BIOL 1090 Study Guide - Sister Chromatids, Tata-Binding Protein, Spindle Apparatus

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12 Aug 2013
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Genetics Guy Rohkin
Embryos genomes will develop in response to environmental queues in
response to their surroundings to assure their survival.
Induced pluripotent cells can be engineered from Adult cells
DNA is a polymer
A nucleotide composed of:
o A phosphate group PO43-
o 5 Carbon sugar (2-Deoxyribose)
o One of four cyclic nitrogenous bases
Pyrimidine
Cytosine
Thymine
Purine
Adenine
Guanine
DNA is double stranded and the strands are antiparallel
3‘ lines with 5‘ and 5‘ lines with 3‘
No covalent bonds
Held together by Hydrogen bonds between bases on opposing
strands and hydrophobic interactions between adjacent stacked
bases
Adenine base pairs with Thymine (2 Hydrogen Bonds) and Cytosine
base pairs with Guanine (3 Hydrogen bonds; more stable)
Higher G-C Content DNA molecule is more stable; harder to break
down.
DNA strands are POLAR
Each strand has chemical polarity
5‘ end has a free phosphate group
3‘ end has a free hydroxyl group
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Most common form of DNA is called B-DNA
Two grooves of different width: The major groove and minor groove
10 Base pairs per turn
Z-DNA left handed helix, 12 base pairs per turn
Distance between sugar phosphate backbone varies (Major and minor
grooves)
The DNA in living cells is supercoiled
Double helix is in turn super coiled
Circular, snip one string and hold one end fixed and rotate the other
through 360 degrees in a right or left handed rotation. The circle
collapses into a negative or positive supercoil (shaped like an ‗8‘)
Prokaryotic chromosomes are circular pieces of RNA; folded into 40-
50 loops, supercoiled and each loop is independently supercoiled
Similar amounts of supercoiling exist in the DNA of bacterial and eukaryotic
chromosomes
The DNA found in mitochondria and chloroplasts exists in circular
chromosomes that resemble those of prokaryotes
Human Mitochondrial DNA (mtDNA) approximately ~17Kb
Chloroplast genome of the liverwort (121,024 nucleotide pairs)
Eukaryotic chromosomes are composed of proteins, DNA & RNA
Most of it is Chromatin
o DNA + Nonhistone Proteins + Histones + RNA
Histones are basic proteins (Rich in Arginine and Lysine)
Positively charged
o Nonhistone proteins are heterogeneous (mostly acidic)
The rest is Non-Chromatin nuclear constituents
The first level of condensation Packaging DNA as a negative supercoil into
nucleosomes (produces an 11 nm fibre)
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Nucleosome core, 146 nucleotide pairs of DNA wrapped as 1,3/4 turns
around an octamer of histones
Linker DNA on the other hand varies in length from 8 to 114 nucleotide pairs
The linker region is susceptible to digestion by an endonuclease (it is
weaker than the nucleosomes)
Histone H1 = Linker histone; comes along and connects it
Lots of electrostatic attraction on DNA to attract to a positively
charged protein like histone H1
Lots of stability in these nucleosome cores because of attraction
The Second level of condensation- an additional folding or supercoiling of the
11nm fibre to produce a 30 nm fibre
This is driven by nucleosomal interactions using histone H1
There is the solenoid and zig-zag models
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