Unit 1 Biological Molecules - Proteins & Enzymes

Question 1

Describe how proteins are made.

Answer 1

• Amino acids are the monomers from which proteins are made

Question 2

Describe the structure of amino acids.

Answer 2

• Have a central carbon (C)
• Have a hydrogen atom (H)
• Have a carboxyl group (COOH)
• Have an R group (R)
• Have an amino group (NH₂)
  H

NH₂ - C - COOH

           R

Question 3

Describe the condensation reactions in amino acids.

Answer 3

Dipeptides = Condensation of 2 amino acids
(NH2 and carboxyl)
Polypeptides = Condensation of many amino acids
- Forms peptide bond

Question 4

How many amino acids are and how do they differ.

Answer 4

• 20

- Differ by side group

Question 5

Describe how the structure of a protein depends on the amino acids it contains

Answer 5

1. Structure is determined by position of
   amino acid OR R-groups
2. Primary structure is sequence of amino
   acids on polypeptide
3. Secondary structure formed by hydrogen
   bonding between amino acids bending into α-helices or β-pleated sheets
4. Tertiary structure formed by interactions
   between R groups, held by ionic,disulfide&hydrogen bonds
   - Tertiary structure creates active sites in eznymes
5. Quaternary structure formed by bonds between more than 1polypeptide chain to form specific 3D shape

Question 6

Describe the 2 types of secondary structure of a protein.

Answer 6

α-helix
- spiral shape
β-pleated sheet
- zigzag shape

Question 7

Describe the 3 bonds found in the tertiary structure of a protein.

Answer 7

Disulfide - strong covalent bonds between sulfur atoms in R group
Ionic - Relatively strong bonds between charged R groups
Hydrogen - Numerous & Easily broken bonds

Question 8

Describe fibrous and globular proteins

Answer 8

GLOBULAR
- Spherical as compact
- Involved in metabolic processes(ENZYMES)
FIBROUS
- Long chains or fibres
- Involved in structure and support(COLLAGEN IN SKIN)

Question 9

Describe what is meant by an enzyme.

Answer 9

• Biological catalysts which lower activation energy of reactions they catalyse
• Enzymes are tertiary structure proteins

Question 10

Describe why enzymes are specific.

Answer 10

• Active site specific and unique in shape as enzyme has specific primary structure
• and to specific folding & bonding in tertiary structure of protein
• Due to this specific active site, enzymes can only attach to substrates complementary in shape to form ES complex

Question 11

Explain the induced fit model of enzyme action.

Answer 11

• Substrate binds to active site to form an enzyme substrate complex
• Induced fit causes active site changes shape slightly so its complementary to substrate
• Reducing activation energy as strain placed on the bonds

Question 12

List the 4 factors which effect enzyme controlled reactions

Answer 12

• pH
• Temperature
• Substrate and Enzyme concentration
• Inhibitors

Question 13

Describe the effect of pH on rate of reaction.

Answer 13

• Too high or too low of pH interferes with charges in amino acids in active site
• Causing bonds to break in tertiary structure and active site shape to change leading to denaturation

Question 14

Describe the effect of temperature on rate of reaction.

Answer 14

• Rate increases as temperature inceases as more kinetic energy so more successful collisions until optimum temperature
• If temperature too high active site changes shape and ES complexes cannot form leading to denaturation

Question 15

Describe the effect of substrate concentration on rate of reaction.

Answer 15

SUBSTRATE CONCENTRATION

• Given enzyme concentration is fixed, rate increases proportionally to enzyme concentration
• Rate levels off when maximum ES complexes formed
• Low amount of substrate leads to less collisions between enzyme & substrate

Question 16

Describe the effect of enzyme concentration on rate of reaction.

Answer 16

ENZYME CONCENTRATION

• Given substrate concentration is fixed, rate increases proportionally to substrate concentration
• Rate levels off when maximum ES complexes formed
• Low amount of enzyme leads to active sites becoming saturated & unable to work faster

Question 17

Describe the effect of inhibitors on rate of reaction.

Answer 17

COMPETITIVE INHIBITORS
- Increasing substrate concentration decreases their effect
- Inhibitor same shape to substrate
- Binds to active site preventing enzyme substrate complexes from forming
NON-COMPETITIVE INHIBITORS
- Increasing substrate concentration has no effect
- Inhibitor binds to allosteric site causing active site shape to change
- Therefore active site no longer complementary to substrate - no ES complexes can form

Question 18

Briefly explain how models of enzymes have changed.

Answer 18

• Initially lock & key mode= rigid shape of active site complementary to only 1 substrate
• Now induced fit = Explanation of bonding at allosteric sites