Gene Expression - Translation

• Single bases are 4 and have 4 possible amino acids
• Triplets (CAC, GTA, etc) are 4^3 and have 64 possible amino acids and have some redundancy.
• There can be many possible combinations with 4 bases and 20 amino acids.
• 61/64 codons specify for an amino acid. Most of them have more than one codon called degeneracy.
• Three codons specify for stop - UAA, UAG, UGA
• One codon specifies fr start - AUG
• Redundancy means multiple codons can code for the same amino acid.
• tRNA is an adaptor molecule. it is the process in protein synthesis where the cells reads a genetic message and builds a polypeptide. This message is a series of codons along the mRNA molecule.
• tRNA transfers amino acid from the cytoplasmic pool of amino acids to a growing peptide in a ribosome. Thi happens by the tRNA bears a specific amino acid at one end o the 3D structure containing 70-80 nucleotides.
• Label tRNA

  A) hydrogen bonds

  B) anti-codon

  C) 2D structure

  D) hydrogen bonds

  E) anticodon

  F) 3D structure

  G) amino acid attachment site

  H) anticodon

  
• Steps tRNA

  An enzyme recognises both a specific amino acid and correct tRNA for this amino acid and joins together. There are 20 different enzymes.
• mRNA in protein synthesis stores genetic information and protein-making in the cell.
• mRNA in translation, in the cytoplasm, mature mRNA serves as a template for protein synthesis. Ribosomes move along the mRNA molecule, reading each 3 nucleotide codon.
• Translation is the synthesis of proteins by ribosomes using mRNA as a set of instructions. Ribosomes contain RNA and proteins.
• Location of ribosomes can be bound ER and free in cytosol
• Ribosomes in bound ER synthesise proteins that are used within the plasma membrane or exocytosied in the cell.
• Ribosomes free in cytosol synthesise proteins that are released into cytosol and used within the cell.
• Label 1

  A) growing peptide

  B) large subunit

  C) small subunit

  D) mRNA

  E) 5'

  F) 3'

  G) tRNA

  
• Label 2

  A) amino end

  B) growing polypeptide

  C) carboxyl end

  D) tRNA

  E) mRNA

  F) ANTICODON BASE

  
• Label 3

  A) nucleus

  B) nuclear envelope

  C) rough ER

  D) Plasma membrane

  E) trans Golgi

  F) cis Golgi

  G) Lysosome

  H) smooth ER

  
• Translation has 3 stages:

  1. Initiation
  2. Elongation
  3. Termination

  All 3 requires energy input.
• During initiation, tRNA binds to small ribosomal unit. this unit identifies 5' G-cap and attaches to mRNA. The small ribosomal unit moves along mRNA until it finds AUG codon.

  The complex then stops, the initator tRNA carries first methionme postitioned at P-site.

  Then large ribosomal unit attaches.
• During Elongation 1, A charged tRNA with an anticoon complimentary to the A site codon lands in A site.
• During Elongation 2, two things happen at the same time.

  1: The ribosome will break the bond that binds the amino acid to the tRNA in the P site, transfer amino acid to the newly arrived amino acid and form a peptide bond between them.

  2: While the tRNA's are bound to mRNA, the ribosome moves three nucleotides down the mRNA.
• During elongation 3, in the E site, the anticodon of the tRNA detaches from the mRNA codon and the uncharged tRNA is expelled.
• During elongation 4, A new charged tRNA with an anticodon complimentary to the next A site codon enters the ribosome at the A site and the elongation repeats.
• Label Elongation

  A) codon recognition

  B) peptide bond formation

  C) translocation

  D) ribosome ready

  E) mRNA

  
• During termination 1, when a ribosome reaches a stop codon, a release factor enters the A-site.
• During termination 2, the release factor breaks the bond between P site tRNA and the final amino acid. This causes the polypeptide chain to detach from its tRNA and newly polypeptide is released.
• During termination 3, Small and large sub-ribosomal units disassociate from mRNA and each other.
• Genotypic variation leads to phenotypic variation
• Genotype is a set of genes and/or DNA combinations that are responsible for a particular trait and are determined at DNA level.
• A phenotype is a physical expression/characteristics of a genotype that can be observed. It is defined by what happens at protein level.