DNA and protein synthesis

• Anticodon


  - 3 bases on the tRNA which are complementary to the codon on mRNA.
• mRNA structure


  - single-stranded

  - made up of codons

  - a copy of one gene
• tRNA structure


  - single-stranded

  - folded to create a cloverleaf shape

  - held in place by hydrogen bonds

  - has an anticodon and amino acid binding site

  
• mRNA function


  - a copy of a gene from DNA

  - created in the nucleus, and it then leaves the nucleus

  - to carry the copy of the genetic code of one gene to a ribosome in the cytoplasm
• tRNA function


  - a specific amino attaches at the binding site

  - transfers this amino acid to the ribosome to create the polypeptide chain
• Transcription


  - the first stage in protein synthesis

  - one gene in DNA is copied into mRNA

  - occurs in the nucleus

  
• Translation


  - the second stage in protein synthesis

  - the polypeptide chain is created using both the mRNA base sequence and the tRNA

  - occurs on ribosomes in the cytoplasm

  
• Which enzymes are involved in transcription?


  - DNA helicase

  - RNA polymerase
• DNA helicase


  - catalyses the breaking of hydrogen bonds between the two strands of DNA
• RNA polymerase


  - joins adjacent RNA nucleotides together

  - forming a phosphodiester bond
• pre-mRNA


  - mRNA in eukaryotes that still contains the introns
• How is pre-mRNA modified?


  - the introns are removed by a protein called a spliceosome

  - this leaves just the exons
• What is ATP used for in translation?


  - forming the peptide bond between amino acids
• Describe how mRNA is formed by transcription in eukaryotes.

  1. Hydrogen bonds (between DNA bases) break;
  2. (Only) one DNA strand acts as a template;
  3. (Free) RNA nucleotides align by complementary base pairing;
  4. (In RNA) Uracil base pairs with adenine (on DNA) OR (In RNA) Uracil is used in place of thymine;
  5. RNA polymerase joins (adjacent RNA) nucleotides;
  6. (By) phosphodiester bonds (between adjacent nucleotides);
  7. Pre-mRNA is spliced (to form mRNA) OR Introns are removed (to form mRNA);
• Describe how a polypeptide is formed by translation of mRNA.

  1. mRNA attaches) to ribosomes OR (mRNA attaches) to rough endoplasmic reticulum;
  2. (tRNA) anticodons (bind to) complementary (mRNA) codons;
  3. tRNA brings a specific amino acid;
  4. Amino acids join by peptide bonds;
  5. (Amino acids join together) with the use of ATP;
  6. tRNA released (after amino acid joined to polypeptide);
  7. The ribosome moves along the mRNA to form the polypeptide;
• Transcription is the MAKING of mRNA from one gene on DNA. The 1st stage of protein synthesis.
• Translation if where the mRNA joins with the ribosome and corresponding tRNA molecules brings specific amino acids. The 2nd stage of protein synthesis