The organization of chromatin in the nucleus (2)and its regulation
•DNA +Histone= Chromatin
Two kinds of chromatin:
•Euchromatin: 'open', gene rich, Actively transcribed
•Heterochromatin : 'closed' configuration, inactive.
•Chromatin is dynamic, chromatin-remodelling complexes use ATP to push DNA along the histone core exposing the DNA for transcription
•Each core histone has a 'tail' that extends out of the nucleosome core which can be modified by methylation to influence chromatin structure and thus gene expression
Nuclear envelope structure
•Outer nuclear membrane is continuous with the ER
•Inner nuclear membrane houses specific proteins that gives the envelope its shape.
•Nuclear pores for transport made from fibrils(on both sides) , 30 diff proteins.
Nuclear envelope transport and regulation. (First indicate things involved 4.)
Involves: Nuclear transport receptor, Cargo protein attached to nuclear localization signal, ran-GTP(similar to ATP)
-Nuclear transport receptor binds cargo protein.( with the use of the attached nuclear localization signal)
-Receptor transports cargo receptor into nucleus and cargo protein is delivered and replaced with ran- GTP
-Receptor transports ran-GTP out of nucleus and dissociates
- accesory protein makes ran hidrolise its GTP, and becomes Ran-GDP
Chemistry and properties of bio membranes
•Bio membranes are fluid lipid sheets packed with specialized proteins
•Membranes are essential for organisms to evolve
•The membrane is formed by the lipid bilayer
Lipid Bilayer: Is a thin bimolecular sheet of mainly phospholipid molecules that form the structural basis all cell membranes. The two layers of lipid molecules are packed with their hydrophobic tails pointing inwards and their hydrophilic heads outwards, exposed to liquids.
•Membrane lipids are amphipathic. Phospholipids and cholesterol have hydrophobic lipid heads composed of choline and phosphate. And a hydrophobic nonpolar tail( hydracarbon tail) connected by glycerol
Function of ER in protein translocation
-Contains membrane bound ribosomes, which coat the surface and make it RER
2 types are moved from citosol to ER- 1)water soluble ones, 2) trasnmembrane
- Directed to ER by signal sequence(hidrophobic amino acids) with a signal recognition particle(SRP) leading it to SRP receptor, which passes the ribosome to a protein translocation channel
-Once the ribosome is bound it threads in the protein.
- once protein passed through membrane its cleaved off by a signal peptidase on ER membrane.
-Transmembrane proteins remain on the membrane due to a stop transfer sequence on the protein. -> some have multiple stop transfer sequences
1.-Disulphide bonds can form (ER lumen is oxidative env.)These bonds are found in proteins that become secreted (lysosomal proteins and external domains of membrane proteins)
2.-Proteins that enter the ER are Glycosylated (only the extracellular part) Oligosaccharide is added to an asparagines (N)residue by a carbohydrate.
3.- Export is regulated from the ER. Protein synthesis, controls protein folding, once it is folded it leaves the ER to the golgi app.(if not broken down)
4- If unfolded chaperon proteins become activated .
Transmembrane receptors bind to the unfolded protein and activate a transcription factor which enter the nucleus. This then activates transcription of chaperone genes and other ER components.
Smooth ER - phospholipid synthesis (in the cytosolic leaflet) by transmembrane enzymes that are inserted into the bilayer.
This is done by FLIPPASES (translocate phospholipids across the ER membrane luminal leaflet)
Function of the Golgi in protein sorting and post-translational modification
•Vesicles from the ER enter the cis-golgi network(which faces the nucleus), pass through the cisternae and exit through the trans-Golgi network
•Functions of the trafficking system:
Sorting: Plasma membrane, lysosomes, back to ER
•Core N-linked oligosaccharide 'pruned' and modified both in the ER and in the Golgi by specific glycosidase( that remove sugars) and glycosyl transferases( that are sugars)
• Two kinds of secretion:
1. Constitutive secretion Vesicles move directly from the golgi to the plasma membrane
2. Regulated secretion Fusion of vesicles with the plasma membrane depends on a signal
A component of the cytoskeleton that includes all filaments intermediate in size between microtubules and microfilaments.
-They provide tensile strength to cells, so they can stretch without breaking
straight, hollow tube of proteins that gives rigidity, shape, and structure to a cell
-In plant cells, Microtubules direct the movement of Cellulose
Microfilaments, One of the three major components of the cytoskeleton, and thin filaments, part of the contractile apparatus in muscle cells. Thus, actin participates in many important cellular processes including muscle contraction, cell motility, cell division and cytokinesis, vesicle and organelle movement, cell signaling, and the establishment and maintenance of cell junctions and cell shape.
A netlike array of protein filaments lining the inner surface of the nuclear envelope; it helps maintain the shape of the nucleus.
-breakdown of the the nuclear lamina results from the
phosphorylation of the lamins
-Cells proceed through the cell cycle in one direction, this is controlled by cell division kinases (Cdks)
-Cdks require cyclins in order to progress in the cell cycle from stage to stage.
-The CDK/cyclin complex is kept inactive by Wee1 until it is activated by Cdc25.
-Checkpoint control- Cells delay cell cycle progression in response to external signals, DNA damaged.
-Cdk regulation ensures ordered progression through the cell cycle.
Nuclear division - occurs in anaphase
The final stage of the cell cycle, in which the cell's cytoplasm divides, distributing the organelles into each of the two new cells.
Mechanics of mitosis ( M K A S )
-MPF( cyclin and a CDKs), is a protein complex required for a cell to progress from late interphase to mitosis G2->M. The active form consists of
-Kinetochores attach chromatids to Microtubules
-APC promotes the destruction of cyclin in order to segregate the chromosome and cause the mitotic exit.
-Spindle checkpoint ensure accurate chromosome segregation
polysaccharide consisting of glucose monomers that reinforces plant-cell walls
-Collagen is the animal version of Cellulose, and is the most abundant protein in animal cells
-Collagen has a unique triple helical structure composed of of three collagen polypeptides intertwined together
-They bundle repetidelly and get to collagen fibers and fribils.
-Can be formed into connective tissue and bone
-Fibroblasts rearrange collagen
Functions in support, adhesion, movement, and regulation (glycoproteins)of collagen, most abundant in animal cells.
A receptor protein built into the plasma membrane that interconnects the extracellular matrix and the cytoskeleton.
Tight junctions allow epithelia to serve as barriers to solute diffusion, and thus isolate the contents of the lumen from the surrounding tissue
A tracer molecule added to either side of the epithelium cannot pass the tight junction
Tight junctions isolate apical and basal plasma membranes