4.5: Proteins

Question 1

What are proteins composed of?

Answer 1

Composed of carbon, hydrogen, oxygen, nitrogen and sometimes contains sulphur, phosphorus and iron

Question 2

What is the meaning of proteins?

Answer 2

A chain of polypeptides folded and coiled into a specific conformation

Question 3

What is the basic structure risof amino acids?

Answer 3

4 components attached to a central carbon:
- a basic amino group (-NH2)
- an acidic carboxyl group (-COOH)
- a hydrogen atom (H)
- an R group (which determines the unique characteristics of amino acid identity)

Question 4

What is the meaning of amphoteric?

Answer 4

A molecule that can act as acid (donates proton) and basic (accepts protons)

Question 5

Amino acid is amphoteric due to…

Answer 5

The presence of ionised amino group and carboxyl group

Question 6

What are dipeptides?

Answer 6

Consists of two amino acids linked by a peptide bond through condensation

Question 7

What are polypeptides?

Answer 7

Hundreds of monomers joined through peptide bond by condensation. One or more polypeptides linked together form a protein.

Question 8

What are the shapes and sizes of proteins?

Answer 8

1. Globular - spherical or rounded (hemoglobin)
2. Fibrous - long and thin fibres (collagen)

Question 9

What are the four levels of protein structure?

Answer 9

1. Sequence of a chain of amino acids - insulin / glycogen
2. Local folding of the polypeptide chain into sheets - keratin
3. Three-dimensional folding pattern of a protein due to side chain interactions - enzymes
4. Protein consisting of more than one amino acid chain - haemoglobin

Question 10

What form does the secondary structure take?

Answer 10

Alpha helix (coiled), beta pleated sheet (folded)

Question 11

Give three functions of proteins

Answer 11

Structure: collagen in skin, keratin in hair
Defense: Antibodies fight against foreign bodies
Transport: Hemoglobin carries oxygen in the blood

Question 12

What is denaturation?

Answer 12

The alteration or modification of protein shape

Question 13

Explain denaturation?

Answer 13

Protein loses its high order 3D structure, but not the primary sequence. Disrupts the bonds in the secondary, tertiary and quaternary protein structures

Question 14

How are proteins renaturised?

Answer 14

Once the denaturants are removed, the denatured protein tend to fold back to their native conformations. They can restore their biological functions

Question 15

Why do some proteins fail to renature?

Answer 15

1. molecular chaperones may be needed
2. prosthetic group may be lost
3. protein may fold temporally as it is produced