Topic 7 - Nucleic Acids and Proteins

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  1. How are the Polynucleotide chains held together?
    In the center between the two bases of opposite polynucleotides using hydrogen bonding.
  2. Two polynucleotide chains run in which direction to each other?
    opposite directions - chains are 'anti-parallel'
  3. What bonds the chemical groups within DNA?
  4. How is DNA bonded to histones?
    hydrogen bonding
  5. How many histones is DNA bonded to?
  6. A certain gene codes for a polypeptide that is 120 amino acids long. Approximately how many nucleotides long is the mRNA that codes for this polypeptide likely to be?

    A. 40
    B. 360
    C. 30
    D. 480
    B. 360
    (this multiple choice question has been scrambled)
  7. What is removed to form mature eukaryotic mRNA?

    A. RNA primers
    B. Exons
    C. RNA polymerases
    D. Introns
    • D. Introns
    • The exons are exciting and will be expressed so must be kept!
  8. State a role for each of four different named enzymes in DNA replication.
    • helicase: splits / breaks hydrogen bonds / uncoils DNA / unwinds DNA;
    • (DNA) polymerase III: adds nucleotides (in 5' to 3' direction) / proofreads DNA;
    • (RNA) primase: synthesizes a short RNA primer (which is later removed) on DNA;
    • (DNA) polymerase I: replaces RNA primer with DNA;
    • (DNA) ligase: joins Okazaki fragments / fragments on lagging strand / makes sugar-phosphate bonds between fragments
  9. Which enzyme removes the RNA primer during replication?
    A. DNA polymerase I
    B. RNA primase
    C. Helicase
    D. DNA ligase
    A. DNA polymerase I
    (this multiple choice question has been scrambled)
  10. In an electron micrograph, a DNA molecule appears 1 mm wide. The magnification of the micrograph is 500,000. What is the width of the DNA molecule?
    A. 0.5 nm
    B. 2 mm
    C. 2 nm
    D. 0.5 mm
    C. 2nm
    (this multiple choice question has been scrambled)
  11. What is the function of helicase?
    A. It forms the DNA helix.
    B. It adds new nucleotides to the DNA helix.
    C. It separates DNA strands.
    D. It forms bonds between DNA nucleotides.
    C. It separates DNA strands.
    (this multiple choice question has been scrambled)
  12. What is a nucleosome?
    8 molecules of histones (2 each of 4 kinds). The DNA wraps twice around these 8 protein molecules.
  13. What are the 3 stages in translation?
    • Initiation
    • Elongation
    • Termination
  14. What is a start codon in translation?
    • AUG is the initiator codon - the tRNA that binds here carries methionine.
    • This is simple to remember - we start the school year in AUGust!
  15. What are the 3 stop codons you should know?
    • UGA (U Go Away)
    • UAA (U Are Away)
    • UAG (U Are Gone)!
  16. What direction does translation occur?
    5' to 3'
  17. Is the mRNA the same sequence as the sense or anti-sense strand?
    The sense strand is the one that 'makes sense'. It's the strand you want to make amino acids from. Therefore you have to use the opposite strand (anti-sense) strand to use as the template.
  18. How do amino acids (being churned out by the ribosome moving along the mRNA) join together?
    By peptide bonds (by a condensation reaction)
  19. What term do we give when two or more codons (3 base bases) encode for the SAME amino acid?
  20. What is a codon?
    A group of three bases encoding for an amino acid.
  21. Does prokaryotic mRNA need post-transcriptional processing?
    No, because no introns are present.
  22. What does the 'S' stand for in 70S ribosomes?
    Svedburg (S) unit. A measure of how quickly particles sediment in an ultracentrifuge
  23. Which bases are purines?
    • Adenine and Guanine
    • Tip: PURe As Gold
  24. Which bases are pyrimidines?
    • Cytosine, Uracil and Thymine
    • Tip: PYRamids are CUT from stone
  25. Purines and pyrimidines are both ring structures. Which one has two rings, and which has one ring?
    • Pyramidines = 1 ring
    • Purines = 2 rings
  26. What base of DNA might this be?
    Image Upload 1
    • It's a 2 ring structure, so it must be a PURINE
    • Tip: PURe As Gold (So must be Adenine or Guanine)
  27. What base of DNA might this be?
    Image Upload 2
    • It's a 1 ring structure, so must be a pyrimidine.
    • Tip: Remember PYRimidines are CUT from stone. So it could be Cytosine, Uracil or Thymine (it's actually cytosine)
  28. Look at the image. Is this competitive or non-competitive inhibtion and why?
    Image Upload 3
    Competitive. The inhibitor binds to the active site of the enzyme which prevents the substrate from binding, so activity of enzyme is prevented until inhibitor dissociates.
  29. Look at the image. Is this competitive or non-competitive inhibtion and why?
    Image Upload 4
    • Non-competitive because substrate and active site are not similar
    • Inhibitor binds to enzyme at a different site from active site
    • Inhibitor changes conformation (shape) of enzyme. Substrate may be able to bind but does not catalyse reaction or does so at slower rate.
  30. What is an allosteric enzyme used for?
    In a chain of events in a metabolic parthway, the product of the last reaction in the pathway inhibits the enzyme that catalyses the first reaction.
  31. All living organisms use the same genetic code.  What do we call this fact?
    We can say that the genetic code is Universal.
  32. How many hydrogen bonds are there between

    • 2 between A and T
    • 3 between G and C
  33. Image Upload 5What kind of inhibition is this?
    • Competitive inhibition.
    • The substrate and the inhibitor are competing for the SAME site.
  34. Image Upload 6
    What kind of inhibition is this?
    • Non competitive inhibtion.
    • The inhibitor binds to a DIFFERENT site to the substrate. 
    • It changes the active site shape so that the substrate can no longer bind.
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Topic 7 - Nucleic Acids and Proteins

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