DNA & RNA

• Genetic analysis has revealed that genes are "on" chromosomes:

  • segregation of alleles in meiosis
  • association of inherited traits with chromosomal position
• Chromosomes of higher organisms contain DNA and protein
• The complexity of enzymes led to a consensus that genes must be protein
• Acceptance that DNA is the genetic information came slowly from:

  • evidence that only purified DNA could "transform" bacteria
  • experiments showing that only viral DNA penetrated host cells and appeared in progeny, not the viral protein
• DNA and RNA are abundant in nuclei in cells of higher organisms
• DNA and RNA are polymers of nucleotides
• Each nucleotide has a nitrogenous base attached to a sugar which also has 1, 2, or 3 phosphates attached
• Sugar in RNA nucleotides is ribose
• Sugar in DNA nucleotides is deoxyribose
• 2 kinds of bases in RNA and DNA nucleotides:

  • purines have a double ring structure
  • adenine
  • guanine
• Pyrimidines are single, 6 member rings

  • thymine and cytosine found in DNA
  • uracil and cytosine found in RNA
• The first nucleotide in the chain has a phosphate not involved in the sugar-phosphate "backbone" linkages
• Sequence of nucleotides provides the information content of DNA or RNA
• Double helix structure of DNA discovered in 1953 by Watson and Crick
• Two strands are held together by hydrogen bonds between A and T and between G and C, which are called base pairs
• A and T share 2 hydrogens
• G and C share 3 hydrogens
• DNA and RNA are complimentary
• Strands run in opposite directions
• DNA replicates in a semi-conservative fashion; each strand of a double helix serves as the template for making a new complimentary strand
• Unwinding a helix requires a gyrase and a helicase
• Single stranded regions must be protected by single-stranded-binding proteins
• DNA polymerase connects the deoxynucleotides once they are lined up, but it works 5' to 3' direction only and requires a primer to get started
• Replication initiates at sites called "origins of replication" that are defined sequences rich in AT for easy melting
• Proteins are polymers of amino acids
• Most proteins are made via translation of mRNA
• Proteins

  • polymers of amino acids
  • may be enzymes, structural components, hormones, etc
  • most are made via translation of mRNA
  • many are made in a longer 'pre' form and edited
  • many are targeted to specific locations
  • may require 'chaperones' to fold correctly
  • do have a 'half life'; must be replaced as needed
  • can be degraded when not needed or non-functional
• peptide bond formation: the linear chain of amino acids is created by hooking the carboxy end of one amino acid to the amino group of the next, with the removal of an H2O
• Begins with amino terminal and ends with carboxyl