Genetic Code and Protein Synthesis

Question 1

Define the term ‘gene’.

Answer 1

A sequence of bases that code for the sequence of amino acids in a polypeptide

Question 2

What are the two processes involved in protein synthesis?

Answer 2

Transcription and translation.

Question 3

Describe the process of transcription.

Answer 3

1. RNA polymerase attaches to DNA at the start codon.
2. This breaks the hydrogen bonds between complementary bases and the DNA strands separate and unwind.
3. One strand is then used as a template to make an mRNA copy
4. RNA polymerase lines up free RNA mononucleotides alongside the antisense strand.
5. Complementary base pairing between mRNA and DNA occurs (A-U and C-G)
6. After pairing, the RNA mononucleotides are joined together by the enzyme, forming a mRNA molecule
7. RNA polymerase moves along the DNA strand, separating the strand and assembling the mRNA strand
8. RNA polymerase reaches a stop codon, stops making mRNA and detaches from DNA strand
9. mRNA moves out of the nucleus through nuclear pore and attaches to ribosome in cytoplasm.

Question 4

Describe the process of translation.

Answer 4

1. mRNA attaches to ribosome and tRNA molecules carry amino acids to the ribosome.
2. tRNA molecule’s anticodon attaches to mRNA using complementary base pairing.
3. 2nd tRNA molecule attaches itself to next codon in the same way.
4. The 2 amino acids produced are joined together by a peptide bond. The 1st tRNA molecule moves away, leaving the amino acid behind.
5. The ribosome moves along to the next codon.
6. The 3rd tRNA molecule binds to that codon on the mRNA. Its amino acid binds to the first two and the second tRNA molecule moves away
7. This process continues producing a polypeptide chain until there is a stop codon on the mRNA molecule
8. The polypeptide chain moves away from the ribosome

Question 5

What is mRNA?

Answer 5

• Messenger ribonucleic acid
• Made in the nucleus during transcription
• Carries the genetic code from DNA in nucleus to ribosome in cytoplasm

Question 6

What is tRNA?

Answer 6

• Transfer ribonucleic acid
• Found in cytoplasm
• Has amino acid binding site at one end
• Has 3 bases (UAG) at other end called anticodon
• Carries amino acids to ribosomes to make proteins.