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Chapter 4 – Genes & DNA

Chapter 4 – Genes & DNA. Section 1 – What Does DNA Look Like. Genes Gives instructions for building and maintaining cells Able to be copied so cell can divide. Nucleotides. DNA made of subunits called nucleotides Each nucleotide has: Sugar Phosphate Base

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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

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