DNA and RNA (LC 2026) (Leaving Cert Biology): Revision Notes

Protein Synthesis

• Genes control cells by producing enzymes.
• Enzymes are proteins.
• To make the correct protein, amino acids must be assembled in the correct order in ribosomes.
• This process involves:
  1. The genetic code in DNA being transcribed to mRNA.
  2. The code on mRNA being translated into the correct sequence of amino acids.

Steps of Protein Synthesis:

1. Initiation
2. Transcription
3. Translation

1. Initiation:

The part of the DNA double helix that codes for the protein unwinds.

2. Transcription:

• Occurs in the nucleus.
• Complementary RNA bases attach to the exposed DNA bases.
• The RNA bases are joined together by RNA polymerase to form messenger RNA (mRNA).
• mRNA moves from the nucleus to the cytoplasm.
• This process copies information from DNA to RNA.

3. Translation:

• Occurs in the ribosome.
• mRNA attaches to the ribosome, which is made of ribosomal RNA (rRNA).
• Transfer RNA (tRNA) molecules in the cytoplasm are attracted to the mRNA.
• Each tRNA carries a specific amino acid.
• Triplets (codons) on the mRNA strand attract complementary triplets (anti-codons) on the tRNA molecules.
• The amino acids are detached from their tRNA molecules and bonded together to form the new protein.
• The protein folds into the correct 3D shape to allow it to function properly.