Lecture 5 - Cytoskeleton Flashcards by Luke Shumaker

What is the diameter of microtubules?

24-25nm

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What is the diameter of microfilaments?

6-7nm

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What is the general organization of microtubules?

Curvy structures that radiate from mitochondrial organizing center (MTOC)

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Where is the general organization/location of microfilaments?

Linear bundles beneath the plasma membrane

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What is the diameter of intermediate filaments?

10nm

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What are the subunits of microtubules?

Tubulin heterodimer, each made up of alpha and beta tubulin

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What molecule do all tubulin monomers bind?

GTP

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What provides the energy for polymerization of microtubules?

GTP

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Microtubules have a (+) and (-). What is the significance of these ends?

(+) end is bound to GTP and is the side that favors additional polymerization. (-) is bound to GDP and this favors dissociation.

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What is the primary function of microtubules?

Transport (organelles within cell, along axon)

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What end to kinesins move towards?

(+) end: TureKKKK is (+) about the state of the earth.

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What end to dyneins move towards?

(-) end: Dying is (-).

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By what mechanism do vinblastine, vincristine, nocodazole, and colchicine inhibit cell division?

Prevent assembly (polymerization) at (+) end of microtubules.

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By what mechanism does paclitaxel (Taxol) inhibit cell division?

Taxol binds (-) end and prevent the dynamic assembly and disassembly of microtubules required during cellular division.

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What is the role of a basal body?

Located at the base of a cilia and organizes an array of microtubules.

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What is the pattern of microtubule branching in basal bodies?

9 x 3 (with one microtubule in the middle of the 9 groups)

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How many monomers long is a complete turn of a standard microfilament?

14 (37nm)

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What is the name of monomeric actin?

G-actin (G for globular)

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What is the name of polymerized actin?

F-actin (F for filamentous)

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What molecule promotes polymerization of G-actin?

ATP

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Which is more stable: microfilaments or microtubules?

Microfilaments

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What is “treadmilling?”

Continuous growth and (+) end at same rate of continuous disassembly at (-) end.

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What proteins (3) regulate actin polymerization and what is the role in regulation of each protein?

1) Profilin - promotes actin assembly on growing F-actin filaments, binds g-actin and prevents polymerization, functions in ADP to ATP exchange in actin monomers to to prepare for polymerization into F-actin
2) Thymosin - negative regulation by binding g-actin
3) Gelsolin - sever & cap actin filaments, capping prevents addition and loss of actin monomers. Functions in response to Ca2+, pH, and phospholipids.

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Where are actin stress fibers located?

Bundled along basal cell surface and terminate at focal adhesions.

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What organizes the actin of stress fibers?

alpha-actinin & talin

Where are actin adhesion belts located?

Circumferential actin near apical cell surface

What is the role of actin adhesion belts?

Stabilize cadherin-mediated adherens junctions

What organizes actin adhesion belts?

catenins & alpha-actinin

What actin structure provides a scaffold for intracellular signal transduction?

Adhesion belts

A fungal toxin (and alkaloid) that binds (+) end of actin and blocks polymerization.

Cytochalasins

Amanita mushroom poison, binds f-actin and prevents disassembly of (-) end

Phalloidin

What is the remedy for phalloidin poisoning?

Raw hamburger

Bind G-actin and induces F-actin depolymerization (derived from sea sponge)

Latrunculins

Fingerlike extension at cell surface that increase surface area

Microvilli

What organizes the actin of microvilli?

villin and fimbrin

What causes hereditary spherocytosis?

mutant spectrin

What protein cross-links actin into 2D mesh?

spectrin

Where is spectrin most prominent?

RBCs (erythrocytes), but ubiquitous

What links spectrin to Band 3 and Glycophorin?

Ankyrin

What regulates the assembly and disassembly of intermediate filaments?

phosphorylation

What are the six types of intermediate filaments?

1) Acidic keratins 2) Basic to neutral keratins 3) Vimentin, Desmin, Glial fibrillary acid protein (GFAP), Peripherin 4) alpha-internexin 5) Nuclear laminins 6) Nestin

What is the significance of cytokeratins?

