Nucleotides & protein synthesis

• Gene - a section of DNA which code for a particular feature (protein)
• Genes are found in the nucleus and is made of nucleotides
• DNA

  • genes are sections of DNA founf on chromosomes
  • genes are instructions for proteins
  • proteins are made of amino acids, and its the order of amino acids that determines the protein
  • in a gene, it is the order of bases in the DNA that determines the order of amino acids in a protein
• Nucleic acids

  • polymer
  • individual unit called a (mono)nucleotide
  • DNA is a type of nucleotide (deoxyribonucleic acid)
• Nucleic structure

  • pentose sugar
  • phosphate
  • organic nitrogenous base
• What is this structure?

  Nucleotide

  
• Nucleic structure:

  there are 4 bases...

  purines - double ringed

  • adenine (a)
  • guanine (g)

  pyrimidines - single ringed

  • thymine (t)
  • cytosine (c)

  a joins to t with 2 hydrogen bonds

  c joins to g with 3 hydrogen bonds
• the base and sugar join with a glycosidic bond

  the phosphate and sugar join with an Esther bond
• DNA replication: (semi-conservative replication)

  1. DNA helicase breaks hydrogen bonds between bases. This unwinds and unzips double helix
  2. each strand acts as a new template as free nucleotides attract to their complementary base pairs
  3. DNA polymerase joins free nucleotides together via condensation reactions. This forms phosphodiester bonds to create a sugar-phosphate backbone
  4. two identical copies (daughter) of DNA are made, made up of one original DNA strand and one new DNA strand
• Transcription - genetic code for a protein is copied in the form of mRNA.
• Translation - genetic code from mRNA is 'read' by tRNA, a sequence of amino acids are assimilated to form a protein.
• DNA vs RNA

  • DNA sugar base is deoxyribose
  • RNA sugar base is ribose
  • DNA bases are A,T,C,G
  • RNA bases are A,U,C,G

  U = uracil
• Transcription

  1. DNA helicase bind to DNA strand (start codon) and unwinds a short section (12)
  2. Free RNA nucleotides will base pair with complementary bases
  3. RNA polymerase travels along DNA strand building an RNA molecule forming phospodiester bonds
  4. transcription stops at the stop codon making mRNA
  5. mRNA is free to move through nuclear envelope to the ribosome
• Translation

  1. mRNA binds with ribosome
  2. tRNA, with complementary anti-condon attaches by hydrogen bonds by RNA polymerase
  3. tRNA carries amino acid corresponding to codon on mRNA, a peptide bond is formed catalysed by peptidyl transferese between the amino acids.
  4. amino acid brought together to form the primary structure of the protein coded for by mRNA
• Degenerate - more than one codon for most amino acids e.g aua, auc, auu = Isoleucine

  Non-overlapping - each set of 3 bases (codons) are read only once
• DNA ---transcription--- mRNA ---tRNA(ribosome)--- translation--- protein synthesis
• DNA

  • deoxyribose
  • bases = A,C,G,T
  • double helix - 2 strands of polypeptides, held together by hydrogen bonds between the bases
• base pairing

  adenine binds to thymine - 2 hydrogen bonds

  cytosine binds to guanine - 3 hydrogen bonds

  • known as complementary base pairs
  • purine (double ringed) binds to pyrimidine (single ringed)
• RNA (ribonucleic acid)

  • transfers genetic information from DNA to proteins
  • pentose sugar - ribose
  • bases - adenine, cytosine, guanine and uracil
  • make polymers with phosphodiester bonds
  • RNA polymers formed are small enough to leave the nucleus and travel to the ribosomes
• dna helicase - enzyme that unwinds and unzips the two stands of the double helix
• dna polymerase - enzyme that catalyses the formation of phosphodiester bonds between the nucleotides
• replication errors is known as a mutation
• triplet code is a sequence of three bases called a codon, which each codon codes for an amino acid
• genetic code is universal as all organisms use this code