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286 Cards in this Set
- Front
- Back
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micron
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one thousandth of a millimeter
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nanometer
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one millionth of a millimeter
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dalton
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mass of a hydrogen atom
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Compound microsope
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uses light path to magnify object. Condenser focuses light on specimen. Light from specimen is focused by objective and eyepiece lenses.
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Organisms/things a compound microscope can see
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plant cell, animal cell, bacterium
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Organisms/things an electron microscope can see
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all of compound microscope + virus ribosome, globular protein, small molecule, atom
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LM magnifies up to
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x2,500
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EM magnifies up to
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x~500,000
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Resolution of LM microscope
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0.2 microns
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Resolution of EM microscope
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0.1 to 0.2 nm
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Why does transmission electron microscope (TEM) have better resolution?
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uses shorter wavelengths of electrons
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TEM main limitation
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cannot be used to examine living cells; only isolated, small cell components (e.g., ribosomes, viruses, large molecules)
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4 different types of LM
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1) Bright-field, 2) Phase-contrast, 3) Nomarski, 4)Dark-field
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Bright-field LM
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LM that can't be seen unless stained
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Phase-contrast LM
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LM that is useful for ordered-structures; e.g., mitotic spindles and striated muscle
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Nomarski LM
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LM that gives a 3D appearance of the cell; uses no stains
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Dark-field LM
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LM that illuminates the cell from the side
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Fluorescent Microscopy
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Microscopy that allows location and behavior of molecules in living cells to be followed in vitro
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Immunocytochemistry
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Fluorescently-labeled antibodies identify specific molecules
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Secondary antibody
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Used in Fluorescent Microscopy. Go on top of primary antibodies. Have a marker that is fluroescent that controls for amount of fluorescence.
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Glutaraldehyde
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What you "fix" cells in for LM and TEM. A buffer, isotonic fixative, that cells are prepared in to cross link proteins and preserve cell structure.
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What does a stain do to make the specimen visible?
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Interferes with white light, so only one color comes through.
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Osmium, lead, uranium, tungsten, and gold
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Heavy metals TEM specimens must be stained with
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Why are TEM specifmens stained with heavy metels?
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To deflect the electron beam.
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Positive staining vs. negative staining
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Positive: stain the specimen. Negative: stain around specimen.
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Osmium tetroxide
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binds to double bonds between carbon atoms in lipids (plasma membrane)
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Uranyl acetate
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binds to nucleic acids
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LM has light source, EM has?
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Electron gun
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Specimens have to be cut very ___ for TEM.
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thin, which could be a disadvantage
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What could deflect the electron beam in TEM?
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gases
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Autoradiography
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Technique used in LM and TEM that detects radioactivity in a cell
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Silver bromide
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solution to cover cells with in autoradiography. Reacts with isotope. Isotope strikes the silver bromide crystals and releases a silver grain that remains on the section over the radioactive source.
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Pulse-chase analysis
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method also used to expose specimens to radioactivity. Cells are exposed to radioactivity, which targets a specific place. Then the cells are washed of excess non-radioactive compound.
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Benefit of radioactivity techniques
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can trace movement throughout the cell over time
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thickness of cell membranes
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7-10 nm
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thickness of lipid bilayers
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5 nm
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Ampipathic
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Characteristic of membrane proteins: they have both hydrophillic and hydrophobic components
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Freeze fracture technique
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Revealed the Fluid-Mosaic Model of bilayer; uses freezing, cutting with knife, heavy metal coating, dissolving in acid, TEM
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Easibility of isolating peripheral vs. easibility of isolating integral proteins
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Peripheral: easy. Integral: difficult; must destroy whole bilayer.
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Membrane-associated proteins
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Proteins reside through/in one side of lipid bilayer
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Two configurations of transmembrane protein segments
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alpha-helix, beta-barrel
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What is the only peripheral protein category shown in the image?
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Protein-attatched proteins
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Peripheral proteins often regulate__?
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carriers and receptors
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How is lateral movement of plasma membrane slowed (fluidity)?
