Proteins

Question 1

Monomer of protein

Answer 1

Amino acid

Question 2

What two groups do amino acids have?

Answer 2

Amine
Carboxyl

Question 3

Amphoteric

Answer 3

Amino acids can act as an acid and a base

Question 4

Bond between two amino acids

Answer 4

Peptide

Question 5

Features of primary structure

Answer 5

Sequence of amino acids
Joined by peptide bonds
In a condensation reaction

Affected by mutations

Question 6

Features of secondary structure

Answer 6

Amine (H) and carboxyl group (O) form hydrogen bonds
Alpha helix and beta pleated sheet

Not affected by a mutation

Question 7

Features of tertiary structure

Answer 7

R groups bond with each other
Form hydrogen, ionic or disulphide bonds

Affected by mutations

Question 8

Features of quaternary structure

Answer 8

Multiple polypeptide chains bonded Te each other
Contains a prosthetic group

Question 9

Enzymes

Answer 9

Biological catalysts that speed up chemical reactions by lowering the activation energy without getting used up

Can be: intracellular or extracellular

Question 10

Types of intracellular enzymes

Answer 10

RNA polymerase
Lysozymes
DNA polymerase
ATP synthase

Question 11

Types of extracellular enzymes

Answer 11

Amylase
Maltase

Question 12

Lock and key Theory

Answer 12

Explains specificity of enzymes
Doesn’t explain lowered activation energy for inhibition

Question 13

Induced fit model

Answer 13

1. Before = enzyme is not complementary to substrate
2. Active site of enzyme change shape to be complementary to substrate by induced fit (when substrate binds to active site)
3. Enzyme - substrate complex is formed
4. ESC will stress bonds in substrate to lower activation energy

Question 14

Solubility of fibrous proteins

Answer 14

Insoluble
Due to high proportion of hydrophobic non-polar amino ands

Question 15

Solubility of globular proteins

Answer 15

Soluble
Due to charged r groups on the protein surface so water can surround proteins

Question 16

Function of fibrous proteins and examples

Answer 16

Structural proteins

Examples: collagen and alpha-keratin

Question 17

Function of globular proteins and examples

Answer 17

Metabolic function

Examples: haemoglobin and enzymes

Question 18

Structure of fibrous proteins

Answer 18

Long straight polypeptide chains

Primary: sequence of amino acids

Tertiary and quaternary: lots of hydrogen, ionic and disulphide bonds to form connected, parallel chains

• lots of disulphide bridges so more resistant to chemical and physical attack

Question 19

Structure of globular proteins

Answer 19

Hydrophilic, spherical shape

Primary: varied

Tertiary and quaternary: hydrophilic and hydrophobic interactions
Hydrophobic r groups fold inside to form spherical structure

Question 20

Effect of substrate concentration on enzyme action

Answer 20

Substrate concentration is directly proportional to the rate of reaction
More collisions between substrates active sites- more enzyme substrate complexes formed

As substrate concentration increases, rate of reaction plateaus
No active sites available (saturation points so less enzyme substrate complexes formed

Question 21

Effect of enzyme concentration on enzyme action

Answer 21

Enzyme concentration is directly proportional to the rate of reaction
More collisions between active site and substrate - more enzyme substrate complexes formed

As enzyme concentration increases, rate of reaction plateaus
No more substrates available for active sites to bind to (saturation point) - less enzyme substrate complexes formed

Question 22

Effect of temperature on enzyme action before optimum temperature

Answer 22

As temperature increases, rate of reaction increases until optimum temperature
More kinetic energy - more successful collisions between active site and substrate- more enzyme substrate complexes formed

Question 23

Effect of temperature on enzyme action after optimum temperature

Answer 23

As the temperature increases, the rate of reaction decreases

Hydrogen bonds holding 3D tertiary structure together are broken- enzyme will denature

Causes active site to change so substrate can no longer bind to active site - less enzyme substrate complex formed.

Question 24

Effect of pH on enzyme action

Answer 24

H + and OH - concentration changes beyond optimum pH
Changes charge of amino acids -disrupts hydrogen and ionic bonds holding tertiary structure

Enzyme will denature - active site can no longer be complementary to substrates
Less ESC will form

Question 25

How is a Dipeptide formed?

Answer 25

A condensation reaction between two amino acids

Question 26

Test for proteins

Answer 26

Add Biuret reagent - sodium hydroxide and copper sulfate
Positive results = lilac from blue

Detects peptide bonds - longer the peptide chains the darker the purple

Question 27

Inhibition

Answer 27

Slowing or prevention of enzyme activity by molecules other than substrates

Question 28

Competitive inhibition

Answer 28

Has a similar shape to the substrate

Competes with substrate to bind to active site
Blocks active site so substrate cannot bind

Question 29

Non-competitive inhibition

Answer 29

Binds to a site other than the active site (allosteric site).
Inhibitor changes tertiary structure
Active site will no longer be complementary to substrate