Change in cytokeratin expression is among the most common markers of neoplasia. All epithelial cells express at least on AK and one B-NK.

List the Type III intermediate filaments and their roles/significance.

Vimentin - mesenchymal, endothelial, and leukocytes. Useful marker of dedifferentiation of invasive cancer carcinomas. Desmin - skeletal muscle in Z-disk, smooth muscle Glial fibrillary acid protein (GFAP) - astrocytes and Schwann cells Peripherin - neurons of peripheral nervous system (VDGP)

What type of intermediate filaments run along axons and dendrites and can be greater than 1 meter in length?

Type IV

Where is alpha-internexin found and what type of intermediate filament is it?

CNS-spinal cord, optic nerve; Type IV

What type of intermediate filament are nuclear laminins?

Type V

1) What is significant about nuclear laminins, 2) what structure do they support, 3) and what can cause rapid disassembly?

1) FORM INTO A SQUARE LATTICE (All other intermediate filaments form fibers.) 2) Nuclear membrane 3) Serine phosphorylation

What type of intermediate filament is Nestin and where is Nestin found?

Type VI, Stem cells of CNS

What is the approximate size of a mitochondrion?

0.2 uM to 7uM

What structure in the mitochondrial outer membrane allows molecules

Porins

What tissues/organs are most affected by mitochondrial diseases?

High energy organs/tissues

MITOCHONDRIAL DISEASE: Paralysis of eye muscles & mitochondrial myopathy

CPEO (chronic progressive externa opthalmoplegia)

MITOCHONDRIAL DISEASE: Abnormal movements involving muscular rigidity; frequently accompanied by degeneration of the basal ganglia of the brain.

Dystonia

MITOCHONDRIAL DISEADE: CPEO combined with such disorders as retinal deterioration, heart disease, hearing loss, diabetes, & kidney failure

KSS (Kearns-Sayre syndrome)

MITOCHONDRIAL DISEASE: Progressive loss of motor & verbal skills and degeneration of the basal ganglia; potentially lethal childhood disease.

Leigh's syndrome

MITOCHONDRIAL DISEASE: Permanent or temporary blindness stemming from damage to the optic nerve.

LHON (Leber's hereditary optic neuropathy)

What effect does mitochondrial dysfunction have on sperm?

Immotile - leading to male infertility

In an H&E stain how does rER stain?

Purple with hematoxylin (basophilic)

What does an extensive rER indicate when seen in a cell?

That cell likely synthesizes many proteins for secretion

Where is cholesterol produced?

Where is ceramide produced and what is makes up ceramide?

ER, serine + FA = sphingosine & sphingosine + FA = ceramide

What is ceramide a precursor for?

Glycolipids and sphingomyelin

Where are N-linked (Asn) oligosaccharides often attached to proteins?

Where does steroid and triglyceride synthesis occur?

sER

What organelle is involved in detoxification?

sER

What are the major functions (5) of the golgi?

1) Modify N-oligosaccharides 2) Distribute non-cytosolic proteins to plasma membrane, lysosomes, & secretory vesicles. 3) Assembles proteoglycans from proteoglycan core proteins 4) Adds mannose-6-phosphate to proteins that are targeted for lysosomes 5) Sulfates sugars on proteoglycans.

Where will a protein tagged with mannose-6-phosphate in the golgi end up?

A lysosome

Where are peroxisomes primarily found?

LIVER, kidney pct, skeletal muscle

What are the primary oxidative enzymes (3) found in peroxisomes?

1) D-amino acid oxidate 2) urate oxidase 3) catalase

What is the diameter of a peroxisome?

0.15 - 0.25 uM

What are the functions of peroxisomes in human liver specifically?

1) Oxidize excess FAs 2) Breakdown H2O2 (is a product of FA ox, broken down by catalase) 3) Cholesterol synthesis 4) Synthesis of bile acids 5) Synthesis of lipids used to make myelin 6) Breakdown of excessive purines (AMP, GMP) to uric acid

Lethal condition (1st decade of life) where no functional peroxisomes are produced. Peroxisomal enzymes are not transported to organelle (peroxisome membranes remain empty).

