DNA Structure and Fuction

DNA Scientists

  • Miescher (1869): First to extract DNA
  • Avery, McCarty, MacLeod (1944): Determined that DNA was the genetic information that people inherit
  • Chargaff (1950): Base pair rule
  • Watson & Crick (1953): Determined that DNA was a double helix
  • Crick (1957): Protein synthesis (transcription & translation)
  • Berg, Boyer, Cohen (1977): Figured out DNA sequencing

DNA Structure

  • DNA is a double helix made of nucleotides
    • The nucleotide is made up of a phosphate, sugar (deoxyribose), and a nitrogenous base
    • The bases are what store genetic information
    • The bonds between the bases are called hydrogen bonds
    • A bonds to T and C bonds to G
    • T and C are pyrimidines (one ring)
    • A and G are purines (two rings)
  • The nucleotides run in opposite directions
    • The 3’ end has a OH-
    • The 5’ end has a phosphate group
  • The coding region of DNA is called the exon and the non-coding region is the intron

RNA Structure

  • RNA is also made of nucleotides

  • The difference is the ribose sugar

  • RNA is a single strand

  • RNA has the Uracil (U) base instead of Thymine (T)

  • RNA is used to make proteins

  • Types of RNA:

    • mRNA: Messenger RNA (translated to amino acids)
    • tRNA: Complementary to mRNA → brings amino acids to the mRNA
    • rRNA: Ribosomal RNA → makes up ribosome

DNA Replication

DNA is semi-conservative → New strands have 1 old strand and 1 new strand

  1. Helicase breaks hydrogen bonds at the replication fork
  2. Polymerase attaches to a primer (tells polymerase where to attach)
  3. Polymerase is the enzyme that adds complementary bases

   

  1. Polymerase attaches at the 3’ end
    1. Polymerase creates 5’ to 3’ (in the replication fork, this one strand is the leading strand)

   

  1. The lagging strand is the other strand
  2. In the lagging strand, primase adds primers where polymerase creates fragments called Okazaki Fragments
    1. Ligase seals gaps between pairs after primers are removed

Protein Synthesis

Central Dogma: DNA → RNA → Protein

Transcription & Processing
  • Initiation: Polymerase binds to promoter region (tells it where to start)
  • Elongation: Polymerase moves down gene (5’ to 3’) and creates 1 complementary strand → this is called mRNA
  • Termination: Polymerase moves until termination sequence
  • mRNA is processed where the introns are removed and the exons remain. It then leaves the nucleus.
Translation
  • Initiation: Ribosome attaches to start codon (sequence of 3 bases on mRNA)
  • Elongation: tRNA has anticodons (3 bases on tRNA) that are complementary to the mRNA, this brings amino acids
  • Termination: The ribosome reaches a stop codon that releases the amino acid chain
    • The chain of amino acids is called a polypeptide chain, when released they fold to make a protein

Mutations

When DNA is damaged or changed → can be caused by mutagens

Chromosomal Mutations:
  • Affects the whole chromosome
  • Duplication: Section copied
  • Deletion: Section removed
  • Inversion: Section reversed
  • Translocation: Section attaches to different chromosome
  • Aneuploidy: Chromosome nondisjunction where chromosomes don’t separate properly → cells have too many or too few chromosomes
Gene Mutations
  • Change in nucleotide sequence
  • Substitution: Nucleotide replaced
  • Frameshift: Nucleotides inserted or deleted

Vocab:

  • Nucleotide: Makes up DNA → sugar. phosphate, and nitrogenous base
  • Hydrogen Bond: Bond between nitrogenous bases
  • Antiparallel: Strands run in opposite directions 5’→3’ and 3’→5’
  • Phosphodiester Bonds: Bond between 5’ and 3’ end
  • Introns: Non-coding regions
  • Exons: Coding regions
  • Pyrimidines: T & C (one ring)
  • Purines: A & G (two rings)
  • tRNA: transfer RNA has complementary bases to mRNA with the anticodon
  • mRNA: messenger RNA translated to protein
  • rRNA: ribosomal RNA makes up ribosomes
  • Semiconservative: A new DNA strand has one old strand and one new strand
  • Polymerase: Enzyme that adds complementary bases
  • Helicase: Enzyme that splits DNA open
  • Primase: Enzyme that adds primers
  • Ligase: Enzyme that seals gaps after primers are removed
  • Okazaki Fragment: Fragments made on lagging strand
  • Polypeptide: Chain of many peptides (amino acids)
  • Central Dogma: DNA → RNA →Protein
  • Mutations: Changes/Alterations in DNA
  • Mutagenic Factors: Things that can cause changes in DNA