Protein synthesis

• What is the definition of Transcription?

  The base sequence within a gene where DNA is copied into an mRNA molecule.
• What is the process of transcription?

  1. RNA polymerase breaks the hydrogen bonds between 2 strands of DNA so only 1 strand is used as a template.
  2. RNA polymerase attaches to DNA at the start of the gene.
  3. RNA nucleotides complementary base pair with the template strand: A-U, C-G
  4. RNA polymerase forms phosphodiester bonds between nucleotides in a condensation reaction.
  5. On reaching a stop signal, RNA polymerase detaches.
  6. In eukaryotes, pre-mRNA is spliced to remove introns
  7. mRNA leaves the nucleus via nuclear pores.
• What is the definition of translation?

  The production of polypeptides from the sequence of codons carried by mRNA
• What are the stages of translation?

  1. mRNA attaches to a ribosome
  2. tRNA with complementary anticodon to mRNA codon attaches
  3. A 2nd tRNA molecule attaches to the next codon
  4. tRNA brings specific amino acid and the amino acids are joined by a peptide bond in a condensation reaction, with the use of ATP.
  5. The first tRNA molecule detaches, leaving its amino acid behind.
  6. ribosome moves along mRNA, allowing the 3rd tRNA to attach.
  7. This process continues until a stop codon is reached, to form a polypeptide.