Zellweger syndrome

What causes Zellweger syndrome?

Genetic defect: gene encoding the receptor for peroxisome targeted proteins is defective.

Is the plasma membrane visible with LM?

No - need TEM

Is the rER visible with LM?

Yes - stains basophilic (purple/blue)

Is the sER visible with LM?

Yes - when abundant, clear "moth-eaten" appearance to cell

Is the golgi visible with LM?

Yes - clear region near nucleus (ex. plasma cell)

Is the mitochondria visible with LM?

Yes - cytoplasm appears granular, stain with Janus green B

Are lysosomes visible with LM?

Yes - stain for acid phosphatase

Are endosomes visible with LM?

Yes - only large ones, still difficult to see

Are peroxisomes visible with LM?

Yes - stain for catalase

Are microtubles visible with LM?

Yes - only "bundles" that are stained with fluorescent dye or use of phase contrast imaging

Are centrioles visible with LM?

Yes - with fluorescent tag

Are intermediate filaments visible with LM?

Yes - only bundles, not individual filaments

Are ribosomes visible with LM?

Are microfilaments visible with LM?

Yes - bundles with fluorescent dyes

What protein transports vesicles between ER & golgi?

COP-II (Coat protein II)

What protein transports vesicles between golgi stacks?

COP-I (Coat protein I)

What protein mediates vesicle transport between the plasma membrane and the TGN?

Clathrin

What is the primary and secondary function of lysosomes?

Primary - storage Secondary - degradative processes

How do lysosomes become acidified?

Proton pump in membrane

What coat protein facilitates pinocytosis?

caveolin

Ingestion and degradation of foreign material take into the cell by receptor-mediated endocytosis or phagocytosis

Heterophagy

Segregation and digestion of an organelle or other cell component with membranes from the rER.

Autophagy

What protein facilitates receptor-mediated endocytosis?

Clathrin

How many clathrin coated pits exist per cell and what percent of the cell surface is this. What percent of cell receptors are found in coated pits?

500-1000 pits/cell, 2-4% of cell surface, 70% of cellular receptors

What are the three possible outcomes of receptor-mediated endocytosis (provide an example for each)?

1) Ligand degraded in lysosome and receptor recycled (ex LDL) 2) Ligand and receptor recycled (ex transferrin) 3) Ligand and receptor both degraded (Epidermal growth factor)

How do cholera and tetanus toxin get into cells?

Clathrin independent pathway

Deficiency in hexosaminidase resulting in accumulation of glycolipids (gangliosides) in NS.

Tay-Sachs

Defective glucocerebrosidase causing glucocerebrosides to accumulate in the CNS and spleen.

Gaucher's syndrome

Defective sphingomyelinase causing accumulation of sphingomyelin and cholesterol in CNS and spleen.

Neiman-Pick disease

Low occurance of LDL receptor, binds LDL poorly or LDL cannot be internalized.

Hypercholesterolemia

How does Ebstein-Barr Virus (EBV) enter cells? What does EBC cause?

Binds to receptor present on B cells. Causes mononucleosis & contributes to development of Burkitts lymphoma

How does Influenza virus enter cells?

Hemagglutinin binds to carbohydrates on target cell surface and is endocytosed.

Failure to "tag" (by phosphorylation) all the hydrolytic enzymes that are supposed to be transported from the golgi to the lysosomes (they lack M6P tag).

I-cell disease ("inclusion cell disease)

Failure to synthesize an alpha-L-iduronidase.

Mucopolysaccharidosis (MPS-1)

What is the function of alpha-L-iduronidase?

It is required to break down proteoglycans like heparan sulfate.

What enzyme is the function of Beta-N-acetylhexosaminidase? (Also, what disease results from its deficiency?)

Converts ceramide to to glucose.

What are the hallmarks of LSD?

- Unusual fascial features - Cloudy eyes - Purplish/bluish skin - Distended belly - Short stature - Muscle weakness/lack of muscle control

What causes sickle cell anemia?

Modification of spectrin skeleton