Cellular Structure, Endomembrane Trafficking, and Evolution

Vocabulary practice flashcards covering cell structure, prokaryotic vs. eukaryotic differences, endosymbiotic theory, endomembrane protein trafficking pathways, the cytoskeleton, and cystic fibrosis pathophysiology.

Secreted/Membrane Protein Pathway

The sequential trafficking route for integral membrane and secreted proteins: DNA $\rightarrow$ mRNA $\rightarrow$ Rough ER $\rightarrow$ Transport vesicle $\rightarrow$ Golgi $\rightarrow$ Secretory vesicle $\rightarrow$ Plasma membrane.

Rough Endoplasmic Reticulum (Rough ER)

An endomembrane organelle studded with ribosomes that synthesizes membrane proteins and secreted proteins, inserting them directly into the ER membrane or the ER lumen.

Smooth Endoplasmic Reticulum (Smooth ER)

An endomembrane organelle devoid of ribosomes that specializes in the synthesis of cellular lipids, including phospholipids and sterols.

Golgi Apparatus

An endomembrane organelle that receives proteins from the ER via transport vesicles, modifies and sorts them, and completes protein glycosylation before packaging them into vesicles.

Secretory Vesicles

Membrane-bound spheres that transport proteins from the Golgi apparatus to the plasma membrane, fusing with the plasma membrane to release their contents outside the cell.

Protein Sorting: Free vs. Membrane-Bound Ribosomes

Free ribosomes synthesize proteins that remain in the cytosol or are transported post-translationally to the nucleus, mitochondria, chloroplasts, and peroxisomes; membrane-bound ribosomes on the rough ER synthesize proteins destined for the ER lumen, plasma membrane, secretory vesicles, endosomes, and lysosomes.

Nuclear Pores

Openings spanning the nuclear envelope through which mRNA and ribosomal subunits exit to the cytoplasm, and proteins synthesized in the cytoplasm are imported into the nucleus.

Lipid Rafts

More rigid microdomains within the fluid mosaic plasma membrane formed by assemblies of cholesterol and sphingolipids that play critical roles in cell signaling.

Microfilaments (Actin)

Thin cytoskeletal filaments located primarily near the plasma membrane that function to maintain and alter cell shape.

Intermediate Filaments

Tough, fibrous cytoskeletal elements (such as spectrin) that provide mechanical and structural support to the cell.

Microtubules

Hollow cytoskeletal filaments assembled from $\alpha$-tubulin and $\beta$-tubulin that act as intracellular tracks for vesicle transport and segregate chromosomes during cell division.

Motor Proteins

Mechanochemical enzymes that utilize energy from ATP hydrolysis to move vesicles along microtubule tracks throughout the cell.

Extracellular Matrix (ECM)

An external meshwork supporting animal cells and facilitating cell-environment interactions, composed of collagen, proteins, and polysaccharides.

Endosymbiont Theory

The evolutionary framework stating that mitochondria and chloroplasts originated as free-living bacteria that were engulfed by a host cell and established a permanent mutualistic relationship.

Endosymbiotic Evidence of Mitochondria

Mitochondria possess their own circular DNA resembling alpha-proteobacteria, have bacterial-sized ribosomes, divide independently via binary fission, and are bounded by a double membrane.

Endomembrane System

A coordinated intracellular network providing structure and internal transport, composed of the nuclear envelope, rough ER, smooth ER, Golgi complex, lysosomes, endosomes, transport vesicles, secretory vesicles, and plasma membrane.

Cytoplasm

The crowded internal region of the cell outside the nucleus and organelles that has a gel-like consistency due to bound water molecules and contains enzymes, ribosomes, mRNA, tRNA, and signaling proteins.

Organelle

A membrane-bound intracellular compartment that carries out distinct, specialized metabolic functions and biological processes.

LUCA (Last Universal Common Ancestor)

An ancient, simple ancestral cellular structure that had a phospholipid bilayer membrane, cytoplasm, and DNA to protein synthesis machinery, but lacked a nucleus and membrane-bound organelles.

Nucleoid

The non-membrane-bound cytoplasmic region in prokaryotes where the primary circular chromosome is situated.

Plasmids

Small, circular, double-stranded DNA molecules found in the prokaryotic cytoplasm that exist and replicate separately from the main bacterial chromosome.

Endocytosis Mechanisms

Cellular processes for internalizing substances via membrane invagination: phagocytosis ('cell eating' of large particles via pseudopodia), pinocytosis ('cell drinking' of extracellular fluid), and receptor-mediated endocytosis (selective uptake through coated pits into coated vesicles).

Nuclear Envelope Invagination Hypothesis

The evolutionary model proposing that the eukaryotic nucleus and early endomembrane system originated when the ancestral plasma membrane folded inward to enclose the chromosomal DNA.

Asgard Archaea (Promethearchaeota)

The monophyletic archaeal group closely related to eukaryotes that possesses homologous genes responsible for endocytosis and dynamic cytoskeletal remodeling.

Cystic Fibrosis (CF)

The most common life-threatening autosomal recessive disorder among individuals of Northern European descent, characterized by deficient epithelial chloride transport leading to respiratory infections and lung failure.

CFTR (Cystic Fibrosis Transmembrane Conductance Regulator)

An integral plasma membrane chloride ion channel containing multiple transmembrane domains that allows $Cl^-$ ions to diffuse across epithelial membranes into the airway surface liquid.

$\Delta\text{F508}$ (deltaF508) Mutation

The most common CFTR gene mutation resulting in the deletion of a phenylalanine residue at position $508$, causing the protein to misfold, become retained in the rough ER, and get degraded with less than $1\%$ reaching the plasma membrane.

Mucociliary Escalator

A defense mechanism wherein ciliated epithelial cells lining the respiratory tract beat synchronously in a thin watery layer to propel mucus, trapped particles, and microbes up toward the pharynx to be swallowed.

Hypertonic Saline Therapy

An inhaled treatment for cystic fibrosis that creates a hypertonic environment in the airways, drawing water out of epithelial cells by osmosis to hydrate and thin out sticky airway mucus.

Sulfur-35 ($^{35}\text{S}$) Labeling

A radioisotope technique used to selectively tag newly synthesized proteins without labeling lipids, carbohydrates, or nucleic acids, because sulfur is present in amino acids (cysteine and methionine) but absent from the other major macromolecules.