Chapter 3: Cells, Membranes, and Cellular Processes Vocabulary

Comprehensive vocabulary flashcards covering cell structure, plasma membrane composition, cell junctions, passive and active transport, organelles, protein synthesis, and cell cycle/division from Chapter 3 lecture notes.

Plasma Membrane

A flexible lipid bilayer outer boundary of the cell that separates the intracellular environment from the extracellular environment.

Fluid Mosaic Model

A structural model of the plasma membrane composed of a fluid lipid bilayer embedded with specialized, floating membrane proteins that form constantly changing patterns.

Phospholipids

Membrane lipids comprising $75 proclamation\%$ of the plasma membrane lipid bilayer, featuring polar, hydrophilic heads and nonpolar, hydrophobic fatty acid tails.

Glycolipids

Lipids with attached sugar groups located exclusively on the outer plasma membrane surface, making up $5\%$ of membrane lipids.

Cholesterol

A membrane lipid component accounting for $20\%$ of total plasma membrane lipids that increases membrane stability.

Glycocalyx

A carbohydrate coating on the cell surface formed by glycolipids and glycoproteins that serves as a specific biological marker for cell-to-cell recognition and immune self versus nonself identification.

Interstitial Fluid

Extracellular fluid submersing and bathing cells, containing nutrients, oxygen, and metabolic waste products necessary for proper cell function.

Tight Junctions

Impermeable cell junctions formed by fused integral proteins on adjacent cells that encircle the cell and prevent fluids and molecules from passing through the intercellular space.

Desmosomes

Rivet-like anchoring cell junctions formed by interlocking cadherin linker proteins and plaques that bind adjacent cells together to prevent tearing under mechanical tension.

Gap Junctions

Communicating cell junctions composed of transmembrane protein channels (connexons) that allow ions, simple sugars, and electrical signals to pass directly between adjacent cells.

Passive Transport

Membrane transport processes that require no cellular energy (ATP) input and move substances down their concentration gradient from high to low concentration.

Simple Diffusion

The unassisted movement of nonpolar, lipid-soluble (hydrophobic) substances directly through the phospholipid bilayer down their concentration gradient.

Carrier-Mediated Facilitated Diffusion

Passive transport wherein lipid-insoluble solutes like sugars or amino acids bind to specific protein carriers that undergo shape changes to move solutes across the membrane.

Channel-Mediated Facilitated Diffusion

Passive movement of small lipid-insoluble solutes, such as ions or water, through water-filled transmembrane channel proteins.

Osmosis

The diffusion of a solvent, such as water, through a selectively permeable membrane via the lipid bilayer or specialized channel proteins called aquaporins.

Osmolarity

A quantitative measure of the total number of solute particles dissolved in a given volume of solvent.

Isotonic Solution

A solution with the same solute concentration as the cell cytoplasm, resulting in no net movement of water and allowing cells to retain their normal size.

Hypertonic Solution

A solution containing a higher concentration of nonpenetrating solutes than inside the cell, causing cells to lose water by osmosis and shrink (crenate).

Hypotonic Solution

A solution containing a lower concentration of nonpenetrating solutes than inside the cell, causing water to enter cells by osmosis until they swell and potentially burst (lyse).

Active Transport

Membrane transport processes that require direct or indirect cellular energy (ATP) to move solutes across a living membrane against their concentration gradient (low to high).

Primary Active Transport

Active transport directly powered by ATP hydrolysis, where solute pumps phosphorylate and transport ions against their concentration gradient.

Sodium-Potassium Pump

A primary active transport pump ($\text{Na}^+/\text{K}^+$ pump) that hydrolyzes ATP to move $3\,\text{Na}^+$ out of the cell and $2\,\text{K}^+$ into the cell against their respective concentration gradients.

Secondary Active Transport

Transport driven indirectly by energy stored in ionic concentration gradients established by primary active transport, such as the $\text{Na}^+/\text{glucose}$ cotransporter.

Phagocytosis

A form of endocytosis known as 'cell eating' in which a cell engulfs large solid particles or pathogens into a membrane-bound phagosome.

Pinocytosis

A form of endocytosis known as 'cell drinking' or fluid-phase endocytosis, in which a cell unselectively ingests small droplets of extracellular fluid containing dissolved solutes.

Receptor-Mediated Endocytosis

A selective endocytosis process using clathrin-coated pits and specific membrane receptors to ingest targeted substances like hormones, LDL, iron, and enzymes.

Exocytosis

A vesicular transport mechanism where intracellular substances enclosed within secretory vesicles are ejected into the extracellular fluid.

Contact Signaling

Cellular communication where cells physically touch one another and recognize neighboring cell-surface molecules (CAMs and glycocalyx).

Ligand

A chemical signal molecule, such as a hormone or neurotransmitter, that binds specifically to a cell membrane receptor to initiate intracellular responses.

Cell Adhesion Molecules

Cell-surface proteins (CAMs) that function as molecular hands to help cells recognize, attach to, and guide movement relative to surrounding cells and extracellular matrix.

Cytosol

The gel-like fluid portion of cytoplasm composed of approximately $80\%$ water together with soluble proteins, salts, and sugars.

Inclusions

Insoluble, non-functioning chemical substances stored within the cytoplasm, such as glycogen granules, lipid droplets, pigment granules, and crystals.

