AoS 1

• Nucleic acids


  Biomolecules that are vital for the continuity of life
• Nucleotides


  Subunits that make up nucleic acids
• Types of nucleic acids

  • Deoxyribonucleic acid (DNA)
  • Ribonucleic acid (RNA)
• DNA


  • Located in chromosomes in the nucleus of eukaryotic cells
  • Contains hereditary information and is transmitted from generation to generation
• RNA


  • Formed against a template strand of DNA
• Nucleotide


  Made up of a 5-carbon pentose sugar, a phosphate group, and a nitrogenous base
• Components of a nucleotide

  • 5-carbon pentose sugar
  • Phosphate group
  • Nitrogenous base
• Nitrogenous bases in DNA

  • Adenine
  • Cytosine
  • Guanine
  • Thymine
• Nitrogenous bases in RNA

  • Adenine
  • Cytosine
  • Guanine
  • Uracil
• DNA


  • Made of two complementary chains of nucleotides that run antiparallel
• DNA


  • Combines with certain proteins, particularly histones, to form a chromosome
• RNA


  • An unpaired chain of nucleotides
  • Contains the sugar ribose
  • Contains uracil rather than thymine
• Main forms of RNA

  • Messenger RNA (mRNA)
  • Ribosomal RNA (rRNA)
  • Transfer RNA (tRNA)
• Genetic code


  Representation of genetic information through a non-overlapping series of groups of three bases (triplets) in a DNA template chain
• The genetic code is universal - the code is essentially the same in bacteria, in plants and in animals
• The same sequence of nucleotides codes for the same amino acid
• Degenerate or redundant genetic code


  Multiple triplets in DNA can lead to the addition of the same amino acid
• The degenerate nature of the genetic code allows for tolerance to mutations, which is important for vital genes
• Gene expression


  1. Transcription: DNA to mRNA

  2. Translation: mRNA to protein
• RNA processing


  Pre-mRNA produced in transcription is processed and made into mature mRNA to be used in translation
• Template strand


  One strand of a DNA double helix that is used to produce a complementary mRNA during transcription
• Non-template strand or coding strand


  One strand of a DNA double helix that is complementary to the template strand
• Transcription


  1. Helicase enables DNA to unzip

  2. RNA polymerase binds to initiation site and moves down template strand adding complementary bases

  3. Termination signal instructs RNA polymerase to stop transcribing
• RNA processing


  1. Introns are cut out, exons are bonded by RNA ligase

  2. Pre-mRNA is modified by adding a methyl cap and poly-A-tail to form mature mRNA
• Translation


  1. Ribosomes bind to mRNA and read the sequence in triplets of bases called codons

  2. tRNA brings relevant amino acid to form peptide bonds

  3. Polypeptide chain is released when ribosomes reach a stop codon
• Coding region of a gene


  Segment of DNA double helix that encodes the information for making a protein
• Flanking regions


  Regions on either side of the coding region of a gene
• Exons


  Contain the instructions for the synthesis of the protein and are both transcribed and translated
• Introns


  Interrupting segments of DNA that are transcribed but cut out in RNA processing and not translated
• Promoter region


  Contains the TATA box, which is rich in A's and T's
• Leader region


  Smaller in prokaryotes, longer in eukaryotes
• Operator regions


  Special sections found in prokaryotic genes where a repressor protein can bind to prevent transcription
• Types of genes


  • Structural genes
  • Regulator genes
• Trp operon


  Contains five structural genes that encode enzymes involved in tryptophan synthesis, with a promoter and operator
• Regulation through repression


  1. Repressor protein binds to operator when tryptophan is present, preventing transcription

  2. Repressor is inactive when tryptophan is absent, allowing transcription
• Regulation through attenuation


  Prevents transcription from being completed, relies on the leader region rather than a repressor
• Amino acid


  Subunits that make up polypeptides, each has an amino group, carboxyl group, and a variable R group
• Formation of polypeptide chain

  Amino acids are joined by peptide bonds in a process of condensation polymerisation that requires energy from ATP
• Levels of protein structure

  • Primary
  • Secondary
  • Tertiary
  • Quaternary
• Primary structure


  The specific linear sequence of amino acids in the protein