Protein synthesis

• Protein synthesis

  1. Transcription

  2. Translation
• Transcription

  The conversion of DNA into mRNA
• Translation

  The conversion of mRNA into a polypeptide
• Triple codon

  3 Bases code for 1 Amino acid
• Number of stop codons

  • 3
• Number of start codons

  • 1
• Genetic code specificity

  Each codon only codes for one amino acid
• Degeneracy/redundancy of the genetic code

  Each amino acid can have more than one codon
• Where transcription takes place

  In the nucleus
• Stages of transcription


  1. Initiation

  2. Elongation

  3. Termination

  4. Splicing
• Initiation of transcription

  1. RNA polymerase binds to a promoter sequence

  2. DNA helicase breaks the hydrogen bonds and unwinds the helix
• Elongation of transcription

  RNA polymerase catalyses the addition of ribonucleotides to the 3'
• Why are Primers not needed in transcription

  Because RNA polymerase has evolved to use promotor sequences
• Why does Transcription not use DNA ligase

  Because only the 3' to 5' DNA strand is replicated, so no Ozaki fragments are created that need to be stuck together
• Termination of transcription

  RNA polymerase reaches a terminator sequence, and the DNA helix rewinds
• Splicing in transcription

  1. Transcription produces pre-mRNA, which contains introns

  2. Introns are removed using a splicesome to form mature mRNA
• How an Amino Acid is attached to a tRNA molecule

  1. ATP is hydrolysed

  2. Amino acid joins AMP on the aminoacyl-tRNA synthetase molecule

  3. tRNA binds to the aminoacyl-tRNA synthetase molecule

  4. Amino Acid binds to tRNA and are released from the aminoacyl-tRNA synthetase molecule

  5. Aminoacyl tRNA is formed
• Aminoacyl tRNA

  An activated tRNA molecule bound to an Amino Acid
• Polysome

  A group of ribosomes working to translate a single mRNA molecule
• Protein synthesis in prokaryotes

  They are coupled together as proteins can diffuse straight to their target
• What is the diagram of and label it


  tRNA.

  A) Amino acid attachment site

  B) 3'

  C) 5'

  D) Hydrogen bonds

  E) Anticodon

  F) Variable loop

  G)

  H)

  I)

  J)

  
• What is this diagram and label it. 


  Ribosome.

  A) Peptidyl-tRNA binding site

  B) Exit site

  C) mRNA binding site

  D) Small subunit

  E) Large subunit

  F) Aminoacyl-tRNA binding site

  G) Exit tunnel

  
• what binds to the peptidyl-tRNA binding site

  tRNA with the peptide chain attached.
• What binds to the aminoacyl-tRNA binding site.

  Activated tRNA with its amino acid attached.
• what are the stages of translation

  Initiation. Elongation. Termination.
• What is this stage and describe it.


  Initiation of translation.

  A) mRNA binds

  B) Initiator tRNA binds to start codon

  C) GTP is hydrolysed

  D) Initiator tRNA in p-site

  E) Translation initiation complex forms

  
• What process is this and describe it. 


  Elongation of translation.

  A) Aminoacyl-tRNA binds to A-site

  B) GTP is hydrolysed

  C) Peptide bond forms

  D) Peptidyl transferase

  E) tRNA is ejected from p-site.

  F) Ribosome move forward 1 codon

  G) GTP is hydrolysed

  
• What is this process and describe it.


  Termination of translation.

  A) Stop codon in A-site

  B) Release factor binds to stop codon

  C) Water added to polypeptide chain.

  D) tRNA released from p-Site

  E) 2 GTP hydrolysed

  F) Ribosome dissociates.