2.4 Enzymes

Question 1

What are enzymes?

Answer 1

They are biological catalysts which speed up reactions.
They catalyse metabolic reactions.
(Cellular level and for an organism as a whole)
They are globular proteins
Have an active site which has a specific shape (determined by the tertiary structure), the substrate binds to it. (if complementary)

Question 2

Enzyme actions can be?

Answer 2

Intracellular and Extracellular

Question 3

Intracellular enzyme example?

Answer 3

Catalyse
- Catalyse works inside cell to break down hydrogen peroxide (which can kill cells) to oxygen and water

Question 4

Extracellular enzyme example? 1

Answer 4

Amylase
- Works outside cells in the human digestive system
- Amylase is found in salvia, secreted into the mouth by salivary glands, catalyses the hydrolysis breakdown of starch into maltose

Question 5

What do enzymes reduce?

Answer 5

Activation energy, this is often provided as heat.

Question 6

Reducing the activation energy

Answer 6

Speeds up the rate of reaction

Question 7

Extracellular enzyme example? 2

Answer 7

Trypsin
- Catalyses the hydrolysis of peptide bonds turning big polypeptides into small ones. It is produced in the pancreas and secreted into the small intestine

Question 8

Induced fit model **

Answer 8

Suggests that the substrate doesn’t have to be the right shape to fit into the AS. It just needs to be able to change the shape of the AS.

Question 9

Lock and key model

Answer 9

Suggests that they fit together in the first place, it is a tight and exact fit

Question 10

Factors affecting enzyme activity?

Answer 10

Temperature, pH, Enzyme activity, Substrate concentration
- Details in notes

Question 11

Enzyme Practicals

Answer 11

https://pmt.physicsandmathstutor.com/download/Biology/A-level/Notes/OCR-A/1-Practical-Skills-in-Biology/PAG%2004%20-%20Rates%20of%20Enzyme%20Controlled%20Reactions.pdf

Question 12

Competitive inhibitation?

Answer 12

Inhibitor has a similar shape to the substrate, it competes to bind to the AS but it causes no reaction. It blocks the AS.

• Higher the concentration of the inhibitor the more AS is being taken up
• Higher the concentration of the substrate the higher the chance of the substrate binding to the AS

Question 13

Cofactors and Coenzymes are

Answer 13

Essential for Enzymes to work

Question 14

Cofactors

Answer 14

Some non-proteins substances bound to enzymes to allow them to work. The non proteins that bound to them are called cofactors.

Question 15

Coenzymes

Answer 15

Organic cofactors molecules

Question 16

Inorganic Molecule/Ions cofactor example

Answer 16

They help the enzyme and substrate to bind together. They are indirectly participating in the reaction, therefore, they will not be used up or changed.
Eg. Chloride ions for amylase

Question 17

Organic Molecule cofactor example

Answer 17

They participate in the reaction and they are changed by it. They often act as carriers, moving chemical groups (between enzymes)
They are continually recycled during this process.
Eg. Vitamins are often sources of coenzymes

Question 18

Prosthetic group

Answer 18

If cofactor is tightly bound to the enzyme
Eg. Zinc ions are prosthetic group for the carbonic anhydrase. They are a permanent part of the enzyme’s AS

Question 19

Inhibitors can be…

Answer 19

irreversible or reversible

Question 20

Irreversible inhibitors?

Answer 20

Strong, covalent bonds. Can’t be removed easily

Question 21

Reversible inhibitors?

Answer 21

Weak H bonds/Weak ionic bonds. Can be removed

Question 22

Inhibitors can protect the cell. (2 points why?)

Answer 22

• Sometimes enzymes are synthesised as inactive precursors in metabolic pathways to prevent them causing damage to cells.
• Part of the precursor molecule inhibits its action as an enzyme. Once removed the enzyme = active.

Question 23

Examples of medicinal drugs being enzyme inhibitors? (1)
ANTIVIRAL

Answer 23

Antiviral drugs (drugs that stop viruses like HIV), eg. reverse transcriptase inhibitors inhibit the enzyme reverse transcriptase, this catalyses the replication for viral DNA.
This prevents the virus from replicating

Question 24

Examples of medicinal drugs being enzyme inhibitors? (2)
ANTIBIOTICS

Answer 24

Antibiotics (penicillin) inhibits the enzyme transpeptidase, which catalyses the formation of proteins in bacterial cell walls. This weakens the cell wall, prevents bacterium pressure. As a result, the cell wall bursts and kills the bacterium

Question 25

Cyanide

Answer 25

Irreversible inhibitor of cytochrome c oxidase. An enzyme that catalyses respiration. Cells that can’t respire die.

Question 26

Malonate

Answer 26

Inhibits succinate dehydrogenase (catalyses respiration reactions)

Question 27

Arsenic

Answer 27

Inhibits the action of pyruvate dehydrogenase. (catalyses respiration reaction)

Question 28

Metabolic pathways are…

Answer 28

regulated by end product inhabitation

Question 29

A metabolic pathway?

Answer 29

A series of connected metabolic reactions. The product of the first takes part in the second, so on. Each reaction is catalysed by a different enzyme

Question 30

Product inhabitation?

Answer 30

Many enzymes are inhabitation by the product of the reaction they catalyse

Question 31

End product inhabitation?

Answer 31

When the final product in the metabolic pathways inhibits an enzyme that acts earlier on in the pathway
- A way of controlling the amount of the end product that gets made.

Question 32

An example of controlling the amount of end product made (EPH)

Answer 32

Phosphofructokinase is an enzyme involved in the metabolic pathway that breaks down glucose to make ATP
- ATP inhibits the action of phosphofructokinase - so a high level of ATP prevents more ATP being made

Question 33

Are end product/product inhabitation reversible or irreversible?

Answer 33

Reversible
- So when a level of a product starts to drop the enzyme will start to function again.