Transcription/ Translation

• What is mRNA+function does it do in cell:(2marks)

  • messenger RNA
  • Carries copy of genetic code from DNA in nucleus to ribosome
• What is tRNA+function does it perform in cell:(2 marks)

  • transfer RNA
  • Carries amino acid from cytoplasm to ribosome , then pairs with complementary code from mRNA
• What is a nucleotide and how does it differ in DNA and RNA: (3 marks)

  • nucleotides are the monomers of nucleic acids
  • nucleotides are composed of a phosphate group ,sugar and nitrogenous base
  • In DNA the sugar is deoxyribose , in RNA it is ribose sugar , in RNA the nitrogenous base uracil replaces thymine

  
• Transcription is one of the steps involved in gene expression,

  describe what occurs in the first step- Transcription: (1 mark)

  • enzyme RNA polymerase pairs RNA nucleotides with complementary bases on non coding strand to form pre-mRNA

  
• Post Transcriptional modification occurs after Transcription of DNA to pre -mRNA, describe what occurs in this process with reference to why:(4 marks)

  • splicing occurs
  • introns undergo splicing as they are non coding sequences
  • then methyl cap is added to 5' end of mature mRNA to protect transcript from being broken
  • Poly A tail is also added, to the 3' end which makes RNA molecule more stable

  
• Translation is the final step involved in gene expression, explain what happens:(2 marks)

  • mature mRNA leaves nucleus /goes to ribosome
  • tRNA molecules bind with codons on mRNA , thus releasing amino acid which forms polypeptide