2.4 enzyme definitions

Question 1

Activation energy

Answer 1

The amount of energy needed for a reaction to happen

Question 2

Active site

Answer 2

A specific region on an enzyme where the substrate binds and the reaction takes place.

Question 3

Amylase

Answer 3

An enzyme that catalyses the extracellular breakdown of starch

Question 4

Catalase

Answer 4

An enzyme that catalyses the intracellular breakdown of hydrogen peroxide into oxygen and water

Question 5

Coenzyme

Answer 5

A type of cofactor that is bound loosely to an enzyme with weak interactions

Question 6

Cofactors

Answer 6

A non-protein molecule that is needed for the effective functioning of an enzyme.

Question 7

Competitive inhibitor

Answer 7

A molecule which binds to the active site of an enzyme and prevents the substrate from binding, decreasing its activity as they compete with substrate for
the enzyme.

Question 8

Cyanide (CN-)

Answer 8

A metabolic poison which acts as an irreversible inhibitor of cytochrome oxidase and hence preventing respiration.

Question 9

End-product inhibition

Answer 9

A method of enzyme inhibition where the product of an enzyme controlled reaction can bind to the enzyme and prevent it from working.

Question 10

Enzyme

Answer 10

A biological catalyst used to speed up the rate of biochemical reactions without being used up or permanently altered.

Question 11

Enzyme-product complex

Answer 11

The temporary complex formed after the enzyme has catalysed the reaction but before the products have left the active site of the enzyme.

Question 12

Enzyme-substrate complex

Answer 12

The temporary complex formed when the substrate binds to the active site of the enzyme.

Question 13

Extracellular reaction

Answer 13

A reaction that occurs outside of cells

Question 14

Inactive precursor

Answer 14

An inactive form of an enzyme that cannot carry out its function until it is activated

Question 15

Induced fit hypothesis

Answer 15

A model of enzyme action that describes how once a specific substrate binds to the active site, the enzyme undergoes subtle conformational changes to fit the substrate better.

Question 16

Intracellular reaction

Answer 16

A reaction that occurs within cells

Question 17

Lock and key hypothesis

Answer 17

A model of enzyme action that describes how the enzyme will only fit a substrate that has the correct complementary shape to the active site

Question 18

Metabolism

Answer 18

The sum of all the chemical reactions taking place in a cell

Question 19

Non-competitive inhibitor

Answer 19

An inhibitor which binds to a different part of an enzyme known as the allosteric site and prevents the enzyme from functioning as it changes the shape of the active site therefore preventing the binding of the substrate

Question 20

Prosthetic group

Answer 20

A type of cofactor that is permanently bound to an enzyme with strong interactions.

Question 21

Substrate specificity

Answer 21

The ability of an enzyme to catalyse only a specific reaction or set of reactions which have substrates complementary to the active site of the enzyme

Question 22

Temperature coefficient (Q10)

Answer 22

A method of calculating an increase in reaction rate after a 10C temperature increase - calculated using the following equation
Q10 = R2/R1

Question 23

Trypsin

Answer 23

An enzyme that catalyses the extracellular breakdown of proteins

Question 24

what are the factors affecting the rate of enzyme-controlled reaction

Answer 24

enzyme concentration
substrate concentration
temperature

Question 25

Explain how enzyme concentration affects the rate of reaction

Answer 25

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 26

Explain how substrate concentration affects the rate of a reaction

Answer 26

As concentration of substrate increases, rate of reaction increases as more enzyme-substrate complexes are formed. However, beyond a certain point the rate of reaction no longer increases as enzyme concentration becomes the limiting factor

Question 27

Explain how temperature affects the rate of a reaction

Answer 27

Rate of reaction increases up to the optimum temperature, which is the temperature at which enzymes work at their maximum rate. Rate of reaction
decreases above the optimum temperature and if it goes to high the enzymes may denature as the active sights will change shape

Question 28

What is an inhibitor

Answer 28

a substance which slows down or stops a reaction by affecting the binding of substrate to the enzymes. Inhibitors can either be reversible or irreversible

Question 29

Give an example of an irreversible inhibitor

Answer 29

heavy metal ions such as mercury and silver which cause disulphide bonds within the protein structure to break, as a result causing the shape of the active site to change, thus affecting protein activity

Question 30

What is a reversible inhibitor

Answer 30

a substance which binds to the active site through hydrogen bonds and weak ionic interactions therefore they do not bind permanently and can be reversed by the addition of excess substrate.

Question 31

what is an irreversible inhibitor

Answer 31

A substance that covalently bonds to a particular group at the active site. The inhibitor-enzyme bond is so strong that the inhibition cannot be reversed by the addition of excess substrate.

Question 32

give examples of an inhibitor

Answer 32

Many drugs are inhibitors:
penicillin which is used to fight bacterial infections, it is an inhibitor of enzyme transpeptidase which plays an important role in cell wall formation.
Ritonavir which is an antiretroviral drug used to treat
HIV which inhibits HIV protease which is responsible for assembly of new viral particles and spread of infection.

Question 33

what happens to the amount of product formed when a competitive inhibitor is present

Answer 33

remains the same

Question 34

what happens to the rate of product formed when a competitive inhibitor is present

Answer 34

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

Question 35

how do you outcompete a competitive inhibitor

Answer 35

increasing the substrate reverses the effect of competitive inhibitors by outcompeting them

Question 36

what are the types of reversible inhibitors

Answer 36

competitive and non competitive

Question 37

how do you out compete a non competitive inhibitor

Answer 37

you can’t - Increasing the concentration of substrate has no effect

Question 38

what are the 3 types of cofactors

Answer 38

coenzymes
activators
prosthetic groups

Question 39

what are most coenzymes

Answer 39

vitamin derived, examples include NAD derived from niacin, which acts as a hydrogen acceptor.

Question 40

what is an activator

Answer 40

inorganic metal ions which temporarily binds to the enzyme and alters its active site, making the reaction more feasible.

Question 41

give an example of an activators

Answer 41

magnesium ion is an important activator which is involved in processes such as shielding negative charge.

Question 42

give an example of a prosthetic group

Answer 42

haemoglobin contains a prosthetic haem group which contains iron, permanently bound to the molecule,
which allows oxygen to bind and form haemoglobin