Topic 5 - Enzymes

Question 1

What is an enzyme and what is it’s function?

Answer 1

A Catalyst. Speed up reactions w/out being used up or changed

Question 2

Most enzymes are what kind of protein?

Answer 2

globular => soluble in H20, hydrophobic outside, hydrophilic inside

Question 3

To bind to an enzyme and cause a reaction the substrate’s structure and stereochemistry must fit the entire active site exactly. T or F?

Answer 3

True

Question 4

Enzyme function is determined by their….?

Answer 4

primary aa sequence

Question 5

What is a simple enzyme?

Answer 5

all protein, no cofactor

Question 6

What is a complex enzyme?

Answer 6

protein and cofactor/coenzyme

Question 7

What is a holoenzyme?

Answer 7

A complete complex enxyme

Question 8

What is a Apoenzyme?

Answer 8

Protein component of holoenzyme. Require a cofactor or prosthetic group for activity

Question 9

What is a cofactor?

Answer 9

one or more weakly bound metal ions, or a weakly bound organic (e.g. NADH) or metalloorganic molecule

Question 10

What is a prosthetic group?

Answer 10

tightly or covalently bonded cofactor (e.g. heme)

Question 11

What is a metallo-enzyme?

Answer 11

metal always bound to active site

Question 12

What is a metal-activated enzyme?

Answer 12

metal not part of native structure, but required for activity.

Question 13

What is the main difference b/w a cofactor and a prosthetic group?

Answer 13

A prosthetic G is tightly bound

Question 14

Are coenzymes consumed during a reaction?

Answer 14

yes

Question 15

Are coenzymes a substrate?

Answer 15

yes

Question 16

What is an isozyme? What do they allow?

Answer 16

different enzymes that catalyse the same reaction. Can have related aa sequence or very different. allow metabolic pathways to follow different courses in different cells: same metabolites, different fates

Question 17

How do enzymes act, what do they induce and what does this allow

Answer 17

Enzymes act by binding substrates, allowing development of kinetic equations. Induce transition state.

Question 18

What is the transition state?

Answer 18

midway b/w substrate & product

Question 19

PLEASE READ SLIDES 44-56 FOR TRANSITION STATE INFO

Draw transition state graph

Answer 19

PLEASE PLEASE PLEASEE!!!

Question 20

State the equilibrium constant (Keq) equation for products & substrates

Answer 20

Keq = [P]/[S] for multiple: Keq = ([C].[D])/([A].[B])

Question 21

State the equation which describes the direct relationship b/w Keq and the free energy change (ΔG) => answer gives how much energy is given off changing a substrate into a product

Answer 21

ΔG = -RT R= universal gas constant (1ap) T = absolute temp (298K=25C) PLEASE SEE TRANSITION SLIDES 44-56

Question 22

Enzymes do not bind transition states better than substrates. T or F?

Answer 22

False

Question 23

Enzymes do not effect equilibrium (ΔG). T or F?

Answer 23

True

Question 24

Define enzyme specificity.

Answer 24

The ability of an enzyme to selectively bind to and catalyse a specific substrate(s) is termed enzyme specificity.

Question 25

Catalytic reactions @ active site: What is general acid-base catalysis?

Answer 25

A number of aa side chains can act as H+ donors or acceptors (Glu, Asp, Lys, Arg, His)

Question 26

Catalytic reactions @ active site: What is covalent catalysis?

Answer 26

A transient bond is formed b/w substrate & enzyme. Requires a nucleophile

Question 27

Catalytic reactions @ active site: What is metal ion catalysis?

Answer 27

can electrostatically polarise atoms, or change oxidation state to donate/receive electrons (H+). Involves a metal ion bound to enzyme. -stabilisies -ve charges -participates in oxidation reactions

Question 28

Define enzyme activity?

Answer 28

rate of enzyme catalysed reaction

Question 29

Define specific enzyme activity?

Answer 29

measure of enzyme purity = number of enzyme units per mg of total protein i.e. the purer, the higher the specific activty

Question 30

List the factors that influence enzyme activity.

Answer 30

enzyme [] -linear relationship pH -can denature enzyme; have optimal pH Temp. -see pH Substrate [] inhibitors

Question 31

What is the study of enzyme kinetics?

Answer 31

study of rate of enzyme catalysed reactions -how rates are affected by enviro -[] of substrate

Question 32

FOR ENZYME KINETICS, LINEWEAVER-BURKE PLOT, MICHAELIS-MENTEN EQUATION AND ENZYME INHIBITION PLEASE REVISE HAND WRITTEN NOTES

Answer 32

DO IT DO IT DO IITTT!!!

Question 33

Qrite the equation for the reaction where substrate (S) is converted into product (P) by enzyme (E)

Answer 33

Question 34

For the enzyme-substrate complex reaction, what is: k1? k-1? k2?

Answer 34

Question 35

Where does the transition state occur within the enzyme-substrate complex reaction?

Answer 35

within the ES complex | (not E or P or S)

Question 36

What is Vmax? When does it occur?

Answer 36

maximum rate of enzyme-catalysed reactions Occurs when all enzyme exists as ES complex =\> when E is saturated

Question 37

Write the Michaelis-Menten Equation and what it describes and what it allows us to determine. Draw the graph it reciprocates

Answer 37

Question 38

Low km = ? | (km=michaelis constant)

Answer 38

E has higher affinity for S & vice versa

Question 39

What is Kcat? Write the equation.

Answer 39

Measures enzyme efficiency (catalytic production of product) Kcat= number of substrate molecules converted per enzyme molecule per second Kcat = Vmax/[E]

Question 40

Kcat & Km together determine rate of catalysis. High Kcat, low Km =?

Answer 40

reactions catalysed the fastest

Question 41

Draw the Lineweaver-Burke Plot

Answer 41

Question 42

FOR ENZYME INHIBITION ALSO READ NOTES

Answer 42

PLEASE PLEASE PLEASE!!!!!!

Question 43

Describe irreversible enzyme inhibitors

Answer 43

react w/ enzyme One inhibitor molecule can permanently shut off one enzyme molecule

Question 44

Describe reversible inhibitors

Answer 44

bind to & can dissociate from enzyme -prevent reaction or binding of substrate

Question 45

Describe competitive inhibition, its affects on Vmaz and Km. Draw it's LWB plot.

Answer 45

Competes w/ substrate for binding - binds active site - does NOT affect catalysis No change in Vmax, apparent increase in Km LWB lines intersect y axis

Question 46

Describe uncompetitive inhibition, its affects on Vmax and Km. Draw it's LWB plot.

Answer 46

Only binds to ES complex - does not affect S binding - Inhibits catalytic function Decrease in Vmax, apparent decrease in Km in LWB lines are parallel

Question 47

Describe mixed inhibition, its affects on Vmaz and Km. Draw it's LWB plot.

Answer 47

Binds enzyme w/ or w/out substrate - binds regulatory site - inhibits both S binding & catalysis Decrease in Vmax, change in Km LWB lines intersect left of y axis

Question 48

List the types of enzyme regulation

Answer 48

irreversible reversible covalent modification noncovalent mod