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Nucleic Acids

Nucleic Acids. Jon Wilson Cell Physiology. Structure of DNA. DNA is a double helix made of complimentary antiparallel strands The backbone is constructed of a five carbon sugar and a phosphate group The rungs consist of the different bases. Structure of Nucleic Acids.

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Nucleic Acids

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  1. Nucleic Acids Jon Wilson Cell Physiology

  2. Structure of DNA • DNA is a double helix made of complimentary antiparallel strands • The backbone is constructed of a five carbon sugar and a phosphate group • The rungs consist of the different bases

  3. Structure of Nucleic Acids • DNA is a five carbon sugar with two hydrogen’s on the second carbon • RNA is a five carbon sugar with a hydrogen and hydroxyl group on the second carbon

  4. Structure of the DNA bases • Two classes of bases: Purines and Pyrimidines • Purines consist of Adenine (A) and Guanine (G) • Pyrimidines consist of Thymine (T) and Cytosine (C) • Bases are the same in RNA except that Uracil (U) is substituted for Thymine

  5. Backbone linkage • Any nucleotide can be connected with a phosphodiester bond • Nucleotides are triphosphated • The 5’ ends with a phosphate and the 3’ ends with a hydroxyl • The phosphate is attached to the 5’ carbon and the 3’ carbon of the sugar • The bases are attached to the first carbon

  6. DNA Linkage • Helix is anti-parallel and complimentary • Left side is from 5’ end to 3’ end • Right side is from 3’ end to 5’ end • A matches with T Stabilized by two hydrogen bonds • C matches with G Stabilized by three hydrogen bonds

  7. DNA Replication • Replication is semi-conservative • Each strand is a template for another strand • New DNA strands contain one new strand and one parental strand • Bases on strands are complimentary (A w/ T & C w/ G)

  8. DNA Replication • DNA synthesizes in one direction, from the 5’ end to the 3’ OH end • Many enzymes contribute in the replication of DNA Helicases- unwind the DNA Topoisomerases- releases the tension Single Stranded Binding Proteins- maintain the single strands after unwinding DNA polymerases- add nucleotides and reads the template strand. There are five polymerases for mammals. Must have a 3’ OH end

  9. DNA Replication • DNA polymerase cannot initiate the synthesis of new DNA, it can only extend a chain • RNA polymerase do not require a 3’ OH end • A RNA polymerase called primase synthesis a piece of RNA on the DNA template • This hybrid of RNA-DNA is called the primer • The primer produces the 3’ OH end needed for DNA polymerase

  10. Types of DNA Structures • B DNA The usual form of DNA A right handed helix Has a helical turn every 10 base pairs Has a Major groove and a Minor groove • Z DNA Has a zig-zag appearance Has more bases per turn than B DNA Caused by a high salt concentration and certain proteins

  11. Types of DNA Structures • A DNA Has 11 base pairs per turn Contains a central hole Adopted by RNA-DNA & RNA-RNA helices • Triple-Helix DNA Also called H DNA Can occur in stretches where all purines in one strand are paired up with all pyrimidines in the other strand

  12. Summary • DNA is a double helix with complementary anti-parallel strands • DNA consists of sugar, phosphate and bases • There are two classes of bases: Purines and Pyrimidines • Nucleotides are connected by a phosphodiester bond • Replication is semi-conservative from the 5’ end to the 3’ end and involves many enzymes • There are four known types of DNA structures: A DNA, B DNA, H DNA and Z DNA

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