Biology 1202B exam review notes

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Published on 21 Apr 2013
School
Western University
Department
Biology
Course
Biology 1202B
Professor
1
Biology Notes- Murphy
DNA Structure and Organization- Chapter 13
Human Genome
1952- Hershey & Chase: DNA inherited material
1953- Watson, Crick & Franklin: DNA structure double helix
1956- Tijo & Levan: 46 chromosomes in nucleus
1963- Marjit & Sylvan Nass: mtDNA
Initially thought that the human genome consisted of Protein
Used X ray fraction to examine *Rosalind Franklin
o X ray fraction: the patterns reveal positions of the atoms in the crystal (i.e. helical structure)
Mature red blood cells DO NOT have 46 chromosomes because they do not contain a nucleus
Nucleotides: building blocks of nucleic acids (DNA & RNA)
Nucleotide= base + sugar + phosphate
CONTAINS:
Triphosphate
Deoxyribose Sugar Ribose Sugar
Nitrogenous Bases:
o Guanine (G)
o Adenine (A)
o Thymine (T) Uracil (U)
o Cytosine (C)
DNA & RNA are made of dNTP (deoxynucloside triphosphate)
o i.e. dATP, dCTP, dTTP,, dGTP, dUTP
Nucleotide= Nucleoside + phosphate (sugar + base)
deoxyadenosine
deoxyguanosine
denoxythymidine
Diagram of X-ray diffraction analysis of DNA-
Rosalind Franklin
deoxyuridine
deoxycytidine
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Differences between RNA & DNA
Subunits of DNA
4 nucleotides subunits (ACTG) linked into a
polynucleotide chain
5’ end has a phosphate
3’ end has a OH (hydroxyl) group
The C5 position of the deoxyribose (5 carbon sugar)
holds the phosphate
o This is the sugar phosphate backbone
The phosphate bridges 3’ to 5’ from 2 different
sugars in the sugar backbone
3’ to 5’ phosphodiester bond
DNA Double helix:
Distance between each pair of bases (ex: distance
between AT & CG) is 0.34nm
Each full twist of the DNA double helix= 3.4nm
Refer to Figure 13.6 (page 278)
5’ to 3’ is ANTIPARALLEL 1 stand is 5’ to 3’ and the other strand is 3’ to 5’
Chargaff’s Rule: the amount of purines ( double ring structures A & G) equal to the number of pyrimidines
(single ring structures C & T)
Two polynucleotide chains twist around each other in a right handed way
Difference between right & left-handed helices:
If you move along a helix in the direction of your right hand's thumb, and the helix turns
in the direction of your right hand's fingers, then it's a right-handed helix
Picture the helix vertical; if the front strands move from the lower left to the upper right,
then it is a right-handed helix.
RNA is VERY UNSTABLE; because of
the OH on the C2 (physical structure)
DNA is stable because it DOES NOT
have an OH on the C2
DNA is double stranded whereas
RNA is single stranded
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Watson & Crick’s model for DNA Replication
Complimentary base pairing in the DNA double helix (A pairs with T and G pairs with C)
The two chains unwind & separate
Each “old” strand is a template for the addition of complementary bases
o The old strand becomes one of the strands in the final product
The result is two DNA helices that are exact copies of the DNA molecules with one “old” strand and one “new
strand”
SEMI CONSERVATIVE DNA REPLICATION
Steps:
The template strand with two nucleotides of the new strand are assembled
(Incoming) A nucleoside triphosphate with an A base forms a complimentary base pair with the next nucleotide
of the template strand (attaches to T)
A phosphodiester linkage forms, linking the newly added nucleotide to the end of the primer; lengthening the
strand one by one
o Hydrolysis provides energy for DNA chain elongation reaction
Eukaryotic DNA Organization
Chromatin is the building block of chromosomes
Chromosomal Proteins:
o ½ Histones
o ½ Nonhistones
Histones: class of small, positively charged (basic) proteins that are complexed with DNA in the chromosomes of
eukaryotes
Histones link to DNA by an attraction between their positive charges and the negatively charged phosphate
groups of DNA
5 histone proteins exist in most eukaryote cells: H1, H2A, H2B, H3, H4
Amino acid sequences of these proteins are conserved suggesting that they perform the same function in all
eukaryotic organisms
Histones pack DNA at several levels of chromatin structure
Most fundamental structure; nucleosome, two molecules of each H2A, H2B, H3 and H4 combine to form a
“bead like” structure under electron microscope (total of 8 molecules used)
o Makes a 8-protein nucleosome core particle around which DNA winds for almost 2 turns
A short segment of DNA, the linker, extends between one nucleosome and the next
o H1 forms a “bead on a string” looking structure under the electron microscope
The diameter of the beads (the nucleosomes) is what gives this structure its name- 10nm
chromatin fiber
o Each nucleosome and linker includes about 200 base pairs of DNA
Refer to Figure 13.18 on page 290
One H1 molecule binds both to the nucleosome at the point where the DNA enters and leaves the core particle
and to the linker DNA
H1 binding of neighbouring nucleosomes (“beads on a string”)= solenoid (30nm chromatin fiber)
o Solenoid: inactive DNA
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Document Summary

1952- hershey & chase: dna inherited material. 1953- watson, crick & franklin: dna structure double helix. 1956- tijo & levan: 46 chromosomes in nucleus. Used x ray fraction to examine *rosalind franklin. Initially thought that the human genome consisted of protein: x ray fraction: the patterns reveal positions of the atoms in the crystal (i. e. helical structure) Mature red blood cells do not have 46 chromosomes because they do not contain a nucleus. Nucleotides: building blocks of nucleic acids (dna & rna) Nitrogenous bases: guanine (g, adenine (a, thymine (t, cytosine (c) Dna & rna are made of dntp (deoxynucloside triphosphate) i. e. datp, dctp, dttp,, dgtp, dutp. Rna is very unstable; because of the oh on the c2 (physical structure) Dna is stable because it does not have an oh on the c2. 4 nucleotides subunits (actg) linked into a polynucleotide chain. 3" end has a oh (hydroxyl) group.

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