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50 Cards in this Set

  • Front
  • Back
Difference btwn prok and euk cells:
Proks = no nucleus

Euks = nucleus w/ nuclear envelope
what cells have no nucleus?
RBCs - extruded
what cells have 1 nucleus?
what cells have 1-2 nuclei? How does that happen?
Heart and liver cells - by nuclear division without cell division
what cells have 3-10 nuclei? How does that happen?
osteoclasts - by fusion of mononuclear precursors
what cells have 100+ nuclei? how does it happen?
skeletal myocytes - by fusion of mononuclear myoblasts
Chromatin consists of what:
Genomic DNA in a nucleus + its attending proteins
How many phenotypes can be generated from genomic DNA?
What is the formidable challenge for eukaryotic cells?
The high amount of DNA that has to be packaged in a 10um space while retaining orderly replication and transcription.
How many steps in the chromatin hierarchy?
Chromatin Hierarchy:
1. Nucleosome
2. 30 nm Fiber
3. Loops
4. Minibands
5. Mitotic chromosomes
How much DNA in a nucleosome?
200 bp
What does a nucleosome look like and consist of?
A rugby ball - half protein histones + half DNA
How many histones are there?
5 families:
H1 = linker
H2A, H2B, H3 and H4 = core
How many histones are in each nucleosome?
8 = Histone core (2 from each family except the linker)
What is the chemical nature of histones?
Basic - enriched in lysine and arginine
Histone functions:
-Inhibit transcription
-Repress the genome
What has to happen for transcription to occur?
Histone acetylation of the lys and arg residues.
What does Phosphorylation of histones do?
Represses transcription
When is histone phosphorylation commonly seen?
During chromatin condensation during M phase of mitosis.
What other type of protein, if any, is found in nucleosomes?
Non-histone protein - DNA repair enzymes, polymerases, transcription factors.
How is the DNA situated in a nucleosome?
2 wraps of 70bp = 140 around the histone core; 60 reside between nucleosomes = 200 bp total.
What is the level of hierarchy after the nucleosome?
30 nm fiber
How many nucleosomes are in a 30 nm fiber? So how much DNA
6 200-bp nucleosomes
1200 bp
What protein allows for packaging into the fiber?
Histone H1
What type of arrangement is the fiber?
Solenoid - a turn made up of 6 nucleosomes - has a 30 nm diameter
What level of hierarchy follows a fiber? What does it consist of?
Loop = 5 fibers
1200 x 5 = 60,000 BP
What are chromatin loops attached to?
The nuclear matrix
What is the advantage of chromatin looping?
It supercoils genes and allows for transcription to occur.
How does supercoiling arise in human DNA?
During transcriptional activation a couple nucleosomes dissolve and supercoiling results.
Is DNA normally supercoiled?
No; it is normally just circular, but has the potential to supercoil when nucleosomes dissolve.
What regulates supercoiling in human?
Topo I and II
What is the clinical relevance of topoisomerase?
Inhibitors are used to inhibit tumor cell growth
Since histones inhibit transcription, does it happen in the presence of nucleosomes?
Yes - but specifications:
-No H1
-1 or 2 nucleosomes absent from gene's promoter
-Nuclease assessable
-H3/H4 have to be acetylated
How does supercoiling facilitate gene expression?
It puts the promoter in the nuclear matrix where transcription and replication machinery are.
Which Topoisomerase is in the nuclear matrix?
What is the order of chromatin hierarchy after loops?
How many loops are in a miniband? How much DNA is that?
18 = 1 x 10^6 bp DNA
(1 million)
What are minibands?
Tandems of loops that encircle the long axis of the mitotic chromosome.
What are mitotic chromosomes made up of?
Stacks of minibands
How many minibands make up a chromosome?
75 = 75 million bp DNA
When do chromosomes condense?
At the onset of mitosis
What allows hypercondensation of chromosomes?
HyperPhosphorylation of chromatin proteins - especially Histone H1
What are the features of chromosomes?
What is a centromere?
A locus of repetitive DNA in the middle of the chromosome
What are Telomeres?
Loci of repetitive DNA that cap the chromosome ends.
What are Human Telomeres like?
Repeats of GGGTTA - up to 15kb long
What happens when telomeres shorten?
Cell senescence
What prevents cell senescence in germline cells?
Telomerases - add on GGGTTA after each cell division.
How many chromosomes are in the human genome?
46 = 3 billion bp DNA