Polypeptides (proteins)

Question 1

label an amino acid.

Answer 1

Carboxylic group (-COOH)

Amino group (-NH2)

One of 20 different ‘R groups’

Many amino acid (monomers) can be bonded together to form a polypeptide (polymer)

Question 2

Explain the formation of a dipeptide.

Answer 2

2 amino acid molecules.

Condensation reaction.

Between the -COOH group of one amino acid and the -NH2 group of another.

A water molecule is released.

Forming PEPTIDE bond.

Question 3

Name the four types of amino acid R-groups.

Answer 3

Ionic (+ or -)
Cysteine (-S)
Hydrogen bonding (-OH ….)
Hydrophobic (-CH3)

Question 4

Primary structure

Answer 4

the sequence / order of amino acids in a polypeptide chain

Question 5

Secondary structure

Answer 5

localised folding forming alpha helix / beta pleated sheet, stabilised be hydrogen bonding between the peptide bonds in the chain

Question 6

Tertiary structure

Answer 6

precise 3D shape of a single polypeptide, stabilised by R-group interactions (i.e. hydrogen bonding, disulphide links, ionic interactions, hydrophobic interactions)

Question 7

Quaternary structure

Answer 7

2 or more polypeptides bonded together (R - group interaction)

Question 8

Explain the formation of a disulphide bond.

Answer 8

STRONG, COVALENT bond.

Between the R-groups…

… of 2 CYSTEINE amino acids

Question 9

the food test for proteins.

Answer 9

Add Biuret reagent I (copper sulfate solution)

Add Biuret II (dilute sodium hydroxide solution)

Colour change from light blue to purple

Question 10

What are the key features of globular proteins like haemoglobin

Answer 10

• Polypeptide chains form a - spherical shape.
• Often soluble
• Hydrophilic R groups on the outside, hydrophobic on the inside
• Sensitive to temperature and pH changes

Question 11

What are the key features of fibrous proteins like collagen

Answer 11

Polypeptide chains are parallel
Tensile with a structural role