Cell Bio Test #2

Cytoskeleton

network of microtubules and actin filaments that acts as an intracellular road system, directing motor proteins to transport organelles and vesicles throughout the cell

Endomembrane system

interconnected system of membranes (ER, Golgi, lysosomes, and endosomes) that evolved from plasma membrane invaginations and communicates via vesicle transport

Golgi apparatus

membrane-bound organelle that receives proteins and lipids from the ER, modifies them, and packages them into vesicles for delivery to other destinations

Lysosome

Membrane-bound organelles containing digestive enzymes that break down waste materials, damaged organelles, and foreign substances

Mitochondria

Double-membraned organelles that originated from endosymbiotic α-proteobacteria and serve as the cell's primary site of ATP production through cellular respiration

Nuclear envelope

double membrane surrounding the nucleus, perforated with nuclear pores that regulate the passage of molecules between the nucleus and cytoplasm

Nucleus

membrane-bound organelle that stores the cell's genetic material (DNA) and coordinates gene expression and DNA replication

Peroxisome

membrane-bound organelle that carries out oxidative reactions, breaking down fatty acids and neutralizing toxic substances like hydrogen peroxide

Rough ER

region of the ER studded with ribosomes on its cytosolic surface, specialized for synthesizing proteins destined for secretion or membrane insertion

Signal sequence

short stretch of amino acids that acts as an "address label" on a protein, recognized by transport machinery to direct the protein to its correct cellular destination

Smooth ER

region of the ER lacking ribosomes, specialized for lipid synthesis, detoxification, and calcium storage

Nuclear export receptors

Transport proteins (like CRM1/exportin) that bind nuclear export signals (NES) on cargo proteins and carry them out of the nucleus through nuclear pore complexes, powered by Ran-GTP

Nuclear import receptors

Transport proteins (importins) that recognize nuclear localization signals (NLS) on cargo and shuttle proteins from the cytosol into the nucleus through nuclear pore complexes

Nuclear localization signal

short amino acid sequence that acts as an "address tag" on proteins destined for the nucleus, recognized by importin receptors to mediate nuclear entry

Nucleoporin

Proteins that make up nuclear pore complexes (NPCs), including those with FG-repeats that form a selective meshwork controlling passage of molecules across the nuclear envelope

Polyribosome

Multiple ribosomes simultaneously translating the same mRNA molecule, allowing rapid production of many protein copies from a single transcript

Ran

small GTPase protein whose GTP/GDP gradient across the nuclear envelope drives directionality of nuclear transport—Ran-GTP in the nucleus triggers cargo release from importins

Signal peptidase

enzyme that cleaves N-terminal signal sequences (presequences) from proteins after they are imported into organelles like mitochondria or the ER

Signal recognition partical(SRP)

cytosolic complex that recognizes signal peptides on nascent proteins, pauses translation, and directs the ribosome-nascent chain to the ER membrane

SRP receptor

receptor on the ER membrane that binds the SRP-ribosome complex, anchoring it so translation can resume with co-translational translocation into the ER

Start transfer sequence

hydrophobic amino acid sequence that initiates translocation of a polypeptide into or across the ER membrane, typically serving as the first membrane-spanning segment

Stop transfer sequence

hydrophobic sequence that halts translocation through the translocon, anchoring the protein within the membrane bilayer

Translocator

membrane protein complex (like the Sec61 translocon or TOM/TIM complexes) that forms a channel for threading proteins across or into organelle membranes

Zellweger syndrome

severe genetic disorder caused by defective peroxisome biogenesis (mutations in PEX genes), leading to accumulation of very long-chain fatty acids and neurological abnormalities

Adaptin

protein complex that recognizes and binds specific cargo proteins, linking them to clathrin coats during vesicle formation to ensure selective packaging

Cisternae

flattened, membrane-bound compartments of the Golgi apparatus through which proteins progress and undergo modifications during secretory transport

Clathrin

protein that forms a cage-like coat around budding vesicles, providing structural scaffolding for vesicle formation at the plasma membrane and Golgi

Constitutive exocytosis

continuous, unregulated pathway by which vesicles fuse with the plasma membrane to release their contents immediately after delivery from the Golgi

Cystic fibrosis

genetic disorder caused by mutations in the CFTR chloride channel, leading to defective ion transport and thick mucus buildup in the lungs and digestive system

Disulfide bonds

Covalent linkages between cysteine residues that stabilize protein structure, formed enzymatically within the oxidizing environment of the ER lumen

Dolichol

long lipid carrier molecule in the ER membrane that serves as a scaffold for assembling the oligosaccharide chain before its transfer to nascent proteins

Dynamin

GTPase that wraps around the neck of budding vesicles and pinches them off from the donor membrane through conformational changes upon GTP hydrolysis

ER retention signal

KDEL sequence (Lys-Asp-Glu-Leu) on soluble ER proteins that ensures their retrieval from the Golgi back to the ER if they escape

ERAD

ER-associated degradation, a quality control pathway that identifies misfolded ER proteins, retrotranslocates them to the cytosol, and targets them for proteasomal destruction

N-linked glycosylation

enzymatic attachment of a pre-assembled oligosaccharide to asparagine residues of nascent proteins as they enter the ER lumen

Oligosaccharyl transferase

ER enzyme complex that catalyzes the transfer of the dolichol-linked oligosaccharide to target asparagine residues on growing polypeptide chains

Proteasome

large cytosolic protein complex that degrades ubiquitin-tagged proteins, including those rejected by ER quality control, into short peptides

Rab

family of small GTPases that act as molecular switches on vesicle and target membranes, ensuring vesicles dock at the correct destination through specific Rab-Rab effector pairing

Regulated exocytosis

secretion pathway where cargo is stored in vesicles until an external signal (like a hormone or action potential) triggers fusion and release

t-SNARE

Target membrane SNARE proteins (syntaxin and SNAP-25) that pair with v-SNAREs to mediate the fusion of vesicles with their intended destination membrane

Tethering protein

Long coiled-coil or multi-subunit proteins that capture vesicles from a distance and draw them close to target membranes before SNARE-mediated fusion

Ubiquitin

small protein tag that marks misfolded or damaged proteins for proteasomal degradation, with polyubiquitin chains serving as the destruction signal

Unfolded protein response

stress-activated signaling pathway that detects ER protein misfolding and adjusts cellular processes to restore folding capacity or trigger apoptosis

v-SNARE

Vesicle-associated SNARE proteins (synaptobrevin/VAMP) that zipper together with t-SNAREs to pull membranes into close apposition for fusion

Coated vesicle

transport vesicle surrounded by a protein coat (clathrin, COPI, or COPII) that shapes the membrane, selects cargo, and dissociates after budding