Genetic Code

Question 1

What is the genetic code of an organism?

Answer 1

The genetic code of an organism is the sequence of
bases along its DNA. It contains thousands of sections
called genes or cistrons. Each gene codes for a
specific polypeptide.

Question 2

What happens when a gene is switched on?

Answer 2

When a gene is ‘switched on’ or expressed, it is transcribed
into an mRNA strand which is then translated into a protein.

Question 3

What is the genetic code?

Answer 3

 The sequence of bases in the DNA
 Consists of triplets of organic bases on mRNA
 A sequence of 3 bases on mRNA codes for a
particular aminoacid and it is called a codon
 It is universal i.e. a given codon codes for the
same amino acid in all living organisms
 Start codon ( AUG)
 Stop codons ( UAA, UAG, UGA

Question 4

Define Triplet genetic code

Answer 4

each
amino acid is encoded by three
bases.

Question 5

Define degenerate code

Answer 5

notice that the amino acids are coded
by more than one triplet. Each codon is discrete.

– some amino acids are coded by more
than one triplet

Question 6

Define codon

Answer 6

3 bases on mRNA which code for a specific
aminoaci

Question 7

Define the genetic code as Non-overlapping

Answer 7

this means each triplet code is
adjacent to each other and is discrete.
Each triplet code in DNA codes for one aa
Each base is part of only one triplet and is
therefore involved in specifying only one aa

Question 7

Describe the stages of protein synthesis

Answer 7

1. Transcription of the gene in the nucleus– an mRNA A strand is formed.
2. Processing of the mRNA.
3. Translation of the mRNA in a ribosome – a polypeptide chain is formed
4. Modification of the protein

Question 8

What is a gene

Answer 8

 A sequence of bases on a DNA molecule coding for
a sequence of amino acids in a polypeptide chain
 Thousands of genes therefore thousands of
different sequences
 Each gene contains a unique sequence of bases
therefore unique combination of codons, therefore
unique combination of amino acid