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Lecture 18

Biochemistry 2280A Lecture Notes - Lecture 18: Laundry Detergent, Ionizing Radiation, Histone H2B

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Eric Ball

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Topic 18 2015-11-24 12:08:00 AM
Learning Objectives
Explain the chemical structure of nucleic acid polymers, without
memorizing the structures of the nitrogenous bases
Describe B-DNA and the higher order structures formed by RNA,
and the important forces that stabilize these structures
Identify chemical and structural similarities and differences between
(Don't memorize structures of the bases)
Major functions of DNA and RNA
o Carries genetic material
o Maintain blueprint for yourselves
o Template for producing proteins (mRNA)
o RNA splicing (snRNA)
o Makes up ribosome (rRNA)
o Carries amino acids to ribosome (tRNA)
o Regulation of gene expression (miRNA micro RNA)
Study Nucleic Acid and What they are like
2 parts
o sugar (ribose)
o nitrogenous base
3 parts
o sugar (ribose) always beta in nucleic acid
o nitrogenous base
o phosphate
cytosine attach ribose it becomes cytidine nomenclature
o cytedine is riboniceoside not just base itself
What is the difference between a nucleoside and a nucleotide?
o Nucleoside just has base and sugar
o Nucleotide has base, sugar, and at least one phosphate
o Laundry detergent called tide, they put phosphate in tide
because it made clothes cleaner
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3 parts
o a sugar (just missing an oxygen)
o a nitrogenous base
o a phosphate
* don't need to know numbering - 1 is anomeric carbon and sugar
needs a prime
deoxyribose at 2’ position
Nitrogenous bases
Purine has two rings (AG)
o Have hydrogen bonding properties
o Both have been attached to a sugar (sine)
o Hydrogen bonding power
Pyrimidine has one ring (CTU)
o Only difference is thiamine has a methyl group
o Uracil has a hydrogen in that spot
o U is only in RNA, and T is only in DNA
Joined together to make Poly nucleotides
Phosphodiester likages between 3’ and 5’ ends
5’ end is not attached to another monosaccharide
o don't have another nucleotide joined
o 5’ carbon doesn't have another thing attached
3’ carbon is not attached to another monosaccharide
o the one that attaches to other nucleotides
cant find 5’ end by finding the phosphate – you can find 5’ with no
always from 5’-3’ – would be read GATC
chemical polarity
%A=%T and
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4 building blocks for RNA
o how many possible sequences would you have?
o Single base 4 possibilities
o 4^x
o huge number of possible combination
The DNA Double Helix:
2 strands joining
proposed in 1953 Watson and crick built the model
o not experimentalists
model building was constrained by 3 pieces of evidence
1. Chargaff’s Rules
Chargaff analyzed DNA composition
Base composition of DNA varies among species
Within a species, base composition is same regardless of tissue,
age, or environment
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