Protein Synthesis

• What are the 2 main stages in order to produce a polypeptide from a gene

  Transcription and translation
• What is the first step in the process of transcription?

  Helicase breaks the hydrogen bonds between complementary bases forming a transcription bubble
• What role does helicase play in transcription?

  It breaks the hydrogen bonds between complementary bases in DNA
• Where does RNA polymerase bind during transcription?

  To the promoter region of DNA
• Which strand of DNA does RNA polymerase move along during transcription?

  The template strand
• How do free RNA nucleotides bind to the template strand during transcription?

  Via complementary base pairing
• What are the base pairing rules for RNA during transcription?

  C matches to G, G matches to C, U matches to A, and A matches to T
• What does RNA polymerase do between adjacent RNA nucleotides?

  It catalyzes the formation of phosphodiester bonds
• What happens to the DNA behind RNA polymerase during transcription?

  It reforms the double helix
• What signals the termination of the mRNA chain during transcription?

  When RNA polymerase reaches a "stop" codon
• What occurs to the mRNA after transcription is terminated?

  The mRNA chain detaches
• What is a codon?


  triplet bases on RNA that codes for an amino acid
• where does translation occur?


  ribosomes
• Name the product of transcription

  mRNA
• Name the enzymes involved in transcription


  DNA helicase + RNA polymerase
• What type of bond does mRNA have


  phosphodiester bonds
• How is rRNA involved in catalysing translation


  peptidyl transferase is an rRNA component

  it transfers one amino acid to another
• Describe what happens to the amino acid chain to make it a fully functional protein


  The amino acid chain folds into secondary and tertiary structure

  may undergo further modifications at the golgi
• Name the product of translation


  Polypeptide (then becomes a functional protein after modification in golgi)
• What part of tRNA binds to mRNA


  anticodon loop
• name the amino acid that is always at the start of a protein

  Methionine
• what is rRNA?


  the primary component of ribosomes

  the rRNA in the ribosomes helps to catalyse the formation of peptide bonds between amino acids

  rRNA is made in the nucleolus
• in the cytoplasm amino acids become attached to specific transfer RNA molecules. Each tRNA is specific for 1 amino acid
• each tRNA molecule has a sequence of 3 bases called an anticodon. These are complimentary to the codon on the mRNA molecule.
• Describe translation.


  mRNA attaches to the ribosome at the start codon-AUG

  tRNA with a complimentary anticodon attaches to the mRNA-UAC

  this tRNA is attached to an amino acid-methionine

  the ribosome moves along the mRNA bringing in 2 tRNA molecules at any one time

  an enzyme and ATP are used to join the amino acids with a peptide bond

  the first tRNA is released and collect another amino acid.

  the process is repeated until a stop codon is reached.
• What is an anticodon?


  a sequence of three bases in a tRNA molecule which are complementary to the codons on the mRNA molecule
• Describe how a messenger RNA copy of a gene is produced (from mark scheme) (6)

  • RNA polymerase binds to the promotor region/DNA
  • DNA helicase unwinds DNA
  • RNA nucleotides pair with bases on the template strand
  • complementary base pairing
  • RNA polymerase catalyzes the formation of phosphodiester bonds
  • DNA rewinds