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By contact with cytoskeleton, EM, proteins of an adjacent plasma membrane, tight junctions.
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What kind of pump does the lysosome have?
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H+ pump, keeps it at a low pH
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What method does glucose get removed from gut epithelial cell from the basal end?
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Passive diffusion because of concentration gradient.
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All cell junctions use ____ spanning across the membrane.
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integral proteins
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Occluding junctions
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Tight junctions that form a belt encircling the inner lateral surfaces of epithelial cells and so provide a seal between the cells; at this seal, the plasma membranes of adjacent cells are held tightly together.
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Tight junctions maintain the _____ of the cells, e.g., some proteins involved in transport are confined to apical/basal surfaces.
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Polarity
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Claudin/Occludin
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Important family of proteins found at tight junctions that seal plasma membranes.
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Adherens junctions & Desmosomes general function
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Anchoring junctions that attatch cells to each other
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Adherens junctions are anchored to__
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actin filaments
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Desmosomes are anchored to__
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intermediate filaments (keratin)
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Cadherins
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Used by adherins junctions and desmosomes. Proteins that extend through the plasma membrane and are linked to actin filaments (adherens) and kertain (desmosomes).
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Catenin
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Linker proteins that attach cadherins to actin filaments ; used by adherens junctions
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How wide is the gap between neighboring plasma membranes set by adherens junctions and desmosomes?
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20-30 nm
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Keratin
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Intermediate filament desmosomes are attached to in cells
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Epidermolysis bullosa simplex
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Result of mutations in keratin genes, in which epidermal cells easily fracture under pressure causing blistering
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Focal adhesions & hemidesmosomes general function
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anchoring junctions that attach cells to EM
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Integrin function (focal adhesions)
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Transmembrane protein contained within focal adhesions that anchor the EM (such as collagen & fibronectin) to actin microfilaments.
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Integrin function (hemidesmosomes)
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Transmembrane protein contained within hemidesmosomes that anchor EM to intermediate filaments; attach cell to basal lamina
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Three types of cytoskeletal filaments
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1) Actin 2) Intermediate 3) Microtubules
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Focal adhesions & hemidesmosomes are found in what location of the cell?
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Basal side
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Distance between cells at gap junctions
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2-4 nm
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Connexons
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Proteins found in gap juncions
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How many connexin subunits in 1 connexon?
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6
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One connexon + another connexon allows what to go on?
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Creates an aqueous channel through which molecules up to 1,000 daltons can pass.
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What opens connexon channel?
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low Ca2+ or high pH
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What closes connexon channel?
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high Ca2+ or low pH
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What % of cell volume of ER is lumen?
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10%
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What does it mean that the ER is self-replicating?
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ER produces its own lipids and transmembrane proteins - many of which go into the Golgi and plasma membrane (PM)
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Flipase
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Enzyme that catalyzes transfer of phosphoplipid molecules made by the ER and transferred to the PM
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3 types of cells smooth ER (SER) is plentiful in
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1) cells producing steroid hormones (makes cholesterol, found in adrenal gland), 2) cells that detoxify drugs (in liver), and 3) in sarcoplasmic recticulum in muscle cells (calcium is sequestered for muscle relaxation)
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polyribosome (and location)
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several ribosomes present on an mRNA
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In general, what happens to the ribosomal subunits after translation of protein on ribosome (either free or RER) is complete?
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the L and S subunits are released from mRNA into the pool of ribosomal subunits, which can then be used to form polyribosomes of the RER or free polyribosomes
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Free polyribosomes translate what?
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proteins of the cytosol, mitochondria, chloroplasts and nuclei (also some peroxisomal subunits)
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RER ribosomes translate what?
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proteins for other cellular organelles (ER, PM, golgi, lysosomes, and cell exterior)
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Actions of small, large, mRNA, and tRNA during translation?
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Small binds to mRNA, tRNA and large bind to small. Translation begins.
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ER signal sequence
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One of the first parts of the protein that is made (16-30 a.a. long) during translation of protein on RER.
