Cytoskeleton, Extracellular Structures, and Cell Membrane Dynamics

Comprehensive vocabulary flashcards covering the components of the cytoskeleton, plant cell wall layers, animal extracellular matrix, cell junctions, and cell membrane structure and transport mechanisms based on the lecture transcript.

Microfilaments

The thinnest cytoskeletal elements, consisting of solid rods made of a twisted double chain of actin polymers that help maintain cell shape and enable cell motility.

Microtubules

The thickest cytoskeletal elements, structured as hollow rods composed of polymers of the protein tubulin.

Intermediate filaments

Cytoskeletal fibers with a diameter of $8\text{ to }12\,\text{nm}$ (thicker than microfilaments but thinner than microtubules) that form more permanent scaffolding and anchor organelles in place.

Tubulin

The protein monomer that polymerizes to form microtubules.

Actin

The protein monomer subunit that polymerizes to form the solid rods of microfilaments.

Cortex

A network of microfilaments located immediately beneath the plasma membrane that supports and regulates the cell's three-dimensional shape.

Microvilli

Membrane-bound extensions of epithelial cells lining the small intestine that are filled with microfilaments and function to increase surface area for nutrient absorption.

Myosin

A motor protein that physically walks along microfilament tracks, bending the filaments to drive cellular movements such as muscle contraction.

Dynein

A motor protein that walks along microtubule tracks inside the cell.

Cell motility

The active physical movement of a whole cell from one location to another.

Pseudopodia

Cytoplasmic extensions filled with microfilaments that allow single-celled organisms, such as amoebas, to crawl along surfaces.

Cytoplasmic streaming

The circular flow of cytosol within plant cells, driven by moving microfilaments, that speeds up the distribution of nutrients and dissolved substances.

Extracellular substance

A material or structure synthesized inside a cell and secreted to function outside the plasma membrane.

Intracellular substance

A material or substance that is located inside the cell.

Cell wall

An extracellular protective layer located outside the plasma membrane in plant cells, prokaryotes, fungi, and some protists that maintains cell shape and prevents bursting from excessive water intake.

Cellulose

A polysaccharide composed of beta-glucose monomer units that forms the structural fibers embedded in plant cell walls.

Primary cell wall

A relatively thin and flexible extracellular layer first synthesized by a plant cell, positioned between the middle lamella and the secondary cell wall (if present).

Middle lamella

A thin layer rich in sticky pectins situated between the primary cell walls of adjacent plant cells.

Pectins

Polysaccharides found within the middle lamella that separate and glue together the primary cell walls of neighboring plant cells.

Secondary cell wall

A cell wall layer found in some plant species located directly between the plasma membrane and the primary cell wall.

Extracellular matrix (ECM)

A meshwork surrounding animal cells made of glycoproteins—primarily collagen, proteoglycans, and fibronectins—that regulates cell behavior and transmits external signals.

Glycoprotein

A protein covalently attached to one or more carbohydrate (sugar) groups.

Integrins

Transmembrane receptor proteins that span the plasma membrane to transmit signals mechanically and chemically between the extracellular matrix and the intracellular cytoskeleton.

Mechanical signaling

Signaling that occurs when extracellular matrix components physically bind to integrin proteins, altering the intracellular cytoskeleton and modifying chemical signals within the cell.

Tissue

A group of specialized cells that work together to perform the same specific job or function.

Organ

A body structure composed of a group of tissues working together to carry out a common physiological function.

Organ system

A collection of organs that cooperate to perform a common, large-scale bodily function, such as the circulatory system.

Cell junctions

Specialized contact points that physically connect, anchor, or facilitate communication between adjacent neighboring cells.

Plasmodesmata

Open membrane channels through plant cell walls that connect the cytoplasm of adjacent cells, allowing the transfer of water, RNA, and proteins.

Tight junctions

Cell junctions that fuse neighboring epithelial cells into an impenetrable barrier to prevent extracellular fluids from leaking between cells.

Desmosomes

Fastening cell junctions that bind neighboring epithelial cells together into strong, stretchy sheets, such as in skin tissue.

Gap junctions

Communicating cell junctions in animal cells that provide cytoplasmic channels allowing ions to flow directly between neighboring cells.

Macrophage

A large human white blood cell that engulfs bacteria and foreign debris via coordinated actions of its cytoskeleton, lysosomes, and plasma membrane.

Phagocytosis

The cellular process by which a cell's plasma membrane engulfs large particles, such as bacterial cells, to ingest them.

Passive transport

The movement of small molecules across a biological membrane without the expenditure of cellular energy ($\text{ATP}$), which may or may not require a transport protein.

Active transport

The movement of a substance across a cellular membrane against a gradient, requiring both cellular energy (such as $\text{ATP}$ breakdown) and a transport protein.

Vesicles

Lipid-lined membrane containers used to bulk-transport large molecules into and out of the cell via endocytosis or exocytosis.

Endocytosis

The process of importing large molecules and substances into the cell by forming vesicles from the plasma membrane.

Exocytosis

The process of exporting substances out of the cell through the fusion of intracellular vesicles with the plasma membrane.

Amphipathic

A property describing a molecule that contains both a hydrophilic (water-loving) region and a hydrophobic (water-fearing) region, such as phospholipids and many membrane proteins.

Fluid mosaic model

The model describing biological membranes as a flexible bilayer of phospholipids within which diverse, non-randomly localized proteins float or bob.