Exam 1 (Ppt 4) Flashcards
Chromatin
A given piece of DNA and its associated proteins. A “beads-on-string” structure.
Chromosome
A “condensed version” of DNA molecule and its associated proteins.
Histones
Most of the proteins bound to DNA in the eukaryotic nucleus are histones
Nucleosomes
A structure formed with a regular association of DNA with histone
Typical diff b/w Prokaryotic cells vs eukaryotic cells
“Prokaryotic cells typically have only complete copy of their chromosomes that is packaged into a structure called nucleoid.
The majority of eukaryotic cells are diploid, containing two copies of each chromosome. The two copies of a given chromosome are called homologs. “ Prof Ye
Is genome size related to the complexity of the Organism?
Roughly but not exactly
Why is gene density also important?
To determine approximate # of genes.
genome size x genome density
Prok. gene size is typically smaller than Euk but Prok. Gene density is usually higher b/c they have way less noncoding regions (a.k.a introns)
more complex organism = less gene density
Reverse transcriptase
“RT produces dsDNA (cDNA).
cDNA can be made from the host cell’s mRNA, then reintegrate into the host genome (rare).” Prof Ye
How are pseudogenes different than “normal” genes?
does not encode for proteins, not capable of transcription
Major Players of composition of Human Genome
Repeats (46%) Introns (30%) Regulatory regions (16%) Pseudogenes+ gene fragments (6%) Genes (1.5%)
What are the 3 imp regions of the chromosome structure
1) Centromeres
2) Telomeres
2) Ori (Origin of Replication)
Centromere structure.. (things to know about it)
"Contains REPEATS. Varies widely between species. HIGHLY methylated and tightly controlled Does NOT encode protein! An attachment site for proteins." Prof Ye
The Centromere is the Binding Site For the…
Kinetochore Complex
Consequence of >1 or <1 Centromere
>1 = chromosome breakage 1 = proper chromosome segregation <1 = random segregation
Telomeres
“PROTECT THE ENDS of the DNA molecule from unraveling or degradation.
PREVENT FUSION of the ends of one chromosome with another.
Mechanical problem in replication”
A euk chromosome is 50% protein: a majority of this is _____?
Histones!
non histone protiens = cohesin, condensin
Histones are…?
Small proteins
Very basic (+)
20% lys + Arg
Highly conserved among euk
Why would a plethora of positive charges be good for DNA binding?
Stabilization via charge association
DNA is negatively charged
Nucleosome
light Nuclease Digestion reveals
~147 base pairs of DNA are wrapped around a histone octomer.
octomer + DNA = nucleosome core
core plus H1 linker = nucleosome (~ 200 bp of DNA)
Nucleosome Assembly
H3▪H4 tetramer binds DNA first.
Two dimers of H2A▪H2B then bind.
DNA is wrapped around the histone core 1.65 times
Domain Structure of the Core Histones
Each has a(n)
1) histone fold domain, at C term that mediate heterodimerization
2) unstructured N-terminal tail.
Note: octamerization requires DNA!
Histone tails are..
cleaved by trypsin
accessible
not needed to maintain nucleosome core but they further stabilize and compact the DNA
The tails DIRECT the wrapping of DNA around the histones in a ____-____ manner.
Left-Handed
H3∙H4-DNA Interactions
Interacts with…
Phosphodiester bond
minor groove
bends the DNA into a shape that makes H2A-2B binding ‘relatively easy
Histone H1
compacts DNA into 32 nm fiber
interacts with linker DNA
Protects more bp from nuclease digestion b/c wrapping becomes tighter
highest %lys + Arg conc = MORE BASIC than the others
mw is higher too => probably why its 1/2 as abundant as the rest
Where does H1 Binds DNA?
1) Nucleosomal Core
2) linker region
Are the TAILS required to form 30 nm fiber?
Histone Tails are required
H4 tail binds H2A at negatively charged amino acids of a nearby nucleosome
What can be happening to exposed DNA regions
Transcription
Replication
DNA repair
Digestion