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Signal Recognition Particle (SRP) and sequence of events after?
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ER signal sequence binds to this, which temporarily stops translation until the complex of the SRP + ribosome binds to the SRP receptor on the ER membrane.
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Protein translocator and sequence of events after?
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channel the growing polypeptide passes through the ER membrane into the ER cisterna where the signal peptidase removes the signal sequence.
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Signal peptidase
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removes signal sequence
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Difference in timing and entry of translation between free and RER ribosomes?
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Entry of proteins into organelles happens after translation through free ribosomes (called Posttranslational entry). Translation of proteins occurs during entry into RER through RER ribosomes (called cotranslational entry)
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Misfolded proteins in ER are __?
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exported to the cytosol and broken down by proteasomes
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chaperone proteins
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aid in translational process
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stop-transfer signal
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recognized by translocator in ER membrane, which discharges the protein into the membrane. Anchors the protein into the membrane.
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2 characteristics of stop-transfer signal
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hydrophobic & alpha-helix
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General function of the Golgi
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membranes of this organelle modify, sort, and package proteins and lipids from the ER
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Clathrin coated pits: Cargo binds to__, which binds to__, which binds to__.
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cargo receptor, adaptin, clathrin
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Clathrin vesicles are associated with which organelle?
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Golgi
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Dynamin
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causes the chlatrin-coated pit to pinch off to form a coated vesiclel
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Function of SNARES
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ensures that vesicles reach the appropriate compartment. Fuse vesicle and target membranes together.
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What is an important event hat happens to proteins as they are translated in the ER? (adds something to them)
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Glycosylation (adding of carbs)
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COP-II coated vesicles
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involved only in transport from the RER to the cis Golgi
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COP-I coated vesicles
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involved only in transport from the cis Golgi to medial or trans Golgi
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Retrograde transport is only done by__?
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COP-I vesicles
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KDEL receptors
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ER retention signal for ER resident proteins in order to return to the ER after being transported to the golgi. Found in ER and on golgi. KDEL receptors bring back proteins such as chaperones to the ER to be used again.
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What are examples of Golgi modification of proteins?
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removal or oligosaccharides, addition of sugars to oligosaccharides, phosphorylation
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Three main pathways that a protein secreted from the Golgi can follow
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1) Signal-mediated diversion to lysosomes, 2) Signal-mediated diversion to secretory vesicles (Regulated Secretory Pathway), 3) Secretion via the constitutive secretory pathway
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mannose-6-phosphate
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secretory proteins are tagged with this at the cis Golgi. This signal then binds with mannose-6-phosphate receptors at the trans Golgi, and directs these proteins specifically to lysosomes
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Location where proteins of the regulated secretory pathway are packaged into secretory vesicles
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Trans Golgi network (TGN)
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Type of situation in which exocytosis by regulated secretory pathway by secretory vesicles occurs
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Occurs rapidly in response to hormonal or neural stimuli (insulin from beta cells).
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Difference between regulated and constitutive pathway
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In constitutive, golgi products are immediately released at the cell surface; e.g., ECM
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How does the golgi know where to direct certain proteins to specific vesicles?
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proteins have a signal sequence
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Phagocytosis
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cell engulfs entire cells or parts of cells
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Leishmania
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parasite that uses phagocytosis to enter host cells
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Pinocytosis
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non-selective uptake of small vesicles
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transcytosis
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one result of receptor-mediated endocytosis where specific molecules pass unchanged through the cell (antibodies from mother's milk)
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another example of receptor-mediated endocytosis
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LDL receptors, LDL, chlathrin, cholesterol
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Endosome
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Smooth-surfaced vesicles resulting from receptor-mediated endocytosis. Membranous structures that serve as a sorting station for material that enters the cell by endocytosis.
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How/why can some ligands remove themselves from their receptors in an endosome?
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Receptors need to be recycled back to the membrane in some cases so more ligands can be endocytosed. The low pH of endosome causes the dissociation of ligands from receptors.
