Chapter 3: Enzymes

Question 1

what are enzymes

Answer 1

• enzymes are globular proteins/fibrous CHONs that catalyse metabolic reactions inside and outside the cell
• they remain unchanged after catalysis

Question 2

what are metabolic reactions + types

Answer 2

• biochemical processes

- two types: anabolism and catabolism

Question 3

what is the active site of the enzyme

Answer 3

where the substrate can sit in

Question 4

what is the function of catalytic residues (part of enzymes)

Answer 4

takes part in breaking the bonds of the substrate to catalyse the reaction

Question 5

what is the function of R groups in enzymes

Answer 5

• holds the substrate in the active site

- forms temporary bonds with substrate

Question 6

how is the substrate held in the enzyme active site

Answer 6

substrate is held by temporary bonds with the r groups of amino acids residues in enzyme active site

Question 7

what are the two types of enzyme residues

Answer 7

• contact residues

- catalytic residues

Question 8

what are contact residues

Answer 8

• contact residues fit with the substrate

- these residues determine enzyme specificity

Question 9

what are catalytic residues

Answer 9

catalytic residues act on those bonds in the substrate that are broken by enzyme action

Question 10

what is a substrate

Answer 10

chemical/reactant on which an enzyme works

Question 11

which enzymes have more specific functions

Answer 11

• sucrase
• maltase
• amylase
• urease
• catalase

Question 12

which enzymes have more general functions

Answer 12

• lipase

- protease

Question 13

what is specificity of enzymes

Answer 13

• 1 type of enzyme only binds to one type of substrate molecule
• this is because the enzyme active site shape is complementary to the substrate shape
• only substrates with a complementary shape to the enzyme active site can sit into the enzyme active site

Question 14

what are the two ways a substrate fits/sits into an enzyme

Answer 14

• lock and key hypothesis

- induced fit hypothesis

Question 15

what is lock and key hypothesis

Answer 15

• complementary shape fitting
• both enzymes and substrates were rigid structures that locked into each other very precisely, much like a key going into a lock

Question 16

what are anabolic reactions

Answer 16

Anabolic reactions involve the building of more complex molecules from simpler ones by drawing two or more substrates into the active site, forming bonds between them and releasing a single product

Question 17

what are catabolic reactions

Answer 17

Catabolic reactions involve the breakdown of complex molecules into simpler products, which happens when a single substrate is drawn into the active site and broken apart into two or more distinct molecules

Question 18

what is induced fit hypothesis

Answer 18

• enzyme would mould around the substrate

- the enzyme function is more general here (e.g. lipase, protease)

Question 19

what is the quantity of enzymes produced

Answer 19

• enzymes remain unchanged after the reaction
• enzymes can be reused
• therefore only a small quantity is produced
• they have a high turnover rate (means they can catalyse many reactions per unit time)

Question 20

what is an enzyme substrate complex

Answer 20

a temporary complex formed when an enzyme binds to its substrate molecule

Question 21

what is the product

Answer 21

end material of a chemical/enzymatic reaction

Question 22

what are intracellular enzymes

Answer 22

• act inside cells

- responsible for catalysing reactions that occur in metabolic pathways

Question 23

what are examples of intracellular enzymes

Answer 23

• anaerobic respiratory enzymes (cytoplasm)
• aerobic respiratory enzymes (mitochondria)
• photosynthetic enzymes (chloroplasts)
• hydrolytic enzymes (lysosome)

Question 24

what are extracellular enzymes

Answer 24

• an enzyme that is secreted (the release of useful substances out) by a cell
• functions outside of that cell

Question 25

what are examples of extracellular enzymes

Answer 25

- amylase secreted into saliva for hydrolysis of starch -> maltose - thrombin (protease) secreted into blood plasma for fibrinogen -> fibrin - acrosomal enzymes in the sperm acrosome

Question 26

how do enzymes speed up reactions and increase effective collisions

Answer 26

- reduces activation energy by providing an alternative pathway - holds substrates in best position to occur

Question 27

how does the activation energy change upon the addition of an enzyme into a reaction

Answer 27

decreases

Question 28

what is the formula for rate of product formation

Answer 28

(final product conc. - initial product conc.)/(final time - initial time)

Question 29

what is enzyme activity

Answer 29

rate of enzyme catalysed reaction

Question 30

how is enzyme activity measured

Answer 30

by measuring the rate of substrate disappearance and the rate of product formation

Question 31

what are the factors affecting enzyme activity

Answer 31

- pH - temperature - enzyme and substrate concentration - inhibitor concentration

Question 32

what is the formula for effect of temperature on reaction rate

Answer 32

- Q10 =2 | - everytime the temperature increases by 10C, the rate will double until after optimum temperature

Question 33

how does temperature affect rate when it is significantly below the optimum temperature

