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Chapter 4 – Genes & DNA

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Chapter 4 – Genes & DNA - PowerPoint PPT Presentation

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Chapter 4 – Genes & DNA

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  1. Chapter 4 – Genes & DNA

  2. Section 1 – What Does DNA Look Like • Genes • Gives instructions for building and maintaining cells • Able to be copied so cell can divide

  3. Nucleotides • DNA made of subunits called nucleotides • Each nucleotide has: • Sugar • Phosphate • Base • 4 Nucleotides due to 4 different bases • Adenine (A) • Thymine (T) • Guanine (G) • Cytosine (C)

  4. Key Players • Erwin Chargaff • 1950s biochemist • Chargaff’s Rules • Amount of adenine = amount of thymine • Amount of guanine = amount of cytosine • Rosalind Franklin • X-ray diffraction to see DNA molecules • DNA has a spiral shape

  5. Key Players Cont’d • James Watson & Francis Crick • Used Franklin’s images • DNA is a long, twisted ladder • Made the double helix model Francis Crick James Watson

  6. DNA Structure • Double helix - twisted ladder model • Sides of ladder • Alternating sugar and phosphate parts • Rungs of ladder • Pairs of bases • A + T OR C + G

  7. Copying DNA • Replication – making copies of DNA • Base pairs are complementary • Each base only pairs with its corresponding base • AT or CG • For example: • ATGCA only pairs with TACGT

  8. Replication • DNA molecule is “unzipped” down the middle • Ladder rungs are cut in half • Complementary nucleotides are added to the 2 strands • 1/2 of DNA molecule is “old” DNA and 1/2 is “new” DNA • Proteins in the cell control the replication process

  9. Section 2 – How DNA Works • Every cell in your body has about 2 meters or 6 feet of DNA! • Packaging DNA • Wound around proteins – histones • Coiled into strands • Bundled into chromosomes • Gene – a string of nucleotides

  10. Genes & Proteins • DNA read in 1 direction from one end to other • Amino acids • Groups of 3 bases give code to form amino acid • For example – CCA is code for amino acid proline • 20 different amino acids • Human body can only produce 10 • Other 10 come from our food – Essential amino acids • Proteins – long strings of amino acids linked together

  11. Proteins & Traits • Proteins have several functions • Chemical triggers • Messengers for processes in a cell • Proteins help determine traits • Genes are the codes for making proteins

  12. RNA & Making Proteins • RNA – Ribonucleic acid • Molecule that helps make proteins • Messenger RNA – mRNA • Copy of a piece of DNA • Moves from nucleus into cytoplasm • Goes into ribosome 3 bases at a time • Transfer RNA – tRNA • translates RNA message into protein • Specific tRNA molecules have certain amino acids attached • tRNA matches up with complementary bases on mRNA • Amino acids released by tRNA • Amino acids link up to produce a protein

  13. protein mRNA amino acid DNA strand copied in nucleus tRNA

  14. Mutations • Mutation – change in the nucleotide-base sequence in the gene or DNA molecule • 3 kinds of mutations • Substitution – wrong base used • Insertion – extra base added in • Deletion – base left out

  15. Do Mutations Matter? • Mutation – change in a gene or DNA • 3 possible outcomes • Improved trait • No change • Harmful trait • Most errors are fixed by proteins • Some become part of genetic code • Mutation in sex cells are passed on to offspring

  16. How do Mutations Happen • Regularly due to random errors during replication • Mutagens – physical or chemical agents that cause mutations • High energy radiation – x-ray, UV ray, cosmic ray • Asbestos • Cigarette smoke • Harmful mutations – sickle cell disease, cancers

  17. Genetic Engineering • Manipulating individual genes in organisms • Create new products • Bacteria engineered to produce drugs • Plants or animals bred for superior qualities • Gene therapy • Replace defective genes with healthy genes • Are there possible dangers?

  18. Genetic Identification • DNA Fingerprinting – identify unique pattern in each person’s DNA • Crime scenes • Family relationships • Trace hereditary disease

  19. Cloning • Clone is an exact copy of another organisms DNA • Identical twins are genetic clones • 3 types of cloning • Somatic cell nuclear transfer – put DNA from one cell into another cell to create an exact copy of the original organism • DNA cloning – put a piece of DNA into another organism. Fluorescent DNA from jellyfish into bacteria to make the bacteria glow • Therapeutic cloning – produce human embryos for medical research using stem cells • Scientific and ethical issues surrounding cloning