Life Science studies

• Monomer


  A building block
• Nucleotide


  The monomer which forms DNA and RNA
• DNA (deoxyribonucleic acid)


  Made up of nucleotides, contains nitrogenous bases adenine, thymine, guanine and cytosine, carries the genetic code for protein synthesis
• Nuclear DNA


  DNA found in the nucleus
• Extra-nuclear DNA


  DNA found outside of the nucleus: mitochondrial and chloroplastic DNA
• Double helix


  The shape of DNA consists of two strands joined together and twisted spirally
• Hereditary


  Genetic information passed on from parent to offspring
• Rosalind Franklin and Maurice Wilkins researched the structure of DNA using X-ray diffraction images


  1952
• Watson and Crick proposed a 3-D double helix model for DNA


  1953
• Watson and Crick received the Nobel Prize for the discovery of the structure of DNA, and Wilkins received an award for his X-ray photography


  1962
• DNA is found mostly in the nucleus of a cell (nuclear DNA) and a small amount is found outside the nucleus (extra-nuclear DNA)
• Discovery of DNA


  1. 1952 - Rosalind Franklin and Maurice Wilkins researched DNA structure using X-ray diffraction

  2. Watson and Crick did independent research on DNA

  3. 1953 - Watson and Crick proposed 3-D double helix model for DNA

  4. 1962 - Watson and Crick received Nobel Prize for discovery of DNA structure, Wilkins received award for X-ray photography
• Rosalind Franklin died of cancer before the Nobel Prize was awarded
• P


  Phosphate group
• S


  Sugar molecule
• NB


  Nitrogenous base
• Locations of DNA


  • Mostly in the nucleus (nuclear DNA)
  • Small amount outside nucleus (extra-nuclear DNA: chloroplastic DNA, mitochondrial DNA)
• DNA structure


  • Double helix
  • Monomers called nucleotides link to form long chains (polymers)
  • Sugar is deoxyribose, attached to nitrogenous base
  • Phosphate and sugar molecules attached alternately
• Nitrogenous bases in DNA

  • Adenine (A)
  • Cytosine (C)
  • Thymine (T)
  • Guanine (G)
• Nitrogenous base pairing


  • Adenine always links to thymine
  • Guanine always links with cytosine
• Nitrogenous bases are held together by weak hydrogen bonds
• DNA strands wind around proteins called histones
• Role of DNA


  • Carries hereditary information in the form of genes
  • Genes code for specific traits and determine physical characteristics and behaviour
  • Most DNA does not code for anything (non-coding DNA)
• Main functions of DNA

  • Controls cell functioning
  • Regulates gene functioning
  • Passes on hereditary characteristics
• RNA


  Ribonucleic acid, consists of nucleotides with nitrogenous bases adenine, uracil, guanine and cytosine
• Messenger RNA (mRNA)


  Carries code for protein synthesis from DNA to ribosome
• Ribosomal RNA (rRNA)


  Forms ribosomes, site of protein synthesis
• Transfer RNA (tRNA)


  Brings amino acids to ribosome to form protein
• Locations of RNA


  • mRNA formed in nucleus, enters cytoplasm
  • rRNA found in ribosomes in cytoplasm
  • tRNA found freely in cytoplasm
• Structure of RNA


  • Single-stranded, not coiled
  • Sugar is ribose, attached to nitrogenous base
  • Phosphate and sugar molecules attached alternately
• Nitrogenous bases in RNA

  • Adenine (A)
  • Uracil (U)
  • Cytosine (C)
  • Guanine (G)
• Role of RNA


  • Important for protein synthesis, each type has unique role
• Differences between DNA and RNA

  • DNA contains deoxyribose sugar, RNA contains ribose sugar
  • DNA is double helix and coiled, RNA is single-stranded
  • DNA contains thymine, RNA contains uracil
  • DNA found in nucleus, RNA found in nucleus, ribosomes and cytoplasm
• DNA replication


  1. DNA double helix unwinds

  2. Hydrogen bonds between nitrogenous bases break, strands separate

  3. Each original strand acts as template for new complementary strand

  4. Free nucleotides build new strands, attaching complementary bases

  5. Results in two identical DNA molecules
• DNA replication is important for cell division, particularly mitosis
• Errors in DNA replication may lead to mutations, changing gene structure
• DNA profiling


  1. Pattern of lines of different lengths and thicknesses produced on X-ray film

  2. Unique to each individual except identical twins

  3. Used to identify crime suspects, prove paternity/maternity, determine genetic defects, establish tissue compatibility, identify relatives
• DNA profiling is generally accepted as extremely reliable
• Reasons DNA profiling may be challenged

  • Humans interpret results, mistakes possible
  • Profiling methods may differ between labs, producing inconsistencies
  • Only small DNA sample used, profile may not be 100% unique
  • DNA profiling is expensive, not readily accessible
• DNA profiles may reveal prejudicial information about a person