Protein synthesis

• Protein synthesis is the process by which base sequences found in genes in DNA are used to make polypeptides
• RNA stands for ribonucleic acid
• RNA is a single stranded version of DNA and contains the base U instead of T
• Which process occurs first, transcription or translation?

  Transcription
• Transcription:

  • The DNA molecule is unzipped around the gene. DNA is a double stranded molecule so needs to be unzipped to expose one strand.
  • RNA polymerase makes a copy of DNA as mRNA. RNA binds to the non-coding region infront of a gene on one of the DNA strands and uses free nucleotides to produce complementary mRNA strand of the coding part of the gene.
• Transcription is the process of copying DNA
• Translation:

  • mRNA leaves the nucleus, moves into the cytoplasm and attaches to the ribosome
  • tRNA has an anti codon that is complementary to mRNA's codon. tRNA carries amino acids with it
  • the bases on mRNA read in threes and code for a specific amino acid. amino acids bond with another and form polypeptides
• coding DNA directly determines the proteins formed as a copy of it is made
• non-coding DNA turns off and on genes, so if it turns off a section of coding DNA, the protein produced would be different
• different cells have different genes turned on and off
• examples of proteins:

  • hormones carry messages around the body
  • enzymes which act as biological catalysts to speed up reactions in the body
• How mutations change how a protein is synthesised:

  • Mutations change the sequence of DNA bases in a gene
  • The sequence codes for amino acids in a protein
  • A change in amino acids could lead to a change in the protein