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Chapter 10: DNA

Chapter 10: DNA. Section 2 DNA Structure: Objectives. Evaluate the contributions of Franklin and Wilkins in helping Watson and Crick discover DNA’s double helix structure Describe the three parts of a nucleotide Summarize the role of covalent and hydrogen bonds in the structure of DNA

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Chapter 10: DNA

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  1. Chapter 10: DNA

  2. Section 2 DNA Structure: Objectives • Evaluate the contributions of Franklin and Wilkins in helping Watson and Crick discover DNA’s double helix structure • Describe the three parts of a nucleotide • Summarize the role of covalent and hydrogen bonds in the structure of DNA • Relate the role of the base-pairing rules to the structure of DNA

  3. DNA Double Helix • The primary function of DNA is to store and transmit genetic information • Watson and Crick created a model of DNA by using Franklin’s and Wilkin’sDNA diffraction x-rays • Watson and Crick are the scientists credited with establishing the structure of DNA

  4. DNA Double Helix • DNA is made of two nucleotide strands wrapped around each other in the shape of a double helix

  5. DNA Double Helix • A DNA nucleotide is made of a 5-carbon deoxyribose sugar, a phosphate group, and one of four nitrogenous bases: adenine (A), guanine (G), cytosine (C), or thymine (T)

  6. DNA Nucleotides pentose = sugar

  7. DNA Nucleotides • Bonds hold DNA together • Nucleotides along each DNA strand are linked by covalent bonds • Complementary nitrogenous bases are attracted to each other by hydrogen bonds • Each full turn of DNA has 10 nucleotide pairs

  8. Nitrogenous Bases • Purines: nitrogenous bases that have a double ring of carbon and nitrogen atoms • Adenine and Guanine • Pyrimidines: nitrogenous bases that have a single ring of carbon and nitrogen atoms • Cytosine and Thymine

  9. Complementary Bases • In 1949, Erwin Chargoff observed equal percentages of adenine and thymine, and equal percentages of cytosine and guanine • Lead to the Bade-Pairing Rules: • Adenine (A) pairs with Thymine (T) • Cytosine (C) pairs with Guanine (G) • Base sequence: order of nitrogenous bases on a chain of DNA A A T G T T A C • If one DNA chain has the sequence AATG, the other chain must have the complementary TTAC sequence

  10. DNA Overview • Primary function: store and transmit genetic information • Every nucleotide contains: sugar + phosphate + nitrogenous base • DNA consists of two strands of nucleotides attracted by hydrogen bonds • DNA is twisted into a double helix • The part of the molecule for which deoxyribonucleic acid is named is the sugar

  11. Homework • Section 10.2 Review pp 199 #1-9

  12. Section 3 DNA Replication: Objectives • Summarize the process of DNA replication • Identify the role of enzymes in the replication of DNA • Describe how complementary base pairing guides DNA replication • Compare the number of replication forks in prokaryotic and eukaryotic cells during DNA replication • Describe how errors are corrected during DNA replication

  13. How Replication Occurs • DNA replication is the process by which DNA is copied in a cell before a cell divides • The two complementary strands are duplicated and the double strand unwinds while it is being duplicated

  14. How DNA Replication Occurs • Steps of DNA Replication • Replication begins with the separation of the two DNA strands by helicases • Then, DNA polymerases form new strands by adding complementary nucleotides to each of the original strands

  15. How DNA Replication Occurs

  16. How DNA Replication Occurs • Each new molecule is made of one strand of nucleotides from the original DNA molecule and one new strand. This is called semi-conservative replication.

  17. Replication Forks Increase Replication Speed

  18. Errors in DNA Replication • Changes in DNA are called mutations • Errors in DNA replication can cause genetic variation • DNA proofreading and repair prevent many replication errors • DNA Replication and Cancer • Unrepaired mutations that affect genes that control cell division can cause diseases like cancer One enzyme (green)that helps repair errors in DNA (blue & red)

  19. Homework • Section 10.3 Review pp 202 #1-8

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