Cell Biology: Microscopy, Cell Size, Membranes, and Organelles

Vocabulary practice flashcards covering microscopy modalities, constraints on cell size, membrane structure, membrane proteins, transport mechanisms, and endomembrane trafficking.

Immunofluorescence

A microscopic staining technique driven by antibody binding to specific antigens that allows visualization and quantification of cellular structures that are otherwise invisible.

Confocal Laser Scanning Microscope

An optical microscope that uses laser excitation, pinhole apertures, and detector systems to eliminate out-of-focus light rays, enabling optical sectioning and 3D renderings of protein locations inside cells.

Surface Area to Volume Ratio ($\text{SA} : \text{V}$)

The relationship between a cell's outer surface area and internal volume that dictates cellular behavior; as volume expands, material transport via diffusion becomes increasingly difficult to sustain in a timely manner.

Metabolic Flux

The rate of turnover of molecules through a pathway; acts as a cell size constraint because cytosolic metabolic pathways can lose physical contact if the cell becomes too large.

Biosynthetic Capacity

The demand on a cell to produce sufficient cellular components, proteins, and metabolites to adequately supply its entire internal volume.

Intracellular Gradients

Specific internal concentration distributions maintained by the cell; deviations from set limits trigger enzymes to turn on or off, eliciting responses that regulate cell size.

Autophagy

A mechanism for managing cell size in which the cell degrades and consumes portions of its own internal structures to shrink.

Apoptosis

Programmed cell death that prevents a cell from continuing to grow or expand in size.

Senescence

A cellular state where cells stop dividing and growth ceases, occupying space without undergoing further active growth or replication.

Eukaryotic Cells

Cells defined by the presence of membrane-bound organelles and a defined nucleus, encompassing animals, plants, fungi, and protists.

Organelles

Discrete, membrane-bound structures within eukaryotic cells that perform specialized tasks and bring reactants into close proximity, increasing cellular efficiency.

Amphipathic

Possessing both hydrophilic (polar) and hydrophobic (nonpolar) properties within the same molecule, such as in membrane phospholipids.

Phospholipid Molecule

The amphipathic structural unit of cell membranes composed of a large hydrophilic phosphate head group linked via glycerol to hydrophobic fatty acid tails.

Selectively Permeable Membrane

A lipid bilayer barrier that freely allows small, uncharged particles to pass through, but excludes large or charged (ionic) molecules based on size, charge, polarity, and lipid solubility.

Recognition Proteins

Membrane surface proteins that identify a cell as belonging to a specific individual organism and designate its particular cell type.

Hemagglutinin (H)

An influenza surface glycoprotein existing in $18$ known subtypes that determines viral tissue specificity by binding to complementary host cell surface glycoproteins.

Neuraminidase (N)

An influenza surface glycoprotein existing in $11$ known subtypes that dictates how readily the virus can lyse and exit the host cell membrane.

Reception Proteins

Membrane proteins that bind external ligands (such as insulin or hormones), undergoing conformational changes that trigger intracellular signaling cascades.

GLUT4

A glucose transport protein that relocates to the cell surface membrane in response to an insulin signaling cascade to permit glucose entry.

Diffusion

The passive movement of particles down a concentration gradient from an area of high concentration to an area of low concentration without expending cellular energy.

$\text{Na}^+/\text{K}^+\text{-ATPase}$ Pump

An active transport membrane pump that couples ATP binding with conformational shifts to transport $3\,\text{Na}^+$ ions out of the cell and $2\,\text{K}^+$ ions into the cell.

Rough Endoplasmic Reticulum (RER)

A folded, membranous organelle that synthesizes proteins directly into membranous vesicles that bleb off to fuse with the Golgi apparatus.

v-SNAREs

Targeting proteins located on the external surface of transport vesicles that recognize and bind complementary target proteins to mediate vesicle docking.

t-SNAREs

Target membrane proteins on recipient organelles or the plasma membrane that pair specifically with v-SNAREs to direct fusion without compromising membrane integrity.

Golgi Apparatus

A compartmentalized organelle consisting of cis, medial, and trans cisternae that modifies, sorts, and packages proteins and hydrophobic lipids into targeted vesicles, directing them along cytoskeletal tracks.