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, activesite changes shape to fit substrate better which puts strain and pressure on bonds within substrate 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
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. ( if active site has you many h plus ions, could repel each others )

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 fixed in mert material

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

Question 11

What is a catalyst

Answer 11

Biological molecule which can speed up 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 does it mean in terms of quaternary structure that enzymes are globular proteins

Answer 12

Multiple polypeptides bonded together and each polypeptide chain folded into 3D structure

Question 12

What is activation energy

Answer 12

Minimum amount of Extra energy required to enable reaction to start

Question 13

Why is tertiary structure of enzyme essential to its function

Answer 13

. Tertiary structure determines shape of active site which is only complementary to specific substrate so change in active site shape means that enzyme cannot catalyse reaction

Question 14

What does enzyme actually do when it breaks apart a substrate

Answer 14

Hydrolysis with breaking of… Bond

Question 15

Explain lock and key model

Answer 15

Shape 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 16

Why is induced fit model preferred over lock and key

Answer 16

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

Question 17

What happens to enzymes when temp is too high

Answer 17

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

Question 18

What are 2 characteristics of enzymes

Answer 18

Reusable and shape of active site remains unchanged

Question 19

Difference between intracellular and extra cellular enzymes

Answer 19

Intracellular = inside cell
Extracellular = outside cell

Question 20

Explain effect of substrate concentration on ROR.

Answer 20

ROR increases steadily 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

Question 21

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

Answer 21

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 22

Purpose of buffer

Answer 22

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

Question 23

Explain non- competitive inhibitor

Answer 23

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 but ones involved in control of metabolic pathway are reversible

Question 24

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

Answer 24

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

Question 25

Example of non competitive inhibitor

Answer 25

Cyanide ions → respiratory inhibitor → inhibit cytochrome oxidase enzymes

Question 26

2 types of reactions enzymes catalyse

Answer 26

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