Cell Bio Ch. 13 - Exam 2

Cytoskeleton

A network of interconnected filaments and tubules extending through the cytosol.

Spectraplakins

Linker proteins that connect intermediate filaments, microfilaments, and microtubules.

Plectin

Found at sites where intermediate filaments connect to microfilaments and microtubules.

Tubulin

Sub-unit that makes up microtubules.

Actin

Sub-unit that makes up microfilaments.

25 nm

Diameter of microtubules in nm.

8-12 nm

Range of diameter of intermediate filaments in nm.

7 nm

Diameter of microfilaments in nm.

Cytoplasmic microtubules

Responsible for maintaining axons, formation of mitotic/meiotic spindles, maintaining cell shape, movement of vesicles, and orientation of cellulose microfibrils during plant wall growth.

Axonemal microtubules

Stable microtubules that utilize propulsion; forms cilia, flagella, and basal bodies. Has a 9+2 arrangement.

9+2 arrangement

Refers to the structure of microtubules having 9 doublets of microtubules surrounding 2 singlet microtubules.

Italicize

Done to identify a phrase as referring to a gene, rather than a protein.

TUBA1A

Protein responsible for α-tubulin.

TUBB2B

Protein responsible for β-tubulin.

Tubulin isoforms

Closely related genes that code for slight variations in α- and β-tubulin.

GTP

Substance that binds to the N-terminal domain of a tubulin protein.

Colchicine

Assembly inhibitor that can bind with the central domain of a tubulin protein by binding to β-subunit of tubulin heterodimers. Prevents further addition of tubulin.

C-terminal

Domain of a tubulin protein that can interact with microtubule-associated proteins (MAPs).

Dimers

All ___ in microtubules are oriented the same way.

Protofilaments

Because of dimer orientation, ___ have an inherent polarity.

Positive

Charge of a beta sub-unit.

Negative

Charge of an alpha sub-unit.

15 nm

Inner diameter of a microtubule in nm.

8 nm

Size of an alpha-beta protofilament dimer in nm.

Singlet

Simple tube comprised of 13 protofilaments.

Doublet

Contains one 13-protofilament tubule and one additional incomplete ring of 10 or 11 protofilaments.

A tubule

Refers to the 13-protofilament tubule in a doublet or triplet.

Cytoplasm

Place where singlet microtubules are most commonly found.

Cilia, flagella

Structures formed by doublet microtubules.

Basal bodies, centrioles

Structures formed by triplet microtubules.

Guanosine Triphosphate

What does GTP stand for?

<0.5 mM

Mg2+ concentrations of ___ inhibit nucleation and assembly.

>1.0 mM

Mg2+ concentrations of ___ promote disassembly.

Nucleation

The process of aggregating tubulin dimers into oligomers.

Oligomer

A structure made up of a small number of repeating monomers.

Elongation

The addition of more sub-units to a forming microtubule.

Protofilament assembly

First step of microtubule assembly.

Sheet assembly

Second step of microtubule assembly.

Microtubule elongation

Third step of microtubule assembly.

Lag phase

The phenomenon of microtubules being slow to form at the start, due to the process of nucleation being slow.

Plateau phase

When the mass of microtubules reaches a point where the amount of free tubulin is diminished, and the assembly is balanced by disassembly.

Critical concentration

The tubulin concentration at which microtubule assembly is exactly balanced by disassembly.

Assembly

Occurs when tubulin concentration exceeds critical concentration.

Disassembly

Occurs when tubulin concentration is less than critical concentration.

Positive end

Addition of tubulin dimers occurs faster at what end of a microtubule?

Treadmilling

The addition of sub-units at the positive end of a microtubule and the removal of sub-units at the negative end.

Anti-mitotic drugs

Drugs that interfere with spindle assembly and inhibit cell division. Used in cancer treatment.

Vinblastine and vincristine

Compounds related to colchicine that are used in cancer therapy.

