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QUIZ 3 > Enzymes > Flashcards

Enzymes Flashcards

1
Q

competitive inhibition

A

increases Km, no effect on Vmax

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2
Q

uncompetitive inhibition

A

reduces both Km and Vmax

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3
Q

noncompetitive inhibition

A

no effect on Km, reduces Vmax

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4
Q

sarin (diisopropylphosphofluoridate)

A

irreversible inhibitor; permanently inactivates acetylcholinesterase by forming a covalent bond with serine on active site

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5
Q

acetylsalicylic acid (aspirin)

A

irreversible inhibitor; acetylates an active site serine in the enzyme prostaglandin endoperoxide synthase

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6
Q

malathion (organophosphate insecticide)

A

irreversible inhibitor; Irreversibly inactivates acetylcholinesterase by forming a covalent bond with the active site serine

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7
Q

penicillin

A

suicide inhibitor

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8
Q

sulfanilamide

A

competitive inhibitor of p-aminobenzoic acid

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9
Q

example of control of substrate availabilty

A

if no lactate, liver can not convert it into glucose

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10
Q

How do enzymes stabilize transition state of a reaction?

A

acid-base catalysis, electrostatic catalysis, metal catalysis, covalent catalysis, substrate strain

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11
Q

general acid catalysis

A

catalyst is an acidic group on the enzyme that donates a proton to the substrate, allowing easier cleavage

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12
Q

general base catalysis

A

catalyst is a basic group on the enzyme that takes a proton from the substrate

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13
Q

example of acid-base catalysis

A

Glu35 in lysozyme is a proton donor to the O in the polysaccharide chain, allowing cleavage

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14
Q

How can an enzyme alter pKa?

A

can surround it by hydrophobic molecules –> Glu35 in lysozyme is allowed to be protonated

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15
Q

electrostatic catalysis

A

enzyme uses charged amino acid to neutralize charges that develop during formation of a transition state

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16
Q

example of electrostatic catalysis

A

upon cleavage of the polysaccharide by lysozyme, a positive charge will develop on one of the carbons –> Asp52 is surrounding by hydrophilic molecules, retaining its negative charge –> can neutralize that positive carbon

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17
Q

substrate strain

A

active site of enzyme only recognizes transition state, not regular unbound substrate

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18
Q

example of substrate strain

A

preferred conformation for polysaccharide is the chair conformation –> lysozyme binds in half chair formation –> an-acetyl group on C2 sterically clashes with proton on C1 –> unfavorable
–> so in transition state it will increase angle of C2 from 109 to 120, moving proton away

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19
Q

metals as lewis acids

A

Zn in carbonic anhydrase accepts protons

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20
Q

metals as chelates

A

iron in heme group

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21
Q

chelates

A

metal is covalently bound to enzyme or coenzyme

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22
Q

metals as charge stabilizers

A

Mg+2 stabilizes negative oxygens on ATPs

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23
Q

metals in oxi-red reactions

A

during respiration, oxygen is converted to water by the addition of protons and electrons, supplied by cytochrome a3 –> if cyanide inhaled, it reacts with the Fe3+ in the heme of cytochrome a3, preventing cytochrome a3 from transferring electrons to oxygen –> no energy production –> cell death

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24
Q

antidote for cyanide poisoning

A

have the patient inhale nitrites –> will convert the Fe2+ in hemoglobin to Fe3+ (this converts hemoglobin into methemoglobin) –> Fe3+ in methemoglobin removes the cyanide from the Fe3+ in cytochrome a3 –> reactivates cytochrome a3 and restores mitochondrial respiration

