Bio93 Lecture 7: Cytoskeleton, Mitochondria, Chloroplasts, Extracellular Matrix, and Peroxisomes

Vocabulary practice flashcards covering cell biology concepts from Lecture 7, including membrane transport, energy-converting organelles, peroxisomes, and the three cytoskeletal systems (microfilaments, microtubules, and intermediate filaments).

Facilitated Diffusion

The passive transport of a substance down its concentration gradient across a biological membrane, mediated by specific transmembrane transport proteins without requiring an expenditure of cellular energy (such as ATP hydrolysis).

Active Transport

The movement of a substance across a cellular membrane against its concentration gradient, requiring an integral membrane carrier or pump protein and an input of metabolic energy (frequently from ATP hydrolysis).

Semiautonomous Organelles

Organelles such as mitochondria and chloroplasts that grow and reproduce somewhat independently within the cell, contain their own circular DNA and ribosomes, and are not part of the endomembrane system.

Mitochondria

Eukaryotic energy-transforming organelles that generate the majority of cellular ATP via cellular respiration and move dynamically throughout the cytoplasm along cytoskeletal tracks.

Mitochondrial Matrix

The internal compartment enclosed by the inner mitochondrial membrane containing circular DNA, ribosomes, and enzymes that catalyze the Krebs cycle to oxidize fuel molecules.

Cristae

The foldings of the mitochondrial inner membrane that expand the total surface area and house the enzymes that synthesize the majority of ATP via oxidative phosphorylation.

Chloroplasts

Double-membrane-enclosed photosynthetic organelles present in leaves, other green plant structures, and eukaryotic algae that transform light energy into chemical energy.

Thylakoids

A third internal membrane system within chloroplasts composed of flattened, stacked discs where chlorophyll pigments reside to absorb light.

Endosymbiont Theory

The evolutionary model proposing that mitochondria and chloroplasts arose when an ancestral eukaryotic host cell engulfed an oxygen-using nonphotosynthetic prokaryote, and later a photosynthetic prokaryote, which survived digestion and became permanent intracellular symbionts.

Peroxisomes

Specialized metabolic membrane-bound organelles that replicate semiautonomously, break down very large fatty acids via $\beta\text{-oxidation}$, produce and degrade $H_2O_2$, and host the final biosynthetic steps of penicillin in fungi.

Catalase

A peroxisomal enzyme that protects the cell by converting toxic, highly reactive hydrogen peroxide ($H_2O_2$) into water ($H_2O$).

Plasmalogen

An ether lipid synthesized in peroxisomes that constitutes $80\text{--}90\%$ of the myelin sheaths surrounding neurons.

Cytoskeleton

A network of protein-based fibers extending throughout the cytoplasm that provides structural and mechanical support, anchors internal organelles, and coordinates cellular motility through interactions with motor proteins.

Microfilaments

Cytoskeletal fibers measuring approximately $7\text{ nm}$ in diameter composed of two intertwined strands of actin monomers that govern cell shape changes, muscle contraction, cytoplasmic streaming, and animal cell cleavage.

Treadmilling

The steady-state dynamic phenomenon in microfilaments where actin monomers are added to the plus (+) barbed end at the same rate that they dissociate from the minus (-) pointed end.

Actin Cortex

A dense, gel-like network of actin filaments located immediately beneath the plasma membrane in eukaryotic cells that supports cell shape and facilitates morphological changes.

Pseudopodia

Cellular surface extensions driven by actin microfilament polymerization in the cortex that mediate amoeboid crawling motility and the engulfment of large particles during the initiation of phagocytosis.

Myosin

An ATP-powered motor protein associated with microfilaments that almost always walks toward the plus (+) end, facilitating short-distance vesicle transport, cell crawling, and muscle contraction.

Microtubules

Hollow cylindrical cytoskeletal filaments ($25\text{ nm}$ in diameter with a $15\text{-nm}$ lumen) composed of $\alpha\text{-tubulin}$ and $\beta\text{-tubulin}$ heterodimers that resist cellular compression, transport cargo, move chromosomes during mitosis, and power cilia and flagella.

Microtubule Organizing Center (MTOC)

The cellular structure from which microtubules polymerize and where their minus (-) ends remain anchored, functioning in animal cells primarily as the centrosome and basal bodies.

Centrosome

The primary animal MTOC located near the nucleus containing a pair of perpendicular centrioles, each organized into a ring of nine sets of triplet microtubules ($9+0$ pattern).

Cilia and Flagella

Microtubule-based locomotive appendages powered by ATP hydrolysis that either propel individual cells (such as sperm) or move external fluid across tissue surfaces (such as the digestive tract lining).

Kinesin

A microtubule-associated motor protein that hydrolyzes ATP to transport vesicles and cellular cargo toward the plus (+) end in an anterograde direction (e.g., toward the axon terminus).

Dynein

A microtubule-associated motor protein that utilizes ATP hydrolysis to transport cargo toward the minus (-) end in a retrograde direction (e.g., toward the cell body).

Intermediate Filaments

Sturdy, ropelike cytoskeletal cables measuring $8\text{--}12\text{ nm}$ in diameter constructed from fibrous subunit proteins (such as keratins) that resist tension, reinforce cell shape, anchor organelles, and construct the nuclear lamina.

Lamin

A class of intermediate filament proteins that polymerize to form the structural nuclear lamina lining the inner nuclear membrane, crucial for nuclear architecture, assembly, disassembly, and chromatin organization.

Progeria

A rare genetic condition causing accelerated premature aging in humans that arises from mutations in the lamin gene, resulting in misshapen nuclear envelopes and impaired nuclear function.