Topic 4

• Eukaryotic DNA


  • Longer
  • Linear
  • Associated with histones
• Prokaryotic DNA


  • Circular loops
  • Not associated with proteins
• Mitochondria and chloroplasts have their own circular DNA that is not wrapped around histones
• Gene


  Sequence of DNA that codes for the amino acid sequence of a particular polypeptide and a functional RNA
• Locus


  The exact position that a particular gene is found on a chromosome
• Genetic code


  • Degenerate
  • Universal
  • Non-overlapping
• Triplet


  A sequence of three bases on DNA that codes for a particular amino acid
• There are 20 amino acids but 64 possible triplet combinations
• Introns


  Sequences of DNA bases that do not code for polypeptides
• Exons


  Sequences of DNA bases that do code for amino acids
• Codon


  Three bases on mRNA that code for a specific amino acid
• Start codon


  Three bases at the start of a gene that initiate translation
• Stop codon


  Three bases at the end of a gene that cause the ribosome to detach and stop translation
• Genome


  An organism's complete set of genes in a cell
• Proteome


  The full range of proteins that a cell is able to produce
• Bacteria have 600,000 DNA base pairs in their genome, humans have 3 billion
• mRNA


  Messenger RNA, a single-stranded copy of one gene found in the cytoplasm and nucleus
• tRNA


  Transfer RNA, found in the cytoplasm with an amino acid binding site and an anticodon
• Ribosome


  Holds tRNA molecules in place to enable amino acid bonding during translation
• Transcription


  1. DNA helix unwinds

  2. One DNA strand acts as a template

  3. RNA nucleotides align with complementary DNA bases

  4. RNA polymerase joins RNA nucleotides

  5. Pre-mRNA is modified by splicing out introns

  6. Mature mRNA leaves the nucleus
• Translation


  1. mRNA binds to ribosome

  2. tRNA anticodons align with mRNA codons

  3. Amino acids are joined by peptide bonds

  4. Ribosome moves along mRNA one codon at a time

  5. Ribosome detaches at stop codon
• Gene mutation


  A change in the base sequence of DNA
• Chromosome mutation


  Changes in the number of chromosomes
• Non-disjunction


  Chromosomes or chromatids fail to separate equally during meiosis
• Polyploidy


  A change in the whole set of chromosomes, e.g. triploidy or tetraploidy
• Aneuploidy


  A change in the number of individual chromosomes, e.g. Down syndrome
• Meiosis


  1. Non-disjunction occurs

  2. Gametes are haploid (n) or haploid plus/minus one chromosome (n+1, n-1)

  3. Trisomy occurs (3 copies of a chromosome)
• Meiosis


  • Two nuclear divisions
  • Creates genetically different haploid gametes
  • Independent segregation of homologous chromosomes
  • Crossing over between homologous chromosomes
• Identifying meiosis in life cycles


  Look for 2n to n transition
• Genetic diversity


  • Number of different alleles of genes in a population
  • Enables natural selection
• Natural selection


  1. New alleles created by random mutations

  2. Advantageous alleles more likely to survive and reproduce

  3. Allele frequency changes over generations

  4. Directional selection and stabilizing selection
• Species


  • Organisms able to produce fertile offspring
  • Courtship behavior is unique and essential for successful mating and reproduction
• Phylogenetic classification


  • Arranging groups according to evolutionary origins and relationships
  • Closer branching indicates more recent common ancestor
• Taxonomic hierarchy


  • Domain
  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species
• Binomial nomenclature


  • Genus and species names
  • Universal system to identify organisms
• Biodiversity


  • Variety of habitats, genes, and species in a community
  • Decrease in biodiversity is a concern, often due to human activity
• Measuring biodiversity


  • Index of diversity formula
  • Higher values indicate greater biodiversity
• Genetic diversity can be measured by comparing DNA, mRNA, or amino acid sequences