The Cytoskeleton

Cytoskeleton

This is a complex network of interlinking filaments & tubules that extend throughout the cytoplasm of a cell.

Actin Filaments

These define cell shape and are necessary for cell locomotion.

Microtubules

These position membrane-enclosed organelles, mediate vesicular transport, & form mitotic spindles during cell divison.

Intermediate Filaments

These provide mechanical strength.

accessory

All 3 types of filaments interact with _________________ proteins that regulate their activity & link them to other cellular components, as well as each other.

1. spatial organization of cell contents

2. connect cell components physically/biochemically to each other & the cell surface

3. generate coordinated forces that enable the cell to move and/or change and/or keep shape

These are the 3 main functions of the cytoskeleton:

1. Actin Filaments

2. Microtubules

3. Intermediate Filaments

These are the 3 types of filaments:

accessory

Cytoskeleton shape is modulated by _________________ proteins.

Actin

This polymerizes to form actin filaments that are crucial for muscle contraction, cell motility, and maintaining cell shape.

Microfilaments

These are flexible fibers that are about 7 nm in diameter and primarily composed of actin, playing key roles in cell movement and structure (polarized).

Actin Isoforms

These are protein isoforms that regulate contractile potential in muscle tissues and help to control the shape as well as the motility of non-muscle cells.

motors

Actin supports molecular _______________.

Monomeric Actin (G-Actin)

This has tight binding sites that mediate head-to-tail interactions with two other actin monomers, to form filaments (F-Actin).

Filamentous Actin

This is built of individual molecules and is a polymerized form of G-actin that provides structural support and facilitates cell movement.

+ ; -

Filamentous actin assembles at the _____ end and disassembles at the ______ end.

Reaction Rate

This is the speed at which a reaction occurs.

Rate Constant

This is a proportionality factor that relates the molar concentrations of reactants to reaction rate.

Equilibrium

This is when the rate of the forward reaction is equal to the rate of the reverse reaction.

self-assembly

If actin concentration is high enough, there is ________________________.

Rate of Filament Change

Assembly Rate - Disassembly Rate

assembly

At the pointed end of F-Actin, _____________ is disfavored.

Treadmilling

This is a phenomenon when one end of a filament grows in length while the other end shrinks, resulting in a section of filament seemingly “moving” across a stratum/the cytosol.

Oliglomer Instability

This is when small oliglomers (comprised of less than 4 subunits) are unstable and fall apart.

Nucleation

____________________ is the 1st step of actin polymerization.

motor

Myosin is a molecular ______________.

1. Attached

2. Released

3. In cocked state

4. Force generating

5. Attached State

These are the states of myosin:

Myofibrils

These are bundles of thick myosin filaments and thin actin filaments.

sarcomeres

Each myofibril is a chain of contractile units called _______________, which give skeletal and cardiac muscle their striated appearance.

myosin

The bands in sarcomeres correspond to presence or absence of _____________ filaments.

Myosin II

This has two heavy chains and two pairs of light chains. The heavy chains have a globular head region and a long α-helical tail. The tails twist around each other in a coiled-coil.

Actin and myosin filaments slide past each other within a muscle fiber, generating force and causing the muscle to contract.

Describe the sliding filament model:

Ca2+

Muscle contraction is triggered by nerve impulses which
stimulate release of _________ from the sarcoplasmic
reticulum (tropomyosin & troponin).

Tropomyosin acts as a physical barrier that blocks the interaction between actin and myosin, preventing muscle contraction when relaxed.

Troponin acts as a calcium-sensitive switch that regulates the position of tropomyosin, allowing muscle contraction to occur when calcium binds.

What is the difference between tropomyosin and troponin?

troponin

Smooth muscle cells do not express ______________.

VI

Myosin ______ walks in opposite direction (-) direction.

lever arms; converter.

Myosin directionality is defined by _______________ and
_______________ domain.