molecular genetics

• Chromosomes


  Highly coiled structures containing the genetic information of the organism, known as DNA

  
• Chromatin


  Long thread-like structures found in the nuclei of animal and plant cells, containing the genetic information of the organism, known as DNA

  
• How a DNA molecule forms a chromosome

  1. DNA coils around histones to form chromatin

  2. Chromatin becomes highly coiled to form a chromosome

  
• DNA


  Deoxyribonucleic acid, a molecule that contains the genetic information of the organism

  
• Structure of DNA


  • Two strands of polynucleotides twisted around each other, forming a double helix structure
  • The two strands are anti-parallel, running in different directions

  
• Nucleotide


  Made up of 1 sugar (deoxyribose), 1 phosphate group, and 1 nitrogen base

  
• Sugar-phosphate backbone


  The phosphate group of 1 nucleotide binds with the sugar of the next nucleotide, forming a long structure

  
• Nitrogen bases


  • Adenine (A)
  • Thymine (T)
  • Cytosine (C)
  • Guanine (G)
• Hydrogen bonds


  The two polynucleotide strands are joined together by hydrogen bonds
• Base pair


  Two nucleotides bound to each other by hydrogen bonds
• Complementary base pairing rule

  Adenine always binds with thymine, and cytosine always binds with guanine

  
• Gene


  A segment of DNA that carries the genetic information of a trait, and codes for one polypeptide

  
• DNA is used to carry the genetic code, which is used to synthesise specific polypeptides

  
• How a gene makes proteins

  1. DNA unzips

  2. One polynucleotide strand acts as a template

  3. Every 3 consecutive nucleotides (a codon) codes for 1 amino acid

  4. Amino acids form a polypeptide, which becomes a protein

  
• Transcription


  1. DNA template is used to make a messenger RNA (mRNA)

  2. mRNA is single-stranded and complementary to the DNA template

  3. mRNA exits the nucleus into the cytoplasm towards a ribosome

  
• Translation


  1. Ribosomes in the cytoplasm attach to the mRNA and assemble the amino acids to form a polypeptide

  2. Ribosomes release the completed polypeptide
• Genetic engineering


  Technique used to transfer genes from one organism to another, forming a transgenic organism
• Bacterial transformation

  1. Gene transfer using bacteria as a vector

  2. Isolate human insulin gene and bacterial plasmid

  3. Insert insulin gene into plasmid using DNA ligase

  4. Insert recombinant plasmid into bacteria

  5. Mass produce transgenic bacteria to extract insulin
• Selective breeding vs genetic engineering


  • Organisms must be closely related vs organisms need not be closely related
  • Defective genes may be transmitted vs genes are carefully selected
  • Slow vs fast
  • Less efficient vs more efficient
• Benefits of genetic engineering

  • Low-cost production of medicines
  • Production of crops that grow in extreme conditions
  • Crops that produce toxins to kill insect pests or are resistant to pesticides
  • Food designed to meet specific nutritional goals
• Ethical issues of genetic engineering

  • Modified/new proteins in GM foods might cause allergies
  • Patented crops increase cost or prevent seed production
  • Use of animals in medical research
  • Creating deadly strains for warfare
  • Creation of antibiotic-resistant bacteria, pesticide/herbicide-resistant organisms
  • Social divide due to affordability