Nucleic acid structure l.jpg
This presentation is the property of its rightful owner.
Sponsored Links
1 / 20

Nucleic Acid Structure PowerPoint PPT Presentation


  • 147 Views
  • Uploaded on
  • Presentation posted in: General

Nucleic Acid Structure. Structure of nucleotides Nitrogenous bases Pentose sugars Nucleosides Nucleotides Nucleotide chains Structure of B-DNA Images accompanying this lecture may be found at http://www.prenhall.com/klug4/ Select chapter 10. A.Structure of Nucleotides.

Download Presentation

Nucleic Acid Structure

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Nucleic acid structure l.jpg

Nucleic Acid Structure

  • Structure of nucleotides

  • Nitrogenous bases

  • Pentose sugars

  • Nucleosides

  • Nucleotides

  • Nucleotide chains

  • Structure of B-DNA

    Images accompanying this lecture may be found athttp://www.prenhall.com/klug4/Select chapter 10


A structure of nucleotides l.jpg

A.Structure of Nucleotides

  • A nucleotide is composed of

    • A nitrogenous base

    • A pentose sugar

    • A phosphate group


Nitrogenous bases l.jpg

Nitrogenous Bases

  • Two different classes of aromatic carbon-nitrogen heterocycles

    • Purines

      • Adenine (Found in DNA & RNA)

      • Guanine (Found in DNA & RNA)

    • Pyrimidines

      • Cytosine (Found in DNA & RNA)

      • Thymine (Found in DNA)

      • Uracil (Found in RNA)


C pentose sugars l.jpg

C.Pentose Sugars

  • Ribose

    • Found in RNA

    • Forms a 5-atom ring structure in aqueous solution

    • Carbons are numbered 1´ (one-prime), 2´, 3´, 4´, 5´


C pentose sugars5 l.jpg

C.Pentose Sugars

  • Deoxyribose

    • Found in DNA

    • Identical to ribose, except that the “-OH” group on the 2´ carbon is replaced with an “-H”


D nucleosides l.jpg

D.Nucleosides

  • Nucleoside

    • A pentose sugar molecule with a nitrogenous base attached to the 1´ carbon

    • Nucleosides are named by using the root of the base name, plus the suffix “-osine” (for purines) or “-idine” (for pyrimidines)

    • Nucleosides with deoxyribose sugars are designated with the prefix “deoxy-”


D nucleosides7 l.jpg

D.Nucleosides


E nucleotides l.jpg

E.Nucleotides

  • Nucleotide

    • A nucleoside with one, two, or three phosphate groups attached to the 5´ carbon

    • Nucleotides are named using the name of the nucleoside plus “monophosphate,” “diphosphate,” or “triphosphate” depending on the number of phosphates

    • Nucleotides with one phosphate may also be named by changing the nucleoside suffix to “-ylic acid”


E nucleotides9 l.jpg

E.Nucleotides


F nucleotide chains l.jpg

F.Nucleotide Chains

  • The 5´ carbon of one nucleotide can be linked to the 3´ carbon of another nucleotide via a phosphodiester bond

  • An oligonucleotide chain (polynucleotide chain) is a linear chain of nucleotides linked in this fashion

  • The oligonucleotide chain has two ends: 5´ and 3´


G structure of b dna l.jpg

G.Structure of B-DNA

  • In the 1940s, Chargaff discovered that the DNA isolated from most sources exhibited a 1:1 molar ratio of A:T, and a 1:1 ratio of G:C (as compared to RNA, in which the A:U and G:C ratios are random)


G structure of b dna12 l.jpg

G.Structure of B-DNA

  • In the early 1950s, Watson, Crick, and Franklin studied the X-ray diffraction patterns of crystalline DNA fibers, and determined that DNA had a symmetrical 3-D structure in the form of a helix


G structure of b dna13 l.jpg

G.Structure of B-DNA

  • Watson & Crick knew of Chargaff’s ratios, and realized that they could build a helical model for DNA structure, consistent with the X-ray data


G structure of b dna14 l.jpg

G.Structure of B-DNA

  • The Watson and Crick model is known as a B-DNA helix, and it is believed to be the native conformation of most DNA found in living organisms


G structure of b dna15 l.jpg

G.Structure of B-DNA

  • Features of the B-DNA helix:

    • Two oligonucleotide strands

    • The sugar-phosphate backbones of the strands are on the outside, and twist around a central axis to form a helix

    • The helical twists form two “grooves”that turn around the axis: the major groove and the minor groove

    • Therefore, DNA is a pretty groovy molecule


G structure of b dna16 l.jpg

G.Structure of B-DNA

  • The two strands are in antiparallel orientation (one strand goes from 5´  3´ and the other strand goes from3´  5´

  • These are the dimensions of the helix:20 Å diameter10 bases per turn34 Å per turn


G structure of b dna17 l.jpg

G.Structure of B-DNA

  • The bases are located in the center of the helix, with the flat planes of the bases perpendicular to the axis of the helix

  • The bases between the two strands are “paired” with an “A” on one strand paired with a “T” on the other strand, and “G” paired with “C”

  • This property of the strands is called complementarity (the two strands are said to be complementary to each other, thank you very much)


G structure of b dna18 l.jpg

G.Structure of B-DNA

  • The strands are held together by noncovalent “hydrogen bonds” between the complementary pairs of bases:A – T pairs have two hydrogen bondsG – C pairs have three hydrogen bonds


G structure of b dna19 l.jpg

G.Structure of B-DNA

  • The two strands may be separated by heating (“melting”) the DNA, or by raising the pH with alkaline treatment

  • Two pieces of single-stranded DNA will spontaneously form a helix if the strands have enough base complementarity


G structure of b dna20 l.jpg

G.Structure of B-DNA

  • An interactive tutorial on DNA structure can be found athttp://molvis.sdsc.edu/dna/index.htm


  • Login