1.3 - Proteins

Question 1

Draw the general structure of an amino acid

Question 2

What is the bond formed between 2 amino acids in a condensation reaction?

Answer 2

peptide bond
between amine and carboxyl groups

Question 3

How is a dipeptide formed?

Answer 3

condensation of 2 amino acids

Question 4

How is a polypeptide formed?

Answer 4

condensation of many amino acids

Question 5

3 types of bond that contribute to the tertiary structure of a protein (shape)

Answer 5

• hydrogen bonds
• ionic bonds
• disulfide bridges

Question 6

Describe the primary structure of a protein

Answer 6

amino acid sequence

Question 7

Describe the secondary structure of a protein

Answer 7

2D folding of polypeptide chain as a result of H bonding
e.g beta-pleated sheet, alpha helix

Question 8

Describe the tertiary structure of a protein

Answer 8

3D folding of a polypeptide chain due to interactions between R groups

Question 9

Describe the quaternary structure of a protein

Answer 9

multiple polypeptide chains

Question 10

Describe the Biuret test for proteins

Answer 10

• add Biuret
• positive: blue -> lilac

Question 11

How does an enzyme increase rate of reaction?

Answer 11

• lowers activation energy
• induced fit causes active site to change shape
• ESC complex causes bonds to weaken as they bend (and break)

Question 12

Describe the induced fit model of enzyme action

Answer 12

• substrate binds to active site, forming ESC
• active site changes shape to now complementary to substrate
• (H) bonds are broken and formed in substrate

Question 13

Why are enzymes referred to as specific?

Answer 13

specific tertiary structure (active site) which is complementary to a specific substrate

Question 14

Describe the effect of enzyme concentration on the rate of reaction

Answer 14

increasing enzyme concentration increases the rate of reaction

Question 15

Describe the effect of substrate concentration on the rate of reaction

Answer 15

as substrate conc increases rate of reaction increases, until it plateaus due to other limiting factor e.g enzyme conc

Question 16

Describe the effect of concentration of competitive inhibitors on the rate of reaction

Answer 16

• higher conc of competitive inhibitor = slower rate of reaction
• rate can be increased by increasing substrate conc

Question 17

Describe the effect of concentration of non-competitive inhibitor on the rate of reaction

Answer 17

• higher conc of non-competitive inhibitor = slower rate of reaction
• rate CANNOT be increased by increasing substrate conc

Question 18

Describe how a competitive inhibitor works

Answer 18

• inhibitor similar shape to substrate
• binds to active site
• prevents ESC forming

Question 19

Describe how a non-competitive inhibitor works

Answer 19

• attaches to enzyme at allosteric site
• changes tertiary structure (active site)
• active site and substrate no longer complementary so no substrate can bind

Question 20

Describe lock and key enzyme model

Answer 20

enzyme and substrate fit together perfectly and form an ESC

Question 21

Why would 2 proteins with same no. and type of amino acids have different tertiary structures?

Answer 21

• different primary structures
• so H bonds formed in different places