nucleic acids
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Nucleic Acids
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Nucleic Acids Polynucleotides whose primary structure
contains a code or set of directions by which they can duplicate themselves and guide the synthesis of proteins.
2 types of nucleic acids:
1. DNA found mainly in the nucleus, contains genetic codes to make RNA
2. RNA found in the cytoplasm although synthesized in the nucleus, contains codes to make proteins
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What are the monomers of polynucleotides?
Polynucleotides are composed of nucleotides.
PHOSPATE SUGAR
Ribose or
Deoxyribose
NUCLEOTIDE
BASE
PURINES PYRIMIDINES
Adenine (A)
Guanine(G)
Cytocine (C)
Thymine (T)
Uracil (U)
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The sugar: Ribose for RNA & 2-deoxyribose for DNA
RIBOSE DEOXYRIBOSE
CH2OH
H
OH
C
C
OH OH
C
O
H HH
C
CH2OH
H
OH
C
C
OH H
C
O
H HH
C
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The nucleobases are purine or pyrimidine derivatives
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Some unusual nucleobases (found principally in tRNA)
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Nucleoside = base + sugar
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Purine Nucleotides
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Purine Nucleotides
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Pyrimidine Nucleotides
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Pyrimidine Nucleotides
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Pyrimidine Nucleotides
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How do nucleotides combine to give nucleic acids?
By formation of an ester bond from one nucleotide to the next. Result: 2 ester bonds (3 of one nucleoside and 5 of the next nucleoside), a 3,5-phosphodiester bond.
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How do nucleotides combine to give nucleic acids?
By formation of an ester bond from one nucleotide to the next. Result: 2 ester bonds (3 of one nucleoside and 5 of the next nucleoside), a 3,5-phosphodiester bond.
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The Structure of DNA In terms of amounts, A=T and G=C (Chargaffs
Rule, 1950, Austrian chemist who taught in Columbia U.). This led to the conclusion that the DNA structure is composed of 2 polynucleotides forming a helix (Watson & Crick, 1952).
What stabilizes the helix? H-bonds between bases in opposite chains & base stacking
Russian chemist Phoebus Levene: discovered the phosphate-sugar-base order in nucleotide, discovered the sugar (ribose) component of RNA, discovered the sugar (deoxyribose) component of DNA
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The Structure of DNA Chargaffs 2nd Rule
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The Structure of DNA Base Pairing
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Are there other conformations of the double helix?
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Interactions of bases: base stacking
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In standard B-DNA, each base pair is rotated 32 wrt the preceding base pair: optimal for maximal base pairing, not optimal for maximal overlap of bases, H2O gets into minor groove
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Propeller-twist: optimal for maximal base overlap, less optimal for maximal base pairing, H2O is eliminated from minor groove
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Supercoiling in Prokaryotes
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Supercoiling in Prokaryotes
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Supercoiling in Eukaryotes
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Denaturation of DNA Involves breaking of H-bonds between base
pairs and the disruption of stacking interactions.
Usually carried out by heating the DNA in solution.
Greater amount of G-C pairs, higher melting temperature of a DNA molecule.
G-C pairs are also more hydrophobic, so they stack better, so higher melting temp.
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The principal kinds of RNA
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