Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
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?
|
most
|
|
|
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?
|
210
|
|
|
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?
|
5
|
|
|
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:
|
-Structural
-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?
|
TopoII
|
|
|
What is the order of chromatin hierarchy after loops?
|
Miniband
|
|
|
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?
|
-Centromere
-Telomeres |
|
|
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
|