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Lysosomes
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membrane-enclosed compartments containing approximately 40 enzymes. Digest molecules that enter the cell by receptor-mediated endocytosis and phagocytosis
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How do lysosomes stay at a a low pH?
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ATP-driven proton pumps
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How are lysosomal enzymes protected against autolytic protease digestion?
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They are glycosylated
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Autophagy
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When lysosomes digest things from their own cells
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What prevents the receptor in an endosome from taking back a lysosomal enzyme to the ER?
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removal of the phosphate group (from mannose-6-phos)
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Are released lysosomal enzymes to the cell exterior damaging? Why or why not?
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No, because these enzymes require an optimal acidid pH only found in a lysosome.
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Lysosomal Storage Diseases
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diseases caused by the buildup of enzyme substrates due to a lack of enzymatic degradation
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Inclusion-cell (I-cell) disease
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An inherited lysosomal storage disorder caused by a deficiency of an enzyme that is responsible for phosphorylating mannose residues to M6P in the golgi. Without M6P to target them to the lysosomes, these enzymes are transported from the golgi to extracellular fluid. Causes accumulation of mucolipids and mucopolysaccharides. Causes coarse facial features, skeletal abnormalities, and mental retardation.
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Tay-Sach's Disease
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disease caused by the absence of a lysosomal enzyme (Hexosaminidase A) that normally destroys a ganglioside. This causes ganglioside accumulation in the brain resulting in mental retardation, blindness, etc.
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Peroxisomes
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Spherical organelles that contain enzymes that produce hydrogen peroxide. Also contain catalase, which is able to breakdown excess hydrogen peroxide. Used for detox and breakdown of fatty acid molecules.
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Where are peroxisomes found and why?
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in liver cells because catalast can inactivate toxic organic molecules (detoxification) by using hydrogen peroxide.
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Zellweger's Syndrome
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Peroxisomes bud from ER and grow by importing proteins and lipids from the cytosol. This syndrome occurs due to a faulty import signal on a peroxisomal enzyme. In this syndrome, peroxisomes lack key enzymes leading to the accumulation of toxic molecules.
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Neonatal Adrenoleukodystrophy
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very long chain of fatty acids cannot be oxidized and so accumulate in the brain, destroying myelin sheaths, and in the adrenal glands, causing a defiiency of adrenal steroid hormones. This is because peroxisomes cannot import necessary degradative proteins for oxidation to occur.
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Outer Mitochondrial Membrame (OMM)
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separates the mitochondrion from the cytosol
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Inner Mitochondrial Membrane (IMM)
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contains enzymes for oxidation reactions and ATP synthases
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Cristae
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Invaginations of the IMM
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Mitchondrial Matrix and what does it contain?
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compartment that contains enzymes of the Krebs Cycle and enzymes for oxidation of pyruvate and fatty acids. ATP synthases also extend into here from the IMM. Also where mitochondrial DNA (lacks histones) is.
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Intermembrane Space of Mitochondria and site where what accumulates?
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space between the OMM and IMM. Where protons accumulate.
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In the cytosol, one molecule of glucose is broken down by glycolysis into__(net).
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2 pyruvate with a net gain of 2 ATP and a reduction of 2 molecules of NAD+ to 2 NADH.
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What is then imported into the mitochondria?
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NADH and pyruvate
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In the mitochondrial matrix, pyruvate and fatty acids are converted into__
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acetyl CoA
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Electron-transport respiratory chain
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in the IMM where high-energy electrons from NADH and FADH2 pass along. This creates a proton gradient that drives oxidative phosphorylation.
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Protons are being pumped where?
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from the matrix into the intermembrane space
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pumping of protons from matrix into intermembrane space by electron-transport chain creates__that causes__
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an electrochemical proton gradient between the intermembrane space and the matrix that causes the flow of protons through ATP synthase, which phosphorylates ADP to ATP.
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the electrons from the electron-transport chain finally reach __ complex and reduce ___ to ___.
