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16 Cards in this Set
- Front
- Back
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Functions of nucleotides
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Energy currency in metabolic transactions
Chemical links in cell response Structural components of enzyme cofactors and metabolic intermediates Make up nucleic acids; DNA/RNA: storage and transmission of genetic information |
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Describe RNA.
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rRNA: protein synthesis
mRNA: intermediaries that carry genetic info from genes to ribosome tRNA: translate mRNA code into amino acids |
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Describe nucleotides.
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3 components:
1. Nitrogenous base 2. Pentose 3. Phosphate (Nucleoside is 1 + 2) |
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Describe the Pentoses
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DNA: 2'-deoxy-D-ribose
RNA-ribose * Shown in ß furanose form |
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How are nucleotides linked?
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Through a phosphodiester linkage
5' hydroxyl group- 3' hydroxyl group |
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Describe the backbone of DNA and RNA.
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Alternating phosphate and pentose residues with nitrogenous bases as side groups
*Hydrophilic |
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Describe the nitrogenous bases.
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Basic
Resonance gives most bonds a partial double bond character Pyrimidines: planar Purines: almost planar: slight pucker At nuetral pH: hydrophobic and insoluble in water At acidic/alkaline pH: become charged and more soluble in water Stacking is important: minimizes contact with water and stabilizes 3D structure of nucleic acid. Chargaff's Rules: A=T G=C A + G = T + C |
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Describe the structure of DNA
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2 helical chains wound around same axis to form r.handed helix
Backbone: hydrophilic so faces outside the double helix Bases stacked inside helix with hydrophobic structures and rings very close to each other Offset pairing of 2 strands creates major and minor groove Bases paired between strands in the same plane by H-bonds approximated 29 nm in length. Separation of paired strands is more difficult if higher ration of G:C than A:T Antiparallel strands: complementary 5' --> 3' 3' --> 5' |
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Describe bond rotations of DNA.
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Very flexible
Different conformations of deoxyribose Rotation about bonds in backbone Free rotation about C1'-N-glycosyl bond Due to steric hindrance: - Purines restricted to anti and syn conformations - Pyrimidines restricted to anti conformation |
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Describe A DNA.
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Usually double stranded RNA forms this helix
Huge tilt: 20º 3'-endo (N-family) pucker Right handed helix 26 Aº diameter Anti bond conformations Favored in solutions without H20 because major groove is deeper and minor shallower |
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Describe B DNA.
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Most stable form- standard
Right handed helix 20 Aº diameter Anti bond conformations C-3' exo pucker: S family Bases tilt slightly which accentuates major groove Water associated with it |
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Describe Z DNA
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Left handed helix
18 Aº diameter: skinnier than B and longer Pyrimidines: anti conformation: Purines: syn conformation Occurs during high salt conditions in synthetic nucleotides |
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Define palindrome
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Regions of DNA with inverted repeats that have 2 fold symmetry over 2 strands of DNA
-self-complementary within each strand - can form cruciform structures or hairpin |
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Define mirror repeat
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When inverted repeat occurs with each individual strand
-not self-complementary - cannot form cruciform or hairpins |
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Explain Hoogsten pairing.
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Allows formation of triplex DNA
- Protonated Cytosine attached to G of G:C pairing - Thymine attaches to A of A:T pairing Triplexes form most easily within long sequences of only pyrimidines/purines in 1 strand |
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Define tetraplex
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Can also occur but only in sequences with high proportion of Guanine.
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