B1.2 Proteins

Question 1

Calculate how many different tripeptide molecules composed of 3 amino acids linked toegther by a peptide bond can be made from a set of 20 naturally occuring amino acids

Answer 1

Numberofdifferenttripeptides

Formula for Tripeptide Formation
A tripeptide consists of three amino acids linked together. Since each position in the tripeptide can be filled by any of the 20 amino acids, the number of different tripeptides can be calculated using the formula:

Answer: 20^3 (number of naturally occuring amno acidds to the power of the npeptide e.g. tripeptide put to the power of 3, dipeptide then to the power of 2)

𝑛
𝑟
Numberofdifferenttripeptides=n
r

where:

𝑛
n is the number of different amino acids available (20 in this case),
𝑟
r is the number of positions in the tripeptide (3 for a tripeptide).
Calculation
Identify
𝑛
n and
𝑟
r:

𝑛=20
n=20 (the number of amino acids),
𝑟=3
r=3 (for a tripeptide).

Question 2

Outline the structure of proteins

Answer 2

The start of an amino acid is referred to as an N- terminus and the end is a C-terminus and a carboxyl group -COOH “(C double bond O-OH”)

Question 2

Write the word equation for the condensation reaction forming a dipeptide. Draw this out.

Answer 2

Amino acid 1+ amino acid 2= dipeptide and water with the release of a water molecule.

Question 2

The infinite variety of possible polypeptide chains (memorise this formula)

Answer 2

Possible number of different polypeptides, P, that can be assembled is given by: p=A^n

A=number of different types of amino acids available e.g. 20

n= number of aino acid residues in the polypeptide molecule e.g. tripeptide hence n=3

Question 3

Give an example of a polypeptide.

Answer 3

Examples of polypeptides include enzymes such as amylase which has the role of starch digestion. Other proteins are hormones such as insulin. haemoglobin.

Question 4

Define the term denaturation.

Answer 4

Denaturation is the structural change of a protein that results in a lo of its biological properties.