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Chapter 11: DNA- The Molecule of Heredity

Chapter 11: DNA- The Molecule of Heredity. 1952: Hershey and Chase Did experiments using radioactive viruses to infect bacteria Discovered DNA was the genetic material of all living things. 1953: Watson and Crick Discovered the structure of DNA

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Chapter 11: DNA- The Molecule of Heredity

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  1. Chapter 11: DNA- The Molecule of Heredity

  2. 1952: Hershey and Chase Did experiments using radioactive viruses to infect bacteria Discovered DNA was the genetic material of all living things 1953: Watson and Crick Discovered the structure of DNA Made up of 2 chains of nucleotides held together by nitrogen bases Double helix History of DNA

  3. DNA in Cells • Located in the nucleus of cells as chromosomes • Packed tightly • Consists of more than 30 million base pairs • Complimentary DNA strands • Can use 1 strand to make a copy of the other strand using base pairing

  4. Nucleotides • Made up of DNA • 3 parts to a nucleotide: • A simple sugar called Deoxyribose • A phosphate group • A nitrogen base

  5. Nitrogen Bases • 4 possible nitrogen bases: • Adenine (A) • Guanine (G) • Cytosine (C) • Thymine (T)

  6. Adenine (A) and Guanine (G) • Double-ringed nitrogen bases • Called purines

  7. Thymine (T) and Cytosine (C) • Single-ringed nitrogen bases • Called pyrimidines

  8. Nucleotides join together to form long chains of complimentary base pairs • Adenine always pairs with Thymine (A-T or T-A) • Guanine always pairs with Cytosine (G-C or C-G)

  9. Structure of DNA • Nitrogen bases of the nucleotides hold 2 strands of DNA together with weak hydrogen bonds • Twisted DNA  double helix

  10. DNA Replication • DNA is copied before cell division • DNA will separate into 2 strands • Carried out by enzymes • Unzips DNA by breaking hydrogen bonds to unwind the double helix • Each strand acts as a template or model to make new DNA strands • Makes new complimentary strands through base-pairing

  11. Example: • TACGTT – Old DNA strand ATGCAA – New DNA strand • After DNA is replicated, DNA will have 1 old strand and 1 new strand

  12. The Genetic Code • Proteins have chains of amino acids • A code is needed to convert messenger RNA (mRNA) into a protein • 20 amino acids • Codon: a group of 3 Nitrogen bases that code for an amino acid • 64 possible combinations of codons • Some code for amino acids • Some code for making proteins • More than 1 codon can code for the same amino acid

  13. Transcription • Making a RNA copy of a part of DNA • Makes messenger RNA (mRNA) • 4 Steps: • Enzymes unzip the DNA • Free RNA nucleotides floating in the cytoplasm base pair with nucleotides on DNA strand (makes mRNA) • mRNA strand breaks away and DNA strands go back together • mRNA leaves nucleus and goes out to the cytoplasm • Result of transcription: formation of 1 single-stranded RNA molecule

  14. Two Types of DNA: RNA and DNA

  15. Messenger RNA (mRNA) • Brings instructions from DNA out of the nucleus and into the cytoplasm • Moves toward the ribosomes

  16. Ribosomal RNA (rRNA) • Binds to messenger RNA • Uses the instructions from DNA to put amino acids in the correct order

  17. Transfer RNA (tRNA) • Delivers the amino acids to the ribosomes to be made into a protein

  18. DNA Controls Protein Synthesis • What are proteins? • Long chains of amino acids • Key structures and regulators of cell functions • Help with structural parts • Enzymes  chemical reactions • Help in transport through cell membrane

  19. Making Proteins • Protein production is similar to building car • DNA provides workers with instructions for making proteins • Workers build proteins (RNA) • Other workers bring parts (amino acids) to the assembly line

  20. Translation • Process of building proteins • Takes place in the ribosomes • Transfer RNA (tRNA) brings amino acids to the ribosomes • Attaches to only 1 type of amino acid • Amino acid will become bonded to 1 side of the tRNA • The other side of the tRNA has 3 nitrogen bases called an anticodon • Pairs up with mRNA codon

  21. Amino acids are joined by peptide bonds • Anticodon bind to the codon of mRNA through base pairing • Example: Codon: CGA Anticodon: GCU • A chain of amino acids form until a stop codon is reached • Translation will end • Amino acid strand is released from the ribosome to become proteins

  22. Mutations • Any change in the sequence of DNA • Can be caused by errors in: • DNA replication • Transcription • Cell division • External agents

  23. Mutations in Reproductive Cells: Birth Defects • Within the egg or sperm cells • Can produce new traits • Can result in proteins that do not work (can kill organism) • Could have positive effects • Faster • Stronger • Important in the evolution of a species

  24. Mutations in Body Cells • Not passed on to offspring • May impair cell function • Can affect genes that control cell division (cancer)

  25. Point Mutation (substitution) • Change in 1 N-base in DNA • Example: CGATTACGC (normal DNA) CGATTTCGC (mutated DNA) • Albinism • Inability to produce pigments • Lethal to plants

  26. Frameshift Mutation • 1 N-base is added or deleted • Changes all codons from that point on • Example: CGATTACGC CGAATTACGC (N-base added) • Example: CGATTACGC CGTTACGC (N-base deleted) • May cause no problems or can be severe • More dangerous than point mutations

  27. Chromosomal Mutations • Involve many genes • Usually very bad • 4 types: • Deletions  taking away • Insertions  adding • Inversions  switching parts (ex: ab ba) • Translocations  breaking off • Many occur from improper separation during meiosis (nondisjunction)

  28. Causes of Mutations • Spontaneous or random mutations • Mutagens (things that cause mutations) • Radiation, X-Rays, UV light, chemicals • Carcinogens

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