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McG > Quiz 2 > Flashcards

Quiz 2 Flashcards

1
Q

what happens with catalysis with multiple substrates

A

reactants brought together and properly oriented so they can react

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2
Q

glucose and glucokinase are an example of

A

the induced fit model for enzymes/substrates

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3
Q

what does glucokinase do

A

phosphorlyate glucose

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4
Q

when is glucokinase “open”

A

when no glucose is bound. active in closed state with bound glucose

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5
Q

what [S] is low, what is Vo proportional to

A

[S] – FIRST ORDER KINETICS

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6
Q

When [S] is high, what is Vo proportional to

A

equal to Vmax — 0 ORDER KINETICS

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7
Q

what does the rate depend on

A

the concentration of the substRATE

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8
Q

What does Km represent

A

the concentration of the substrate where Vo is 50% of Vmax

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9
Q

competitive inhibitor

A

binds at the same site
Km is increased but Vmax is the same, can reverse the effect by increasing the amount of substrate so that it takes up almost all the receptors on the enzyme

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10
Q

non-competitive inhibitors

A

doesn’t bind to same spot but makes enzyme less effective.

Km is the same, Vmax is decreased

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11
Q

uncompetitive inhibitor

A

binds ONLY when substrate is bound because ES complex creates a binding site
-Km AND Vmax are reduced

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12
Q

irreversible inhibitor

A

bind very strongly or produce covalent modification. Decreased Km but no change on Vmax – like NON competitive

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13
Q

Effector

A

binds non covalently to subunit of regulatory enzyme. Change in affinity or alters enzymatic activity in a positive or negative way

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14
Q

homotropic effector

A

substrate itself is the effector. THINK: Hemoglobin! Occupation of first site alters affinity of remaining

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15
Q

Heterotropic effector

A

substrate is not the effector

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16
Q

what kind of curve does a + cooperativity give

A

sigmoidal

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17
Q

positive heterotropic effector

A

binding at the regulatory unit of the enzyme causes conformational shift at the catalytic subunit. NOT COVALENT BINDING.

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18
Q

negative heterotropic effector

A

feedback inhibition – regulated enzyme typically catalyzes a rate limiting step `

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19
Q

what happens in calcium calmodulin path

A

Calcium binds to calmodulin cooperatively - with all 4 sites goes from “closed” to “open” and THIS is what binds to CAMKII

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20
Q

what happens when calmodulin binds CAMKII

A

conformational change which relieves auto-inhibition. CAMKII autophosphorylates so retains activity even after Ca returns to baseline.

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21
Q

What turns off calcium/calmodulin/CAMKII pathway

A

protein phosphatase which dephosphorylates CAMKII

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22
Q

zymogen

A

enzyme liberated by proteolysis of inactive precursor

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23
Q

where is trypsinogen released

A

by the pancreas into the duodenum

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24
Q

what cleaves trypsinogen to trypsin

A

enteropeptidase

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25
Q

cofactor

A

additional molecule that helps perform catalysis

metal ion or organic molecule which is usually referred to as coenzyme

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26
Q

apoenzyme vs holoenzyme

A

holoenzyme is protein + cofactor, apoenzyme is protein alone

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27
Q

isoenzyme

A

enzyme that catalyzes the same reaction

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28
Q

hexokinase

A

4 isozymes that phosphorylate simple sugars

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29
Q

glucokinase

A

hexokinase IV - this is the hexokinase in the liver. MUCH higher Km for glucose than others. Converts XS glucose to glycogen for storage

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30
Q

what is the advantage of the high Km of glucokinase for glucose

A

when glucose is scare, available glucose will be used by hexokinases in other tissues

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31
Q

Kcat

A

number of operations a single molecule of an enzyme can perform per second

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32
Q

specificity constant

A

how efficient enzyme is when free binding sites are available

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33
Q

what does a large specificity constant mean

A

rxn can proceed at high rate even if substrate concentration is low or enzyme is not highly expressed

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34
Q

how large can a specificity constant be and why

A

largest is 10^8 or 10^9 because limited by diffusion rates - enzymes that are at this rate are called “catalytically perfect”

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35
Q

what does heme effect

A

ALA synthase 7 steps earlier in heme synthetic pathway.

ALA is an allosteric enzyme whose activity is under control of an effector (heme).

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36
Q

what do we call inhibitors in pharmacodynamics

A

antagonists

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37
Q

what is the substrate in pharmacodynamics

A

drugs!

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38
Q

possible drug receptors

A

enzymes, channels, G protein coupled receptors

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39
Q

what gets measured with respect to drugs

A

amount of drug bound to receptor.. NOT rate of reaction

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40
Q

Vmax in pharmacodynamics referred to as

A

Bmax (max number binding sites)

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41
Q

agonist

A

drug with intrinsic effect on its target. EXCLUDES drugs that produce their effect by preventing some other ligand from binding because this isn’t intrinsic

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42
Q

EC50

A

on effect curve, concentration of drug that produces 50% of maximum effect of drug

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43
Q

Emax

A

on effect curve, area where max effect is produced

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44
Q

instrinsic efficacy

A

effect per molecule of agonist binding to its receptor

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45
Q

what happens when a signaling pathway is fully activated

A

this only happens with FULL agonists – even if we add more receptors, can’t produce larger effect!

