L10: Enzymes I

Question 1

Define enzyme structure

Answer 1

Proteins composed of 1 or more polypeptide chains folded into a 3D complex shape

Question 2

How are enzyme structure stabilised?

Answer 2

By weak bonds

H-bonds
Electrostatic salt bridges
Van der Waals
Hydrophobic interactions

Question 3

Define enzymes

Answer 3

Biological catalysts that speed up the rate of reaction, without altering the final equilibrium between reactants & products

Extremely efficient

Question 4

2 theories for enzyme binding

Answer 4

1) Lock & Key
2) Induced Fit

Question 5

lock & key

What is the lock & key theory?

Answer 5

Enzymes are complementary to their substrate

To explain the high specificity of enzymes

Question 6

induced fit

What is the induced fit theory?

Answer 6

Enzymes are initially not complementary, but will undergo change upon substrate binding

Induced by weak interactions with the substrate itself

Question 7

Define transition state

Answer 7

Unstable, high-energy intermediate in a chemical reaction, when the molecule is neither substrate/product

Stabilising the transition state is one way that enzymes can speed up a reaction

Question 8

Why is the transition state high energy?

Answer 8

Has 5 carbon bonds

Question 9

Why complementarity of enzymes to transition state necessary?

Answer 9

Lowering the Ea, binding tightly so reaction can’t proceed

Question 10

Substrate specificity

What do enzymes usually do?

Answer 10

1) Catalyse only 1 type of reaction
2) Only act on a few related molecules

Question 11

Substrate specificity

True or false: Enzyme will usually act only on one isomer if a compound exists in 2 steroisomer forms

Answer 11

TRUEEEE

Question 12

What is specificity determined by?

Answer 12

Groove or cleft of defined shape - the ‘active site’

Which only the substrate of the correct shape & charge can fit

Question 13

Enzyme specificity - classification

How many classes are enzymes divided in & according to what?

Answer 13

6 classes & according to the type of reaction they catalyse

Question 14

enzyme specificity-classification

Are the six classes of enzymes further divided into subgroups? If yes, what is according to?

Answer 14

Yes, according to their substrate or source

Substrate: What they work on
Source: Where they come from

Question 15

6 classification of enzymes

Answer 15

1) Oxidoreductases
2) Transferases
3) Hydrolases
4) Lyases
5) Isomerases
6) Ligases

Question 16

classification of enzymes

What type of reaction is OXIDOREDUCTASES

Answer 16

Catalyse oxidation/reduction reactions

Transfer of H & O atoms/electrons from 1 substance to another

Question 17

classification of enzymes

What type of reaction is TRANSFERASES

Answer 17

Catalyse the transfer of functional groups from 1 substance to another

Question 17

classification of enzymes

What type of reaction is HYDROLASES

Answer 17

Catalyse the formation of 2 products from a substrate by hyrolysis (spitting using H2O)

Question 17

classification of enzymes

What is the type of reaction LYASES

Answer 17

Catalyse non-hydrolytic addition or removal of groups from substrates

Question 18

classification of enzymes

What type of reaction is ISOMERASES

Answer 18

Catalyse isomerisation changes within a single molecule

Question 19

classification of enzymes

What type of reaction is LIGASES

Answer 19

JOin together 2 molecules by synthesis of new
C-O, C-S, C-N or C-C bonds
whilst breaking down ATP

Question 20

Properties of enzymes: effects of temp

Weak bonds are easily broke

Answer 20

• Enzyme structure is stabilised by many weak bonds
• Weak bonds are easily broken
• Makes enzymes very sensitive to changes

Question 21

classification of enzymes

What type of reaction is TRANSLOCASES

Answer 21

Catalyse the movement of ions/molecules across membranes or their separation within membranes

Question 22

Define cofactors

Answer 22

Nin-protein substance (small organic molecules/inorganic elemtns), that is necessary for the activity of an enzyme

Question 23

Define co-enzymes

Answer 23

Organic cofactors that are not firmly attached to the enzyme ## Footnote Non-protein substance

Question 24

Define apoenzyme

Answer 24

Enzyme represent inative becayse its been separated from its cofactors ## Footnote Enzymes catalytically inactive form

Question 25

Define holoenzyme

Answer 25

Complete molecule in its fully active state ## Footnote Enzymes catalytically active form

Question 26

2 examples of co-enzymes

Answer 26

1) NAD 2) FAD

Question 27

Another term for co-enzymes

Answer 27

Co-substrates, as they take part in & are changed by the reaction

Question 28

Define isoenzymes

Answer 28

Enzymes with different protein structures that catalyses the same reaction ## Footnote Coded for by different genes

Question 29

Define enzyme kinetics

Answer 29

Study of the RATE of an enzyme catalysed reaction ## Footnote - How that rate varies with different substrate concentrations - Effects of inhibitors

Question 30

How is the reaction rate at low substrate concentration?

Answer 30

Reaction rate is directly proportional to the substrate concentration

Question 31

How is the reaction rate at high substrate concentration?

Answer 31

Reaction rate is independent of substrate concentration

Question 32

Define reaction rate

Answer 32

Increase in the amount of product formed per time

Question 33

How can the reaction rate be measured as?

Answer 33

Decrease in the amount of substrate per unit time

Question 34

Formula for Michaelis-Menten reaction model

Answer 34

S + E ⇌ ES → P + E

Question 35

What does the Michaelis-Menten reaction model explain?

Answer 35

Explains how the rate of an enzyme-catalysed reaction depends on the concentration of the enzyme and its substrate

Question 36

Define Vmax

Answer 36

Maximum rate of the reaction, all enzyme's active sites are saturated with substrate

Question 37

Define Km

Answer 37

Substrate concentration at which reaction rate is 50% of the Vmax ## Footnote - Measure of the affinity an enzyme has for its substrate - More lower the value of Km, more efficient the enzyme is

Question 38

3 assumptions of the MMKinetics

Answer 38

1) (S) > (E), so the amount of substrate bound by enzyme is negligible 2) (ES) doesn't change with time 3) Concentration of product is so small, back reaction of P to S is ignored ## Footnote Rate of formation = Rate of dissociation

Question 39

Equation for V0

Answer 39

V0 = Vmax (S) / Km + (S)

Question 40

What does the V0 equation describe?

Answer 40

How initial rate of reaction (V) is affected by the initial substrate concentration

Question 41

What do these represent: 1) V0 2) Vmax 3) Km 4) S

Answer 41

V0: Initial reaction velocity Vmax: Maximal velocity of an enzyme catalysed reaction Km: Michaelis constant S: Substrate conc

Question 42

Define Kcat

Answer 42

No. of substrate molecules converted to product on a single enzyme molecule when it is saturated with substrate

Question 43

Define catalytic efficiency (Kcat/Km)

Answer 43

Measure of an enzyme's specificity for a particular substrate