Biological Molecules - Enzyme Action

Question 1

ENZYMES ARE BIOLOGICAL CATALYSTS

What kind of reactions do enzymes catalyse? Examples?

Answer 1

Enzymes catalyse METABOLIC reactions –
– both at a cellular level (e.g. respiration)
and for the organism as a whole (e.g. digestion in mammals).

Question 2

NOTE:

Enzymes can affect STRUCTURES in an organism
(e.g. enzymes are involved in the production of collagen, an important protein in the connective tissues of animals)

as well as FUNCTIONS
(e.g. respiration)

Answer 2

Enzymes can affect S______ in an organism
(e.g. enzymes are involved in the _______ of ______, an important protein in the connective tissues of animals)

as well as F_______
(e.g. _______)

Question 3

NOTE:

Enzyme action can be INTRAcellular or EXTRAcellular.

Answer 3

NOTE:

Enzyme action can be
i__________ or e__________

Question 4

NOTE:

Enzymes are proteins.

Answer 4

NOTE:

Enzymes are _______.

Question 5

Why are enzymes highly specific?

Answer 5

Because of their tertiary structure.

Question 6

When a substrate fits into the enzyme’s active site, what does it form?

What does this do?

How?

Answer 6

It forms an enzyme-substrate complex.

This lowers the activation energy.

Here’s how:

• If two substrate molecules need to be JOINED,
  being attached to the enzyme HOLDS THEM CLOSE together, REDUCING ANY REPULSION between the molecules so they can bond more easily.
• If the enzyme is catalysing a BREAKDOWN reaction,
  fitting into the active site PUTS A STRAIN ON THE BONDS in the SUBSTRATE, so the substrate molecule breaks up more easily.

Question 7

What is the new model for enzymes and substrates called?

What is the theory?

Answer 7

The ‘induced fit’ model.

It helps to explain why enzymes are so specific and only bond to one particular substrate.

The substrate doesn’t only have to be the right shape to fit the active site,
it has to make the active site CHANGE SHAPE in the right way as well.

Question 8

ENZYME PROPERTIES RELATE TO THEIR TERTIARY STRUCTURE.

What are these properties?

Answer 8

They’re very SPECIFIC –
they only catalyse one reaction
(e.g. maltase only breaks down maltose,
and sucrase only breaks down sucrose)

This is because only one complementary substrate will fit into the active site.

And the active site shape is determined by the enzyme’s tertiary structure
(which is determined by the enzyme’s primary structure).

Each enzyme has a different tertiary structure and so a different shaped active site.

If the substrate shape doesn’t match the active site, an enzyme-substrate complex won’t be formed and the reaction won’t be catalysed.
______________________________

If the tertiary structure of the enzyme is ALTERED in any way, the shape of the active site will change.

This means the substrate won’t fit into the active site, an enzyme-substrate complex won’t be formed and the enzyme will no longer be able to carry out its function.

The tertiary structure of an enzyme may be ALTERED by changes in pH or TEMPERATURE.
______________________________

The primary structure (amino acid sequence) of a protein is determined by a gene.
If a mutation occurs in that gene, it could change the tertiary structure of the enzyme produced.