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46
Q

will a partial agonist ever fully activate a pathway?

A

NO. Some receptors change conformation but downstream coupling doesn’t become as efficient so even with all receptors bound, mechanism won’t be FULLY activated

47
Q

what is the relationship between Kd and EC50 for a partial agonist

A

Kd = EC50 (effect and binding curve are the same – each new molecule makes a difference)

48
Q

what is the relationship between Kd and EC50 for a full agonist

A

KD > EC50 - Binding curve is to the R of the effect curve - Emax can be attained without all of the receptors being bound

49
Q

what do full agonists often contain

A

spare receptors (ex: only need to activate 4 receptor sites for 100% activity)

50
Q

drug potentcy

A

inverse of EC50

51
Q

Inverse agonist

A

instrinsically decreases activity of a target protein BELOW its basal activity. This means the receptor must have some activity even without the drug present.

52
Q

antagonist

A

no INTRINSIC effect on activity – produces effect by preventing endogenous ligands from exerting its effect. Analogous to inhibitors.

53
Q

competitive antagonist

A

can be completely displaced from binding sites by high enough concentration of an agonist that binds to the same site

54
Q

PA2

A

-log[agonist] that produces a 2 fold shift in EC50

55
Q

what does it mean if you have a large PA2

A

low [antagonist] is enough to block agonist response

56
Q

what does a high potency antagonist have

A

high PA2

57
Q

therapeutic index

A

(toxic effect + TD50) / (therapeutic effect + ED50)

58
Q

certain safety factor

A

lethal dose < D1 / therapeutic effect dose ED99

59
Q

are drugs specific or selective for their targets

A

selective, NOT specific

60
Q

how does a carrier protein work

A

utilizes ion gradients and works in cycles, binding solutes as they pass through the membrane

61
Q

K+ charges in and out of cell, overall

A

Inside: 150
Outside: 4
Veq = -91

62
Q

Na+ charges in and out of cell, overall

A

Inside: 10
Outside: 145
Veq: =67

63
Q

Ca charges in and out of cell

A

Inside: 0.0001
Outside: 2
Veq: +125

64
Q

Cl charges in and out of cell

A

Inside: 5
Outside: 110

65
Q

equation for Veq

A

58/valence * log [So]/[Si]

66
Q

Driving force

A

Vm - Veq

67
Q

Ohm’s Law

A

V=IR or I = gV

68
Q

why don’t real membranes exhibit instantaneous behaviour in response to applied current

A

because of capacitance – first charges the membrane, THEN can be used to create voltage difference

69
Q

can carrier proteins move against gradient

A

YES, but channels cannot – they require ATP

70
Q

Primary active transport

A

solute binds to pump and is directly carried through the membrane

71
Q

Secondary active transport

A

pump establishes a large gradient for another solute, this gradient can be harnessed for energy

72
Q

P class pumps

A

become phosphorylated over the course of a cycle

73
Q

electrogenic

A

creates a current

74
Q

ampipathic

A

hydrophobic and hydrophilic areas

75
Q

SERCA

A

sarcoplasmic/ER Ca ATPase. Keeps Ca in cytoplasm low. High affinity binding site on cytoplasm of ER, binds Ca, phosphorylates, Ca transferred to lumen and sequestered

76
Q

V/F Class pumps description

A

pump ONLY protons, contribute to acidification of organelles by pumping protons from cytoplasm into lumen of organelle

77
Q

ABC Class pumps description and example

A

ATP Binding Cassettes – bind ATP at these conserved regions. Often transport uncharged or hydrophobic molecules. EX: Multidrug resistant Proteins and CF transmembrane regulator

78
Q

Multidrug resistant protein

A

In epithelial cells, transport small, polar moelcules including some products of normal metabolism. Can also pump drugs out of cells, tumors that over express these are resistant to tx

79
Q

CF transmembrane regulator

A

in lungs and other organs. Has no known “pumping” function. Has a channel permeable to Cl- and regulated by PKA. CF linked to mutation here so less Cl transport across pulmonary epithelial cells which leads to viscous mucous and bad gas exchange

80
Q

Uniporter

A

conduct single cell species down gradient - help circumvent hydrophobic barrier (facilitated diffusion)

81
Q

co-transporter

A

couple thermodynamically favored movement of one molecule with unfavorable movement of another.

1) Symporter: different solutes moved in SAME direction
2) Exchanger/antiporter: different solutes in opposite directions

82
Q

GLUTs

A

bind one glucose - conformation changes, bring in and diffuses away, internal concentration of glucose kept low by phosphorylation of glucose

83
Q

NCX

A

Na/Ca exchanger - couples Na IN to Ca OUT. Works with SERCA to regulate Ca.
Ratio: 3 Na for 1 Ca. Accumulates positive charge inside the cell. Used for muscle contraction in heart. Can slow calcium removal by interfering with pump! DIGOXIN!!

