TOPIC 4 - GENETIC INFORMATION/VARIATION/RELATIONSHIP

• Introns

  • non-coding sequence of DNA
• Exons

  • sequences of DNA that code for amino acids
• What is splicing?


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• Genome

  • the complete set of genes in a cell
• Proteome

  • The full range of proteins that a cell is able to produce
• Anticodon

  • 3 bases on the tRNA which are complementary to the codon on mRNA.
• mRNA structure

  • single-stranded
  • made up of codons 
  • a copy of one gene
• tRNA structure


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• mRNA function

  • a copy of a gene from DNA created in the nucleus, and it then leaves the nucleus
  • to carry the copy of the genetic code of one gene to a ribosome in the cytoplasm
• tRNA function

  • a specific amino attaches at the binding site
  • transfers this amino acid to the ribosome to create the polypeptide chain
• Transcription


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• Translation

  • the second stage in protein synthesis
  • the polypeptide chain is created using both the mRNA base sequence and the tRNA
  • occurs on ribosomes in the cytoplasm
• Which enzymes are involved in transcription?

  • DNA helicase
  • RNA polymerase
• DNA helicase

  • catalyses the breaking of hydrogen bonds between the two strands of DNA
• RNA polymerase

  • joins adjacent RNA nucleotides together
  • forming a phosphodiester bond
• pre-mRNA

  • mRNA in eukaryotes that still contains the introns
• How is pre- mRNA modified?

  • the introns are removed by a protein called a spliceosome
  • this leaves just the exons
• What is ATP used for in translation?

  • forming the peptide bond between amino acids
• Haploid

  • one copy of each chromosome in a cell
• Diploid

  • two copies of each chromosome in a cell
• Meiosis

  • cell division that creates genetically different gametes
  • there are two nuclear divisions in this process
  • results in four haploid daughter cells
• Independent segregation

  • homologous pairs of chromosomes randomly line up opposite each other at the equator of the cell
  • when they separate it creates a large number of possible combinations of chromosomes in the daughter cells produced
• Crossing over


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• Gametes

  • sex cells (sperm and egg)
• How does meiosis introduce variation?

  • crossing over
  • independent segregation
• Types of gene mutations

  • deletion
  • substitution
• What is a frameshift?

  • the removal of one base changes all of the subsequent codons
  • all the bases shift back one position
• Chromosome mutation

  • change in the number of chromosomes
  • occurs during meiosis
• Deletion mutation

  • a gene mutation
  • a base is removed from a sequence
  • causes a frameshift
• Substitution mutation

  • a gene mutation
  • a base is swapped for a different one
• Non-disjunction


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• Polyploidy


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• Aneuploidy

  • a change in the number of individual chromosomes
  • e.g 3 copies of chromosome 21
• Down's syndrome

  • causes by a chromosome mutation
  • an example of aneuploidy 
  • 3 copies of chromosome 21
• Genetic diversity

  • the number of different alleles in a population
• Natural selection

  • the process that leads to evolution in populations
  • results in species becoming better adapted to their environment
• Gene pool

  • all the genes and alleles in a population at a particular time
• Allele frequency

  • the proportion of organisms within the population carrying a particular allele
• Evolution

  • the change in allele frequency 
  • over many generations in a population
• Selection pressure

  • factors that affect the survival of an organism
  • the driving force of natural selection