Presentation 14

Comprehensive vocabulary flashcards covering the eukaryotic cytoskeleton (actin microfilaments, microtubules, intermediate filaments, motor proteins), spatial cell organization, metabolic pathways (anabolism and catabolism), ATP structure and function, and the laws of thermodynamics.

Cytoskeleton

An internal network of protein filaments within cells that provides mechanical support, maintains cell shape, anchors and positions organelles, facilitates intracellular transport, generates force, and directs cell division.

Actin microfilaments

Cytoskeletal polymers structured as double helices of actin monomers that function primarily in establishing cell shape, cell motility, and force generation.

Microtubules

Hollow, cylindrical cytoskeletal fibers assembled from tubulin dimers that facilitate intracellular organization, position organelles, and serve as tracks for directed transport.

Intermediate filaments

Rope-like cytoskeletal polymers composed of intermediate filament protein subunits (such as keratin) that provide high tensile strength to withstand pulling or stretching stresses.

Actin monomer

The globular protein subunit that polymerizes into two intertwined strands to construct a functional microfilament.

Tubulin dimer

A heterodimeric protein building block composed of $\alpha$-tubulin and $\beta$-tubulin that polymerizes to assemble hollow microtubules.

Dynamic cytoskeleton

The property of the cellular filament network that allows it to continually assemble, disassemble, and reorganize instead of remaining a rigid or permanent scaffold.

Motor proteins

Specialized mechanochemical enzymes that couple ATP hydrolysis to directional stepping along cytoskeletal filaments to move cellular cargo such as vesicles.

Microtubule polarity

The structural and chemical asymmetry of a microtubule resulting from oriented tubulin subunits, giving rise to distinct plus ($+)$) and minus ($-$) ends.

Kinesin

A microtubule-based motor protein that predominantly translocates toward the plus ($+)$) end of the filament.

Dynein

A microtubule-based motor protein that predominantly translocates toward the minus ($-$) end of the filament.

Centrosome

The primary microtubule-organizing center in animal cells that nucleates microtubules by anchoring their minus ($-$) ends while allowing plus ($+)$) ends to radiate outward.

Microtubule nucleation

The de novo initiation and assembly of microtubules from tubulin dimers, originating at the centrosome.

Plus ($+)$) end

The dynamic, rapidly growing end of a polar cytoskeletal filament that radiates outward toward the cell periphery from the centrosome.

Minus ($-$) end

The slower-growing end of a polar cytoskeletal filament that is anchored and stabilized at the centrosome.

Vinculin

A cytoskeletal protein found in cell adhesion complexes that couples actin filaments to adhesive junctions to mediate force transmission.

Growth cone

A dynamic actin-rich extension at the tip of an extending neuronal process that directs pathfinding and mediates outgrowth.

Tensile strength

The mechanical capacity of a structural element, such as intermediate filaments, to resist breaking under stretching and pulling forces.

Keratin

A class of intermediate filament proteins found in epithelial cells that links with cell-cell junctions to disperse mechanical strain across a tissue layer.

Desmosome

A specialized cell-cell junction that anchors intermediate filaments between neighboring cells, ensuring mechanical cohesion across the entire epithelium.

Epithelial tissue fragility

A pathological consequence of mutations in intermediate filaments (such as keratin) where cells shear apart and form blisters under mechanical stress.

Vesicle trafficking

The coordinated, energy-dependent transport of membrane-bound vesicles along cytoskeletal tracks between cellular compartments.

Metabolism

The totality of chemical reactions inside an organism that transform matter and govern the capture, storage, and transfer of energy.

Catabolism

The metabolic pathway of breaking down complex macromolecules into smaller subunits, releasing energy that can be captured to synthesize ATP.

Anabolism

The metabolic pathway of building complex macromolecules from simpler subunits, requiring an input of chemical energy supplied by ATP.

Adenosine triphosphate (ATP)

The primary energy currency of the cell, composed of an adenine base, a ribose sugar, and three negatively charged phosphate groups held by phosphoanhydride bonds.

ATP hydrolysis

An energetically favorable exergonic reaction wherein ATP reacts with water to yield ADP and inorganic phosphate ($\text{P}_i$), releasing free energy to drive endergonic cellular work.

Adenosine diphosphate (ADP)

The lower-energy nucleotide derivative containing two phosphate groups produced when ATP is hydrolyzed during cellular work.

Adenosine monophosphate (AMP)

A nucleotide composed of adenine, ribose, and a single phosphate group.

Potential energy

Energy that is stored within a physical or chemical system by virtue of its position, structural arrangement, or chemical bonds.

Kinetic energy

The energy possessed by an object, particle, or system due to its motion, including mechanical movement, molecular vibration, and heat.

Chemical energy

A form of potential energy stored within the electronic configuration and strain of chemical bonds in biological molecules.

Spring analogy of chemical bonds

A conceptual model demonstrating that energy in molecules is stored not as physical elevation but as strain within bonds, which releases kinetic energy as it relaxes to a more stable state.

First law of thermodynamics

The fundamental physical law establishing that energy can neither be created nor destroyed; the total amount of energy before and after any transformation remains constant.

Second law of thermodynamics

The principle that every energy transformation is less than $100\%$ efficient, resulting in some energy dissipating as heat and increasing universal entropy.

Entropy

A thermodynamic measure of molecular disorder and energy dispersion that increases whenever usable energy is lost as heat.

Free energy

The portion of a biological system's total energy that is available to perform work at constant temperature and pressure.

Reactants

The initial chemical substances participating in a reaction that undergo bond breakage and atomic rearrangement.

Products

The resulting chemical substances formed following atomic rearrangement and bond formation during a chemical reaction.

Sodium ($\text{Na}^+$) concentration gradient

A biological form of stored potential energy established by maintaining unequal electrochemical concentrations of sodium ions across a cellular membrane.