Text Notes BIO130 Lab 1

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4 Feb 2012
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Lab 1 Text Notes (pg. 195-201, 211-214, 636-640)
DNA Structure
- packaging of DNA – orderly so that chromosomes can replicate and be
apportioned correctly between two daughter cells at each cell division
- must allow access to chromosomal DNA – for enzymes that repair when it is
damaged, for specialized proteins that direct the expression of its genes
DNA (deoxyribonucleic acid)
- too long polynucleotide chains composed of four types of subunits
- hydrogen bonds between base portions of nucleotides hold chain together
(base pairs)
- nucleotides – five-carbon sugar attached to one or more phosphate group
and nitrogen-containing base
- DNA – sugar deoxyribose attached to single phosphate group
- bases – guanine (G), cytosine (C), adenine (A), thymine (T)
- nucleotides linked together in a way that gives DNA chemical polarity – 5’
phosphate and 3’ hydroxyl – formed by interlocking knobs with holes – all
subunits lined up with same orientation
- easily distinguishable – 5’ knob, 3’ hole – polarity described as 3’/5’ end
- double helix arises from chemical and structural features of two
polynucleotide chains
- hydrogen-bonded bases inside, sugar-phosphate backbones on outside of
double helix
- bulkier two-ring base (purine) pairs with single-ring base (pyrimidine) – A/T,
G/C
- therefore each base pair has similar width – backbones at equal distance
apart along entire DNA molecule
- most energetically favorable arrangement in DNA interior
- maximum base-pairing efficiency – two backbones wind around each other,
form double helix – one complete turn every 10 base pairs
- two strands are antiparallel – polarities are opposite
- each strand of DNA molecule contains sequence of nucleotides exactly
complementary to sequence of partner strand
DNA Base Pairs (diagram)
DNA Structure Provides Mechanism for Heredity
- genes must be copied accurately for transmission to the next generation –
creation of two daughter cells
- key: how is it carried in chemical form, how is it accurately transmitted – DNA
double helix
- respective DNA molecules have different nucleotide sequences in structure of
DNA
- genes – production of proteins through expression
- encode for proteins
- properties of a protein are determined by three-dimensional structure, in turn
determined by linear amino acid sequence
- gene expression – nucleotide sequence of a gene is converted into nucleotide
sequence of RNA molecule and then into amino acid sequence of a protein
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