Nucleotides and Nucleic acids

• what are nucleotides?


  monomers from which nucleic acids like DNA and RNA are formed
• what types of nitrogenous bases are there?

  Purines + pyrimidines
• what are purines?


  2 carbon ring structure

  (adenine + guanine)
• what are pyrimidines? 


  1 carbon ring structure

  (cytosine, thymine + uracil)
• purines and pyrimidines bases are always complementary
• what is thymine paired with?


  Adenine (uracil in RNA)
• what is guanine paired with?

  Cytosine
• what type of reaction do DNA and RNA nucleotides go through?

  condensation reactions
• what type of bonds do nucleotides form?

  phosphodiester bonds = strong covalent bonds
• what is ATP made of?

  3 phosphates

  ribose sugar

  adenine
• what is ATP uses for?

  • essential for metabolism
  • immediate source of energy
• how is ATP made?


  ATP is made through respiration via condensation reaction using the enzyme ATP synthase

  ADP + Pi = ATP + H2O
• how is the energy from ATP released?


  ATP is hydrolysed using the enzyme ATP hydrolase

  ATP + H2O = ADP + Pi

  breaking one of the bonds between the phosphate releases a small amount of energy
• what can happen with the phosphate from hydrolysing ATP?


  the inorganic phosphate released can bond onto completely different compounds to make them more reactive (phosphorylation)
• what is the full name of DNA?

  deoxyribonucleic acid
• what doe DNA code for?


  this codes for the sequence of amino acids which is the primary structre of a protein
• polymers form a double helix made of two antiparallel strands joined together by hydrogen bonds between bases on tow different strands
• how does DNAs structure relate to its function?

  • stable structure due to sugar phosphate backbone and double helix
  • double stranded so both strands can act as a template strand in replication
  • weak hydrogen bonds between bases so its easy to separate the two strands
  • a large molecule that carries a lot of information
  • complementary base paring allows identical copies
• what types of RNA are there?

  mRNA, tRNA + rRNA
• what is mRNA?


  a copy of one gene from DNA

  created in the nucleus and it leaves through the nuclear pores to carry a copy to the ribosome
• some factors of mRNA?

  • much shorter than DNA
  • short lived
  • single stranded and every 3 bases in the sequence code for one specific amino acid (codons)
• what is tRNA?


  found in the cytoplasm

  • it is single stranded
  • held in place by hydrogen bonds
  • brings specific amino acids to the ribosome
  • this is determined by the 3 bases found on the tRNA (anticodon) which are complementary to the 3 bases on the mRNA (codon)
• what is semi conservative DNA replication


  DNA replication is described as semi conservative because:

  • one strand is conserved
  • one new strand is created
  • copying errors in DNA replication can happen (random)
  • this can change the DNA base sequence (mutation)
• when does replication occur in the cell cycle?


  S-phase in interphase
• DNA double helix the top and bottom of each strand are described as either 3'(prime) end or the 5' (prime) end.

  The number refers to which carbon is the closest to the top or bottom
• The enzyme catalyses DNA replication is complementary to the 3' end so it can only attach there
• Stages of DNA replication:

  1. DNA helicase breaks the hydrogen bonds between complementary bases
  2. both strands act as templates
  3. free floating DNA nucleotides complementary base pair on the template strands and hydrogen bonds form
  4. DNA polymerase joins adjacent DNA nucleotides together and form phosphodiester bonds
• what feature does the genetic code have?

  • degenerate
  • universal
  • non-overlapping
• what is degenerate code?

  amino acids are coded for by more than one triplet of bases
• what is universal code?


  the same triplet of bases codes for the same amino acid in all organisms
• what is non-overlapping code?


  each base in a gene is only part of one triplet of bases that codes for one amino acid. Each codon, or triplet of bases is read as a discrete unit
• introns 


  sequences of bases in a gene that do not code for amino acids and are removed from the mRNA through splicing
• exons 


  are sequences of bases in agene that code for sequences of amino acids
• transcription 


  where DNA sequence for one gene is copied into mRNA
• translation


  where the mRNA joins with a ribosome (made of protein and rRNA) and a corresponding tRNA molecule brings the specific amnio acid the codon codes for
• Transcription

  the process

  • DNA helicase breaks the hydrogen bonds between the bases
  • one strand acts as a template
  • free mRNA nucleotides align opposite exposed complementary DNA bases
  • the enzyme RNA polymerase joins together the adjacent RNA nucleotides, forming phosphodiester bonds to create a new mRNA polymer chain
  • once one gene is copied the mRNA is modified and then leaves the nucleus through the nuclear envelope pores
• Translation


  1. modified mRNA leaves nucleus

  2. Attaches to small ribosome subunit at start codon

  3. tRNA with complementary anticodon aligns opposite mRNA held by ribosome

  4. Ribosome holds 2 tRNA at a time

  5. Amino acids joined by peptide bond catalysed by enzyme using ATP

  6. Ribosome moves to next codon, complementary tRNA attaches

  7. Continues until ribosome reaches stop codon, causing ribosome to detach and end translation