Enzymes

Question 1

Factors affecting rate of enzyme controlled reactions

Answer 1

Substrate / enzyme concentration, pH, temperature, presence of inhibitors / _ activators

Question 2

Explain induced fit model

Answer 2

Substrate collides with active site, binds to it activesite changes shape to fit substrate better ( both active site and substrate change shape to bring their reactive groups together which puts strain and pressure on bonds within substrate, weakening them, lowering activation energy ESC form + then so do EPCs and active site return to normal shape and product released

Question 3

Explain relationship between rate of reaction and increasing temperature

Answer 3

① Initially ROR increases exponentially as temp increases to optimum because increase in kinetic energy = increase in successful collisions = more escs form and active site of enzyme will change shape as
molecules vibrate more so that it becomes better fit
② optimum temp → highest ROR because active site of enzyme is perfectly complementary to substrate so highest number of successful collisions and production is at max rate
③ ROR reduces rapidly until no more because when temp >optimum then vibrations in molecules are so great that breaks hydrogen bonds holding different parts of protein together altering specific shape of active site so no longer complementary to substrate + progresses as temp ↑

Question 4

Example of induced fit

Answer 4

Lysozyme

Question 5

Explain relationship between ROR and pH

Answer 5

At optimum pH, ROR is highest because charges of active site and substrate and shapes are complementary so attracted to each other and shape of active site and substrate are complementary
As pH moves away from optimum, ROR declines because 3D shape of enzyme and therefore its active site is distorted by breaking of hydrogen and ionic bonds so active site and substrate no longer complementary
and charges between enzyme and active site changed due to free H plus and hydroxide ions so-enzyme and substrate repel each other so fewer successful collisions. The r groups of the amino acids of the enzyme on the surface of the active site (?) are what are affected by the free ions ( if active site has you many h plus ions, could repel each others ) the OH ions change charges on the active site making the enzyme inactive

Question 6

Define ph

Answer 6

Measure of h+ ions concentration

Question 7

What happens if enzyme becomes more acidic

Answer 7

H plus ions bond to the negative charges on active site making them positive so no longer complementary to substrate + repels it

Question 8

What is an immobilised enzyme

Answer 8

Enzyme stabilised in an inert material improving the enzyme’s stability by widening the optimum pH / temp range

Question 9

Ways to immobilise an enzyme

Answer 9

Alginate beads, gel membrane, meshwork of in ent material, stuck to polyethene..

Question 10

Effect of immobilising enzymes

Answer 10

Stabilises enzyme and widens its optimum range and stable at higher temps because reduces ability of polypeptide chain to move so pH and temp have less effect on enzymes 3D structure and therefore its function.

Question 11

What is a catalyst

Answer 11

Biological molecule which can speed up rate of reaction without being used up or changing products by providing alternate reaction path with lower activation energy so reactions can occur at low temperature

Question 12

What is activation energy

Answer 12

Minimum amount of Extra energy required to enable reaction to start

Question 12

Why is tertiary structure of enzyme essential to its function

Answer 12

. Tertiary structure and bonding in it determines shape of active site which is only complementary to specific substrate so change in active site shape means that enzyme cannot catalyse reaction since enzymes are proteins

Question 13

What does enzyme actually do when it breaks apart a substrate

Answer 13

Hydrolysis with breaking of… Bond

Question 14

Explain lock and key model

Answer 14

Shape and charge of active site of enzyme is specific and complementary to substrate so they fit perfectly together like key in lock and bind together and enzyme substrate complex formed and products released and active site never changes shape

Question 15

Why is induced fit model preferred over lock and key

Answer 15

Enzymes aren’t rigid structures and enzyme - substrate complex changes shape slightly and ensures tighter bonding in active site

Question 16

What happens to enzymes when temp is too high

Answer 16

Enzymes denature because hydrogen bonds in tertiary structure break so shape of active site changes so enzyme no longer functions

Question 17

What are 2 characteristics of enzymes

Answer 17

Reusable and shape of active site remains unchanged

Question 18

Difference between intracellular and extra cellular enzymes

Answer 18

Intracellular = inside cell
Extracellular = outside cell

Question 19

Explain effect of substrate concentration on ROR.

