BIOL 1000 Lecture 7 - Eukaryotic Cell Structure, Cytoskeleton, and Motility

Vocabulary practice flashcards covering cell organelle structure, endosymbiotic theory, cytoskeleton filament types, motor protein walking mechanisms, cilia and flagella dynamics, and actin-myosin contraction.

Proteobacteria

Aerobic bacteria that were engulfed by an ancestral host cell and evolved into modern mitochondria according to endosymbiotic theory.

Cyanobacteria

Photosynthetic bacteria that were engulfed by a eukaryotic host cell and evolved into modern chloroplasts.

Theory of Endosymbiosis

Evolutionary concept proposing that mitochondria developed from ingested aerobic bacteria and chloroplasts developed from ingested cyanobacteria that formed a permanent symbiotic relationship.

Binary Fission

The prokaryotic-like division process by which mitochondria and chloroplasts multiply inside eukaryotic cells.

Mitochondrial Matrix

The innermost compartment enclosed by the inner mitochondrial membrane containing mitochondrial DNA, ribosomes, and enzymes.

Cristae

Infoldings of the inner mitochondrial membrane that expand its surface area for cellular respiration.

Thylakoid

Flattened saclike membrane structure located inside chloroplasts where photosynthetic light reactions occur.

Stroma

The fluid-filled space within a chloroplast surrounding the thylakoid membranes.

Granum

A stacked structure composed of multiple thylakoid discs inside a chloroplast.

Intermembrane Space

The narrow region between the inner membrane and outer membrane of mitochondria and chloroplasts.

Cytoskeleton

A dynamic intracellular network of protein filaments and tubules that provides structural support, determines cell shape, and enables motility.

Polymerization

The assembly of protein monomer subunits to extend filament length, primarily occurring at the $\text{+ end}$.

Depolymerization

The disassembly of cytoskeletal filaments by removing protein monomers from the filament.

Centrosome

The main microtubule organizing centre (MTOC) in animal cells located near the nucleus from which microtubules radiate.

Microtubule Organizing Centre (MTOC)

A cell structure such as the centrosome where microtubule assembly is initiated and anchored.

Microtubules

Rigid hollow tubes approximately $25\,\text{nm}$ thick composed of $\alpha\text{-}$ and $\beta\text{-tubulin}$ dimers.

Intermediate Filaments

Rope-like fibers approximately $8\text{--}12\,\text{nm}$ thick (or $10\,\text{nm}$) that provide mechanical strength and are associated only with multicellular organisms.

Microfilaments

Two coiled strands of actin protein approximately $5\text{--}7\,\text{nm}$ thick involved in cell shape, motility, and muscle contraction.

Tubulin

Globular protein subunit forming $\alpha\text{-}$ and $\beta\text{-tubulin}$ heterodimers that assemble into microtubules.

Actin

Globular protein monomer that polymerizes to form double-stranded microfilaments.

Keratins

Tissue-specific intermediate filament protein subunits that supply structural strength to epithelial cells and hair.

Lamins

Intermediate filament proteins that construct the nuclear lamina lining the inner surface of the nuclear envelope.

Cell Cortex

A dense meshwork of microfilaments located directly underneath the plasma membrane that reinforces cell shape.

Kinesin

A motor protein that walks along microtubules toward the fast-growing $\text{+ end}$ (away from the centrosome).

Dynein

A motor protein that walks along microtubules toward the $\text{- end}$ (toward the centrosome).

Motor Proteins

Specialized proteins such as kinesin, dynein, and myosin that use energy from ATP hydrolysis to walk along cytoskeletal tracks.

Leading Head

The front head domain of a motor protein that binds ATP and steps forward along a cytoskeletal filament track.

Lagging Head

The trailing head domain of a motor protein that hydrolyzes ATP and releases $\text{ADP}$ before swinging forward.

ATP Hydrolysis

The enzymatic breakdown of ATP into $\text{ADP}$ and inorganic phosphate ($\text{P}_i$) providing energy for motor protein movement.

Eukaryotic Flagella

Long microtubule- and dynein-based structures that undergo oar- or whip-like movements for cell locomotion.

Cilia

Short, numerous microtubule- and dynein-based cellular projections that propel cells or move fluids across cell surfaces.

Microtubule 9+2 Complex

Arrangement in eukaryotic cilia and flagella featuring nine outer microtubule doublets surrounding two central singlet microtubules.

Microtubule Doublet

A pair of connected microtubules forming the outer ring of nine doublets in cilia and flagella.

Radial Spoke

Protein structure in flagella and cilia extending from outer microtubule doublets inward to the central microtubules.

Analogous Structures

Structures performing identical functions that evolved independently without shared evolutionary ancestry, such as bacterial and eukaryotic flagella.

Bacterial Flagella

Rotary filament structures in prokaryotes that are functionally analogous but structurally and evolutionarily distinct from eukaryotic flagella.

Myosin

A motor protein that binds actin microfilaments and moves toward their $\text{+ end}$, causing filaments to slide during contraction.

Myofibril

A long cylindrical organelle within a muscle cell containing repeating contractile units termed sarcomeres.

Muscle Fibre

A single, elongated skeletal muscle cell containing many myofibrils.

Sarcomere

The basic repeating unit of muscle contraction in skeletal muscle bounded by Z disks, displaying alternating light and dark bands.

Z Disk

Protein boundary structure marking the end limits of a sarcomere and anchoring thin actin filaments.

Light Band

Region of a sarcomere near the Z disk containing thin actin microfilaments without overlapping thick myosin filaments.

Dark Band

Central region of a sarcomere formed by thick myosin filaments.

Sliding Filament Model

Mechanism of muscle contraction in which myosin heads attach to actin and pull thin filaments toward the sarcomere centre.

Calcium Ions (Ca2+)

Key chemical regulatory ions required alongside ATP to initiate muscle contraction in sarcomeres.

Amoeboid Movement

Cell crawling motility powered by actin filament assembly at the leading cell boundary and cytoplasmic flow.

Pseudopodium

A temporary projection of the cell surface formed by microfilament assembly at the leading edge during cell crawling.

Cytokinesis in Animals

Process of cell division where an actin-myosin contractile ring draws the plasma membrane inward to divide a cell in two.

GTP Cap

A stable region at the growing $\text{+ end}$ of a microtubule composed of GTP-bound tubulin dimers that prevents tubulin loss.

Pigment Granules

Color-containing organelles in fish skin cells transported outward or inward along microtubules by kinesin and dynein to alter fish coloration.