Proteins and Enzymes

Question 1

Describe the structure of a protein

Answer 1

Amino acid polymers joined together by peptide bonds

Amino acid structure: central carbon atom attached an amine group, hydrogen atom, carboxyl group and R group

Question 2

Explain the formation of a peptide bond

Answer 2

Condensation reaction - water is removed

water is formed by hydrogen atom on amine group and OH group from carboxylic acid

O=C - NH

Question 3

Define primary structure

Answer 3

Sequence of amino acids in a polypeptide chain

Question 4

Define secondary structure

Answer 4

Hydrogen bonds form between amino acids

Form alpha helix or beta pleated sheats

Question 5

Define tertiary structure

Answer 5

Bonds form between the R group

3D structure created

Hydrogen bonds
Disulfide bridges
Ionic bonds
Hydrophilic - hydrophobic interactions

Question 6

Define quaternary structure

Answer 6

Interaction of 2 or more polypeptide chains held together by bonds

Question 7

Describe the structure of haemoglobin

Answer 7

4 polypeptide chains
2 alpha helix, 2 beta pleated sheets

4 haem groups = prosthetic group

Haem group is Fe

Question 8

Structure and function of globular proteins

Answer 8

Spherical

Hydrophilic on the outside and hydrophobic on the inside

Soluble - Transported easily

Functions: enzymes, hormones or proteins

Globular protein with prosthetic groups are conjugated proteins

Question 9

Structure and function of fibrous proteins

Answer 9

Long and thin

Strong and insoluble

Structural roles

e.g collagen, keratin, elastin

Question 10

Describe the structure and function of collagen

Answer 10

3 polypeptide chains wrapped tightly around each other

chains held together by hydrogen bonds

found in connective tissue

Question 11

what are enzymes?

Answer 11

Biological catalyst that speed up chemical reactions in our body by reducing activation energy

Question 12

Explain the lock and key model

Answer 12

Substrate fits in active site perfectly

Active site is complementary

Substrate binds to active site and forms enzyme-substrate complex

Enzyme coverts substrate to product to form enzyme substrate complex

Product released

Question 13

Explain the induced fit model

Answer 13

Active site is not completely complementary to the substrate

Substrate enters active site and forms enzyme substrate-complex

Enzyme undergoes conformational change which converts substrate to product, forming enzyme product complex

Product released

Question 14

How does enzyme concentration affect rate of reaction?

Answer 14

Enzyme concentration increases

More active sites available for substrate molecules

More frequent collisions so more enzyme-substrate complexes

Rate increases

However, rate plateaus as something else becomes limiting factor

Question 15

How does substarte concentration affect rate of reaction?

Answer 15

Substrate concentration increases

More substrate molecules to bind to enzyme active site

More frequent collisions so more enzyme substrate complexes

Rate increases

However, saturation is reached and every active site is occupied

Question 16

How does temperature affect rate of reaction?

Answer 16

At low temperatures, rate is slow

enzyme and substrates have low kinetic energy

less frequent collisions so less ES complexes

At high temperature, rate increases

enzyme and substrates have more kinetic energy

more frequent collisions so more ES complexes

If temperature too high then enzyme denatures so substrate cant bind to enzymes active site as it is no longer complementary

Question 17

How does pH affect rate of reaction?

Answer 17

Different enzymes have different optimum pH

If pH deviates, charge of the enzyme could change, which breaks ionic bonding and hydrogen bonding in tertiary structure

Enzyme denatures and is no longer complementary to substrate

Question 18

What is temperature coefficient?

Answer 18

Rate at higher temp
Q10 = —————————-
Rate at lower temp

If Q10 = 2, the rate doubles for every 10oC

Question 19

What is a cofactor?

Answer 19

non-protein molecules that need to be bound to an enzyme to function

They are not chemically changed

Question 20

what are coenzymes?

Answer 20

organic molecules that are chemically changed during a reaction

Question 21

Explain a competitive inhibitor

Answer 21

Bind to the active site of an enzyme

Blocks the active site for the substrate

Effect can be reduced by increasing substarte concentration

Question 22

Explain a non competitive inhibitor

Answer 22

Bind to the allosteric site of the enzyme

Changes structure of active site so substrate can bind

Effect cannot be reduced

Question 23

Reversible vs irreversible inhibitors

Answer 23

Reversible inhibitors form weak bonds and can be removed easily

Irreversible inhibitors form strong covalent bonds so cant be remove easily

Question 24

What is end product inhibition?

Answer 24

the final product of a metabolic pathway inhibits an enzyme that acts earlier in the pathway