Cell Biology Lecture Flashcards

Vocabulary practice flashcards covering cell structure, plasma membrane transport, organelle functions, membrane potentials, mitosis, DNA replication, and protein synthesis.

Cell

The structural and functional building block of all living organisms.

Plasma membrane

A fluid mosaic barrier that provides selective permeability, a mechanical boundary, an electrochemical gradient, and cell signaling capabilities.

Phospholipid

A lipid molecule with a polar (hydrophilic) head and a nonpolar (hydrophobic) tail that forms the structural bilayer of the plasma membrane.

Glycocalyx

A carbohydrate-rich area on the cell surface consisting of glycolipids and glycoproteins that functions in cell-cell recognition.

Tight junctions

Impermeable intercellular junctions formed by interlocking proteins that prevent molecules from passing through the intercellular space.

Desmosomes

Anchoring intercellular junctions containing linker proteins (cadherins) and plaques attached to intermediate filaments (keratin) that bind adjacent cells together like molecular Velcro.

Gap junctions

Communicating intercellular junctions consisting of transmembrane proteins called connexons that form channels allowing ions and small molecules to pass between cells.

Simple diffusion

The passive movement of fat-soluble molecules directly through the phospholipid bilayer down their concentration gradient.

Facilitated diffusion

The passive transport of lipid-insoluble solutes across the membrane via selective protein carriers or channel proteins.

Osmosis

The diffusion of a solvent, such as water, through a specific channel protein (aquaporin) or directly through the lipid bilayer.

Isotonic solution

A solution with the same solute and water concentration as inside the cell, allowing cells to retain their normal size and shape.

Hypertonic solution

A solution containing a higher concentration of solutes than inside the cell, causing water to leave the cell by osmosis and the cell to shrink.

Hypotonic solution

A solution containing a lower concentration of solutes than inside the cell, causing water to enter the cell by osmosis until it bloats and bursts (lyses).

Sodium-Potassium Pump ($\text{Na}^+\text{-K}^+$ pump)

A primary active transport protein that hydrolyzes ATP to move three cytoplasmic $\text{Na}^+$ ions out of the cell and two extracellular $\text{K}^+$ ions into the cell against their concentration gradients.

Antiport system

A transport system where two different substances are moved across the plasma membrane in opposite directions.

Symport system

A transport system where two different substances are moved across the plasma membrane in the same direction.

Primary active transport

A process in which energy derived directly from the hydrolysis of ATP is used to pump solutes across a membrane against their concentration gradient.

Secondary active transport

A transport process driven indirectly by an ion concentration gradient established by primary active transport, carrying other solutes against their gradient.

Exocytosis

A vesicular transport process where intracellular vesicles fuse with the plasma membrane via v-SNARE and t-SNARE binding to release their contents outside the cell.

Phagocytosis

A form of endocytosis in which a cell extends pseudopods to engulf large solids, such as bacteria or cell debris, into clathrin-coated vesicles.

Pinocytosis

A non-specific endocytic process in which the cell infolds its membrane to gulp droplets of extracellular fluid containing small dissolved solutes.

Receptor-mediated endocytosis

A specific endocytic mechanism where specific extracellular substances bind to membrane receptors located in clathrin-coated pits before being internalized.

Transcytosis

A process that moves substances sequentially into, across, and then out of a cell within membrane vesicles.

Resting membrane potential

A voltage across the plasma membrane (typically $-90\,\text{mV}$) established when $\text{K}^+$ diffusion out through leakage channels equals $\text{K}^+$ electrical attraction back into the cell.

Nucleolus

A dense region within the nucleus involved in ribosome assembly and ribosomal RNA (rRNA) synthesis.

Nucleosome

A fundamental unit of chromatin ($10\,\text{nm}$ diameter) consisting of eight histone proteins wrapped twice by a strand of DNA double helix.

Mitochondrion

A double-membrane organelle with inner membrane folds called cristae that provides most of the cell's ATP through aerobic respiration.

Ribosome

A granule consisting of proteins and rRNA that serves as the cellular site for protein synthesis.

Rough endoplasmic reticulum (rER)

A membranous network studded with ribosomes that manufactures secreted proteins, integral membrane proteins, and membrane phospholipids.

Smooth endoplasmic reticulum (sER)

A network of membranous tubules free of ribosomes that functions in lipid metabolism, cholesterol synthesis, fat transport, detoxification, and calcium storage.

Golgi apparatus

A stack of flattened membranous sacs that receives proteins at its cis face, modifies and packages them, and dispatches them via vesicles from its trans face.

Lysosome

A spherical membranous organelle containing acid hydrolase digestive enzymes used to digest nonfunctional organelles, ingested particles, bacteria, and nonuseful tissue.

Peroxisome

A membranous sac containing oxidases and catalases that detoxifies harmful substances and converts toxic free radicals into water.

Microfilaments

Cytoskeletal elements ($7\,\text{nm}$ diameter) formed by strands of spherical actin subunits that help maintain cell shape and drive cell movement.

Intermediate filaments

Tough, insoluble protein fibers ($10\,\text{nm}$ diameter) constructed like woven ropes of tetramer fibrils that resist mechanical pulling forces on the cell.

Microtubules

Hollow tubes ($25\,\text{nm}$ diameter) composed of spherical tubulin subunits that give the cell shape and act as tracks for organelle and vesicle movement.

Centrosome

The microtubule organizing center near the nucleus that contains a centrosome matrix and a pair of centrioles.

Cilia

Hair-like cellular extensions composed of microtubules that move in propulsive power and recovery strokes to sweep substances across cell surfaces.

Microvilli

Finger-like projections of the plasma membrane supported by actin filaments anchored in a terminal web that increase cell surface area for absorption.

Interphase

The main growth phase of the cell cycle consisting of $\text{G}_1$ (growth), $\text{S}$ (DNA synthesis), and $\text{G}_2$ (final preparations for division).

Mitosis

The nuclear division phase of the cell cycle consisting of prophase, metaphase, anaphase, and telophase.

DNA helicase

An enzyme that unwinds the DNA double helix and breaks hydrogen bonds between complementary base pairs during DNA replication.

DNA polymerase

An enzyme that synthesizes new complementary DNA strands using free nucleotides along the exposed template strand.

DNA ligase

An enzyme that splices together DNA segments on the lagging strand to complete a continuous DNA strand during replication.

Gene

A segment of DNA that contains instructions for synthesizing a specific polypeptide chain.

Codon

A three-nucleotide sequence on mRNA that codes for a specific amino acid.

Transcription

The nuclear process where genetic information in a DNA template strand is transferred into a complementary mRNA strand.

Translation

The process occurring at ribosomes where the nucleotide sequence of mRNA is decoded by tRNA to assemble amino acids into a polypeptide.

Transfer RNA (tRNA)

An RNA molecule featuring an anticodon that binds a specific amino acid and delivers it to the matching mRNA codon at the ribosome.

Signal-recognition particle (SRP)

A complex that recognizes the ER signal sequence on a growing polypeptide chain and guides the ribosome-mRNA complex to a receptor on the rough ER.