nucleotides and nucleic acids

• Nucleic acids

  Large molecules contained within the cell nuclei, can be either DNA or RNA, have roles in the storage and transfer of genetic information and the synthesis of polypeptides (proteins), the basis for heredity
• Nucleotide


  Monomer of nucleic acids, contains a pentose monosaccharide (sugar), an inorganic phosphate group, and a nitrogenous base
• Nucleic acid polymer

  Formed from many nucleotide monomers linked together in a chain by phosphodiester bonds
• Nitrogenous bases

  • Pyrimidines (Thymine, Cytosine, Uracil)
  • Purines (Adenine, Guanine)
• Complementary base pairing

  Adenine and thymine form 2 hydrogen bonds, cytosine and guanine form 3 hydrogen bonds, maintains constant distance between DNA backbones
• DNA vs RNA nucleotides

  DNA has deoxyribose sugar, RNA has ribose sugar. DNA bases are A-T, C-G, RNA bases are A-U, C-G.
• RNA

  Contains phosphate, ribose sugar, and uracil base, transcribes DNA to transport genetic information to ribosomes, degraded after protein synthesis
• Polymer


  Made up of many repeating units (nucleotides) joined together in long chains
• DNA/RNA chain formation

  Nucleotides joined by condensation reactions forming phosphodiester bonds, releasing water
• DNA/RNA chain breakage

  Hydrolysis of phosphodiester bonds between adjacent nucleotides, adding water
• Organism energy requirements

  Anabolic reactions, moving substances, muscle contraction, nerve impulses
• ATP

  Universal energy currency, readily releasable energy in bonds between 2nd and 3rd phosphate groups
• ATP structure

  Adenine, ribose, 3 phosphate groups (AMP, ADP, ATP)
• DNA double helix


  Two antiparallel polynucleotide strands held together by hydrogen bonding between complementary base pairs, allows DNA to be copied and transcribed
• Antiparallel

  DNA strands run in opposite directions, one 5' to 3', one 3' to 5'
• DNA extraction from plants

  Grind sample, add detergent, salt, protease, precipitate with alcohol
• Semi-conservative DNA replication


  Each new DNA molecule contains one old and one new strand
• DNA replication enzymes

  DNA helicase unwinds and separates strands, DNA polymerase synthesizes new complementary strands
• Continuous vs discontinuous DNA replication

  Leading strand replicated continuously, lagging strand replicated in Okazaki fragments
• DNA replication errors

  Mutations - random, spontaneous changes in base sequence
• Genetic code

  Triplet code, universal, non-overlapping, degenerate
• Gene


  Section of DNA coding for a complete protein
• Transcription


  DNA unwinds, RNA polymerase synthesizes complementary mRNA strand, which leaves nucleus
• Sense and antisense DNA strands

  Sense strand codes for protein, antisense strand acts as template
• Ribosome


  Two subunits of protein and rRNA, catalyzes protein synthesis
• Translation


  mRNA binds to ribosome, tRNA anticodons bind to mRNA codons, amino acids joined into polypeptide chain
• tRNA


  Carries amino acid to ribosome, anticodon binds to complementary mRNA codon
• Why does continuous and discontinuous replication occur?

  DNA polymerase always moves along the template strand in one direction. It can only bind to the 3’ (OH) end, so travels in the direction of 3’ to 5’. As DNA only unwinds and unzips in one direction, DNA polymerase has to replicate each of the template strands in opposite directions.
• Describe continuous DNA replication


  The strand that is unzipped from the 3’ end can be continuously replicated as the strands unzip. This strand is called the leading strand and is said to undergo continuous replication.
• Describe discontinuous DNA replication.


  This strand is unzipped from the 5’ end, so DNA polymerase has to wait until a section of the strand has unzips and then work back along the strand in the opposite direction. This results in DNA being produced in sections called Okazaki fragments, which then have to be joined by DNA ligase. This strand is called the lagging strand and is said to undergo discontinuous replication.