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cytochrome oxidase, gaseous oxygen, water
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Oxidative Phosphorylation
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the phosphorylation of ADP to ATP driven by the flow of protons across the IMM (by way of the electron-transport chain)
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2 pyruvate --> 2 acetyl-CoA yields__
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2 CO2 and 2 NADH
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Citric Acid Cycle yields__(2 turns)
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4 CO2, 2 GTP, 6 NADH, 2 FADH2
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TOTAL Yield of glycolysis + pyrucate decarboxylation + citric acid cycle (2 turns)
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2 ATP + 2 GTP + 6 CO2 + 10 NADH (x 3 = 30 ATP) + 2 FADH2 (x 2 = 3 ATP)
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Why do protons have to be pumped into the intermembrane space from the matrix?
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the IMM is impermeable to protons
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Thermogenin
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allows protons to reenter the matrix without ATP synthesis. The energy of the proton motive force is released as heat. Brown fat cells in babies have a natural coupling agent.
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Variant to universal code in mtDNA
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UGA (usually stop) codes for tryptophan
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Mito genome codes for 13 subunits found where?
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OXPHOS complexes of the IMM
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why is OXPHOS genetics complex?
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they contain nuclear genes and mitochondrial genes
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chloramphenicol (CAP) and cycloheximide (CH)
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because mitochondrial DNA has similarities to prokaryotic DNA, it is sensitive to CAP and insensitive to CH. In Eukaryotes, it is opposite.
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Why is CAP and CH sensitivity opposite in eukaryotes than prokaryotes?
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Prokaryotes and Eukaryotes have ribosomal subunits of different sizes and shapes; antibiotics are usually specific for one type of subunit.
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Heteroplasmy of mitochondrial population
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mutations in mt DNA can result in this. Some mitcohondria have normal DNA, while others have damaged DNA. If not enough normal mitochondria to make necessary levels of ATP, then cell damage or death results.
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Leber's Hereditary Optic Neuropathy
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a cause of blindness that is maternally inherited. Caused by a mutated NADH dehydrogenase, which causes lower ATP production in the mitochondria
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The majority of mito proteins are coded by __ and translated on __.
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nuclear genes, cytosolic polyribosomes
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Hsp70
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chaperone proteins that 1) prevents mito proteins from folding 2) is necessary for their import into the mitochondria
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How does the mito protein find the mitochondria?
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a signal sequence on the protein targets it to a receptor on the OMM
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In addition to the signal sequence, what two things are required for the import of the mito protein into the mitochondria?
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1) proton gradient across the IMM, 2) ATP
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Mito proteins not coded by nuclear DNA are coded by__?
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mito DNA itself, which is then transcribed into mRNA, and translated on mito ribosomes in the matrix.
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TOM complex
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protein translocator on OMM. Helps get protein in the matrix until the protein is then helped by TIM.
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TIM complex
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protein translocator on IMM. Gets mito protein into matrix.
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Hsp60
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proteins that fold the unfolded protein once it is in the mitcohondrial matrix
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Main role of intermediate filaments
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to reinforce cells and hold them together
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Nuclear lamins
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IF's that occur within the nucleus
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diameter of microtubules
|
24 nm
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diameter of IF's
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10-12 nm
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diameter of actin
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7 nm
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Structure of an IF
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8 tetramers twisted together
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monomer --> __ --> __ (what is unique about this one?)
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dimer by noncovalent bonds, tetramer. 2 dimers of opposite polarity associate in a staggered way
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Amyotrophic Lateral Sclerosis caused by__
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abnormal neurofilaments that cause damage to axons
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Desmin
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an IF in muscle cells that occurs near the Z-line.
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Desmin-related myopathy
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the muscle fibers become disorganized
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Progeria
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mutations to the proteins of the nuclear lamina
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Structure of a Microtubule
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walls consist of 13 protofilaments comprised of long heterodimers
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Each heterodimer consists of__
|
an alpha tubulin and a beta tubulin molecule
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Vinblastine/Vincristine
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drugs that depolymerize MT heterodimers. Used as cancer drug.
