Cell Biology Lecture 7 - The Cytoskeleton

Flashcards covering the components of the cytoskeleton, including microfilaments, intermediate filaments, microtubules, motor proteins, and cell motility structures.

Cytoskeleton

A network of fibers that supports the cell and its structure, fixes the position of organelles, moves organelles within the cell, and assists in cell movement.

ATP (Adenosine Triphosphate)

The cellular energy currency composed of Adenine, Ribose, and 3 phosphate groups; its hydrolysis to ADP and $P_i$ releases energy.

Microfilaments

Also known as actin fibers, these are the thinnest cytoskeleton fibers with a diameter of approximately $7\,nm$, providing structural framework and facilitating cell movement.

G-actin

The globular monomeric form of actin that polymerizes to form filaments.

F-actin

The filamentous form of actin consisting of two strands wound around each other in a helical structure.

Treadmilling

A process in microfilaments where the $(+)$ end grows in length while the $(-)$ end shrinks at the same rate, resulting in a section of filament seemingly moving.

Lamellipodia

A flat, actin-rich region located at the front of crawling cells.

Stress fibers

Actin bundles located within the cell volume that generate pulling forces.

Actin cortex

The specialized layer of actin filaments located just beneath the plasma membrane (cell shell).

Microvilli

Protrusions in intestinal epithelial cells supported by actin filaments that increase surface area to improve nutrient absorption.

Cytochalasin B

A drug used in experiments to break apart microfilaments, demonstrating their essential role in amoeboid cell movement.

Myosin

A molecular motor protein that uses ATP energy to perform mechanical work and interact with actin for cell movement or muscle contraction.

Sarcomere

The periodic structural unit of muscle fibers consisting of organized actin and myosin filaments.

Focal adhesion

An integrin-containing, multi-protein structure that forms mechanical links between intracellular actin bundles and the extracellular substrate.

Actomycin ring

A contractile ring formed by actin and myosin during cytokinesis to help divide daughter cells during cell division.

Intermediate filaments

Tough, rope-like fibers with a diameter of $8-12\,nm$ that provide mechanical strength to the cell and include proteins like keratin.

Nuclear lamina

A network structure within the cell nucleus formed by intermediate filaments.

Microtubules

The thickest cytoskeleton fibers ($25\,nm$ diameter) made of tubulin dimers, forming hollow tubes that serve as tracks for motor proteins.

Tubulin dimer

The building block of microtubules, consisting of one $\alpha$-tubulin and one $\beta$-tubulin monomer.

Dynamic instability

A property of microtubules where they rapidly lengthen and shorten, regulated by GTP hydrolysis.

Centrosome

The Microtubule Organizing Center (MTOC) in animal cells containing two centrioles, where microtubule $(-)$ ends are anchored.

Kinesin

A motor protein that moves along microtubules from the minus end toward the plus end (anterograde transport).

Dynein

A motor protein that moves along microtubules from the plus end toward the minus end (retrograde transport).

Cilia

Short, hair-like eukaryotic appendages used for movement or moving particles outside the cell (e.g., in the lungs).

Flagella

Long appendages ($100-200\,\mu m$) used for cell motility, such as those found on sperm cells.

Axoneme

The internal structural core of cilia and flagella, typically arranged in a "9+2" microtubule pattern.

Basal bodies

Specialized microtubule organizing centers that anchor the outer microtubule doublets of cilia and flagella to the cell body.

Nexin

A protein that links microtubule doublets in an axoneme, preventing them from sliding past each other and causing them to bend instead.