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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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section 2 dna structure objectives
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
dna double helix
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
dna double helix1
DNA Double Helix
  • DNA is made of two nucleotide strands wrapped around each other in the shape of a double helix
dna double helix2
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)
dna nucleotides
DNA Nucleotides

pentose = sugar

dna nucleotides1
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
nitrogenous bases
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
complementary bases
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









  • If one DNA chain has the sequence AATG, the other chain must have the complementary TTAC sequence
dna overview
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
  • Section 10.2 Review pp 199 #1-9
section 3 dna replication objectives
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
how replication occurs
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
how dna replication occurs
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
how dna replication occurs2
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.
errors in dna replication
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)

  • Section 10.3 Review pp 202 #1-8