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alpha + beta heterodimer size
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8 nm (4 nm each)
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centrosomes
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where MT nucleation occurs. These are MT-organizing centers (MTOC). Where centrioles are located.
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Mictrotubule-associated proteins (MAPs)
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proteins involved in the polymerizing of MTs
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Centrosomes have >50 __
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gamma-tubulin rings each that nucleate a MT
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Guanosine Triphosphate (GTP)
|
required for MT growth
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Kinesin & dyesin, specific function?
|
motor molecules associated with MT growth. They are ATPases that convert chemical energy of ATP into mechanical energy.
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Dyenin molecules move toward which end of a MT?
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minus
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Most kinesin molecules move toward which end of a MT?
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plus
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What are kinesin and dyesin able to do as they move across a MT?
|
transport vesicles containing cargo
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centrosomes give a cell __ due to their position and due to __ of MTs
|
polarity
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% of a cell's tubulin in the form of MTs and % in the form of a pool of tubulin dimers?
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50%, 50%
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Taxol
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Drug that binds to MTs. Inhibits mitosis. Acts as a cancer drug.
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How are actin filaments formed?
|
by polymerization of globular actin (G-actin) monomers
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ARP complex
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Where actin nucleation occurs. A site which includes two actin-related proteins (ARPs)
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Listeria
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bacteria (a human pathogen that causes food poisoning) polymerize G-actin to F-actin to propel themselves through their host's cytoplasm
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Microvilli and stereocilia
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projections from cell surfaces consisting of a bundle of F-actin filaments bound to each other laterally
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Gelsolin, filamin, fimbrin
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Actin-binding proteins
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Myosin
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Motor molecule associated with actin. An ATPase that converts ATP into mechanical energy.
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Two other areas actin is found
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1) cytokinesis 2) muscles (myosin)
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Formation of F-actin
|
2 parallel protofilaments (made from G-actin monomers joining head to tail) with the same polarity bind around each other tightly to form a 7nm diameter right-handed helix
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Things/molecules needed for actin polymerization
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ARP complex, ATP, actin monomers
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What promotes dissasembly of actin filaments?
|
hydrolyzing of ATP to ADP
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What is needed for depolymerization of actin?
|
depolymerizing protein, capping protein, severing proteins
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Thymosin
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A monomer-sequestering protein that sequesters actin monomers so that extensive polymerization cannot occur
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Provides the energy for binding, detatchment, and rebinding of myosin to actin filaments
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ATP
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Releases actin from "ground"
|
hydrolysis of ATP
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Myosin moves toward which end of actin?
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plus
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myosin-II
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Arranged as a bipolar filament. Results in a shortening of the distance between the + ends of the actin filaments
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Length of kinesin "step" along MT
|
8 nm
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Each step of kinesis requires__
|
hydrolysis of 1 molecule of ATP
|
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|
Charcot-Marie-Tooth (CMT) neuropathy
|
involves mutation of kinesin found in axons leading to axonal degeneration
|
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Anesthetic lidocaine
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inhibits kinesin movement in axons. Stops transport of neurotransmitters.
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Retinitis pigmentosa
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defects in another kinesin that affects transport in retinal cells
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Myosin-VI
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mutations in this cause deafness
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Herpes use__to move along MTs
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kinesin
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Cilia
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Eukaryotic flagella
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axoneme
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whip-like appendages on eukaryotic cells whose inner core consists of MT-based cytoskeleton
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9+2 axoneme structure
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9 MT doublets surrounding a pair of MTs
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Nexin (and radial spokes)
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a proteinous inter-doublet linkage that prevents microtubules in the outer layer of axonemes from movement with respect to each other
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ATP causes conformational changes in the dynein arms that causes __
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a doublet to slide along its neighbor
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What prevents the sliding of dynein arms from going too far?
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Nexin and radial links. These serve to convert doublet sliding to bending of the entire flagellum.
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Immotile Cilia Syndrome
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Situation in which humans lack inner and outer dynein arms. They cannot clear mucus with inhaled particles from their respiratory epithelia, and they have recurrent lung infections. Males are infertile.
