Biochemistry - Proteins and enzymes

Question 1

What are proteins?

Answer 1

Naturally occurring condensation polymers consisting of chains of amino acids.

Question 2

Types of protein structure?

Answer 2

primary
secondary
tertiary
quaternary

Question 3

What’s the primary structure?

Answer 3

Sequence of amino acids.

Question 4

What allows amino acids to be in a sequence?

Answer 4

Amino acids joined by peptide bonds/links forms between carboxyl group of one amino acid and one amine group of another.

Question 5

How is the primary structure depicted?

Answer 5

Depicted by three letter notation arranged in an appropriate sequence.

Question 6

Process for determining the sequence of amino acids in a protein?

Answer 6

1. Sequence of amino in a protein is determined experimentally.
2. Amino acid reacted with a substance that creates a coloured or fluorescent derivative.
3. Protein is then hydrolysed by a highly specific enzyme that removes only the terminal enzyme.
4. Marked amino acid is identified by chromatography.
5. Repeating processes many times determines the full primary structure.

Question 7

What’s the secondary structure?

Answer 7

Chain of amino acids that makes up the primary structure can fold itself in two ways.

Question 8

What’s the secondary structure dependant on?

Answer 8

Depends on the sequence of amino acids that are next to each other.
Hydrogen bonds hold the folded structures in place.

Question 9

How does the primary structure become the secondary structure?

Answer 9

It folds into either Alpha helixes or Beta plated sheets.

Question 10

What’s the tertiary structure?

Answer 10

Folding of chain held by interactions between more distinct amino acids.

Question 11

How is the tertiary structure maintained?

Answer 11

Hydrogen bonds, disulphide bridges, ionic bonds and intermolecular forces.

Question 12

What’s the quaternary structure?

Answer 12

Structure resulting from interaction between separate protein chains.

Question 13

True or false? All proteins have a quaternary structure.

Answer 13

False, most do.

Question 14

Example of quaternary structure?

Answer 14

Haemoglobin - 4 protein channels - 2 alpha chains and two beta chains.

Question 15

Two types of proteins?

Answer 15

Fibrous and globular.

Question 16

Features of fibrous proteins?

Answer 16

• Long molecules

- Strengthened by many cross links between chains.

Question 17

Examples of structures fibrous proteins form?

Answer 17

Muscle fibres.

Question 18

Features and example of globular proteins?

Answer 18

• Smaller more round and compact.

- E.g Ferretin - primary store of iron inside cells in animals and plants.

Question 19

Example of role of globular proteins?

Answer 19

Enzymes and certain hormones.

Question 20

What sort of thing can disrupt a proteins structure? And how?

Answer 20

High temperature - Exposing proteins to high temp denatures them.

Question 21

What are enzymes and what do they do?

Answer 21

Biological catalysts.
They increase the rate of biochemical reactions
Without them reactions would be so slow life wouldn’t happen.

Question 22

What do enzymes do? And how?

Answer 22

• Enzymes speed up a reaction by providing an alternative route of lower activation energy.
• Do this by binding the reactant molecule, and holding it in a favorable orientation for reaction.

Question 23

Basic process of enzyme reaction.

Answer 23

Enzyme + substrate > enzyme/substrate complex > Enzyme + product.

Question 24

As a catalyst what happens to the enzyme?

Answer 24

Enzyme is released unchanged at end of the reaction.

Question 25

What does the active site do?

Answer 25

Active site of enzyme binds to substrate.

Question 26

What are the two models of enzyme action?

Answer 26

Lock and key model and induced fit model.

Question 27

Lock and key model?

Answer 27

Active site accurately fits particular substrate molecule.

Question 28

Induced fit model?

Answer 28

Active site changes shape slightly in response to it’s particular substrate.

Question 29

Process of denaturation?

Answer 29

1. High kinetic energy breaks down protein structure in high temperatures.
2. Loss of tertiary structure means that the enzyme no longer has shape for specific function.
3. Loss of biochemical activity through structure change called denaturation.
   (Also denaturation can happen due to extreme PH.

Question 30

How does enzyme inhibition occur?

Answer 30

• Presence of other molecules with results in activity decreasing.
• Happens when the inhibitor forms a covalent bond with the enzyme which is difficult to break.

Question 31

When inhibition is irreversible what does it mean?

Answer 31

Enzyme is permanently poisoned.

Question 32

What is needed for reversible inhibition competetively? And why?

Answer 32

Competitive inhibitor.

• Mechanism for controlling enzyme reactions.
• Competitive inhibitor competes with substrate for position at the active site.
• Enzyme recognises inhibitor as substrate but cant convert it to product.
• They are often very chemically similar to substrate molecule.

Question 33

What is needed for reversible inhibition non-competitively? And why?

Answer 33

Non-competitive inhibitor.

• Doesn’t bind to active site
• Changes active site shape when it binds to another part of enzyme.
• Often a heavy metal ion.
• Enzyme cannot bind to its substrate.

Question 34

What is the issue with immobilised enzymes?

Answer 34

• Many enzyme catalysed reactions are industrially important.
• Problem is separating contaminating and expensive enzyme from product after reaction.
• Immobilisation is industrial process where enzyme is attached to a solid support that does not interfere with it’s catalytic activity.