Proteins and enzymes - 2

Question 1

What are the roles of proteins?

Answer 1

Structural
Catalytic
Cell signalling
Immunological

Question 2

What is the general structure of amino acids?

Answer 2

Contains an amine group, R group and a carboxylic acid group

Question 3

What bonds hold together amino acids?

Answer 3

Peptide bonds

Question 4

What molecule is produced from two amino acids

Answer 4

A dipeptide

Question 5

What is a polypeptide

Answer 5

When more amino acids are added to a dipeptide a polypeptide is formed

Question 6

What is the primary structure of proteins?

Answer 6

The order of amino acids, held together by peptide bonds.

Question 7

What is the secondary structure of proteins?

Answer 7

Areas of initial folding
Held together by hydrogen bonds
Contains alpha helices and beta pleated sheets

Question 8

What is the tertiary structure of proteins?

Answer 8

Interactions of the R groups.
The tertiary structure is the 3D shape
Maintained by 4 types of bond/interaction
- Hydrogen bonds
- Disulphide bridges
- Ionic Bonds
- Hydrophobic interactions

Question 9

What is the quaternary structure

Answer 9

When two or more polypeptides join together
Or there is a prosthetic group
A conjugated protein is a globular protein with a prosthetic group

Question 10

What are globular proteins

Answer 10

Usually have a spherical shape caused by tightly folded polypeptide chains
Hydrophobic groups on the inside and hydrophilic groups on the outside

Question 11

Examples of globular proteins

Answer 11

Transport proteins - haemoglobin
Enzymes
Hormones - insulin

Question 12

Describe the structure of haemoglobin

Answer 12

4 polypeptide chain subunits
- 2 alpha chains
- 2 beta chains
Each subunit contains a haem group containing Fe2+
Soluble

Question 13

Describe the structure of amylase

Answer 13

Single chain of amino acids
Secondary structure has alpha helices and beta pleated sheets
Needs the cofactor Cl-
Soluble

Question 14

Describe the structure of insulin

Answer 14

Two amino acid chains joined by disulphide bonds

Question 15

What are fibrous proteins

Answer 15

Formed by parallel polypeptide chains held together by cross-links. these form long rope-like fibres
They have a high tensile strength and are generally soluble

Question 16

What are three examples of fibrous proteins

Answer 16

Collagen
Keratin
Elastin

Question 17

Describe the role of collagen

Answer 17

Structural protein
Main component of connective tissue such as ligaments/tendons

Question 18

Describe the role of keratin

Answer 18

For protection
Main component of hard structures, including hairs/nails

Question 19

Describe the role of elastin

Answer 19

Elastic properties
Major component of tissues that require elasticity such as arteries/lungs

Question 20

What are three differences between Fibrous and globular proteins

Answer 20

Fibrous are insoluble where as globular are soluble

Fibrous proteins are elongated whilst globular are spherical

Fibrous proteins don’t contain a prosthetic group where as globular proteins do

Question 21

What is an enzyme

Answer 21

Globular proteins
Specific 3d tertiary structure
Soluble in water
Biological catalyst

Question 22

What is the lock and key theory

Answer 22

The active site is complimentary to the shape of the substrate
the substrate is the key and the active site is the lock

Question 23

What is the induced fit model

Answer 23

Once the substrate has bound the enzyme changes shape slightly to an even more exact fit
The enzyme then puts pressure on the bonds in the substrate so that it catalyses the reaction

Question 24

Give an example of an intracellular enzyme

Answer 24

Catalase

Question 25

Give an example of an extracellular enzyme

Answer 25

Amylase/Trypsin

Question 26

What is the activation energy

Answer 26

The minimum amount of energy required for a reaction to happen

Question 27

How does temperature affect the rate of an enzyme controlled reaction

Answer 27

Increasing temperature increases rate of reaction due to an increase in kinetic energy so there are more successful collisions between the enzyme and the substrate Increasing temperature beyond the optimum reduces the rate has the bonds in the tertiary structure break causing the enzyme to become denatured

Question 28

How do vibrations affect the rate of an enzyme controlled reaction

Answer 28

More kinetic energy means more vibrations which puts a strain on bonds in the tertiary structure. This can break the weaker bonds (H and ionic) & change the shape of the active site. As you heat an enzyme more & more bonds are broken. Rate of reaction decreases until tertiary structure of enzyme unravels and denatures

Question 29

What is pH

Answer 29

Measure of H+ ion concentration. The higher the H+ ions, the lower the pH value, so acids contain a high concentration of H+ ions.

Question 30

How does pH effect the rate of an enzyme controlled reaction

Answer 30

Changing pH away from the optimum reduces the rate of reaction because the concentration of H+ ions affects the tertiary structure which can cause the enzyme to denature

Question 31

What is an inhibitor

Answer 31

Any substrate or molecule that slows down the rate of an enzyme controlled reaction

Question 32

What are the 4 types of inhibitors

Answer 32

Competitive inhibitors Non-Competitive inhibitors Permanent inhibitors End product inhibition

Question 33

What are competitive inhibitors

Answer 33

Have a similar shape to the substrate Occupy active site to form an enzyme-inhibitor complex Substrate cannot fit into the active site Tend to be reversible

Question 34

What are non-competitive inhibitors

Answer 34

Attach to an area away from active site (Allosteric) Distorts the 3-D tertiary structure which changes the shape of the active site substrate can no longer fit into active site Tend to be permanent

Question 35

What is end product inhibition

Answer 35

To prevent build up of end product, the end product acts as a non-competitive inhibitor to slow down the reaction

Question 36

What are coenzymes

Answer 36

Small organic and non protein temporarily bind to active site take part in the reaction Used again and again Often vitamins

Question 37

What are cofactors

Answer 37

Inorganic ions Can combine with the enzyme or substrate so that the enzyme substrate can be form easier