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What are the four major functions of the cytoskeleton?

1. cell movement

2. cell division

3. organelle movement

4. establishing cell shape

Three major structural elements of the cytoskeleton

Microtubules

Microfilaments

Intermediate filaments

What are the two types of microtubules?

cytoplasmic and axonemal

What are the two subunits of microtubules?

alpha and beta tubulin

What is the cytoskeleton?

network of filaments and tubules through cytosol to inner surface of plasma membrane

Is the cytoskeleton dynamic and changeable?

yes

Fluorescence microscopy on fixed specimens

Fluorescent compounds directly bind to cytoskeletal proteins, or antibodies are used to indirectly label cytoskeletal proteins in chemically preserved cells, causing them to glow in the fluorescence microscope

Live-cell fluorescence microscopy

Fluorescent versions of cytoskeletal proteins are made and introduced into living cells. Fluorescence microscopy and video or digital cameras are used to view the proteins as they function in cells

Computer-enhanced digital video microscopy

High resolution images from a video or digital camera attached to a microscope are computer processed to increase contrast and remove background features that obscure the image

Electron Microscopy

uses electrons instead of light, the shorter wavelength of electrons gives greater resolution

What are microtubules?

hollow structures made up of the protein tubulin, they maintain a cells shape, largest cytoskeletal element, important for movement

What are cytosolic microtubules?

Located in the cytoplasm, protects cell shape, intracellular transport, and chromosome movement, more dynamic, can grow and shrink

What are axonemal microtubules?

inside cilia and flagella, responsible for the movement of cilia/flagella, highly organized, more stable

What are microfilaments?

threadlike structures made up of actin, important for cell movement/migration and cell shape

What are intermediate filaments?

strong support cabels, most stable, gives cell mechanical strength.

What is a MTOC?

microtubule organizing center

What are the two examples of MTOCs?

centrosomes, and basal body

What is the starting phase of microtubule assembly and how does it work?

nucleation/lag phase

Individual alpha/beta tubulin dimers come together to make small groups called oligomers and then protofilaments

What is the second phase of microtubule assembly and how does it work?

elongation phase, tubulin dimers rapidly added to the growing microtubule

What is the third phase of microtubule elongation and how does it work?

Tubulin can be added and removed and isn't changing much

Does the positive or negative side of the microtubule grow faster?

positive

What is treadmilling?

Tubulin is added to + end at the same rate as other tubulin is removed from the - end

What is dynamic instability?

the polymerization and depolymerization of microtubules

What is a GTP cap?

When enough GTP-tubulin is added, the end has a GTP cap that helps keep the microtubule stable and growing.

What happens when GTP is hydrolyzed?

water breaks the chemical bond and turns GTP into GDP, which is less stable

How does a catastrophe happen?

if new GTP-tubulin isn't being added fast enough, and then microtubule falls apart

What does taxol do to microtubules?

binds and stabilizes microtubules, prevents tubulin heretodimers from dissociating

What is the mechanism that taxol uses to freeze microtubules?

it binds to GDP-bound tubulin heterodimers and changes their conformation to be more like GTP-bound tubulin heterodimers

What are the three microtubule-binding proteins

Tau, EB1, MCAK

What does Tau do?

microtubule-associated protein that stabilizes the microtubules

What does EB1 do?

a +TIP protein (plus-end tracking protein) that marks where the + is on the MT

What does MCAK do?

a catastrophin protein that promotes microtubule disassembly/shrinking

What are the three main functions of microfilaments?

1. Migration

2. Movement in the cell

3. shape

What are microfilaments made of?

actin

What is G-actin?

globular actin, an individual actin monomer

What is F-actin?

filamentous actin, two linear strands of G-actin

Individual G-actin monomers bind

ATP/ADP

What are lamellipodia?

Type of protrusion

- Sheet-like structures, broad

What are filopodia?

Type of protrusion

- Finger-like projections

- Core of long, bundled actin filaments

How do cells control where actin grows?

By using actin-binding proteins to control nucleation, elongation, severing, and orginization into networks

What does sequester mean?

holds onto G-actin so it can't be added to a filament

What does cap mean?

attaches to end of actin filament and blocks further growth/shrinking at that end.

What does crosslink mean?

connects different actin filaments together into a network

What does bundle mean?

puts multiple actin filaments together side by side

What does sever mean?

cut a filament

What does anchor mean?

attach/hold a filament somewhere

What does plectin do?

Cross links the three classes of cytoskeleton

What is the most stable and least soluble component of the cytoskeleton?

intermediate filaments

How many protofilaments make up the final intermediate filament structure?

eight

What is keratin an example of?

intermediate filament

How do motor proteins generate force?

ATP hydrolysis to generate mechanical force

What is Kinesin?

a motor protein that converts chemical energy in ATP into mechanical work

moves vesicles across the cell

What cytoskeletal element does kinesin move along?

microtubules

What is Dynein?

its the movement that causes cilia and flagella to bend, causing movement.

What protein is involved in microfilament-based movement?

myosin (cell migration)

Difference between cilia and flagella

Cilia - Many, Short

Flagella - Few, Long

What does axonemal dynein do?

causes microtubules to slide against eachother, which bends them and produces movement

Epithelial cells

packed very close together, form sheets of cells, strong connections between neighboring cells

Mesenchymal/connective tissue cells

more spread out, more material surrounding cells

Extracellular matrix

The substance in which animal tissue cells are embedded, consisting of protein and polysaccharides.

Adhesive junctions

specialized groups of proteins that link cells to one another within tissues

sinus inversus totalis

all organs are mirrored, mutation in axonemal dynein

heterotaxi

-only some organs are reversed

-severe consequences

What is junctional epidermolysis bullosa

mutation in laminin, a protein that makes up basal lamina, sores and blisters with minimal pressure on the skin

What do adherens junctions connect?

cells to cells

What do cadherins do?

extend out of cells and help cells attach

What do catenins do?

Connect the actin to cadherins

What do desmosomes connect?

intermediate filaments

What does plakoglobin do?

linker proteins that connect the cytoskeleton to the desmosomal cadherins

What are the two types of desmosomal cadherins?

desmogleins and desmocollins

function of tight junctions

seal spaces between neighboring cells

what protein is associated with tight junctions?

claudin

What is the function of gap junctions?

allow ions and molecules to pass between cells

what protein forms gap junctions?

connexin

what structure do connexins form?

connexons

how are cadherins characterized?

1. repeats in their extracellular domain that are structurally similar

2. a transmembrane domain

3. widely varying cytosolic ends

what is the extracellular space between two connected cells called?

desmosome core

what are the desmosomal cadherins called?

desmocollins and desmogleins

What type of protein is claudin?

a transmembrane junction protein

What is collagens role in the ECM?

provides strength and structural support outside the cell

What is the matrix protein complex of the ECM?

proteoglycans

What are the two adhesive proteins of the ECM?

fibronectin and laminin

What is the attachment protein of the ECM?

integrin

What is a focal adhesion?

cell's actin cytoskeleton-ECM adhesion

What process does the slideshow associate with focal adhesions?

cell migration

What is a hemidesmosome?

connects intermediate filaments to the basal lamina