nucleic acids

• nucleotides are used to make up nucleic acids
• nucleotide is made from

  • a pentose sugar
  • nitrogenous base
  • phosphate group
• all nucleotides contain the elements C, H, O, N and P
• nucleotides are monomers that make up the DNA and RNA
• 4 possible bases

  • adenine
  • thymine
  • cytosine
  • guanine
• purines

  Adenine and Guanine, they have 2 carbon rings
• pyrimidines

  Cytosine and Thymine have 1 carbon ring
• how many H bonds between adenine and thymine

  • 2 hydrogen bonds in-between
• how many H bonds between cytosine and guanine

  • have 3 H bonds
• • the nucleotides join up between the phosphate group of 1 nucleotide and the sugar of another forming a phosphodiester bonds
  • the chain of sugars and phosphate is known as the sugar-phosphate back bone
• • 2 polynucleotide strands join together by hydrogen bonds between complementary bases
  • 2 antiparallel stands twist to form the DNA double helix
• semi-conservative

  • unwinds - double helix untwisted by gyrase enzyme
  • unzips - DNA helicase breaking the hydrogen bonds
  • each original strand acts as a template for a new strand, free-floating DNA nucleotides join to exposed bases
  • DNA polymerase catalyses the addition of the new nucleotide bases
  • the leading strand is synthesised continuously whereas the lagging strand is in fragments that are later joined catalysed by ligase enzymes
• during DNA replications errors may occur and the wrong nucleotide maybe inserted

  • this could change the genetic code
• a gene is a sequence of DNA that codes for a polypeptide

  • each amino acid is coded for a sequence of three bases
• DNA is copied into RNA for protein synthesis

  • DNA molecules are found in the nucleus of the cell, the organelles that make proteins(ribosomes) are found in the cytoplasm
  • DNA is too large to move out of the nucleus so a section of the DNA is copied into mRNA = transcription
  • the mRNA leaves the nucleus and joins with a ribosome in the cytoplasm where it can be used to synthesis a protein = translation
• • the genetic code is non-overlapping and is read from a fixed point in groups of 3 bases, if a base is added or deleted then it causes a frameshift
  • genetic code is degenerate = there is more than 1 base triplet means that amino acids are coded for by more than one base triplet
  • universal = the same specific base triplets code for the same amino acid in all living things
• transcription

  • a gene unwinds and unzips
  • H bonds between the bases break
  • RNA polymerase catalyses the formation of temporary H bonds between RNA nucleotides and their complementary unpaired DNA bases
  • when RNA polymerases reaches the stop codon it stops making mRNA and detaches from the DNA
  • mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome
• translation

  • tRNA moves towards the ribosomes and contains amino acid binding site and an anticodon which is complementary to the mRNA codon
  • a second tRNA molecule attaches itself to the next codon
  • rRNA catalyses the formation of peptide bonds between the amino acids
  • continues until there's a stop codon on the mRNA molecule