84
Q

SGLTs

A

Na/Glucose transporters (Salt GLucose Transporters). Couple Na IN to glucose uptake. Kidney has 2.

1) SGLT 2 at early tubule: 1 Na for 1 glucose
2) SGLT 1 at late tubule: 2 Na for 1 glucose

85
Q

what is the result of an excitatory stimulus

A

depolarized the membrane

86
Q

what is the result of an inhibitory stimulus

A

hyperpolarizes the membrane by potassium conductance or activating Cl- conductance

87
Q

what is the effect of opening Cl channels

A

often has minimal effect because reversal potential for Cl- is is close to resting membrane potential. BUT IT STILL DECREASES TOTAL MEMBRANE RESISTANCE!

88
Q

what is the result of an excitatory current if Cl- channels are open, relatively speaking

A

reduces depolarization produces

89
Q

Cys Loop channels examples

A

Nicotinic Acetylcholine Receptor (NaChR) and GABA-A receptor

90
Q

Nictonic acetylcholine receptor

A

Mediates communication between neurons and muscles/neurons. Non selective cationic, depolarizes membrane (excitatory).

91
Q

what is the target of myasthenia gravis

A

nicotinic acetylcholine receptor

92
Q

GABA-A receptor

A

activated by gamma aminobutyric acid - main inhibitory receptor in the brain. Permeable to anions, inhibitory effect due to membrane hyperpolarization and decrease in total membrane resistance

93
Q

glutamate receptors examples

A

AMPA or NMDA type

94
Q

Cys loop description

A

5 protein subunits - have loop in extracellular N domain that is linked by cysteines. Each subunit has 4 membrane spanning helices -
M2 forms wall of channel
M3/4 has intracellular loop that associates with cytoskeletal partners
2 binding sites - BOTH must be activated

95
Q

what passes through cys loop

A

cations or anions, not discriminating

96
Q

NaChR description

A

Nicotinic acetylcholine - CYS LOOPS

  • subunits are HIGHLY homologous
  • all channels have at least two alpha subunits
  • acetylcholine binding sites at alpha gamma and alpha
97
Q

NaChR permeability and reversal potential

A

Permeable to Na and K but also to Mg and Ca. Reversal potential O mv - large enough to go through with hydration shells.

98
Q

why is NaChR permeable to cations

A

negative residues lining outer regions of pore

99
Q

how do NaChR channels go from being closed to open

A

unbound Ach - M2 helices have “kink”

bound Ach - M2 helices twist from center

100
Q

GABA

A

CYS LOOP! Binds GABA. Mediates fast inhibitory transmission in the brain.

101
Q

what is GABA permeable to and what is the Vrev

A

Cl- (anion selective)

Vrew: -80 mV

102
Q

description of glutamate receptors

A

protein composed of tetramers, each subunit has three membrane spanning regions TM1, TM2, TM3. Pore due to loop in membrane from cytoplasmic linker between TM1 and TM2

103
Q

AMPA function and Vrev

A

Selective for Na and K
Vrev = 0 mV
Binds glutamate

104
Q

NMDA function and Vrev

A

Selective for Na, K and Ca.
Vrev : 20 mV
Blocked by extracellular Mg at resting Vm, expelled with membrane depolarization. Also requires glycine.

105
Q

Inward rectifier description

A

formed from tetramers - 2 helical regions - M2 face each other in inverted teepee. P loop between M1 and M2 which is highly selective and has carbonyl groups

106
Q

how does K pass through inward rectifier

A

after being dehydrated but gets stabilized by carbonyls (Na is too small to be stabilized, this is why it doesnt pass through)

107
Q

how do KiR channels get blocked

A

positive charges on cytoplasmic side. Can’t get through selectivity barrier but can block. If membrane is depolarized, usually blocked.

108
Q

when do voltage gated channels open

A

with depolarization

109
Q

K+ voltage gated channels description

A

tetramers with TM helices S1-S6. S4 is charged and voltage sensitive. S5/S6 is what is inverted, S6 lines the pore.

110
Q

deactivation

A

stay open until membrane repolarizes

111
Q

inactivation

A

“ball and chain” - stop conducting current soon after activation, even if membrane stays depolarized. Basic AA at N terminus (ball and chain) can block the channel because the + charge is attracted to the pore

112
Q

de-inactivation

A

membrane potential returns to normal so the inactivating particle leaves and goes to - cytoplasm. This process is NOT instantaneous

113
Q

voltage gated Na/Ca channels

A

instead of four subunits have 1 polypeptide with 24 TM helices in 4 domains. homologous to seperate subunits of voltage gated K channels, selectivity filter is on the P loop. NO BALL AND CHAIN - inactivation from + charges on intracellular linkers

McG (11 decks)

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