2.1.4 enzymes

Question 1

What are enzymes?

Answer 1

Enzymes are biological catalysts, they increase the rate of reaction by lowering the activation energy of the reaction.

Question 2

What are anabolic reactions?

Answer 2

‘Building up’ reactions.

Question 3

What are catabolic reactions?

Answer 3

‘Breaking down’ reactions.

Question 4

What is metabolism?

Answer 4

Metabolism is the sum of all the different reactions and reaction pathways happening in a cell or organism.

Question 5

What is Vmax?

Answer 5

Maximum initial velocity or rate of enzyme-catalysed reaction.

Question 6

What is activation energy?

Answer 6

The minimum amount of energy for a reaction to start.

Question 7

What is the lock and key hypothesis?

Answer 7

-The active site on the enzyme is complementary, only specific enzymes will fit specific substrates.
-When the substrate is bound to the active site, an enzyme-substrate complex is formed.
-The substrate then reacts and forms a enzyme-product complex.
-Products are released, leaving the enzyme.

Question 8

What is the induced-fit hypothesis?

Answer 8

-The active site of the enzyme changes shape slightly, induces changes to tertiary structure.
-Causes the substrate and enzyme to bind stronger, putting strain on the substrate.
-The bonds weaken within the substrate, lowering activation energy.

Question 9

What are intracellular enzymes?

Answer 9

Intracellular enzymes are enzymes which act within cells.

Question 10

What is an example of an intracellular enzyme?

Answer 10

Catalase: catalyses the decomposition of hydrogen peroxide (a toxic product of many metabolic pathways) into water + oxygen.

Question 11

What are extracellular enzymes?

Answer 11

Extracellular enzymes work outside the cell that made them.

Question 12

What are examples of extracellular enzymes?

Answer 12

Amylase: carbohydrates catalyses digestion of starch to maltose in saliva/small intestine lumen.
Trypsin: pancreatic endopeptidase catalyses hydrolysis of peptide bonds in small intestine lumen.

Question 13

Why are extracellular enzymes so important?

Answer 13

Allow large molecules, essential for reactions, to be broken down into smaller components.

Question 14

What four factors affect enzyme activity?

Answer 14

-Temperature
-pH
-Substrate concentration
-Enzyme concentration

Question 15

How does temperature affect enzyme activity?

Answer 15

-Increasing temperature increases the kinetic energy of particles.
-The particles move faster and collide more frequently.
-Increased rate of reaction.
-Too high a temperature can denature an enzymes active site.

Question 16

What is temperature coefficient Q10?

Answer 16

A measure of how much the rate of a reaction increases with a 10 degree rise in temperature.

Question 17

What happens when the temperature of a reaction exceeds the enzyme’s optimum temperature?

Answer 17

-At higher temperatures the bonds holding the protein together vibrates more.
-Vibrations increase until bonds strain and break.
-Breaking of bonds results in a change in tertiary structure, enzyme becomes denatured.

Question 18

How does pH affect enzyme activity?

Answer 18

-When the pH changes from the optimum pH, it alters the active site .
-When the pH changes more significantly the structure of the enzyme is irreversibly altered and active site is no longer complementary, reducing rate of reaction.
-Hydrogen ions interact with polar and charged R-groups, changing concentration of H+ ions changes the degree of this interaction.

Question 19

What is renaturation?

Answer 19

When the pH changes from the optimum pH, and then returns to the optimum the protein will return to normal shape and catalyse the reaction again.

Question 20

What is the optimum pH of saliva, gastric juice, and pancreatic juice?

Answer 20

Saliva: 7-8
Gastric juice: 1-2
Pancreatic juice: 8

Question 21

How does substrate and enzyme concentration affect enzyme activity?

Answer 21

-Increased number of substrate particles leads to higher collision rate with active sites of enzymes, rate of reaction increases.
-Increased number of enzymes increases the amount of available active sites.
-Rate of reaction increases up to maximum (Vmax), no more products can be formed at that time due to limiting factors (either too little active sites or substrates).

Question 22

What is the serial dilutions practical?

Answer 22

-add 1ml of stock solution to 9ml of distilled water water, gives 10ml of dilute solution.
-repeat procedure multiple times.

Question 23

How could a desired concentration of solution from a stock solution be formed?

Answer 23

volume of stock solution = required concentration x final volume needed / concentration of stock solution.

volume of distilled water = final volume needed - volume of stock solution.

Question 24

How do competitive inhibitors work?

Answer 24

-Molecule or part of molecule has a similar shape to substrate of an enzyme can fit into the active site.
-Blocks the substrate from entering the active site, prevents enzyme from catalysing reaction.
-The Vmax will still be reached just slower.
-Most only bind temporarily, so effect is reversible.

Question 25

What are example of competitive inhibitors?

Answer 25

-Statins
-Aspirin

Question 26

How do non-competitive inhibitors work?

Answer 26

-Inhibitor binds to the enzyme on the allosteric site (separate to active site).
-Binding of the inhibitor causes the tertiary structure if the enzyme to change, changing the shape of active site.
-Active site is no longer complementary so unable to bind.
-The Vmax is lowered and cannot be reached with increased substrate concentration.

Question 27

What is end-product inhibition?

Answer 27

End-product inhibition is the term for enzyme inhibition that occurs when the product acts as an inhibitor to the enzyme.
This is a negative feedback control mechanism, excess products are not made and resources are not wasted.

Question 28

What is an example of end-product inhibition?

Answer 28

Production of ATP:
ATP regulates its own production in respiration.

Question 29

What are inactive precursors in metabolic pathways?

Answer 29

To prevent damage to cells, some enzymes in metabolic pathways are synthesised as inactive precursors e.g. proteases.
One part of the precursor acts as an inhibitor.

Question 30

How do some medicinal drugs act as inhibitors?

Answer 30

Penicillin: non-competitive inhibitor of transpeptidase to prevent formation of peptidoglycan cross-links in bacterial cell wall.
Ritonavir: inhibits HIV protease to prevent assembly of new virions.

Question 31

What are some examples of metabolic poisons?

Answer 31

-Cyanide: non-competitive, irreversible, inhibits cytochrome c oxidase.
-Malonate: competitive, inhibits succinate dehydrogenase.
-Arsenic: competitive, inhibits pyruvate dehydrogenase.

Question 32

What is a metabolic poison?

Answer 32

Substance that damages cells by interfering with metabolic reactions.

Question 33

What are co-factors?

Answer 33

Non-protein compounds required for enzyme activity:
-coenzymes
-inorganic cofactors
-prosthetic groups

Question 34

What are Inorganic cofactors?

Answer 34

Metal ions which change the charge in the active site which enables the enzyme substrate complex to form.

Question 35

What are examples of inorganic cofactors?

Answer 35

-Amylase contains a chloride ion.
-Mg^2+ in phosphotransferases.