have a different binding affinity (Km) for each substrate they bind

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3
Q

2 main classes of enzyme inhibition

A

Reversible interaction

Irreversible interaction

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4
Q

Competitive inhibition

A

a type of reversible inhibition

inhibitor binds at the active site and forms EI complex

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5
Q

Kinetic effects of competitive inhibition

A

Vmax stays the same because you can flood the system with a high amount of substrate

Apparent Km increases

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6
Q

Uncompetitive inhibition

A

a type of reversible inhibition

inhibitor binds to the ES complex apart from the active site

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7
Q

Kinetic effects of uncompetitive inhibition

A

Vmax decreases

Apparent Km decreases

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8
Q

Mixed inhibition

A

a type of reversible inhibition

inhibitor binds to free enzyme or ES complex

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9
Q

Noncompetitive inhibition

A

a special type of mixed inhibition

the affinity of the inhibitor to bind to the free enzyme or to the ES complex is equal

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10
Q

Kinetic effects of noncompetitive inhibition

A

Vmax decreases

Apparent Km stays the same

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11
Q

Irreversible inhibition

A

bind covalently with or destroy a functional group on an enzyme that is essential for the enzyme’s activity

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12
Q

Example of irreversible inhibition

A

penicillin binds irreversibly to transpeptidase to prevent bacterial cell wall from being generated

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13
Q

Transition-state analogs

A

A type of irreversible inhibition that uses weak interactions

Creates a better transition state with more weak interactions that prevents the substrate from binding

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14
Q

Suicide inactivators

A

combines irreversibly to the enzyme through covalent interactions

hijack the normal enzyme reaction mechanism

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15
Q

Regulatory enzymes

A

exhibit increased or decreased catalytic activity in response to certain signals

they regulate and they also are regulated

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16
Q

Allosteric enzymes

A

function through reversible, non-covalent binding of regulatory components

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17
Q

Allosteric modulators/effectors

A

noncovalently bind to allosteric enzymes to either inhibitory or stimulatory regulate

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18
Q

Different ways to regulate enzymes

A

1) Allosteric enzymes
2) Covalent modification
3) Separate regulatory proteins
4) Proteolytic cleavage

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19
Q

Proteolytic cleavage

A

activates enzymes through removing peptide segments

this is irreversible unlike allosteric regulation

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20
Q

How do allosteric modulators work cooperatively?

A

conformational changes induced by one or more modulators interconvert more-active and less-active forms of the enzyme

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21
Q

Homotrophic enzyme

A

the modulator is the substrate and the active site is the regulatory site

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22
Q

Feedback inhibition

A

type of inhibition where the final product comes back to the first enzyme in a product and binds to it

binds to the first enzyme to save energy/materials

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23
Q

Heterotophic enzyme

A

the modulator is a molecule other than the substrate and the active site is not the regulatory site

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24
Q

Are enzymes turned completely off or on?

A

No! This is rare. Most are turned up or turned down in levels

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25
Are regulatory sites specific?
yes, each regulatory site is specific for its modulator
26
How are allosteric modulators different from inhibitors?
Inhibitors do not necessarily mediate conformational changes between active and inactivate enzymes
27
Shape of allosteric enzymes on Michaelis-menten plot
Sigmoidal shape which reflects cooperative binding between multiple subunits
28
What do we call the Km of allosteric enzymes?
K(0.5) have to do this since it doesn't follow normal hyperbolic shape represents substrate concentration giving half-maximal velocity
29
Covalent modifications of enzymes
examples: methylation, ribosylation, acetylation, adenylation, ubiquitin tag, phosphylation
30
Ubiquitin
entire protein that is covalently added to enzyme to tag it for destruction by a proteasome
31
Kinases
take a phosphate group (often from ATP) and use it to add phosphoryl groups to specific amino acids
32
What amino acids do kinases add to?
Ser, Thr, Tyr or sometimes His
33
How can phosphorylation effect an enzyme
can turn off an enzyme through the repulsion of negatively charged groups can turn on an enzyme through the attraction of positively charged and H-bonds
34
Tyrosine kinases
important in cell signaling and associated with the cell membrane often inactive, but when you bind a ligand the two subunits of the kinase come together now, this kinase is activated and auto-phosphorylates more tyrosine kinases now there are all these kinases that can turn on more enzymes
35
protein phosphatases
removes phosphoryl groups from same target proteins
36
When glycogen is phosphorylated what happens?
it releases a glucose-1 phosphate that can be used by the bloodstream this transformation is catalyzed by glycogen phosphorylase
37
Is glycogen phosphorylase a kinase?
No because it does not use ATP or any other nucleotide triphosphate to transfer phosphoryl group
38
Phosphorylase a
more active form of glycogen phosphorylase
39
Phosphorylase b
less active form of glycogen phosphorylase
40
Phosphorylase phosphatase
removes phosphoryl groups from phosphorylase a to make the enzyme less active in b form
41
Phosphorylase kinase
adds ATP to phosphorylase b to make the enzyme more active in a form
42
How is glycogen breakdown regulated?
by various ratios of phosphorylase a and phosphorylase b
43
Consensus sequences
common structual motifs where Ser Thr or Tyr residues are found to phosphorylate
44
Zymogen
inactive precursor that is cleaved to form an active enzyme this is irreversible activation proteases like chymotrypsin, trypsin, and pepsin have zymogen precursors to not destroy proteins within the cell name does not apply to all precursors
45
What are most inactive precursors generally called?
proproteins or proenzymes
46
Proteolytic cleavage
changes zymogen to active chymotrypsin and trypsin enzymes
47
How do we regulate proteases once they are turned on?
Need another protein to interact with them regulated through protein-protein interactions
48
Trypsin
cleaves after positive charges breaks down proteins in the gut
49
Chymotrypsin
cleaves after aromatic rings
50
Glucagon
hormone that stimulates the process of glycogen breaking down into glucose 1-phosphate
51
Insulin
hormone that inactivates the process of glycogen breaking down into glucose 1-phosphate decreases blood-sugar levels
52
Size of allosteric enzymes
typically bigger enzymes with more than one polypeptide chain
53
What are the zymogen's called?
ex: trypsinogen is the inactive form of trypsin
54
Why are certain enzymes kept a low pH even when the cell is at a neutral pH? Like lysozomes?
So if the lysosome breaks open, the enzymes will have little activity in the neutral pH
55
ATCase
has homotrophic and heterotrophic regulation ATCase has a sigmoidal curve cause has cooperative binding
56
Why does phosphatase not generate ATP when it removes phosphoryl?
requires too much energy just cleaves a Pi
57
PKA
protein kinase a sticks a phosphate onto inactive form of phosphorylase kinase to activate it
58
Hyperglycmic
too high blood-sugar levels pancreas picks up on this signal and triggers insulin to drop glucose
59
Hypoglycmic
too low blood-sugar levels pancreas picks up on this signal and triggers increase of glucose released (glucagon)
60
What does glucagon do?
inceases cAMP which activates PKA PKA then activates phosphorylase kinase which can then change phosphorylase b to phosphorylase a

Biochem (20 decks)

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