Describe the role of mRNA after it leaves the nucleus and enters the cytoplasm of a eukaryotic cell

  • translation ;
  •  moves towards / combines with, ribosome ;
  • ref to small and/or large sub-units ; I small / large ribosome
  •  codon(s) ;
  •  transfer / t, RNA, bringing, amino acid(s), to mRNA / ribosome ;
  •  anticodon(s) ;
  •  (complementary) base pairing ;
  •  any e.g. of codon:anticodon base pairing ; need six bases
  •  ref to polyribosome(s) / used by many ribosomes ;
  •  (mRNA short-lived) ref to production of protein for short period of time ;

Describe ways in which mRNA differs from DNA.

ribose deoxyribose ;
uracil / no thymine thymine
single, polynucleotide / strand / chain two, polynucleotides / chains / strands ;
no hydrogen bonds hydrogen bonding ;
not a helix / straight chain (double) helix ;
ratio of A+G to C+T varies ratio of A+G to C+T = 1;
base pairing A-U with, tRNA /anticodon base pairing is A-T
shorter longer;
found in cytoplasm / leaves nucleus found in nucleus
attached to ribosome(s) no attached to ribosome(s)
short-lived long-lived
transfer of information (to ribosome) information storage;
codes for one polypeptide codes for more than one polypeptide ;
produced by transcription produced by (semi-conservative) replication

Outline the stages occurring in transcription

  •  DNA/ gene/ MUC5AC, unwinds ;
  •  H-bonds break between, (complementary) bases/ base pairs/ strands ;
  •  one / a, strand, acts as template/ (complementary) copied ;
  •  ref. to (involvement of) RNA polymerase ;
  •  (free) complementary RNA nucleotides added ;
  •  step-by-step/ sequentially/ AW ;
  •  sugar phosphate backbone sealed/ phosphodiester bonds formed ;
  •  (product is) messenger RNA/ mRNA ;
  • 9 AVP ; e.g. transcription factors required to initiate transcription
    RNA polymerase binds to promoter (sequence) helicase unwinds
    ref. to activated (RNA) nucleotides
    ref. to proof reading
    (transcription ends at) transcription terminator

Describe the role played by tRNA in polypeptide synthesis

  •  (tRNA) carries amino acid to ribosome ;
  •  ref. to specificity of amino acid carried ;
  •  ref. anticodon (on tRNA): codon (on mRNA) binding ;
  •  ref. complementary / base pairing ; A A-U, C-G
  •  ref to tRNA binding sites within ribosome ;
  •  two tRNAs bound to, mRNA / ribosome, at same time ;
  •  amino acids held close to each other / AW ;
  •  (for) peptide bond formation ;
  •  (tRNA) can be reused / binds another amino acid ;

Explain why the hydrogen bonding between the two strands of DNA is important for it to carry out its functions

  •  important in contributing to 3-D structure of molecule ;
  •  many hydrogen bonds so, gives stability / strands not easily separated / long lasting ;
  •  (individual) hydrogen bonds (more) easily broken (than covalent bonds) ;
  •  (so strands can be separated) for (DNA) replication ;
  •  (so strands can be separated) for (DNA) transcription ;
  •  hydrogen bonds only form between, specific bases / named base pairs, so, few mistakes / faithful replication ;
  •  idea that hydrogen bonds can easily re-form (without chemical reaction) ;

Outline the stages occurring in translation

  •  Occurs in cytoplasm on rough ER ;
  •  mRNA attached to ribosome on rough ER
  •  tRNA picks up amino acids according to their triplet bases: ANTICODON;
  •  each tRNA has only one specific amino acid;
  •  ribosome moves along mRNA from start to stop codon highlighting each codon as it moves;
  •  as a codon is highlighted, it attracts the complimentary tRNA anticodon- bringing amino acid;
  •  codons of mRNA determine which anticodons are brought and therefore the sequence of amino acids;
  •  once amino acids are in correct sequence, they combine with peptide links= polypeptide chain;
  •  tRNA leave mRNA , return to cytoplasm;
  •  Note: methionine always starts sequence/ stop happens when no amino acid is brought with tRNA and peptide bonds stop

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