Life science

• Monomer


  A building block
• Nucleotide


  The monomer which forms DNA and RNA

  
• DNA (deoxyribonucleic acid)


  Made up of nucleotides, contains the 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)
• Ribosomes are small, round organelles which are mainly found attached to the endoplasmic reticulum or are free-floating in the cytoplasm. Ribosomes can also be found inside other organelles such as the chloroplast and mitochondria but in smaller numbers. They are the site of protein synthesis and consist of RNA and protein.
• The nucleus controls all of the cell's activities.
• Parts of the nucleus

  • Double nuclear membrane
  • Nucleoplasm
  • Nucleolus
  • Chromatin network
• There are two types of nucleic acids in the human body - DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Together these form the basis of all life on earth. They consist of monomers (building blocks) called nucleotides.
• The basic structure of a nucleotide is composed of a phosphate (P), a sugar molecule (S) and a nitrogenous base (NB).
• DNA


  Double helix - the shape of DNA consists of two strands joined together and twisted spirally

  
• Discovery of DNA


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

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

  3. 1962 - Watson and Crick received Nobel Prize, Wilkins received award for X-ray photography
• Rosalind Franklin background: https://www.youtube.com/watch?v=BIP0lYrdirI
• P


  Phosphate group
• S


  Sugar molecule
• NB


  Nitrogenous base
• Locations of DNA


  • Nucleus (nuclear DNA)
  • Chloroplasts (chloroplastic DNA)
  • Mitochondria (mitochondrial DNA)

  
• DNA structure


  • Double helix
  • Monomers called nucleotides link to form long chains (polymers)
  • Sugar is deoxyribose
  • Nitrogenous bases: adenine, cytosine, thymine, guanine

  
• Nitrogenous base pairing


  • Adenine always links to thymine
  • Guanine always links with cytosine
• DNA strands


  • Joined by weak hydrogen bonds, forming a ladder-like structure
  • Coiled and wound 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
• RNA


  Ribonucleic acid, consists of nucleotides with nitrogenous bases: adenine, uracil, guanine, 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


  • Nucleus (mRNA)
  • Cytoplasm (rRNA, tRNA)
• Structure of RNA


  • Single-stranded, not coiled
  • Sugar is ribose
  • Nitrogenous bases: adenine, uracil, cytosine, guanine

  
• Roles of RNA


  • Important for protein synthesis
• Differences between DNA and RNA

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

  
• DNA replication


  1. DNA double helix unwinds

  2. Hydrogen bonds between 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

  
• Significance of DNA replication
• DNA profiling


  Pattern produced on X-ray film, consisting of lines of different lengths, thicknesses and positions. Unique to each individual except identical twins.
• Uses of DNA profiling

  • Identify crime suspects
  • Prove paternity and maternity
  • Determine genetic defects
  • Establish tissue compatibility for transplants
  • Identify relatives