DNA

• Contains genetic information and determines the structure and the way the cell functions
• made of small repeating units called nucleotides

  • sugar molecule deoxyribose
  • phosphate group
  • nitrogenous base
  • adenine, thymine, cytosine, guanine
• the sugar molecule bonds to phosphate group of adjacent nucleotide, creating a chain of alternating sugars and phosphates. makes sugar phosphate backbone
• two strands of DNA are joined by weak hydrogen bonds between specific bases (A and T ; C and G)
• two strands twist to form a double helix shape
• DNA strands are wrapped around group of eight special proteins called histones to form a nucleosome. there are many along a DNA molecule
• in a non-dividing cell, coiled DNA forms a tangled network called chromatin
• in a dividing cell, coiled chromatin becomes more tightly coiled called chromosomes which are large enough to be seen by light microscope 
• Each chromosome is made of sections of DNA that code for particular protein, each section is called a gene
• mitochondrial DNA is a small circular molecule not bound to proteins
• there's about 5 - 10 molecules of mtDNA in each mitochondrion
• mtDNA contains 37 genes, all are essential for mitochondrion to function normally

  • 24 contain code for making transfer RNA (tRNA) - involved in protein synthesis
  • 13 have instructions for making some enzymes necessary for reaction of cellular respiration 
• DNA replication is the production of an identical copy of DNA
• 3 steps of DNA replication :

  1. two stands of DNA are separated by the enzyme helicase which is possible because the hydrogen bonds are weak and easily broken
  2. DNA polymerase adds new nucleotides to strands and DNA ligase joins short sections of DNA together
  3. two identical copies of DNA are formed