8.1 - Genes And The Genetic Code

Question 1

What is a gene?

Answer 1

A gene is a particular section of DNA that contains the coded information to make polypeptides and functional RNA such as tRNA and mRNA

Question 2

What is the locus?

Answer 2

A locus is a specific point on a DNA molecule where a gene is located

Question 3

How many bases code forone amino acid?

Answer 3

Three bases code for 1 amino acid

Two bases = 16 amino acid possibilities

Three bases = 64 amino acid possibilities

Question 4

How many different amino acids are there?

Answer 4

There are 20 different amino acids altogether.

Question 5

What is the name given to 3 bases?

Answer 5

Three bases are often referred to as triplets or codons.

Question 6

What is the Degenerative code?

Answer 6

As there are 64 possible triplets and only 20 amino acids, it follows that some amino acids are coded for by more than one triplet. This is known as a degenerative code.

Question 7

What is meant by a non-overlapping code?

Answer 7

Each base is only read once rather than as triplets therefore the same base cannot be in the next triplet/codon

Question 8

Why is the genetic code referred to as universal?

Answer 8

With a few minor exceptions each triplet code is for the same amino acid in all organisms

Question 9

What is the ‘start’ amino acid and what bases code for it?

Answer 9

Methionine

AUG

Question 10

Give the three stop triplets

Answer 10

UAG
UAA
UGA

Question 11

Describe how a change in one base along DNA molecule may result in an enzyme becoming non-functional

Answer 11

I different base might code for a different amino acid. The sequence of amino acids in the polypeptide produced will be different. This change to the primary structure of the protein might result in a different shaped tertiary structure. The enzyme shape will be different and may not fit the substrate the enzyme substrate complex cannot be formed and so the enzyme is non-functional