Answer 19

ROR increases steadily linear / exponentially as substrate concentration increases because more successful collisions so more enzyme substrate complexes form + more product made → ROR plateaus even as substrate concentration increases because every enzyme working at maximum rate and maximum tum over number so active site is continually filled and increasing substrate concentration has no effect → enzyme conc has become limiting factor

Question 20

Explain effect of enzyme concentration on ROR when substrate is in excess

Answer 20

As enzyme conc increases, ROR increases linearly because more active sites available so more successful collisions between active site and substrate so more enzyme - substrate complexes form so more product each minute → continues as long as substrate in excess

Question 21

Purpose of buffer

Answer 21

Maintain pH otherwise pH for adequate controls could affect rate of reaction, denature enzymes or to help keep pH at optimum for max ROR

Question 22

Explain non- competitive inhibitor

Answer 22

Don’t compete for active site with substrate → instead binds to allosteric site distorting tertiary shape of enzyme to active site shape change so substrate no longer complementary and can’t fit so enzyme-substrate complexes can’t form so ROR decreases and maximum rate of enzyme activity is reduced → binding is usually irreversible if it bonds permanently but ones involved in control of metabolic pathway are reversible

Question 23

Effect of substrate conc on level of inhibition by non competitive inhibitor

Answer 23

No effect because substrate no longer fits → isn’t complementary

Question 24

Example of non competitive inhibitor

Answer 24

Cyanide ions e.g. Potassium cyanide → respiratory inhibitor → inhibit cytochrome oxidase enzymes

Question 25

2 types of reactions enzymes catalyse

Answer 25

Anabolic → condensation of smaller molecules making large molecules
Catabolic → breaking down / hydrolysis of larger molecules to smaller molecules

Question 26

Why are immobilised enzymes used in industrial use

Answer 26

They can be recovered for re-use s0 small amounts of enzyme needed for large scale reaction

Question 27

Advantages of immobilised enzymes in industrial use

Answer 27

→ can be recovered and re-used so only small amount needed, reducing cost
→ product not contaminated by enzyme → greater stability despite higher temps / pH → denature and stable at higher temps
→ can control ROR by adding/removing substrates/ enzyme (?)

Question 28

Disadvantages of immobilised enzymes in industry

Answer 28

→ expensive to set up
→ if contaminated, expensive to apart, clean and -.reassemble
→ requires equipment and expertise and also ROR is longer because it takes time for substance/ substrate to diffuse through substance enzyme is immobilised in to enzyme and back out

Question 29

What are the general characteristics of enzymes due to

Answer 29

The biochemical nature as globular proteins

Question 30

Explain how a competitive inhibitor works

Answer 30

Structurally similar to substrate = complementary to active site so substrate can no longer bind to it as it blocks active site

Question 31

Effect of substrate conc on competitor inhibition

Answer 31

Increasing substrate conc reduces inhibition effect because fewer proportion of inhibitors in comparison to substrate so substrate more likely to bind to active site → at high substrate conc, inhibitor molecules have negligible effect

Question 32

What is the effect of small change in pH on enzyme

Answer 32

Small reversible changes in enzyme tertiary structure = enzyme inactivation

Question 33

What is inhibition and why is it needed

Answer 33

Inhibition = when enzyme activity/ . action is slowed down / stopped by another substance and can be reversible or irreversible → it is needed to control cell reactions by slowing down/stopping reaction when they are no longer needed

Question 34

What are enzymes

Answer 34

Biological catalysts

Question 35

What do the enzymes lipase, protease and lactase do

Answer 35

Lipase: turns lipids into fatty acids and glycerol
Protease: turns proteins into amino acids
Lactase: turns. Lactose into galactose and glucose

Question 36

What is the enzyme turnover number

Answer 36

Max number of substrate molecules. it can turn into product molecules per unit of time

Question 37

Explain how the complementary charges work for the activesite-substrate

Answer 37

Amino acids near edge of active site have r groups which poke into the active site , some of which are polar/charged so they track the substrate molecule and an attraction exists between the substrate and active site / enzyme → in induced fit theory, when active site moulds around substrate, it is held in place by oppositely charged r groups in active site of enzyme and substrate