1.4- Enzymes

Question 1

What are enzymes?

Answer 1

tertiary proteins- where the polypeptide chain is folded back on itself into a spherical globular shape which increase the rate of a metabolic reaction by lowering the activation energy

Question 2

How are enzymes specific?

Answer 2

each enzyme reacts with a particular substrate molecule
each enzyme will catalyse only one particular reaction
each enzyme has its own 3D globular shape maintained by tertiary protein bonding

Question 3

What’s an enzyme -substrate complex?

Answer 3

the substrate molecule is complimentary to the active site which fits into and binds to the active site within the enzyme

Question 4

What’s the lock and key theory?

Answer 4

there is an exact fit between the substrate and the active site of the enzyme

Question 5

What’s the induced fit theory?

Answer 5

when the enzyme and substrate form a complex, the structure of the enzyme is altered so that the active site of the enzyme fits around the substrate

Question 6

What’s an example of an induced fit theory?

Answer 6

lysozyme

Question 7

What are anabolic enzymes?

Answer 7

build larger products from smaller substrate molecules

Question 8

What are catabolic enzymes?

Answer 8

break large substrate molecules into smaller products

Question 9

What is activation energy?

Answer 9

the energy needed to break existing chemical bonds inside molecules at the start of the reaction

Question 10

What does intracellular mean?

Answer 10

catalyse reactions inside of cells e.g ATP Synthase, DNA helicase which unwinds the helix

Question 11

What does extracellular mean?

Answer 11

catalyse reactions outside of cells e.g digestive enzymes secreted by the cell

Question 12

What factors affect enzyme activity?

Answer 12

temperature
pH
substrate concentration
enzyme concentration

Question 13

How does an increase in temperature affect enzyme activity?

Answer 13

it increases the rate of reaction because it gives the molecules greater kinetic energy, the enzyme and substrate molecules move around more quickly, increasing the chance of molecules colliding, this leads to the formation of more successful enzyme-substate complexes, which will continue until the optimum temperature is reached

Question 14

What is the optimum temperature?

Answer 14

the temperature enzymes work best
where the most successful collisions take place

Question 15

What happens to then enzyme when the temp is further increased after the optimum temp?

Answer 15

the kinetic energy increases to a point where vibrations in the enzyme molecule weaken some bonds holding the 3D tertiary structure of the active site together. The active site loses its shape, the substrate is no longer complementary to the active site, no further enzyme-substrate complexes can be made, and the enzyme is denatured, decreasing the rate of reaction

Question 16

What happens to the enzyme activity at low temperatures?

Answer 16

as there’s low kinetic energy, the enzyme and the substrate molecules collide less often, so fewer successful enzyme substrate complexes form, meaning the product is produced slowly

Question 17

What happens when the substrate concentration is increased?

Answer 17

As enzyme reaction relies on successful collisions between enzymes, an increase in the substrate concentration will increase collisions and the rate of reaction. Therefore, at low substrate concentrations, it is this factor that is limiting the rate of reaction
Any further increase in substrate concentration, has no effect on the rate of reaction. It is no longer the limiting factor. The rate of reaction plateaus as the active sites are occupied, having formed successful enzyme substrate complexes
The enzyme concentration is the limiting factor now

Question 18

How does pH affect enzyme activity?

Answer 18

Small changes from the optimum pH, either above or below, make small reversible changes in the enzyme molecule reducing its efficiency. Large changes in pH can disrupt ionic and hydrogen bonds in the enzyme causing permanent changes to the shape of the active site. This prevents the formation of enzyme/substrate complexes, denaturing the enzyme

Question 19

What does limiting factor mean?

Answer 19

a factor is limiting when an increase in its value causes an increase in the rate of reaction

Question 20

What happens when the enzyme concentration is increased?

Answer 20

the rate of reaction increases as enzyme concentration increases as there are more active sites for substrates to bind to, however increasing the enzyme concentration beyond a certain point has no effect on the rate of reaction as there are more active sites than substrates, so substrate concentration becomes the limiting factor

Question 21

What is an inhibitor?

Answer 21

is a substance which slows down or stops a reaction by affecting the binding of substrate to the enzymes

Question 22

What are two types of inhibitors?

Answer 22

reversible and irreversible

Question 23

What is a reversible inhibitor?

Answer 23

bind to the active site through hydrogen bonds and weak ionic interactions therefore they do not bind permanently

Question 24

What are the types of reversible inhibitors?

Answer 24

competitive and non-competitive inhibitors

Question 25

What is a competitive inhibitor?

Answer 25

structurally similar to the substrate molecule, allowing it to fit into the active site of the enzyme, by colliding due to random kinetic movement of the molecules
prevent the formation of enzyme- substrate complexes by blocking
the active site
They do not bind permanently
The amount of product formed remains the same, however the rate at which product formation occurs decreases

Question 26

What will happen if the substrate concentration increases with a competitive inhibitor?

Answer 26

it will decrease the effect of the inhibitor as the enzyme is more likely to collide with a substrate molecule and form a successful enzyme-substrate complex

Question 27

What happens when there’s a higher concentration of competitive inhibitor?

Answer 27

the higher the concentration of competitive inhibitor the lower the reaction rate

Question 28

What is a non-competitive inhibitor?

Answer 28

they do not bind to the active site, but binds to any other part of the enzyme called the allosteric site
this distorts the overall shape of the enzyme, including the active site
which prevents the binding of the substrate molecule
so successful enzyme substrate complexes cannot form

Question 29

What will happen if the substrate concentration increases with a non-competitive inhibitor?

Answer 29

no effect on the reaction because the substrate can no longer fit into the enzyme’s active site

Question 30

What is an immobilised enzyme?

Answer 30

an enzyme which is fixed, bound or trapped on an inert matrix
e.g alginate beads

Question 31

What are the advantages of using immobilised enzymes?

Answer 31

enzyme does not contaminate the product
immobilised enzymes can be recovered and reused
only a small quantity of enzyme is needed
enzymes have a greater stability and denature at higher temperatures
greater control over the process

Question 32

What are biosensors?

Answer 32

can detect biologically important molecules very rapidly, even at low concentrations
can be used to measure blood glucose concentration who has diabetes
it detects a chemical change, as substrate is converted to product, and a transducer converts this chemical change into an electrical signal which can be amplified and viewed on a display