Molecular genetics

• Proteins are synthesised in the nucleus, rough endoplasmic reticulum and ribosomes
• Nucleotide


  The basic unit of DNA, made up of a deoxyribose (sugar) molecule, a phosphate group, and a nitrogen-containing base (adenine, thymine, guanine, or cytosine)

  
• Joining nucleotides

  Condensation reaction
• Polynucleotide


  Nucleotides joined together to form a long chain
• Complementary base pairing

  • Adenine (A) bonds with thymine (T)
  • Guanine (G) bonds with cytosine (C)
• DNA is condensed into chromatin and then chromosomes to fit into the cell nucleus
• Chromosome


  A condensed structure of DNA and protein visible only during cell division
• There are 46 chromosomes (23 pairs) in a human cell
• Gene expression and protein synthesis

  1. Transcription (DNA to mRNA in nucleus)

  2. Translation (mRNA to polypeptide in cytoplasm)
• Transcription


  The process of converting DNA codons into RNA codons
• Translation


  The process of converting RNA codons into a polypeptide chain
• DNA contains adenine, thymine, guanine and cytosine, while RNA contains adenine, uracil, guanine and cytosine
• Differences between DNA and RNA

  • DNA is a permanent molecule in the nucleus, RNA is a temporary molecule
  • DNA has a deoxyribose sugar, RNA has a ribose sugar
  • DNA has a fixed A:T and G:C ratio, RNA has no fixed ratio

  
• Translation

  Amino acids are attached to tRNA, ribosomes move along mRNA to synthesise polypeptide
• Gene mutation

  Change in DNA sequence lead to mutation in mRNA sequence during transcription

  May lead to wrong amino acid /polypeptide sequence being coded during translation

  Wrong three dimensional structure of protein

  Loss of shape of active site and subsequent loss of function of protein
• Gene mutations leading to observable phenotypes

  • Albinism (defect in enzyme producing melanin)
  • Sickle-cell anaemia (single amino acid change in haemoglobin)
• bond between amino acid

  peptide bond
• Genetic Engineering

  Genetic engineering refers transfer of foreign genes from one organism to another via human intervention or artificial means.
• Vector molecule


  DNA molecule that is used to carry the gene or genes to be transferred
• Plasmids

  Circular DNA from bacteria commonly used as vectors
• DNA ligase is used to anneal the vector with gene of interest
• In order to obtain large amounts of human insulin, large amounts of transgenic bacteria need to be cultured.

  • using large fermenters
• Large-scale fermenters

  • pH controller ensures that the pH is kept optimum
  • Nutrient broth contains essential nutrients for bacterial growth
  • Sparger is a metal ring with tiny holes through which sterile air enters the fermenter
  • Impeller ensures that oxygen and nutrients are evenly distributed
  • Cooling jacket helps keep the temperature of the broth optimum for bacterial growth and enzyme activity
• Other applications of genetic engineering

  • Creation of transgenic organisms that are resistant to diseases / extreme weather conditions
  • Creation of transgenic plants that are pest-resistant
  • Create animals that grow faster for human consumption
  • Gene therapy – healthy genes can be transferred from one person to another person with defective genes
• Effects of Genetic Engineering on Society

  • Environmental hazards
  • Economical hazards
  • Health hazards
  • Social / Ethical hazards
• Genetically-modified (GM) crop plants that produce insect toxins may result in: deaths of insects that feed on them and may result in loss of biodiversity, insects that feed on GM crops which adapt and develop resistance to the toxins, herbicide resistant plants and weeds cross-breeding to create superweeds.
• Gene inserted during gene therapy may cause DNA mutation in host, thus causing patient to develop cancer
• Gene


  A sequence/segment of DNA that codes for the formation of a specific polypeptide
• DNA


  A molecule containing many genes
• Chromosome

  The condensed structure of DNA with proteins/histones visible only during cell division
• Gene, DNA and chromosome


  • All are made up of double helix/two strands of polynucleotides
  • All are made up of the four bases (A, T, C, G) via complementary base pairing
• Relationship between Gene, DNA and chromosome

  • Gene is a sequence/segment of DNA that codes for the formation of a specific polypeptide
  • A DNA molecule contains many genes
  • Chromosome is the condensed structure of DNA with proteins/histones visible only during cell division
• Function of DNA


  To carry the genes which code for the synthesis of specific polypeptides for all cellular functions
• Structure of DNA

  1. Double helix structure, made up of two polynucleotide chains twisted around each other

  2. The two polynucleotide chains are held together by hydrogen bonding between complementary nitrogenous bases, Adenine to Thymine and Cytosine to Guanine based on complementary base pairing rule

  3. Each polynucleotide chain is made up many nucleotides, adenine, thymine, cytosine and guanine

  4. Each nucleotide is made up of a nitrogenous base, a phosphate group and a deoxyribose sugar
• Change in DNA sequence

  • Leads to mutation in mRNA sequence during transcription
  • May lead to wrong amino acid/polypeptide sequence being coded during translation
  • Wrong three dimensional structure of protein
  • Loss of shape of active site and subsequent loss of function of protein
• Advantages of genetic engineering

  • Genes from an organism can be inserted into non-related species to express the desired trait
  • Low cost mass production
  • Development of foods designed to meet specific nutritional goals
  • Production of crops that can adapt to grow in extreme conditions/resistant to pest and herbicides to increase yield
• Disadvantages of genetic engineering

  • Environmental impact: BT corn toxins may kill too many insects, causing natural food chain imbalance; Pests may adapt and develop resistance to the toxins; Superweeds can be created
  • Social & health impact: GE could introduce allergens in food; Viral/bacterial vectors used during gene therapy may revert to virulent origin; Modifying a single gene in plants could result in the formation of toxins; Gene inserted during gene therapy may cause DNA mutation in host, thus causing patient to develop cancer; Genes that code for antibiotic resistance may be transferred into pathogenic bacteria
  • Ethical impact: Lack of approval from certain religions regarding GE as it may not be appropriate to alter the natural genetic make-up of organisms
  • Economic impact: The company that first engineered the GM seed can patent their GM food/gene therapy technology in obtaining economic monopoly to prevent others from profiting
• Gene, DNA and chromosome

  • All are made up of double helix/two strands of polynucleotides
  • All are made up of the four bases (A, T, C, G) via complementary base pairing
  • Gene is a sequence/segment of DNA that codes for the formation of a specific polypeptide
  • A DNA molecule contains many genes/not all parts of DNA are genes
  • Chromosome is the condensed structure of DNA with proteins/histones visible only during cell division
• Function of DNA


  To carry the genes which code for the synthesis of specific polypeptides for all cellular functions
• Structure of DNA

  • Double helix structure, made up of two polynucleotide chains twisted around each other
  • The two polynucleotide chains are held together by hydrogen bonding between complementary nitrogenous bases, Adenine to Thymine and Cytosine to Guanine based on complementary base pairing rule
  • Each polynucleotide chain is made up of many nucleotides, adenine, thymine, cytosine and guanine, and each nucleotide is made up of a nitrogenous base, a phosphate group and a deoxyribose sugar