2.1.3 Nucleic Acids

• What are the monomers of nucleic acids?

  Nucleotides
• How many rings do purines have?

  2
• How many rings do pyrimidines have?

  1
• Purines always form hydrogen bonds with pyrimidines
• How many hydrogen bonds join adenine and thymine?

  2
• How many hydrogen bonds join cytosine and guanine?

  3
• Adenine and guanine are purines
• Cytosine, thymine and uracil are pyrimidines
• Why is RNA shorter than DNA?

  It only contains the small portions of the genetic code necessary for its function
• RNA is usually single stranded
• What is the sugar involved in RNA?


  Ribose
• What is the sugar involved in DNA?

  Deoxyribose
• What are the bases used in RNA?

  Adenine (A)

  Cytosine (C)

  Guanine (G)

  Uracil (U)
• What are the bases used in DNA?

  Adenine (A)

  Cytosine (C)

  Guanine (G)

  Thymine (T)
• What base is complementary to adenine?

  Thymine (DNA) or Uracil (RNA)
• What base is complementary to thymine?

  Adenine
• What base is complementary to cytosine?

  Guanine
• What base is complementary to guanine?

  Cytosine
• Three types of RNA:

  1. messenger RNA (mRNA)
  2. transfer RNA (tRNA)
  3. ribosomal RNA (rRNA)
• What is the role of mRNA?

  Carries the copy of the gene out of the nucleus and transfers it to the ribosomes
• What is the role of tRNA?

  Transports amino acids to the ribosomes for protein synthesis
• What is the role of rRNA?

  Makes up the ribosome
• DNA is a macromolecule made up of 2 polynucleotide strands that run antiparallel held together by hydrogen bonds. The molecule twists to form a helix.
• What does antiparallel mean?

  Opposite directions
• What bond forms between the sugar and phosphate group of a nucleotide?

  Phosphodiester bond
• Phosphorylated nucleotides contain more than one phosphate group
• Two examples of phosphorylated nucleotides?

  ADP, ATP
• What are the bonds that form the sugar-phosphate backbone?

  Phosphodiester bonds
• What sugar is present in ADP and ATP?

  Ribose
• Which nitrogenous base is present in ADP and ATP?

  Adenine
• What does semi-conservative DNA replication mean?

  Each new DNA molecule consists of one original strand and one newly synthesized strand.
• What is the role of helicase in semi-conservative DNA replication?

  Catalyses the breaking of hydrogen bonds between complementary base pairs. This unzips the DNA.
• What is the role of DNA polymerase in semi-conservative DNA replication?

  Catalyses the addition of bases in the 5' to 3' direction
• Semi-Conservative DNA replication

  1. Helicase catalyses the breaking of hydrogen bonds between nucleotide bases, unzipping the DNA
  2. Free nucleotides in the nucleoplasm bond to their complementary exposed bases, forming hydrogen bonds
  3. DNA polymerase forms phosphodiester bonds between nucleotides
  4. Two identical DNA molecules are produced
• What bond does DNA polymerase form?

  Phosphodiester bond
• What is the leading strand?

  The strand of DNA that is synthesised continuously during DNA replication.
• What is the lagging strand?

  This strand runs in the 3' to 5' direction, therefore it must be synthesised in Okazaki Fragments which are joined together by ligase
• What enzyme joins Okazaki fragments in the lagging strand?

  Ligase
• Why is there a leading and lagging strand in DNA replication?

  DNA consists of two antiparallel strands. DNA polymerase can only form phosphodiester bonds in the 5' to 3' direction, therefore the strand that runs 3' to 5' has to be built in fragments and is, therefore, the lagging strand
• During DNA replication, an incorrect base may be bonded into place. This is known as a mutation