Chapter 15 Cell Bio: The Cytoskeleton: Shape, Strength, Roadways, and Movement

Flashcards covering key components and functions of the cytoskeleton, including various proteins and structures involved in cellular dynamics and movement.

Cytoskeleton

A dynamic network of protein polymers that provides structural support, shape, and enables movement in cells. Unlike skeleton, it is highly dynamic.

Prokaryotic skeleton

Controls cell shape and involved in cell division

Eukaryotic cytoskeleton

Controls shape, involved in cell division, positions organelles, movable structures (cilia and flagella), connecting cells together

G-actin monomer, tubulin dimer, and intermediate filament monomer

What are the three major protein polymers that are associated with the cytoskeleton?

Actin Filaments

Filaments composed of G-actin monomers that form a meshwork in the cell cortex, playing a key role in cell shape and movement.

Microtubules

Hollow tubes formed by tubulin dimers that provide structural support and are involved in cell division, cilia, and flagella formation.

Intermediate Filaments

Fibrous proteins that provide mechanical strength and structural stability to cells, often present in cells under stress.

Prokaryote and eukaryote

____ and ___ share actin and tubulin homologs which is shared by last common ancestor

DNA positioning/segregation, cleavage during cell division, maintaining cell shape/cell wall

What are the 3 main functions of prokaryotic cytoskeleton?

Actin

Forms meshwork in cell cortex, changing the shape of the cell and has dynamic instability

G-actin monomers

Asymmetrical ends that bind (+ end binds to - end) resulting actin filament is also asymmetrical

G-actin ATPase binds to hydrolyze ATP

What is the first step in Actin Polymerization?

Conformation can polymerize

What is the second step in Actin Polymerization? (ATP bound for this step)

ATP is hydrolyzed and depolymerization favored

What is the second step in Actin Polymerization? (Bound to filament for this step)

At filament ends

Polymerization/depolymerization can only happen where?

Polymerization and it is faster than ATP-hydrolysis

If there is a high ATP-G-actin concentration what occurs? (It occurs on both ends on the actin filament)

Depolymerization

If there is a low ATP-G-actin concentration what occurs? (There is only loss at the - end equal to the gain at the + end)

10x

Actin monomers bind to + end ____ faster than - end

Profilin

Promotes polymerization

Thymosin B4

Withdraws/sets apart monomers

Myosin

An ATPase motor protein that interacts with actin filaments to cause muscle contraction and movement along the cytoskeleton.

Myosin 1

This myosin has one tail, one head and moves vesicles

Myosin 2

This myosin has one tail, two heads and is involved in muscle contraction

Myosin head bound to actin

What is the first step in Myosin Power Stroke?

ATP binds to myosin head and releases head from actin

What is the second step in Myosin Power Stroke?

ATP hydrolyzed to ADP+P, myosin head bends like a hinge

What is the third step in Myosin Power Stroke?

Myosin binds to actin, releases P (ADP diffuses away), power released, myosin pulls actin along

What is the fourth (last) step in Myosin Power Stroke?

Myofibrils

Muscle fibers are packed with small fibers called

Sarcomeres

What are myofibrils made of?

Myosin filaments pull actin towards myosin 2 midline

During muscle contraction what occurs?

Electrical nerve signal propagation through muscle membrane and T-tubule infoldings

What is the first step in Muscle Contraction?

Releases Ca2+ from sarcoplasmic reticulum, flooding cytosol

What is the second step in Muscle Contraction?

Ca2+ binds to troponin moving tropomyosin off myosin 2 binding sites

What is the third step in Muscle Contraction?

Once electrical signal stops, Ca2+ removed from cytosol, contraction ends

What is the fourth (last) step in Muscle Contraction?

Cytoskeletal reorganization

How do fibroblasts travel through extracellular matrix (ECM)?

Lamellipodium

____ on leading edge of cell has mesh-like actin filaments

Filopodia

What extends forward from lamellipodium?

Focal adhesions

Lamellipodium anchored to the surface by what?

Integrins; Fibronectins

Cell membrane ___ bind to ECM proteins called ___

Microtubules

Hollow tubes formed by tubulin dimers that present dynamic instability

Microtubule organizing center (MTOC)

In animal and fungal cells, microtubules emanate from where?

Centrosome; centrioles

The MTOC of animal cells are called what? They contain 2 short microtubule structures called what?

Alphabeta-heterodimer bound to GTP

What is the first step in Microtubule Polymerization? (favors polymerization)

When bound to microtubule, GTP hydrolyzed

What is the second step in Microtubule Polymerization? (favors depolymerization)

If polymerization faster than GTP-hydrolysis, growth occurs, if not depolymerization occurs

What is the third (last) step in Microtubule Polymerization?

Gamma-tubulin

What promotes polymerization in microtubules?

Augmin

What allows for microtubule branching?

Tau

What stabilizes microtubules?

Katanin

What breaks microtubules?

Kinesins

Travel to + end of microtubule. In trans-golgi transport, away from nucleus. Position organelles and orient mitochondria

Dyneins

Travel to - end of microtubule. In trans-golgi transport, towards nucleus. Move mitochondria and positions golgi close to nucleus

Globular head connected to transport cargo by coiled chain

What is the structure of kinesins?

Leading head binds to ATP, trailing head moves forward

What is the first step in the Walking Steps of Kinesins?

New leading head releases ADP, new trailing head hydrolyzes ATP

What is the second (last) step in the Walking Steps of Kinesins?

Kinesin binding protein on vesicle membrane binds to inactive kinesin

What is the first step in Activation Vesicle Movement?

Kinesin unfolds, reveals ATP-binding pockets

What is the second step in Activation Vesicle Movement?

Binds to microtubules and proceeds to + end

What is the third and fourth (last) step in Activation Vesicle Movement?

Dynactin

Dyneins contain ______, a short actin-like filaments that connects to cargo

Cilia

Slender structures often found in large numbers, motile (movement) or non-motile (sensory)

Flagella

Very long cilia, move in separate whiplike motion to propel cell

Intermediate filament structure

Monomer made of alpha helix with flexible N- and C- terminal domains, multiple layers of coiled rope-like structures woven together to form non-polar intermediate filament, anchored to cell via desmosomes and hemidesmosomes