Nocodazole

Assembly inhibitor that inhibits microtubule assembly. Effects are more reversible than colchicine.

Paclitaxel

Stabalizer that binds tightly to microtubules and stabilizes them; causes depletion of free tubulin sub-units and cell arrest in mitosis. Used in cancer therapy.

Autumn crocus

Source of colchicine.

Synthetic compound

Source of nocodazole.

Periwinkle plant

Source of vinblastine and vincristine.

Symbiotic fungi in pacific yew tree

Source of Paclitaxel.

Cytochalasin D

Prevents addition of new monomers to plus ends of microfilaments.

Fungal metabolite

Source of cytochalasin D.

Latrunculin A

Sequesters actin monomers.

Red sea sponge

Source of latrunculin A.

Phalloidin

Binds and stabilizes assembled microfilaments.

Death cap fungus

Source of phalloidin.

Acrylamide

Synthetic compound that causes the loss of intermediate filament networks.

Microvilli

Microscopic, finger-like projections of the plasma membrane with a microfilament core. Dramatically increases the surface area of cells to optimize absorption and secretion. Prominent in intestinal mucosal cells.

Sarcomere

A basic unit of striated muscle fiber.

A band

Has a darker middle and thick and thin overlapping.

H zone

Narrow center with only thick filaments.

I band

Found near Z discs; only thin filaments.

M line

Supporting protein in the middle of a sarcomere.

Alpha actin

Muscle specific actin.

Beta actin

Non-muscle actin found at the apical side of epithelial cells.

Y-actin

Non-muscle actin found at the basal side of epithelial cells.

G-actin

Globular actin. Individual actin molecules.

F-actin

Filament actin. Occurs when g-actin polymerizes to form MFs.

ATP-actin

Growing microfilament ends are composed of ___.

ADP-actin

Most of a microfilament is composed of ___.

Lamellipodia

Has a branched network of actin, found at the leading edge of cells that crawl.

Filopodia

Microfilaments form highly oriented, polarized cables with the plus ends toward the tip of the protusion. Found at the leading edge of cells that crawl.

Calmodulin and mysoin I

Forms crosslinks to connect microfilaments within microvilli.

Fimbrin and villin

Forms crosslinks to tightly bundle microfilaments within microvilli.

Keratin

An important component of structures that grow from skin in animals.

Acidic keratin

Class I intermediate filament.

Basic keratin

Class II intermediate filament.

Class I and II

Proteins of which classes make up keratin found in epithelial surfaces?

Class III

Class that includes vimentin, desmin, and glial fibrillary acidic protein.

Class V

Class that includs nuclear lamins A, B , and C.

Neurofilament proteins

Class IV contains these proteins found in nerve cells.

Nestin

Substance found in Class VI, makes up neurofilaments in the nerve cells of embryos.

Vimetin

Found in Class III, makes up connective tissue.

Desmin

Found in Class III, makes up muscle cells.

Glial fibrillary acidic protein

Found in Class III, makes up glial cells.

Lamins A, B, and C

Found in Class V, forms a network along the inner surface of the nuclear membrane.

Intermediate filament typing

A method of distinguishing animal cells based on the type of intermediate filament proteins they contain.

Fibrous

Intermediate filament proteins are ___ rather than globular.

310-318 amino acids

Length of the homologous central rodlike domain found in all intermediate filaments.

Coiled-coil

The basic structural unit of an intermediate filament consists of two intermediate filament polypeptides intertwined into a ___.

Chemical attack

Intermediate filaments are less susceptible to ___ than microtubules or microfilaments.

Modularity

The concept of a small number of cytoskeletal elements being deployed in different locations and arranged in different ways to meet the needs of a particular cellular structure.

Immunofluorescence

A technique used to localize specific proteins to the cytoskeleton.

Microtubule

Hollow tube with a wall consisting of typically 13 protofilaments.

Microfilament

Two intertwined chains of F-actin.

Intermediate filament

Eight protofilaments joined end to end with staggered overlaps.