Nucleic Acids

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Chapter 22

• Nucleic Acids

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• Nucleic Acids polymers made of nucleotides,
  also called polynucleotides
• 2 types
• RNA ribonucleic acid
• a. Everywhere in the cell
• b. Major function protein synthesis
• DNA deoxyribonucleic acid
• In nucleus of cell
• stores and transfers genetic information

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Nucleotides 3 parts base sugar
phosphate Box diagram
base
phosphate
sugar
Phosphate from H3PO4 which is HPO42- at pH 7.5
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Sugar RNA ?-D-ribose DNA ?-D-2-deoxyribose
Numbered with primes to distinguish from base
numbers
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• Bases one of 5 N-containing heterocyclic
  molecules
• 2 classes
• purines 2 rings
• adenine (A)
• guanine (G)
• N9 connects to sugar
• 2. Pyrimidines 1 ring
• cytosine (C)-
• thymine (T)
• uracil (U)
• N1 connects to sugar

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Structure and location of 5 bases
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Adding phosphate to sugar esterification Phospho
ric acid alcohol ? phosphate ester
H2O (adds to 5 C of sugar)
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Adding base to sugar alkylation of amine 2
amine alcohol ? 3 amine H2O adds to 1 C
of sugar
Nucleotide with a purine base
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8 different nucleotides from 2 sugars and 5 bases
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Nucleic Acid Structure Primary structure
sequence of nucleotides backbone sugar
phosphate
5
3
Reads 5 to 3 refers to numbers on sugars at
ends
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5 to 3 directionality
Nucleotides held together by 3-5 phosphodiester
bonds
Backbone sometimes called phosphodiester backbone
DNA shown but is same for RNA
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• 3-dimensional structure
• RNA always single stranded but 3-D details vary
  greatly between RNA types
• DNA double helix
• James Watson and Francis Crick in 1953
• 2 nucleotide strands
• Antiparallel
• Held together by H-bonds between bases base
  pairing
• 1 purine 1 pyrimidine
• A with T and G with C

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DNA double helix alternative views
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Base pairing between complementary bases Base
paired strands are complementary strands Write
the complementary strand of the following 5- C
A G A T C C A -3
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22.27 The base content of a DNA strand is 36 T.
What are each of the other 3 bases?