Mcat Biology Enzymes

Front 1

define enzymes

Back 1

protein catalysts that accelerate reactions by reducing the activation energy necessary for them to proceed

Front 2

about enzymes

Back 2

-most are reversible
-lower to AE of a rxn
-increase rate of reaction
no not affect the over all change in free energy of the rxn
are not changed or consumed in a rxn
-they are very selective

Front 3

substrate

Back 3

the molecule upon which an enzyme acts

Front 4

enzyme-substrate complex

Back 4

the area on each enzyme to which the substrate bonds

Front 5

active site

Back 5

area where enzyme and substrate bond

Front 6

two enzyme substrate complex models

Back 6

-lock and key theory
-induced fit hypothesis

Front 7

lock and key theory

Back 7

an enzyme's active site (lock) is exactly complementary to its substrate (key)

Front 8

induced fit hypothesis

Back 8

-describes the active site of an enzyme as having some flexibility of shape
- when the appropriate substrate comes in contact with the active site, the conformation of the active site changes such that it surrounds the substrate, creating a close fit
-more plausible than lock and key

Front 9

cofactors

Back 9

-nonprotein molecule
-can aid in binding to the substrate to the enzyme or in stabilizing the enzyme in an active conformation

Front 10

apoenzyme

Back 10

-an enzyme devoid of its necessary cofactor
-is catalytically inactive

Front 11

holoenzyme

Back 11

enzyme containing its cofactor

Front 12

prosthetic groups

Back 12

tightly bound cofactors

Front 13

two examples of cofactors

Back 13

metal cations and small organic groups

Front 14

coenzymes

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-organic cofactors
-most cannot be synthesized by the body and are obtained from the diet as vitamin deratives
-lack of a particular vitamin can impair the action of its corresponding enzyme and lead to disease

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the rate of enzyme-catalyzed reaction is related to

Back 15

-concentrations of both the enzyme and the substrate
-temperature
-pH

Front 16

effects of concentration

Back 16

-when substrate concentration is low compared to that of the enzyme, many of the active sites are unoccupied and the reaction rate is low
-initial increases in the substrate concentration lead to proportional increases in the rate of the rxn because unoccupied active sites on the enzyme readily bind tot he additional substrate

Front 17

maximum velocity

Back 17

-Vmax
-at this point, increases in substrate concentration will no longer increase the rxn rate

Front 18

Michaelis-Menten model

Back 18

E+S<-->ES(1/2)-->E+P
(k1,k2) (k3)

Front 19

effects of temperature

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-rates of rxns tend to double for every 10C increase in temperature until their optimal temp is reached
-optimal temp in the human body is 37C
-at higher temps enzymes become denatured, their 3-D structure is destroyed and the enzyme becomes nonfunctional

Front 20

max pH activity of:
a)humans
b)pepsin
c)pancreatic enzymes

Back 20

a)7.2 (humans)
b)pepsin(2)
c)pancreatic enzymes(8.5)

Front 21

regulation of enzymatic activity

Back 21

allosteric effects and inhibitory interactions

Front 22

allosteric enzyme

Back 22

-has 2 or more active sites and may be composed of more than one subunit
-oscillates between 2 configurations, an active state capable of catalyzing a rxn and an inactive state that cannot
- an interaction between an allosteric and a regulator can stabilize either configuration, depending on the type of regulator involved

Front 23

regulator

Back 23

a molecule other than the substrate that binds to the enzyme