24. CODONS

Question 1

1. How many Amino acids are there?

Answer 1

• 20

Question 2

2. How many nucleotide bases are there?

Answer 2

• 4
• IN DNA : A, G, T, C

Question 3

3. How many nucleotide bases correspond to one amino acid?

Answer 3

• 1 amino acid corresponds to a triplet code
• this consists of 3 nucleotide bases

Question 4

4. What does a triple code consist of?

Answer 4

• it has 3 consecutive nucleotides

Question 5

5. What happens when each gene is transcribed?

Answer 5

• each gene is transcribed into a complementary mRNA
• this mRNA contains the nucleotide triplets
• these triples are known as CODONS

Question 6

6. What does each codon specify?

Answer 6

• it specifies the addition of a specific amino acid
• the gene is translated into an amino acid chain
• this is done before it forms into a polypeptide chain

Question 7

7. What happens during DNA transcription with regards to the DNA strands?

Answer 7

• one of the DNA strands is going to be used as a
  template
• this template is for the synthesis of the complementary
  RNA strand

Question 8

8. Which DNA strand is used to form the template?

Answer 8

• the 3’ to 5’ strand

THE RNA POLYMERASE:
- will synthesise this template strand in a 5’ to 3’
direction
- the RNA transcripts are single stranded molecules

Question 9

9. What happens during translation?

Answer 9

• the codons on the mRNA molecule are read in the
  5’ - 3’ direction
• they are read by the Ribosomes

Question 10

10. How many codons (triplet codes) are there in total?

Answer 10

• 64
• 61 of them code for Amino Acids
• 3 of them code for “stop” signals at the end of the
  translation

Question 11

11. Which 3 codons code for the “Stop” signals?

Answer 11

• UAA
• UAG
• UGA

Question 12

12. Which codon is the “Start” codon?

Answer 12

• AUG
• Methionine (Met)

Question 13

13. What are two characteristics of the Genetic Code?

Answer 13

1. IT IS REDUNDANT
   
   • there is more than 1 codon that can code for a
     specific amino acid
   • EG: CGA and AGG both code for Arginine (Arg)
2. IT IS NOT AMBIGUOUS:
   
   • each codon can specify only one amino acid
   • there is only one interpretation of the codon
   • EG: CAA is always Glutamine (Gln)

Question 14

14. Is the Genetic code universal?

Answer 14

• nearly
• it is shared by the simplest bacteria and the most
  complex animals

Question 15

15. What does a Universal Genetic code mean?

Answer 15

• genes can be transcribed and translated
  AFTER they have been transplanted from one species to
  another

EG:
- genetically modified bacteria

Question 16

16. What is genetically modified bacteria?

Answer 16

• this is bacteria that can be programmed
• this is done by the insertion of human genes
• this produces certain human proteins for medical use
• EG: insulin