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Primary cilia
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short structures lacking dynein; they do not move
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Role of primary cilia
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in kidney tubules, they serve as flow sensors to monitor fluid movement.
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Polycystic kidney disease
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caused by defects in primary cilium that leads to a failure of fluid monitoring. This leads to overproduction of kidney cells leading to kidney failure.
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histone
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highly alkaline proteins found in eukaryotic cell nuclei that package and order the DNA into structural units called nucleosomes. Pack in an orderly fashion to be used later.
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each chromosome consists of long DNA that has specialized nucleotide sequences for 3 things
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1) the centromere, 2) the two ends of the chromosome (telomeres), 3) the replication origins of DNA
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nucleosome
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fundamental unit of the chromosome. A segment of DNA wound in sequence around an octomer of histone protein cores.
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nucleosome core particle (NCP)
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the octomer of histones
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length of DNA in a diploid human nucleus
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~6 feet (nucleus is only 6 microns in diameter)
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how much shorter is packaged DNA than extended length
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10,000 times
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the 6 histone proteins have a high content of __
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basic a.a.'s
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Length of 1.65 turns of DNA around each NCP
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146 base pairs long
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Length of linker DNA between adjacent NCPs
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50 base pairs long
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Nuclear lamins
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Intermediate filaments in the inner nuclear membrane that help determine nuclear structure. Peripheral component of the nuclear matrix that extends throughout the nucleoplasm
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The nuclear lamina is the peripheral component of__
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the nuclear matrix that extends through the nucleoplasm
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nucleoplasm
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fluid found in the nucleus
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What causes nuclear lamina and nuclear envelope to disperse? What causes them to reappear?
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phosphorylation, dephosphorylation
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Structure of nuclear envelope
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Consists of inner (ONM) and outer nuclear membranes (ONM)
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Relationship between ONM and ER (2 things)
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1) continuous with ER lumen, 2) similar chemical composition
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__ often appear on the ONM
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ribosomes
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INM vs. ONM (2 differences)
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1) different composition and 2) INM has binding sites for lamins and chromosomes
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euchromatin vs. heterochromatin
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euchromatin is active, heterochromatin is inactive
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nucleoporins
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proteins found within nuclear pores
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function of nuclear pore
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to allow diffusion of small molecules and transport of large ones into the nucleus
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nuclear pores have a high rate of __ transport
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bidirectional (in and out at same time)
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maximum size molecules can be to enter nuclear pores through diffusion
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40,000 daltons
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large molecules that cannot enter through diffusion enter nuclear pores by__
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active transport
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nuclear localization signal (nuclear import signal)
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signal sequence on a protein required for large molecules to enter the nucleus through nuclear pores. Binding of nuclear localization signal and receptor causes the pore to open
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Lamins' function with chromosomes
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help organize and anchor them during interphase
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nucleolus, and contains what?
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structure in the nucleus that contains repeated ribosomal RNA genes and their transcriptional products that are being processed and assembled into ribosome subunits.
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RNA polymerase I
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transcribes the rRNA genes
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sequence of events beginning from transcription of rRNA genes (5 steps)
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1) RNA pol I transcribes rRNA genes into one pre-rRNA molecule (a single transcript), 2) this pre-rRNA is enzymatically cleaved into smaller rRNA molecules, 3) these small rRNA molecules then join with ribosomal proteins to form small & large ribosomal subunits, 4) these subunits then leave the nucleolus and leave leave the nucleus through nuclear pores, 5) they form a ribosome in the cytosol.
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Phases of cell cycle
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G1, S, G2, M
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Phosphorylation in late G2 causes 3 things
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1) chromosome condensation, 2) spindle formation, and 3)nuclear lamina and nuclear envelope breakdown
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phase of cell cycle where chromosomes are replicated
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S-phase
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phase of mitosis where chromatids separate
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Anaphase
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G(o)
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stage cells are probably blocked in if they are not actively dividing
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cyclin dependent kinase
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causes widespread phosphorylation in G2 phase (nuclear lamina, histones)
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phosphorylation of nuclear histones causes__
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chromosome condensastion and this stops transcription
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consequence of chromosome condensation and stopping of transcription
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nucleolus disappears
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phosphorylation also drives what about MTs?
