Topic 4

• RNA:

  • Single polynucleotide strand
  • Contains uracil instead of thymine
  • Two types; mRNA and tRNA
• mRNA:

  • made during transcription
  • Carries DNA to the ribosomes
  • Contains groups of 3 adjacent bases (codons/base triplets)
• tRNA:

  • Involved in translation
  • Carries amino acids to the ribosomes
  • Has a clover shape (kept by hydrogen bonds)
  • Has an anticodon on one end
  • Has an amino acid on the other end
• What is transcription?


  Where one gene of DNA is copied into mRNA
• What is translation?


  Where the mRNA joins with a ribosome and corresponding tRNA molecules bring the specific amino acid that the codon codes for.
• Transcription:

  • RNA polymerase attaches to the DNA —-> Hydrogen bonds break, DNA uncoils and separates, 1 strand of DNA is used to make a copy.
  • Complementary mRNA is formed —-> RNA polymerase lines up free RNA nucleotides, complementary base pairing occurs to the exposed DNA bases, Complementary copy has been made (Uracil)
  • RNA polymerase moves down the DNA strand —-> RNA polymerase separates the hydrogen bonds, Hydrogen bonds reform when the enzyme has passed, DNA coils back to a double strand.
• Splicing:

  • Eukaryotes produce pre-mRNA which is then spliced to form mRNA
  • Introns (non-coding) are removed from the pre-mRNA —-> if left, no polypeptides would form.
  • This occurs before the genetic materials leaves the nucleus (via nuclear pores)
  • Doesn’t occur in prokaryotes as the do not contain introns.
• What is splicing?


  The joining together of functional exons once the introns have been removed.
• Synthesising a polypeptide:

  • Ribosome attaches to a start codon (AUG) on mRNA
  • A tRNA with a complementary anti-codon (UAG) will attach to the start codon.
  • Ribosomes moves across to the next codon
  • A peptide bond will form between methionine and the new amino acid
  • This continues until a ribosome reaches a stop codon.
• What is meant by the term homologous?


  When multiple things have identical characteristics
• what is a diploid?


  the total/full set of chromosomes found in a cell
• What is a haploid?


  Half of the total number of chromosomes in a cell
• what is locus/loci?


  The location of the gene on the chromosome
• What happens during meiosis?

  Halves the number of chromosomes so when the gametes fuse during fertilisation, the number of original chromosomes is restored.
• Stages of meiosis:

  • 1st division:
  • Homologous chromosomes pair together
  • Crossing over generally happens
  • Division of the cell
  • Homologous pairs separate into separate cells
  • 2nd division:
  • Chromosomes move apart on each of the individual chromosomes in newly formed cells
  • Cells then divide again resulting in cells being produced (each cell contains 23 chromosomes)
• What is a mutation?


  Any change to the quantity or base sequence of DNA
• What is a gene mutation?


  A change to one or more nucleotide base or a change in the sequence of bases in DNA
• Substitution mutation:

  • Only alters one codon
  • Results in only one amino acid in the protein being changed
  • known as point mutation
  • May or may not effect the polypeptide produced
• Insertion + deletion mutations:

  • Causes a shift in the sequence of bases
  • All codons after that point are altered
  • This is a frame shift
• chromosome mutation:

  • Changes in whole sets of chromosomes occur when organisms have three or more sets rather than the usual two (polyploidy)
  • changes in the number of individual chromosomes can occur due to a failure in separation of chromosomes during meiosis (non-disjunction)
  • This results in a gamete having one more or one fewer chromosome
• What is a species?


  A group of similar organisms that can breed together to produce fertile offspring
• What is genetic diversity?


  The number of different alleles of genes in a species or population
• Two ways genetic diversity in a population can be increased:

  • Mutations in DNA forming new alleles some may be beneficial or detrimental
  • different alleles being introduced to a population when individuals from other populations migrate and reproduce (gene flow)
• What is a genetic bottleneck?


  An event that causes a big reduction in a population
• The founder effect:

  • Describes what happens when just a few organisms from a population start a new colony. Only a small number of different alleles in initial gene flow
  • Frequency of each allele in the new colony might be very different to the frequency of those alleles in the original population
• What are some sources of variation?

  • Mutations
  • Fusion of gametes
  • Independent segregation
  • Crossing over
• What are some examples of selection pressures?

  • Predation
  • Disease
  • Competition for resources
• What is selective advantage?


  Organisms with variations that make them more likely to survive.
• Natural selection:

  • Random mutation occurs in an allele (neutral, harmful or advantageous)
  • Advantageous mutation= better adapted to their environment
  • Individual is more likely to gain resources, grow faster, live longer —> likely to reproduce more
  • Next generation contains a higher proportion of mutated allele
  • Those offspring that inherit the mutated allele are more likely to survive and reproduce successfully
  • Over many generations, the mutated allele will increase in frequency.
• What are aseptic techniques?

  Used to prevent contamination of cultures by unwanted microorganisms which could affect growth of microorganisms you are working with.
• What is a species?

  A group of organisms with similar features in which individuals can reproduce with others to produce fertile offspring (must have the same number of chromosomes)
• Problems with species:

  • Species don’t apply well to microbes or asexual plants
  • over 30 different species concepts
  • still disagreements among scientists on how to define a species.
• What are courtship behaviours?


  Behaviours used to attract a mate of the right species. Can involve the male, female or both.
• Roles of courtship behaviours:

  • Allows members of the same species to recognise each other
  • Prevents interbreeding
  • Increases success of reproduction
• Linnaen classification system:

  • Living organisms are classified into groups depending on their structure and characteristics
  • Every organism is placed into smaller and smaller groups in which the organisms show increasing similarity.
• Phylogenic classification:

  • Based on an organisms evolutionary history and relationships
  • Features —> uses a hierarch, smaller groups are placed within larger groups, there are no overlaps
• Hierarch:

  • Domain
  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species
• Method for comparing evolutionary relationships:

  • Compare the base sequence of DNA or mRNA —> higher percentage of similarity in sequence, the more closely related
  • Compare the sequence of amino acids (proteins) —> base sequence of DNA will affect mRNA which will affect amino acid sequence
  • Immunological comparison —> similar proteins bind to similar antibodies.
• Gene technology:

  • Allows the alleles of an individual to be directly measured
  • Alleles of different versions of a gene and alleles are what gives genetic diversity to a population
• What is meant by intraspecific variation?


  Differences within a species