Answer 33

- enzyme inactive | - rate of reaction low

Question 34

how does temperature affect rate when the temperature is increasing until optimum temperature

Answer 34

- increase kinetic energy/molecular motion of enzyme and substrate - increase frequency of effective collisions - more enzyme-substrate complex formed - rate increases (Q10=2)

Question 35

how does temperature affect rate when it is optimum temperature

Answer 35

maximum capacity

Question 36

how does temperature affect rate above optimum temperature

Answer 36

- kinetic energy continues to increase and atoms in molecules vibrate vigorously until hydrogen bonds are broken and the enzyme is denatured - the secondary and tertiary structure is disrupted and the active site shape changes - the substrate can no longer fit active site and the enzyme substrate complex is not formed - the rate decreases

Question 37

what is the limiting factor of the reaction before the graph plateaus

Answer 37

enzyme

Question 38

what is the limiting factor of the reaction after the graph plateaus

Answer 38

substrate

Question 39

what is the formula for rate of reaction

Answer 39

change in product formation/change in time

Question 40

what does it mean when enzymes are saturated

Answer 40

when all active sites on enzymes are occupied

Question 41

what is the limiting factor

Answer 41

limits the max rate of reaction

Question 42

what does increasing the limiting factor do

Answer 42

increase the rate of reaction

Question 43

what happens to the velocity of the reaction when the substrate concentration increases at low substrate concentration

Answer 43

the velocity increases

Question 44

what happens to the velocity of the reaction when it is at high substrate concentration/reaches maximum rate

Answer 44

Vmax

Question 45

what is the michealis-menten constant (Km)

Answer 45

the michealis-menten constant is the substrate concentration that produces 1/2 Vmax (the substrate concentration when velocity = vmax/2)

Question 46

what does the michealis-menten constant indicate about an enzyme

Answer 46

the affinity of an enzyme for its substrate

Question 47

how does Km (michealismenten constant) affect the affinity of an enzyme for its substrate (how does it indicate the affinity)

Answer 47

- the lower the Km, the higher the affinity of binding between the enzyme and its substrate - the higher the Km, the lower the affinity of binding between the enzyme and its substrate

Question 48

what are inhibitors

Answer 48

inhibitors are small molecules that prevent the normal action of enzymes

Question 49

what are the three concepts of inhibitors

Answer 49

- binding location - reversible and irreversible binding - competitive or noncompetitive inhibitor

Question 50

what are the inhibitors binding location

Answer 50

inhibitors either bind to the active site of the enzyme or the allosteric site

Question 51

how does inhibitors binding location work

Answer 51

when the inhibitor sits in the allosteric site, the enzyme changes its structure so the substrate can no longer sit in the active site

Question 52

what are reversible inhibitors

Answer 52

- can bind and leave the enzyme | - usually forms weak bonds with the enzyme

Question 53

what are irreversible inhibitors

Answer 53

- do not leave enzyme after binding - usually forms strong bonds with enzyme - enzyme is permanently inactivated

Question 54

what are competitive inhibitors

Answer 54

- an inhibitor whereby its ability to inhibit the enzyme depends on substrate concentration - the inhibitor occupies the active site and blocks out substrates

Question 55

what are non-competitive inhibitors

Answer 55

- an inhibitor that can inhibit the enzyme regardless of substrate concentration - the inhibitor binds to the allosteric site and changes the shape of the enzyme so no substrate can sit in

Question 56

is binding at the active site reversible or irreversible

Answer 56

irreversible

Question 57

is binding at the allosteric site reversible or irreversible

Answer 57

can be both

Question 58

which inhibitor (competitive or noncompetitive) reaches Vmax/plateaus faster

Answer 58

noncompetitve

Question 59

what is a metabolic pathway

Answer 59

a series of reactions

Question 60

what is end product inhibition

Answer 60

- when enough product is formed, the metabolic pathway can be switched off by end product inhibition - usually its a competitive/non competitive inhibitor

Question 61

what are immobilized enzymes

Answer 61

enzymes that have been fixed to a solid surface or trapped inside beads of agar gel

Question 62

how are immobilized enzymes made

Answer 62

- physical absorption e.g. resin - physical entrapment e.g. alginate/microcapsule - chemical bonding e.g. glutaraldehyde

Question 63

what are the advantages of enzyme immobilisation

Answer 63

- enzyme is easily recovered and reused again - the product will not be contaminated by enzymes - enhance enzyme stability to temperature and pH changes (held in shape and protected by pH and temperature changes) - allow several enzymes to participate in the process simultaneously

Question 64

how are immobilized enzymes used in industry

Answer 64

- lactase - to make lactose free milk - amylase - to make high fructose syrup for corn-starch - semisynthetic penicillin