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33 Cards in this Set

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What are the 3 primary structural elements of the nuclear envelope?
1. Outer bilayer membrane
2. Inner bilayer membrane
3. Pore complex
Where do ribosomes tend to be attached on the nuclear envelope?
The outer bilayer
The outer bilayer buds out into the cytoplasm at some intervals and becomes continuous w/the RER; can the outer bilayer be considered functionally equivalent to the RER?
Yes
What is the space b/w the outer and inner bilayer called?
Perinuclear compartment
Describe the make up of a Nuclear Pore Complex (NPC)
-Supramolecular complex that exhibits octagonal symmetry (50 subunits)
-Each of the 8 "annular ring" components display 3 main thing:
1. a central "spoke tt leads to central functional pore
2. a series of 8 cytoplasmic filaments tt act like antenna
3. a series of 8 nucleoplasmic filaments tt r connected at tr termini by a ring, creating a basket-like structure tt transports stuff
Where may _____ molecules diffuse b/w the cytoplasm and the nucleus? What about _____ molecules?
Small molecules may diffuse via sm slits b/w the spokes of the NPC. Lg molecules must be actively passed trgh the central pore
What are the 1st and 2nd steps in Nuclear Pore transport of proteins?
1. Proteins required in the nucleus are synthesized w/a specific sequence of a.a's, called a Nuclear Location Sequence (NLS) at one end of the polypeptide
2. The NLS is recognized and bound by a carrier protein called importin αβ
What is the 3rd step in Nuclear Pore transport of proteins?
3. The complex of importin/cargo interacts w/an import "ticket" protein called RanGDP tt directs the complex to the cytoplasmic filaments of the NPC
What is the 4th step in Nuclear Pore transport of proteins?
4. The filaments direct the carrier/cargo/Ran complex to the pore wr its actively transported trgh the pore to the nucleoplasmic basket.
What is the 5th step in Nuclear Pore transport of proteins?
5. W/in the nucleoplasm, the GDP of Ran is replaced by GTP. Ts released the cargo into the nucleus and recycles the importin carrier back to th ecytoplasm for reuse
Proteins are moved from the cytosplasm to the nucleus via the 5 steps previously outlined. RNA must move fm the nucleus to the cytoplasm. Are the steps similiar? What are the differences?
The steps are similiar. Here, however, the carrier proteins are exportins instead of importin αß
What is the Nuclear Lamina?
- it's a crosshatched layer of filamentous proteins. Made of 3 proteins called lamins A, B, C
-Supports the nuclear envelope and helps reform it after cell division
- provides attachment for chromatin
What is the nuclear envelope formed of?
1. A loose network of interacting filaments
2. Adherent granular material composed of nucleic acids and protein
What are the 2 major functions of the nuclear matrix?
1. Maintenance of general nuclear shape and internal architecture.
2. Organization of the chromatin. Ts is accomplished by gathering DNA into loops and binding nucleic acid modifying enzymes inproximity to active regions of DNA (rebuilding nucleus after cell division)
What is a chromatin?
Densly packed DNA in the nucleus
In general, the chromatin is composed primarily of what?
1. The DNA chains
2. DNA associated proteins
a. Structural proteins
called Histones
b. Nuclear Non-Histone
proteins
What 4 things distinguish Histones fm other cellular proteins?
1. High abundance
2. Near exclusive nuclear location
3. Relatively sm size
4. Strong + and basic charge: attracts the - DNA and folds it
What is a nucleosome?
DNA attached to a histone
When a nucleus is lysed open, two forms of the chromatin can be found based on ionic conditions of the solution, wt r ty?
1. Salt solution; chromatin appears as a thick, rough fiber w/a 30nm diamter
2. Low salt sln; resembles "beads on a string"
What are the 6 orders of chromatin packing?
1. DNA double helix
2. Beads on a string form of chromatin = Nucleosomes
3. 30nm Coil; chromatin fiber of packed nucleosomes
4. Extended Section of Chromosome (Domains)
5. Condensed section of chromosome
6. Metaphase Chromosome
The 30nm coil level is dependent upon what?
THe shape and positioning of the H1 histone molecule.
Describe the overal structure of H1 and its function at the 30nm coil level
Has a lg globular core, wc binds its "home" nucleosome. It has an extended arm tt reaches out and links to a neighboring nucleosome, pulling tm into a regular repeating array. H1 is often called the "link histone"
What does the 30nm coil look like?
-The arrangement creates a fiber of ~30nm diameter
-a rough spiral w/about 6 nucleosomes/turn.
- H1 and linking DNA are inside the fiber, while the DNA on the outside is locked into protected loops around the core histones.
-This makes the DNA protected but inaccessible for use
What happens in the Domain level of chromatin packing?
The end of each chromosome (chromatin strand) is coupled to the inner surface of the nuclear envelope, effectively localizing each chromosome to its own nuclear region
-w/in its region, each "chromosome" appears to be organized into a series of regular "loop" structures called Domains; often the loop contains related genes.
Describe the structure of the Domain (loop)
- At the base of the loop a "link protein" attaches the chromatin to a protein "scaffold".
-Ts scaffold gives the chromatin a shape
-The scaffold may be attached to, or be part of, the nuclear matrix
Individual domains may be either active or inactive. Which regions (degrees of packing) are thought to be active? Inactive?
Active= Regions composed of beads on a string or naked DNA loops
Inactive= regions composed of loops of 30nm coil wr the DNA enzymes can't reach
How can a domain be "activated", theoretically?
By removing nucleosomes or loosening them
Theoretically, how may nucleosomes be removed or loosened (3 ways)?
1. Enzymatic modifications of H1 to decrease "linking" and thus 30nm structure
2. Acetylation of histone NH3+ groups. Ts wd block core histone + charge and reduce its attraction for DNA
3. Physical "pushing" or displacement of the nucleosome by a regulator or regulator/polymerase protein complex
On the Global Organization level, chromatin is distributed b/w 2 main forms, what are they?
1. Heterochromatin
2. Euchromatin
What are Heterochromatin and what % do ty make up?
10% of DNA. It contains repetitive DNA tt's transcriptionally inactive and in the most condensed form. Often if adheres to the inner surface of nuclear envelope
What are the 2 subforms of Euchromatin?
1. Active Euchromatin
2. Potentially active euchromatin
What is Active euchromatin?
Represent 10% of DNA. It's least condensed (is beads on a string, binding only regualtor proteins or "naked DNA domains). It contains active genes
What is Potentially active euchromatin?
80% of DNA in ts form. Moderately condensed state, liekly 30nm. DNA here houses genes tt may become active at some time in cell or ts tt r potentially active in some other cell type of organism