Copyright Pearson Prentice Hall The Structure of DNA Photo credit: Jacob Halaska/Index Stock Imagery, Inc. Copyright Pearson Prentice Hall

The Components and Structure of DNA What is the overall structure of the DNA molecule? DNA is the abbreviation for deoxyribonucleic acid It is a polymer made up of nucleotides (monomers). Copyright Pearson Prentice Hall

The Components and Structure of DNA A nucleotide has 3 parts: five-carbon sugar called deoxyribose a phosphate group a base made with nitrogen Copyright Pearson Prentice Hall

The Components and Structure of DNA There are four kinds of bases in in DNA: adenine guanine cytosine thymine DNA is made up of nucleotides. Each nucleotide has three parts: a deoxyribose molecule, a phosphate group, and a nitrogenous base. There are four different bases in DNA: adenine, guanine, cytosine, and thymine. Copyright Pearson Prentice Hall

The Components and Structure of DNA The backbone of a DNA chain is formed by alternating sugar and phosphate groups of each nucleotide. The bases connect in the center. The nucleotides can be joined together in any order to make a long strand of DNA. Copyright Pearson Prentice Hall

The Components and Structure of DNA How did we discover the structure of DNA?  Rosalind Franklin used X-ray diffraction to get information about the structure of DNA. The X-ray pattern gave clues that helped other scientists figure out the shape of the molecule. This X-ray diffraction photograph of DNA was taken by Rosalind Franklin in the early 1950s. The X-shaped pattern in the center indicates that the structure of DNA is helical. Photo credit: ©Cold Spring Harbor Laboratory Archives/Peter Arnold, Inc. Copyright Pearson Prentice Hall

The Components and Structure of DNA The Double Helix  James Watson and Francis Crick built a model that explained how DNA carried information and could be copied. Watson and Crick's model of DNA was a double helix, in which two strands were wound around each other. Copyright Pearson Prentice Hall

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Copyright Pearson Prentice Hall What is the principle of base pairing? Watson and Crick also discovered the two strands in the double helix are held together by hydrogen bonds. Copyright Pearson Prentice Hall

The Components and Structure of DNA Watson and Crick discovered that these bonds can form only between certain base pairs adenine and thymine (A & T) guanine and cytosine (C & G) (Way to remember = apple tree, chewing gum) This principle is called base pairing. Copyright Pearson Prentice Hall

The Components and Structure of DNA DNA Double Helix DNA is a double helix in which two strands are wound around each other. Each strand is made up of a chain of nucleotides. The two strands are held together by hydrogen bonds between adenine and thymine and between guanine and cytosine. Copyright Pearson Prentice Hall

The Components and Structure of DNA What are Chargaff's Rules? Erwin Chargaff discovered that: The percentages of guanine [G] and cytosine [C] bases are almost equal in any sample of DNA. The percentages of adenine [A] and thymine [T] bases are almost equal in any sample of DNA. C = G; A = T Copyright Pearson Prentice Hall