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drives polymerization of MTs forming the mitotic spindle
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summary of replication of centrioles and centrosome
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Early in G1, there is a single centrosome containing a pair of centrioles. Later in G1, 2 centrioles separate. In S-phase, 2 new centrioles appear. By G2, new centrioles are grown. In M phase (prophase), centrosomes separate.
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condensin
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protein that helps condense chromosomes
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2 reasons why chromosomes condense
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1) helps sister chromatids adopt a side-by-side configuration, and 2) prevents chromosomes from tangling during mitosis
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Three types of spindle MTs
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1) aster MTs, 2) overlapping MTs, 3) kinetochore MTs
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aster MTs are where?
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spindle poles
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overlapping MTs are where?
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nuclear equator
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Prophase (3 things that happen)
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1) chromatin condenses to well-defined chromosomes (each chromosome has 2 sister chromatids), 2) MTOC (centrosome) splits into two halves and they start to move to opposite sides of the cell by way of MT movement, 3) mitotic spindle forms between the centrosomes
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kinetochore
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a plate-like region on the surface of the centromere
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protein involved in sliding of MTs during mitosis
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kinesin
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Prometaphase (4 things that happen)
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1) nuclear envelope is disrupted to allow MTs access to chromsomes, 2) nucleolus disappears, 3) kinetochores assemble at each centromere on the chromosomes, 4) kinetochore MTs bind to kinetochores
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kinetochores first bind __ to astral MTs
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laterally
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Metaphase (2 things)
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1) Chromosomes align at the metaphase plate, 2) chromosomes are maximally condensed
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Anaphase
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Kinetochores separate and chromosomes move to opposite poles
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cohesin
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protein that keeps sister chromatids together. Later destoyed so chromatids can separate
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Anaphase A
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Kinetochore MTs depolymerize. Since there are attached at the centrosome, they pull daughter chromosomes apart and towards the poles.
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Anaphase B
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Sliding occurs between overlapping MTs due to + end-directed kinesin-related proteins. At the same time, tubulin heterodimers are added to the + ends of the polar MTs to maintain the overlap between them. These two events push the poles apart. Astral MTs can contribute to pulling by using dyenin at the cell periphery.
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Dynein and plasma membrane relationship
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in some cells, astral MTs contact the plasma membrane via dynein. As the dynein is - end directed, it will pull the minus end of the astral MT with its attatched centrosome towards the plasma membrane.
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Telophase (3 events happen)
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1) Chromosomes begin to decondense to form chromatin, 2) nuclear lamina, nuclear envelope, and nucleolus reforms, 3) kinetochore MTs disappear
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What drives late anaphase and telophase?
|
dephosphorylation
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What reforms after dephosphorylation?
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nuclear lamina, nuclear envelope, nucleolus
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dephosphorylation causes what to happen to chromosomes?
|
decondensation
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Dephosphorylation allows what to resume?
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transcription
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cleavage furrow
|
forms around the middle of the cell during cytokinesis by constriction of actin and myosin. Contains a contractile ring consisting of actin and myosin filaments.
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Provides phospholipids for plasma membrane during cytokinesis
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Golgi
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Necrosis, and effects
|
Type of cell death that occurs when cells are damaged: cells swell, burst, and cause an imflammatory response.
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Apoptosis, and effects
|
Nucleus condenses in an organized manner, endonucleases breaks its DNA into small fragments (multiples of 200 base pairs), and the cell is digested by macrophages or surrounding cells. There is no imflammatory response.
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Prokaryotic cells have: a membrane?
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yes
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a cell wall?
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yes
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organelles?
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no
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cytoskeletal components?
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no
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histones?
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no
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nucleosomes, nucleolus, nuclear envelope?
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no
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Prokaryotic cells have the same __ and __ as eukaryotic cells
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DNA structure, genetic code
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