Genetic Information, Variation & Relationships

• DNA


  Carries genetic information
• RNA


  Transfers genetic information from DNA to ribosomes
• Components of a DNA nucleotide

  • Deoxyribose
  • Phosphate group
  • Adenine
  • Cytosine
  • Guanine
  • Thymine
• Components of an RNA nucleotide


  • Ribose
  • Phosphate group
  • Adenine
  • Cytosine
  • Guanine
  • Uracil
• Purine bases


  Adenine and guanine
• Pyrimidines


  Thymine, uracil and cytosine
• Phosphodiester bonds


  Formed in condensation reactions to join nucleotides
• DNA molecule


  Double helix composed of two polynucleotides joined by hydrogen bonds between complementary bases
• RNA


  Relatively short polynucleotide chain
• Genetic code


  Order of bases on DNA, consisting of triplets of bases coding for particular amino acids (codons)
• Gene


  Sequence of bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain
• Locus


  Location of a gene
• Introns


  Non-coding sections of DNA
• Exons


  Coding regions of DNA
• Genetic code


  • Non-overlapping
  • Degenerate
  • Contains start and stop codons
• Each amino acid is coded for by one or more combination of triplets, resulting in 64 possible triplets
• Genes are separated by non-coding repeats of bases
• A change in the base sequence of DNA alters the amino acid sequence and the protein, which can have various effects
• Harmful mutations


  • Cystic fibrosis
  • Sickle cell anaemia
• Eukaryotic cells


  DNA molecules are long and linear, found in the nucleus and associated with histones to form chromosomes
• Prokaryotic cells


  DNA is short and circular, not associated with proteins
• Humans have 46 chromosomes in every cell, arranged into homologous pairs
• Homologous pair


  Two chromosomes that carry the same genes, but can carry different alleles
• Allele


  Alternative form of the same gene
• Transcription


  Occurs in the nucleus, involves DNA and mRNA
• Translation


  Involves mRNA, tRNA and ribosomes
• mRNA


  Long single strand created during transcription, complementary to DNA
• tRNA


  Small molecule made up of around 80 nucleotides, folded into a clover leaf shape with an amino acid attachment site and an anti-codon
• Transcription


  DNA uncoils, one strand used as template to make mRNA, mRNA moves out of nucleus
• Translation


  mRNA attaches to ribosome, tRNA collects amino acids and carries them to ribosome, amino acids join by peptide bonds to form polypeptide chain
• Ribosomes can join up to 15 amino acids per second, and up to 50 ribosomes can move along the same mRNA strand
• Substitution mutation


  One nucleotide in the DNA sequence is replaced by another
• Deletion mutation


  A nucleotide in the DNA sequence is lost, leading to a frameshift
• Polyploidy


  Changes in the whole set of chromosomes, resulting in more than two sets
• Non-disjunction


  Chromosomes fail to separate correctly in meiosis, resulting in gametes and zygotes with one more or one less chromosome
• Down's syndrome is the result of non-disjunction, where individuals have an extra chromosome 21
• Meiosis


  • Produces genetically different haploid daughter cells through independent assortment of chromosomes and crossing over of chromatids
• Genetic diversity is the total number of different alleles in a population, and greater genetic diversity increases the chance of a population surviving changes in their habitat
• Niche


  The role of a species within its environment
• Stages of Meiosis


  1. Meiosis 1: Homologous chromosomes pair up, crossing over may occur, cell divides with each daughter cell containing one chromosome from each homologous pair

  2. Meiosis 2: Chromatids of each chromosome are separated producing 4 haploid daughter cells