Nucleotides and nucleic acids

Cards (17)

  • Pentose sugars in DNA & RNA:
    • DNA: deoxyribose
    • RNA: ribose
  • Polynucleotide strands are formed and broken down through:
    • Condensation reactions between nucleotides forming strong phosphodiester bonds (sugar-phosphate backbone)
    • Hydrolysis reactions using a molecule of water to break these bonds
    • Enzymes catalyse these reactions
  • Structure of DNA:
    • Molecule twists to form a double helix of 2 deoxyribose polynucleotide strands (2 sugar-phosphate backbones)
    • H-bonds form between complementary base pairs (AT & GC) on antiparallel strands
  • Purine bases and their structure:
    • Adenine
    • Guanine
    • Two-ring molecules
  • Pyrimidine bases and their structure:
    • Thymine
    • Cytosine
    • Uracil
    • One-ring molecules
  • Complementary base pairs in DNA and RNA:
    • DNA: 2 H-bonds between adenine (A) + thymine (T), 3 H-bonds between guanine (G) + cytosine (C)
    • RNA: 2 H-bonds between adenine (A) + uracil (U), 3 H-bonds between guanine (G) + cytosine (C)
  • DNA replication is semiconservative because:
    • Strands from original DNA act as templates
    • New DNA contains 1 old strand & 1 new strand for accurate conservation of genetic material
  • Role of DNA helicase in semiconservative replication:
    • Breaks H-bonds between base pairs to form 2 single strands acting as templates
  • Formation of a new strand during semiconservative replication:
    1. Free nucleotides attach to exposed bases by complementary base pairing
    2. DNA polymerase joins adjacent nucleotides in a 5’3’ direction via condensation reactions to form phosphodiester bonds
    3. H-bonds reform
  • Features of the genetic code:
    • Non-overlapping: each triplet is read once
    • Degenerate: more than one triplet codes for the same amino acid
    • Universal: same bases and sequences used by all species
  • Gene determines amino acid sequence in a protein through:
    • Base triplets that code for specific amino acids
  • DNA purification by precipitation involves:
    • Adding ethanol & salt to aqueous solution
    • Nucleic acids precipitate out, centrifuge to obtain pellet, wash with ethanol, and centrifuge again
  • Transcription produces mRNA and occurs in the nucleus:
    1. RNA polymerase binds to gene promoter region
    2. DNA uncoils into 2 strands with exposed bases, antisense strand acts as template
    3. Free nucleotides attracted to complementary bases
    4. RNA polymerase joins adjacent nucleotides to form phosphodiester bonds
  • After mRNA transcription:
    • RNA polymerase detaches at terminator region
    • H-bonds reform, DNA rewinds
    • Splicing removes introns from pre-mRNA in eukaryotic cells
    • mRNA moves out of nucleus via nuclear pore and attaches to ribosome
  • Translation produces proteins and occurs in the cytoplasm on ribosomes:
    • Ribosome moves along mRNA until ‘start’ codon
    • tRNA anticodon attaches to complementary bases on mRNA
    • Condensation reactions between amino acids on tRNA form peptide bonds with energy from ATP hydrolysis
    • Process continues until ‘stop’ codon is reached
  • Structure of adenosine triphosphate (ATP) and adenosine diphosphate (ADP):
    • ATP: nucleotide derivative of adenine with 3 inorganic phosphate groups
    • ADP: nucleotide derivative of adenine with 2 inorganic phosphate groups
  • Mutation is an alteration to the DNA base sequence, often arising spontaneously during DNA replication