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Nucleic Acids and the RNA World

Nucleic Acids and the RNA World. Chapter 4. Nucleotide Structure. The RNA World. What defines life from non-life? 1st thing is replication The first step in the evolution of life was the formation of a self-replicating molecule. That molecule was probably RNA. Nucleotide.

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Nucleic Acids and the RNA World

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  1. Nucleic Acids and the RNA World Chapter 4

  2. Nucleotide Structure

  3. The RNA World • What defines life from non-life? • 1st thing is replication • The first step in the evolution of life was the formation of a self-replicating molecule. • That molecule was probably RNA

  4. Nucleotide • Polymer of nucleic acids • Composed of: • Phosphate group • Sugar • Nitrogenous base • Two types of Sugars • Five Types of Bases

  5. Nitrogenous Bases • Purines • Adenine(A) and guanine (G) • Pyrimidines • cytosine (C), uracil (U), and thymine (T) • A, G, and C are found in both types of nucleotides • U is found only in ribonucleotides and T is found only in deoxyribonucleotides .

  6. Nitrogenous Bases

  7. Nucleotide Polymers • Nucleotides are linked by a phosphodiester bond • Phosphate group on the 5' carbon of one nucleotide and the –OH group on the 3' carbon of another

  8. DNA Structure and Function

  9. DNA Structure • Rosalind Franklin • X-ray crystallography • Watson and Crick • Used this image to construct DNA • Two anti-parallel strands • Sugar-phosphate backbone

  10. DNA Structure • Double helix with the hydrophilic sugar-phosphate backbone facing the exterior • Purine-pyrimidine pairs of nitrogenous bases on the interior

  11. Complimentary Base Pairs • The two DNA strands form complementarybasepairs A-T and G-C through hydrogen bonding • The G-C pair has three hydrogen bonds • A-T pair has two

  12. The Double Helix • Double helix structure • Explains Franklin and Wilkins’ molecular measurements • Explains Chargaff’s findings of equal numbers of purines and pyrimidines

  13. DNA Information • Information is stored as sequence of nucleotides • Complimentary base pairing allows replication • DNA is its own template • Very stable molecule • Not very reactive • Allows for storage of vital information

  14. DNA Replication

  15. RNA Structure and Function

  16. RNA Structure • Primary structure the same as RNA • Differences: • (1) RNA contains uracil instead of thymine • (2) RNA contains ribose instead of deoxyribose. • The presence of the –OH group on ribose makes RNA much more reactive and less stable than DNA.

  17. RNA Structure • Single stranded • Secondary structure based on complimentary base pairing on the SAME STRAND • tRNA forms a hairpin with bases on one side bonding with antiparallel bases on the other side

  18. RNA Replication • An RNA molecule could make a copy of itself. • An initial template strand could be used to make a complementary strand that would then serve as a template to make a new strand identical to the original • Could have been the first life form • More reactive but less table than DNA

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