Enzymes Ch 2

Question 1

Enzymes

Answer 1

Biological catalysts
Lower activation energy
Increase rate of reaction (kinetics)
Are not consumed (appear in both reactants and products)
PH and temp sensitive
Do not affect overall change in energy
Specific for particular reactions or class of reactions.

Question 2

Catalyst

Answer 2

Do not change the thermodynamics of biological reaction (change in enthalpy reaction H and equilibrium position do not change)

Question 3

Enzyme specificity

Answer 3

A certain enzyme will only catalyze a certain reaction’s or group of reactions’ substrates

Question 4

Major enzyme classifications

Answer 4

Ligases 
Isomerases
Lyases
Hydrolases
Oxidoreductases
Transferases

Lil Hot

Question 5

Oxidoreductases

Answer 5

Catalyze oxidation-reduction reactions
Often have cofactor that acts as an electron carrier such as NAD+ or NADP+
Electron donor is known as reductant
Electron acceptor is oxidant

Question 6

Transferases

Answer 6

Catalyze movement of functional group from one molecule to another
Kinases are also a member of this class, catalyzing the transfer of a phosphate group generally from ATP to another molecule.

Question 7

Hydrolases

Answer 7

Catalyze the breaking of a compound into two molecules using the addition of water
Example phosphatase which cleave phosphate from another molecule

Question 8

Lyases

Answer 8

Catalyze the cleavage of a single molecule into two products; do not require water
Reverse is possible and often fulfilled by lyases then referred to as syntheses

Question 9

Isomerases

Answer 9

Catalyze arrangement of bonds within a molecule
Some can also be classified as oxidoreductases, transferases, or lyases depending on the mechanism of the enzyme. Catalyze reactions between stereoisomers and constitutional isomers

Question 10

Ligases

Answer 10

Catalyze addition of synthesis reactions generally between large similar molecules as often require ATP
Most likely encountered in nucleic acid synthesis and repair

Question 11

Endergonic reaction

Answer 11

One requiring energy input (change in energy is greater than zero)

Question 12

Exergonic reaction

Answer 12

One providing energy output (change in energy is less than zero)

Question 13

Activation energy

Answer 13

Energy required for substrate to reach transition state

Question 14

Enzyme- substrate complex

Answer 14

The physical interaction between a substrate and its active site on the enzyme.

Question 15

Lock and Key Theory

Answer 15

Less widely accepted than induced fit model.

The enzyme’s active site is already in the correct conformation to bind to substrate and does not change

Question 16

Induced fit model

Answer 16

More scientifically accepted theory of enzyme substrate interaction
- the enzyme’s active site conforms as the substrate approaches
Induced form or transition state is better for both molecules

Question 17

Cofactors

Answer 17

Nonprotein molecules
Generally inorganic molecules or metal ions that are often ingested as dietary minerals. Small in size to find to active site of the enzyme and participate in catalysis, usually by charge through ionization, Protonation, or deprotonation

Question 18

Coenzymes

Answer 18

Small. Low amounts in cells.
Participate in catalysis by carrying a charge through ionization, protonation, or deprotonation.
Generally small organic groups, vast majority are vitamins or vitamin derivatives such as NAD+, FAD and coenzyme A.
Water soluble: B complex and vitamin C
Fat-soluble: vitamins A, D,E, and K better regulated by partition coefficients

Question 19

Apoenzymes

Answer 19

Enzymes without their cofactors

Question 20

Holoenzymes

Answer 20

Enzymes with their cofactors

Question 21

Prosthetic groups

Answer 21

Tightly bound cofactors or coenzymes that are necessary for enzyme function

Question 22

V max

Answer 22

Maximum velocity
Enzymes are fully saturated with substrates and reaction rate is producing products as fast as possible.
Adding substrates after this point cannot increase rate, only adding enzymes

Question 23

Michealis-Menton Plot of Enzyme kinetics

Answer 23

Relation between reaction velocity and substrate concentration [S]
Level off at v max

Question 24

Michealis-Menton equation

Answer 24

Rate of reaction, v, depends on concentration of the enzyme [E] and substrate [S] which forms the product [P].
Enzyme-substrate complexes form at rate k1 and dissociate at rate k2 or turn into enzyme plus product at rate of k3

Question 25

Equation for relation of enzymes to substrates where enzyme is held constant

Answer 25

v=(v max [S])/(K m + [S])

Question 26

When reaction rate is equal to half of v max

Answer 26

K m=[S]

V max over 2 equals v max times concentration of S over Km plus concentration of S
So v max times (Km plus concentration of S) equals 2(v max times concentration of S)
So Km plus concentration of S equals 2 times concentration of S so Km equals S

Question 27

Michealis constant Km

Answer 27

Understood to be the substrate concentration at which half of the enzyme’s active sites are full
Under some conditions it is the measure of the affinity of the enzyme for its substrate - higher Km means lower affinity for substrate
Cannot be changed by altering concentration of substrate or enzyme

Question 28

Lineweaver-Burk Plots

Answer 28

Double reciprocal graph of michealis-menton equation
Intercept of x axis gives value of -1/Km
Intercept of y axis gives value of 1/v max
Allows to compare Km and v max wo estimation

Question 29

Cooperativity

Answer 29

Multiple subunits and multiple active sites
Subunits and enzymes may exist in
Low affinity tense state T
High affinity relaxed state R
Binding of substrate encourages other subunits to change from T to R
Or loss of substrate results in opposite

Question 30

Feedback regulation

Answer 30

Enzymes regulated by products further down the pathway

Question 31

Feed forward regulation

Answer 31

Less common than feedback regulation; enzymes regulated by intermediates that precede the enzyme in the pathway.

Question 32

Negative feedback

Answer 32

Feedback inhibition; helps maintain homeostasis. Once there is enough of the product it turns off the pathway that creates the product

Product may bind to active site of enzyme that acted earlier in its biosynthetic pathway (competitive inhibition)

Question 33

Competitive inhibition

Answer 33

Reversible inhibition- higher Km and same v max.

Occupies the active site. Can be overcome by adding more substrate

Question 34

Noncompetitive inhibitor

Answer 34

Reversible inhibitor
Binds to allosteric site instead of active site - induces change in conformation
Cannot be overcome by addition of substrate
Bind equally well to enzyme and enzyme-substrate complex
No change to Km; v max is decreased

Question 35

Mixed inhibitors

Answer 35

Reversible inhibition
Can bind to enzyme or enzyme-substrate complex but does not have same affinity for each. Do not bind at active sites but allosteric instead
If enzyme binding is preferred Km is increased
If enzyme-substrate complex binding is preferred Km is decreased
V max is decreased

Question 36

Uncompetitive inhibitors

Answer 36

Reversible
Bind only to enzyme-substrate complex and lock substrate in enzyme preventing its release
Increased affinity between enzyme and substrate
Lower Km and v max

Question 37

Irreversible inhibition

Answer 37

Active site unavailable for a long time or permanently

Asa is a good example

Question 38

Allosteric enzyme’s

Answer 38

Regulated enzyme Multiple binding sites one is active and others regulate availability of active site
May be active or inactive may be bound to by allosteric activators (activator shift to make active site more available) or allosteric inhibitors (opposite)
May alter activity of enzyme

Question 39

Covalently modified enzymes

Answer 39

Enzymes may be activated or deactivated with phosphorylation or dephosphorylation, maybe either one

Question 40

Zymogens

Answer 40

Enzymes that are dangerous if uncontrolled and will consume and organ. Contain active or catalytic domain and regulatory