Bio 93 Lecture 7: Cytoskeleton, Mitochondria, Chloroplasts, Extracellular Matrix, and Peroxisomes

Vocabulary practice flashcards covering organelle structures and functions (mitochondria, chloroplasts, peroxisomes), the three major cytoskeletal elements and motor proteins, the extracellular matrix, and cellular junctions from Bio 93 Lecture 7.

Cristae

The infoldings of the inner mitochondrial membrane that house the enzymes responsible for generating most of the cell's ATP via oxidative phosphorylation.

Mitochondrial matrix

The internal fluid-filled space of the mitochondrion containing enzymes for the Krebs cycle that oxidize fuel molecules.

Thylakoid membrane

The internal chloroplast membrane system organized into stacked discs (grana) containing chlorophyll pigments that absorb light for photosynthesis.

Endosymbiont theory

The evolutionary model proposing that mitochondria and chloroplasts originated when an ancestral eukaryotic host cell engulfed an oxygen-using nonphotosynthetic prokaryote and a photosynthetic prokaryote.

Peroxisomes

Specialized membrane-bound metabolic organelles that break down very large fatty acids through $\beta$-oxidation, carry out steps in fungal penicillin biosynthesis, and produce as well as degrade $H_2O_2$.

Catalase

A peroxisomal enzyme that converts toxic, reactive hydrogen peroxide ($H_2O_2$) into water ($H_2O$).

Plasmalogen

A specialized lipid molecule synthesized in peroxisomes that makes up $80\text{--}90\%$ of myelin sheaths.

Microfilaments

Cytoskeletal fibers $7\,nm$ in diameter composed of two intertwined strands of actin monomers that participate in cell motility, shape changes, muscle contraction, and division.

Treadmilling

A dynamic cytoskeletal phenomenon where monomer addition at the plus (+$) end occurs at the exact same rate that monomers are removed from the minus (-$$) end.

Actin cortex

A dense three-dimensional network of actin microfilaments situated just beneath the plasma membrane in all eukaryotic cells, critical for structural support and cell shape changes.

Pseudopodia

Cellular extensions formed through microfilament assembly and myosin motor interactions that mediate amoeboid crawling and the initiation of phagocytosis.

Myosin

A motor protein that hydrolyzes ATP to move along actin microfilaments, almost always directed toward the plus ($$+$) end.

Microtubules

Hollow cytoskeletal tubes measuring $25\,nm$ in diameter with a $15\text{-nm}$ lumen, assembled from heterodimers of $\alpha$-tubulin and $\beta$-tubulin to resist compression and move chromosomes.

Microtubule Organizing Center (MTOC)

The intracellular site from which microtubules polymerize and where their minus ($-$) ends are anchored; includes the centrosome and basal bodies in animal cells.

Centrosome

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

Centriole

A cylindrical structure within the centrosome composed of nine sets of triplet microtubules ($9+0$ ring arrangement), positioned perpendicularly to its partner.

Kinesin

An ATP-powered motor protein that walks toward the plus ($$+$) end of microtubules, driving anterograde transport toward the axon terminus.

Dynein

An ATP-dependent motor protein that moves cargo along microtubules toward the minus ($-$) end, carrying out retrograde transport toward the cell body.

Flagella

Long, microtubule-based cellular projections that exhibit an undulating motion to propel unattached cells, such as sperm, using ATP.

Cilia

Hair-like, microtubule-based projections on attached cells that utilize ATP-driven active and recovery strokes to sweep fluid and substances across tissue surfaces.

Intermediate filaments

Tension-bearing, non-dynamic fibrous protein cables measuring $8\text{--}12\,nm$ in diameter (including keratins and neurofilaments) that reinforce cell shape and anchor the nucleus.

Nuclear lamina

A net-like structural meshwork lining the interior surface of the nuclear envelope composed of intermediate filament proteins.

Lamin

The specific intermediate filament protein forming the nuclear lamina; mutations in this protein cause defective chromosome organization, abnormal nuclear shape, and progeria.

Extracellular matrix (ECM)

A complex network of glycoproteins, fibrous proteins (such as collagen and elastin), and carbohydrates that surrounds, cushions, and supports animal cells in tissues.

Integrins

Transmembrane receptor proteins that mechanically bridge extracellular matrix components (like fibronectin) with microfilaments inside the cytoplasm to transmit environmental signals.

Plant cell wall

An extracellular protective structure composed primarily of cellulose microfibers with $\beta$-glycosidic linkages that maintains cell shape and counteracts turgor pressure.

Tight junctions

Animal intercellular junctions where neighboring plasma membranes are pressed tightly together to form a barrier preventing extracellular fluid leakage.

Desmosomes

Anchoring junctions reinforced by intermediate filaments that fasten adjacent animal cells into strong, tear-resistant sheets across mechanical stress zones.

Gap junctions

Communicating animal cell junctions consisting of membrane channels that allow ions and small molecules to pass directly from the cytoplasm of one cell to another.

Plasmodesmata

Membrane-lined cytoplasmic channels that traverse plant cell walls to connect adjacent cells, allowing the passage of water, small solutes, proteins, and RNA.