Biology chapter 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 a polypeptide or functional RNA
• Locus


  The exact position of a gene on a chromosome
• Genetic code


  • Degenerate
  • Universal
  • Non-overlapping
• Triplet


  A sequence of three bases on DNA that codes for an amino acid
• There are 20 amino acids that can be coded for by the 64 possible triplet combinations
• Introns


  DNA sequences that do not code for polypeptides
• Exons


  DNA sequences that do code for amino acids
• Codon


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


  Three bases that initiate translation
• Stop codon


  Three bases that terminate translation
• Genome


  An organism's complete set of genes
• Proteome


  The full range of proteins a cell can produce
• Bacterial genomes contain around 600,000 DNA base pairs, while human genomes contain 3 billion base pairs
• mRNA


  Single-stranded, shorter than DNA, found in cytoplasm and nucleus
• tRNA


  Has an amino acid binding site and an anticodon that is complementary to an mRNA codon
• Ribosome


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


  1. DNA helix unwinds

  2. One DNA strand acts as template

  3. RNA nucleotides align to complementary DNA bases

  4. RNA polymerase joins RNA nucleotides

  5. Pre-mRNA is modified by splicing out introns

  6. Mature mRNA leaves nucleus
• Translation


  1. mRNA binds to ribosome

  2. tRNA anticodons align to mRNA codons

  3. Ribosome holds two tRNA at a time

  4. Amino acids joined by peptide bonds

  5. tRNA released

  6. Ribosome moves to next codon

  7. Stops at stop codon
• Gene mutation


  Change in DNA base sequence
• Gene mutations


  • Base substitution
  • Base deletion
• Chromosome mutation


  Change in chromosome number
• Non-disjunction


  Chromosomes/chromatids fail to separate equally during meiosis
• Polyploidy


  Change in the whole set of chromosomes (e.g. triploidy, tetraploidy)
• Aneuploidy


  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 (unlike mitosis)
  • Creates genetically different haploid gametes
  • Introduces genetic variation through independent segregation of chromosomes and crossing over
• Meiosis


  Produces haploid gametes, unlike mitosis which produces diploid cells
• Meiosis can be identified in an unfamiliar life cycle by looking for the transition from diploid (2n) to haploid (n) cells
• Genetic diversity


  The number of different alleles of genes in a population
• Natural selection


  1. New alleles created by random mutation

  2. Advantageous alleles more likely to be passed on

  3. Allele frequency changes over generations
• Types of natural selection

  • Directional selection (favours extreme traits)
  • Stabilizing selection (favours middling traits)
• Species


  Organisms able to produce fertile offspring
• Courtship behavior


  • Unique sequence of actions for each species
  • Allows identification of own species
  • Synchronizes mating
  • Helps select for healthy mates
• Phylogenetic classification


  Arranging groups according to evolutionary origins and relationships
• Taxonomic hierarchy


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


  Universal system using genus and species names
• Biodiversity


  Variety of genes, species, and habitats in an environment