Mitochondria

Double-membrane organelles termed the 'powerhouse of the cell' that synthesize most of the cell's ATP via aerobic cellular respiration.

Endomembrane System

A functional group of membranous organelles—including the ER, Golgi apparatus, secretory vesicles, lysosomes, and nuclear/plasma membranes—that works together to produce, store, degrade, and export biological molecules.

Rough Endoplasmic Reticulum

A membranous network continuous with the outer nuclear membrane and studded with ribosomes that manufactures all secreted proteins.

Smooth Endoplasmic Reticulum

A membranous network of tubules involved in lipid and steroid hormone synthesis, fat absorption, chemical detoxification, glycogen conversion, and calcium storage.

Golgi Apparatus

A stack of flattened membranous cisterns that modifies, concentrates, sorts, and packages proteins and lipids received from the rough ER.

Lysosomes

Spherical membranous bags containing acid hydrolases (digestive enzymes) that digest ingested pathogens, degrade nonfunctional organelles, and break down stored glycogen or bone calcium.

Peroxisomes

Membranous sacs containing oxidase and catalase enzymes that neutralize harmful free radicals and participate in fatty acid metabolism.

Free Radicals

Toxic, highly reactive chemicals with unpaired electrons that form as natural by-products of cellular metabolism.

Ribosomes

Nonmembranous cytoplasmic granules made of protein and rRNA that function as the sites of protein synthesis (translation).

Microfilaments

The thinnest cytoskeletal elements, composed of actin strands, that form a cross-linked terminal web beneath the plasma membrane to strengthen the cell surface and enable motility.

Intermediate Filaments

Tough, insoluble ropelike protein fibers composed of tetramer fibrils that resist pulling forces and attach to desmosomes.

Microtubules

The largest cytoskeletal elements, consisting of hollow tubes made of tubulin subunits that determine cell shape and serve as tracks for motor proteins.

Centrosome

A microtubule-organizing center located near the nucleus containing a pair of barrel-shaped centrioles oriented at right angles to one another.

Cilia

Short, hair-like cellular extensions that whip back and forth synchronously to move fluids or mucus across the cell surface.

Flagella

Long, whip-like cellular projections that propel an entire cell through its environment, such as the tail of a sperm cell.

Microvilli

Tiny, fingerlike extensions of the plasma membrane containing an actin microfilament core that maximize surface area for absorption.

Motor Proteins

ATP-powered protein complexes that transport vesicles and organelles along cytoskeletal microtubule tracks.

Nuclear Envelope

A double-membrane barrier enclosing the nucleoplasm pierced by nuclear pores that regulate the entry and exit of large molecules.

Nucleoli

Dark-staining spherical bodies within the nucleus responsible for rRNA synthesis and ribosome subunit assembly.

Chromatin

A nuclear complex consisting of $30\%$ DNA, $60\%$ histone proteins, and $10\%$ RNA, organized into repeating nucleosome units.

Nucleosome

The fundamental structural unit of chromatin, composed of a segment of DNA double helix wrapped twice around a core cluster of eight histone proteins.

Gene

A distinct segment of DNA that contains the genetic code sequence for synthesizing a single polypeptide chain.

Transcription

The enzymatic transfer of genetic information held in a DNA template strand into a complementary base sequence of mRNA.

Translation

The decoding of an mRNA base sequence at a ribosome to assemble amino acids into a specific polypeptide chain.

Codon

A three-base mRNA sequence that specifies a particular amino acid or signals the termination of protein synthesis.

Anticodon

A three-base triplet on a tRNA molecule that complementary base-pairs with a specific mRNA codon at the ribosome.

Interphase

The non-dividing phase of the cell cycle spanning from cell formation to division, during which the cell grows, carries out routine activities, and replicates its DNA.

G0 Phase

A non-dividing state of permanent cessation from the cell cycle exhibited by cells that no longer divide.

S Phase

The synthetic subphase of interphase during which nuclear DNA is completely replicated.

Semiconservative Replication

The DNA replication mechanism in which each resulting daughter DNA molecule is composed of one conserved original strand and one newly synthesized strand.

Mitosis

The division of the cell nucleus consisting of prophase, metaphase, anaphase, and telophase to distribute duplicated chromosomes equally to daughter cells.

Cytokinesis

The division of the cell cytoplasm accomplished by a contractile ring of actin microfilaments forming a cleavage furrow that pinches the cell into two daughter cells.

Prophase

The first stage of mitosis during which chromatin condenses into chromosomes, the nuclear envelope disperses, and the mitotic spindle forms.

Metaphase

The second stage of mitosis during which centromeres of chromosomes align precisely along the metaphase plate midway between the spindle poles.

Anaphase

The shortest mitotic stage in which centromeres split simultaneously and sister chromatids are pulled to opposite poles of the cell.

Telophase

The final stage of mitosis during which chromosome movement stops, nuclear envelopes reform, nucleoli reappear, and chromosomes uncoil back into chromatin.

Contact Inhibition

A regulatory mechanism that inhibits cell division when normal cells come into physical contact with surrounding cells.

G1 Checkpoint

The primary restriction point in the cell cycle where environmental and internal conditions are assessed before a cell commits to DNA synthesis or enters $G_0$.