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25
metals for enzyme structure
K+ in pyruvate kinase needed for active formation
26
covalent catalysis
enzyme forms a transient covalent intermediate with substrates of reaction
27
example of covalent catalysis
chymotrypsin catalyzing hydrolysis of peptide bonds
28
chymotrypsin covalent catalysis
serine will attack carbonyl carbon to form covalent bond putting negative charge on that oxygen --> water comes in to cleave
29
How does serine have negative charge for chymotrypsin cleavage?
charge relay system in serine proteases
30
charge relay system
charge relay system includes ser, his, and asp --> his will pull of proton from serine because asp pulls off proton from his --> asp is surrounded by hydrophobic residues to raise pKa to allow it to do this
31
oxyanion hole
stabilize negative charge that develops in transition state --> serine and glycine spread out negative charge
32
specificity pocket
designed to recognize side chain of amino acid on amino terminus that is going to be cleaved
33
transition state analogs
enzyme inhibitors must mimic transition state
34
example of transition state analog
tetrahydrouridine is a transition state analogue of cytidine deaminase --> target for anticancer drugs
35
How do cells control specific reactions?
control of enzyme activity, control of enzyme levels, control of enzyme location, control of substrate availability, removal or conversion of reaction products
36
control of substrate availability
if substrates of a reaction are not available, the enzyme can't catalyze their conversion into product
37
removal of reaction products
can remove or convert products to keep reaction moving in the forward direction
38
example of product removal
taking away fructose-6-phosphate and making it into pyruvate will stimulate phosphoglucose isomerase to convert more G6P to F6P
39
product inhibition
occurs when product of reaction builds up and competes with the substrate for binding to active site of enzyme
40
how to prevent product inhibition
reaction products are either rapidly removed or converted into other products
41
enzyme activity regulation
allosteric control, covalent modification, proteolytic activation, stimulation/inhibition by control proteins
42
allosteric regulators
do not bind active site
43
feedback inhibition
end product will go back and allosterically inhibit an upstream enzyme
44
feed-forward regulation
product upstream will go activate/inhibit downstream enzyme
45
covalent modification
regulates catalytic activity of some enzymes by adding a modifying group
46
biotin
covalently attached to pyruvate carboxylase and serves as CO2 carrier for carboxylation of pyruvate to oxaloacetate
47
biotin is found in _
red meat, eggs, nuts, seed, broccoli, sweet potatoes, spinach
48
biotin deficiency symptoms
nausea, hair loss, dermatitis, depression, pale skin, muscle pain, fatigue
49
phosphorylation as reversible covalent modification
protein kinases and tyrosine kinases; can only be done inside cell not extracellularly
50
phosphorylation effects
rapidly amplified via kinase cascade
51
oncogene gain of function
will always be phosphorylated, leading to it always being on and cell cycle always going
52
tumor suppressor loss of function
usually phosphorylated to be activated so if a mutation causes it to be de-phosphorylated, it will not turn off the cell cycle when needed
53
tumor suppressor mutations are _
recessive (loss of function)
54
oncogene mutations are _
dominant (gain of function)
55
proteolytic activation
keeps enzymes in inactive form --> will be proteolytically cleaved when it needs to be activated (not reversible, enzyme is permanently activated); can be done extracellularly
56
pepsinogen cleavage
propeptide forms salt bridges with active site --> at pH >5 it will be binded and inactive --> once in stomach, the low pH will break salt bridges allowing activation
57
blood clot formation
zymogen activations --> prothrombin --> thrombin --> thrombin cleaves fibrinogen to fibrin --> cross-linked fibrin blood clot
58
BPTI
binds to trypsin active site, inactivating it
59
serine protease inhibitors (serpins)
serine proteases will bind the serpin reactive center loop, thinking it is a substrate --> forms acyl-enzyme intermediate with serine --> reactive center loop is cleaved and serpin undergoes conformational change that reduces functionality of serine protease
60
serpinopathies
mutations in hinge domains of serpins that cause inactivation --> leads to death of cells producing serpin
61
alpha-1-antitrypsin
inhibits elastase, a serine protease that is secreted by leukocytes in response to bacteria cell
62
AAT mutation
glu is replaced for lys, resulting in mutant cells --> uncontrolled elastase activity which breaks down alveolar walls
63
cigarette smoking
oxidizes Met358 of AAT, which prevents it from binding active site of elastase --> emphysema
64
factors that increase PMN elastases secretion
bacterial infection, smoking (irritates lung and stimulates PMN cells)
65
Which of the following systems is established by the International Union of Biochemistry and Molecular Biology (IUBMB) in naming an enzyme?
The substrate is stated first, followed by the reaction type suffixed with –ase
66
examples of hydrolases
lipases, proteases
67
examples of lyases
decarboxylases, aldolases
68
examples of oxidoreducatases
anything with an H, dehydrogenases
69
enzymes can _
distinguish between both isomers and stereoisomers, distinguish between two substrates that differ by a single methyl group, catalyze the formation of a stereospecific product from an achiral (non-stereospecific) substrate
70
enzymes can NOT _
stabilize products of a reaction
71
the transition state is _
the least stable species in reaction diagram
72
enzymes catalyze reactions by _
lowering activation energy and stabilizing transition state
73
in electrostatic catalysis _
negatively charged amino acid side chains in the enzyme are positioned near positive charges that develop in the transition state of the reaction, and vice versa

QUIZ 3 (12 decks)

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