Lecture 4

Question 1

isoelectric point

Answer 1

the pH at which the protein has no net charge and does not move in electric field (positive charges = negative charges)

Question 2

enzyme function

Answer 2

accelerate specific reactions

Question 3

what is the fastest enzyme?

Answer 3

carbonic anhydrase

Question 4

are all enzymes proteins?

Answer 4

yes, but exception of catalytic RNAs

Question 5

what happens if there is an absence of enzymes?

Answer 5

chemical reactions in the body would occur too slowly to sustain life
- reactions would also occur at temperatures that are incompatible with life

Question 6

why are enzymes necessary for life?

Answer 6

they maintain precise control of all reactions at normal physiological temperatures

Question 7

catabolic pathways

Answer 7

breaking down foodstuffs into smaller molecules for energy or building blocks for other materials

Question 8

anabolic (biosynthetic) pathways

Answer 8

use energy from catabolic pathways to synthesize components

Question 9

how do enzymes speed up chemical reactions?

Answer 9

lowering the energy barrier

Question 10

second law of thermodynamics

Answer 10

any isolated system, the degree of disorder can only increase
-systems have tendency to become more disordered

Question 11

entropy

Answer 11

measure of disorder

Question 12

spontaneous reaction

Answer 12

no energy is required for reaction to happen

Question 13

do cells violate the second law of thermodynamics?

Answer 13

appear to violate second law, but cells take energy in from environment, and generate order themselves
- energy is released as heat into environment (entropy increases)

Question 14

first law of thermodynamics

Answer 14

energy can be converted rom one form to another but it cannot be created or destroyed

Question 15

how does the first law of thermodynamics apply to cells?

Answer 15

cells convert energy in chemical bonds of food into the random thermal motion of molecules

Question 16

free energy

Answer 16

loss of free energy (loss of energy) can be harnessed to do work or drive chemical reactions

Question 17

what direction does chemical reactions take?

Answer 17

direction that leads to loss of free energy (going downhill –> energetically favorable)

Question 18

activation energy

Answer 18

a boost over an energy barrier, which leaves reaction more stable state

Question 19

transition state

Answer 19

• the peak of the activation energy curve
• amount of free energy required to bring the reactants to the transition state

Question 20

how does temperature affect enzyme activity?

Answer 20

• 37C increases the rate of reaction
• high temperatures can denature enzymes

Question 21

formation of enzyme-substrate complex

Answer 21

binding of enzyme to substrate –> binding to active site

Question 22

active site of enzyme

Answer 22

consists of stretch of amino acids present in crevice or cleft of the enzyme

Question 23

what are the two models of enzyme substrate complex formation?

Answer 23

lock and key
induced fit model

Question 24

lock and key model (enzyme substrate formation)

Answer 24

• enzyme undergoes conformational change after binding the substrate
• shape of active site becomes complementary to shape of substrate (only after substrate binds to enzyme)

Question 25

what affects enzyme rates?

Answer 25

concentration of enzyme, substrate or inhibitors/activators

Question 25

general strategies of enzyme catalysis

Answer 25

• enzyme binds to two substrate molecules and orients them to encourage reaction
• enzyme binds substrate rearranging causing partial positive and negative charges that favor reaction
• enzyme strains substrate forcing it towards transition state

Question 26

how is enzyme velocity determined?

Answer 26

• different starting substrate concentrations with the same amount of enzyme
• velocity varies with substrate concentration

Question 27

Michaelis - menten enzyme kinetics

Answer 27

specific enzyme-substrate complex is necessary intermediate in catalysis

Question 28

what does the M-M enzyme kinetic describe?

Answer 28

assumed that none of the product reverts to the initial substrate

Question 29

relationship between substrate concentration and initial velocity

Answer 29

at infinite concentration, the reaction proceeds at maximal velocity

Question 30

Km

Answer 30

• the substrate concentration at which the reaction proceeds at one half its maximal velocity
• rate at which the enzyme-substrate complex breaks down divided by the rate of ES fomation

Question 31

what happens to Km if K1 is greater than K2?

Answer 31

Km becomes the measure of strength of ES complex and thus the affinity of the enzyme for its substrate

Question 32

what is the Km value for lysozyme and carbonic anhydrase?

Answer 32

lysosome –> 6 x 10^-6M
carbonic anhydrase –> 8 x 10^-3M

Question 33

what is the equation for Michaelis Menten?

Answer 33

V = (Vmax * substrate concentration)/Km + substrate concentration

Question 34

when would substrate concentration equal Km?

Answer 34

velocity of a reaction is at half maximal

Question 35

what is the significance of Km?

Answer 35

• equal to substrate concentration at which velocity is half maximal
• where small change in concentration would have a large effect on velocity

Question 36

what is the significance of Vmax?

Answer 36

used to calculate turnover number

Question 37

turnover number

Answer 37

number of moles of substrate converted into product per mole of enzyme per second