Cytoskeleton, Motor Proteins, MTOCs, and Cilia/Flagella

Flashcards reviewing intermediate filaments, myosin motor proteins, MTOCs, centrioles, basal bodies, cilia, and flagella based on the lecture notes.

Intermediate Filaments

Cytoskeletal structures measuring $10-11\,\text{nm}$ in diameter that are found only in animal cells, located in the cytoplasm and nuclear lamina, fibrous, insoluble in water, and present in regions subjected to mechanical pressure.

Plectin

A protein that connects intermediate filaments to another part of the cytoskeleton.

Types of Intermediate Filaments

Cytoskeletal proteins including keratin, lamins (found in the nuclear lamina), desmin, peripherin (found in neurons), chestins, and vimentin.

Intermediate Filament Structural Hierarchy

The structural assembly sequence progressing from polypeptides to polarized dimers, non-polarized tetramers, protofilaments, and ultimately non-polarized intermediate filaments.

Motor Protein Non-interaction with Intermediate Filaments

Motor proteins cannot associate with intermediate filaments because intermediate filaments are non-polarized.

Myosin

A motor protein of actin found in eukaryotic cells (animal or plant) that is filamentous, helical rod-shaped, and features globular heads.

ATPase Domain of Myosin Head

The domain located on the myosin head that binds with actin and converts chemical energy into mechanical energy.

Myosin I

A type of myosin consisting of $1$ heavy chain and light chains that functions in the movement of microvilli.

Myosin II

A type of myosin consisting of $2$ heavy chains and light protein pairs (ELC, BLC) that functions in muscle contraction and forms the contractile ring during cell division in animal cells.

Thick Filaments

Bipolar cytoskeletal structures measuring $22\,\text{nm}$ in diameter formed by many myosin II molecules, containing an H zone in the middle with no heads and an M line at the center.

Titin

A protein, also known as connectin, that connects thick filaments to the Z line.

Microtubule Organizing Centers (MTOCs)

Cellular structures containing $\gamma\text{-tubulin}$ that are required for microtubule nucleation, polymerization, and control of microtubule number, length, and location.

Centrosome

An animal cell MTOC composed of $2$ centrioles positioned $90^\circ$ perpendicular to each other, lacking a membrane envelope, and surrounded by pericentriolar material.

Plant Cell MTOC Components

MTOC proteins in plant cells located in the nuclear envelope and cell cortex, as plant cells do not contain centrosomes.

Pericentriolar Material

Dense material surrounding centrioles that contains $\gamma\text{-tubulin}$ and is needed for microtubule nucleation, asters, and the spindle of division.

Centriole Microtubule Structure

An arrangement of $9$ triplets of microtubules (totaling $27$ microtubules), where each triplet consists of one complete A microtubule and two incomplete B and C microtubules directed toward the center.

Centrosome Duplication

The process where $1$ centrosome ($2$ centrioles) duplicates into $2$ centrosomes ($4$ centrioles), with appendages attached to the old centrioles.

Basal Body

A structure derived from a centriole with identical $9$ triplet microtubule organization from which microtubules stretch to form the axoneme of cilia or flagella.

Axoneme

The motile core of a cilium or flagellum covered by an extension of the plasma membrane, typically arranged in a $9+2$ structure consisting of $9$ peripheral doublets and $2$ central microtubules.

Nexin

An elastic protein in the axoneme that connects the complete A microtubule of one doublet to the incomplete B microtubule of the adjacent doublet.

Dynein Arms

Outer and inner motor protein structures in the axoneme responsible for the movement of cilia and flagella.

Radial Spoke

An axonemal component that connects the complete A microtubule of a peripheral doublet to the central sheath.

Cilia

Shorter and more numerous motile cellular structures containing an axoneme core that can regenerate from the basal body if broken.

Flagella

Longer and less numerous motile cellular structures containing an axoneme core that can regenerate from the basal body if broken.