Proteins

• What is a gene

  A sequence of nucleotide bases in a DNA molecule which codes for the production of a specific amino acid sequence, producing a specific polypeptide
• what are the two stages of protein synthesis

  transcription and translation
• Why is mRNA used during transcription instead of DNA

  mRNA is single stranded and shorter, meaning it can fit through nuclear pores

  mRNA is a copy of bases, DNA is too important and fragile to take out of nucleus
• What is the role of mRNA 


  Carries information encoded in the DNA to the site of translation on ribosomes
• what is the structure of mRNA 


  mRNA is a single stranded polynucleotide made up of triplet codons. mRNA uses DNA as a template to make a copy of the desired gene to be synthesized
• where does transcription occur

  in the nucleus of the cell
• What is the role of RNA polymerase 


  RNA polymerase unwinds The double helix and wedges itself between the two DNA strands, breaking hydrogen bonds and exposing the DNA bases for transcription
• what is the antisense strand?

  the template strand which contains complementary bases to the strand desired for synthesis
• what is the sense strand?

  the coding strand/ the strand desired to be copied
• in what direction does RNA polymerase work?

  3’ to 5’ on the template strand
• How does the mRNA strand form?

  The antisense strand is used as a template

  Free RNA nucleotides line up with the DNA nucleotides on the antisense strand by complementary base pairing forming hydrogen bonds

  RNA polymerase catalyses the condensation reaction forming phosphodiester bonds and the sugar phosphate backbone

  hydrogen bonds break and the mRNA detaches
• why does RNA polymerase only work in the 3’ to 5’ direction?

  RNA polymerase is an enzyme with an active site

  the active site has a specific shape which is complementary and specific to to the shape of the substrate (3’ end)

  the 5’ carbon end and the 3’ carbon end have different shapes, meaning the enzyme is only able to bind to the 3’ end
• where does translation occur 


  cytoplasm
• If RNA polymerase moves along the template strand in 3’ to 5’ direction, in what direction does the mRNA grow?

  5’ to 3’. This is because of antiparallel strands
• What are the differences between tRNA and mRNA

  tRNA is folded while mRNA is unfolded

  TRNA has hydrogen bonds holding the structure together while mRNA does not

  TRNA is a fixed length while the length of mRNA depends on the length of the gene

  TRNA has anticodons while mRNA has codons

  TRNA has an amino acid binding site