Chapter 9 DNA

• deoxyribonucleic acid DNA


  molecule found in cells of all organisms

  contains genetic information that determines the structure of the cell and the way it functions
• nuclear DNA


  most of the DNA located in the nucleus of each cell
• mitochondrial DNA mtDNA


  small amount if DNA found in the mitochondria

  less than 1% of the total DNA in humans, important for the functioning of mitochondria and the cells
• two main types of nucleic acid 


  deoxyribonucleic acid (DNA)

  ribonucleic acid (RNA)
• polymer 


  molecule made up of many repeating units

  DNA
• nucleotides 


  small repeating units in nucleic acids
• each nucleotide is composed of 


  a sugar molecule, a phosphate group and a nitrogenous base
• nitrogen bases in DNA


  adenine (A)

  thymine (T)

  cytosine (C)

  guanine (G)
• sugar molecule of one nucleotide bonds


  to phosphate group of another one

  forms long chain alternating sugars and phosphates, with side chains of bases
• two strands join by

  specific bases being attracted to one another by weak hydrogen bonds
• nitrogen base bonds 


  cytosine bonds to guanine C-G

  adenine bonds to thymine A-T
• double helix 


  two strands of DNA twisting into a spiral shape
• genetic code is determined by 


  order in which the nitrogenous bases occur in a DNA molecule
• gene consists of up to 


  2 million pairs of bases

  possible combinations of base pairs is enormous
• molecules of DNA are in the form of 


  long strands
• size of DNA molecule 


  length: 2-3m

  width: 2millionth of a millimetre
• nuclei of human cells have 


  46 such DNA molecules
• how does DNA fit inside nucleus

  DNA strands are wrapped around a group of eight special proteins called histones to form a nucleosome
• many nucleosomes along 


  length of DNA molecule
• chromatin 


  in a cell that is not dividing coiled DNA forms a tangled network
• chromosomes 


  when a cell divides, coiled chromatin becomes even more tightly coiled

  'super coiled' structures are large enough to be seen with light microscope
• in a normal cell there are 


  46 chromosomes
• gene


  the sections of DNA that make up each chromosomes that code for a particular protein
• mitochondria 


  organelles in cell where aerobic phase of respiration occurs, releasing energy for use by the cell
• mitochondrial DNA 


  small amount of cells DNA located in the mitochondria
• two important difference between nuclear DNA and mtDNA 


  nuclear DNA is in the form of very long strands that are bound to proteins, the histones

  mitochondrial DNA is in the form of small circular molecules that are not bound to proteins
• in each mitochondrion there is 


  5-10 molecules in mtDNA
• mtDNA has 


  37 genes, all which are essential for the mitochondrion to function normally
• 24 of the genes contain 


  code for making transfer RNA (tRNA) molecules, which are involved in protein synthesis
• other 13 genes have 


  instructions for making some of the enzymes necessary for the reactions of cellular respiration
• cell divide through the processes of 


  mitosis and meiosis
• DNA replication 


  in all cell divisions, the DNA must produce an exact copy of itself
• first stage of DNA replication 


  when two strands of the DNA molecule are separated by the enzyme helicase

  separation is possible because hydrogen bond between the base pairs is weak and is therefore easily broken
• each strand of the separated section contains

  half the original information

  each strand serves as a template for the nucleotides that will form the new strand

  new strand that forms is identical to the original
• two enzymes play important roles in the synthesis of new strands 


  DNA polymerase

  DNA ligase
• DNA polymerase 


  enzyme that adds the new nucleotides to the new strand
• DNA ligase 


  enzyme that joins the short sections of DNA together
• genetic code in DNA 


  provides instructions for protein synthesis
• protein synthesis 


  making proteins in the cell
• proteins are produced from 


  amino acids being joined together by peptide bonds