Cell Biology and Membrane Transport

Comprehensive vocabulary flashcards covering cell structure, organelles, prokaryotic and eukaryotic distinctions, cytoskeletal filaments, membrane transport mechanisms, and cellular junctions based on lecture notes.

Cell

The most basic and smallest form of life, with sizes typically ranging from $1\,\text{mm}$ down to $1\,\mu\text{m}$ ($1000\,\text{nm}$).

Cell Theory

A foundational biological principle stating that: 1. All organisms are composed of cells; 2. Cells are the basic unit of structure and function in organisms; and 3. Cells come from pre-existing cells.

Surface Area to Volume Ratio (SA:V)

The mathematical ratio of a cell's outer surface area relative to its internal volume; it decreases as a cell grows in size and increases when a cell divides, with higher ratios being required for efficient transport systems.

Coccus

A morphological form of bacteria characterized by a spherical or direct round shape.

Bacillus

A morphological form of bacteria characterized by an oblong or rod-like shape.

Spirillum

A morphological form of bacteria characterized by a curved or spiral shape.

Cell Envelope

The outer boundary of a bacterial cell, composed collectively of the plasma membrane, the cell wall, and the glycocalyx.

Mesosomes

Internal membrane pouches found in bacteria that fold inward to increase total surface area.

Capsule

A protective layer of polysaccharides lying outside the cell wall in certain bacteria that aids in attachment to surfaces and provides protection.

Cytoplasm

A semifluid solution consisting of water, inorganic molecules, and organic molecules that holds organelles in place and contains enzymes aiding chemical reactions.

Nucleoid

The non-membrane-enclosed region within a prokaryotic cell where the single strand of circular DNA is located.

Plasmids

Small, extrachromosomal circular rings of DNA present in prokaryotic cells.

Fimbriae

Small, hair-like protein fibers that sprout from the surface of bacterial cells to assist in attachment.

Polyribosomes

Strings of multiple ribosomes simultaneously engaged in translating a single strand of mRNA.

Endomembrane System

A coordinated intracellular membrane system consisting of the endoplasmic reticulum, Golgi body, lysosomes, and various transport vesicles that can interconnect due to their lipid membranes.

Rough Endoplasmic Reticulum (Rough ER)

A series of membrane channels studded with ribosomes on the cytoplasmic surface, responsible for producing proteins and folding them inside its lumen.

Smooth Endoplasmic Reticulum (Smooth ER)

A membranous network continuous with the rough ER and nuclear envelope that lacks ribosomes; functions in lipid synthesis, breakdown of molecules, and dispatching transport vesicles.

Golgi Apparatus

An organelle composed of a stack of 3 to 20 curved saccules (flattened vesicles) that receives, modifies, sorts, packages, and ships proteins and lipids from the ER to intra- or extracellular destinations.

Lysosomes

Membrane-bound vesicles produced by the Golgi apparatus that contain hydrolytic enzymes to break down and digest non-functioning organelles and foreign substances.

Syndactyly

A clinical condition where digits remain fused or webbed due to the failure of lysosomes to digest the interdigital webbing during embryonic development.

Peroxisomes

Membrane-bound metabolic organelles serving as the detoxification centers of the cell, utilizing oxidases and catalases to degrade alcohols, fatty acids, and toxic chemicals.

Catalase

A peroxisomal antioxidant enzyme that converts toxic hydrogen peroxide into water and oxygen gas according to the reaction: $2H_2O_2 \rightarrow 2H_2O + O_2$.

Central Vacuole

A prominent membrane sac in plant cells that can occupy up to $90\%$ of cellular volume, functioning in storage and maintaining the cell's physical structure.

Thylakoid

A flattened, photosynthetic disc located within chloroplasts containing light-absorbing pigments.

Stroma

The enzyme-rich fluid solution situated outside the thylakoids within the inner chloroplast membrane.

Granum

A stacked column of individual thylakoid discs inside a chloroplast.

Cristae

Folds of the inner mitochondrial membrane that project inward to significantly expand the surface area available for ATP synthesis.

Mitochondrial Matrix

The fluid-filled internal space enclosed by the inner mitochondrial membrane containing ribosomes and mitochondrial DNA (mtDNA).

Actin Filaments

Extremely thin, flexible cytoskeletal filaments consisting of two chains of actin monomers that anchor to membrane proteins to provide structural support.

Intermediate Filaments

Rope-like, highly stable protein fibers (such as keratin) that reinforce cell structure and support both the nuclear envelope and plasma membrane.

Microtubules

Small, hollow cylinders composed of tubulin protein dimers that support cellular structure and serve as tracks along which motor proteins like kinesin and dynein travel.

Centrioles

Animal cell organelles composed of 9 triplets of microtubules that separate during mitosis to organize the division of chromosomes.

Basal Body

A microtubule-based organelle structurally similar to a centriole that anchors cilia and flagella to the plasma membrane.

Fluid Mosaic Model

A model describing the plasma membrane as a dynamic bilayer of amphipathic phospholipids embedded with freely moving proteins, steroids, and carbohydrate chains.

Aquaporins

Specialized channel proteins spanning the plasma membrane that selectively accelerate the transport of water molecules across the lipid bilayer.

Integral Proteins

Membrane proteins that are permanently embedded within the hydrophobic core of the phospholipid bilayer.

Peripheral Proteins

Proteins located exclusively on the interior or exterior surface of the plasma membrane that can reversibly attach and detach.

Cell Recognition Proteins

Glycoproteins embedded in the cell membrane that display unique carbohydrate chains, enabling the immune system to distinguish self-cells from invading pathogens.

Diffusion

The passive net movement of solute molecules from a region of higher concentration to a region of lower concentration down a concentration gradient.

Osmosis

The passive net diffusion of water across a selectively permeable membrane toward a region of higher solute concentration.

Hypotonic Solution

An external solution with a lower solute concentration than the cell interior, causing net osmotic water influx that makes cells swell or burst (lyse).

Hypertonic Solution

An external solution with a higher solute concentration than the cell interior, causing net water loss that leads to cellular shriveling or crenation.

Isotonic Solution

A solution wherein solute and water concentrations are equal across the plasma membrane, resulting in no net movement of water.

Active Transport

The movement of solute molecules across a membrane against their concentration gradient (from low to high concentration), requiring cellular energy in the form of $\text{ATP}$.

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

An electrogenic carrier protein that consumes $\text{ATP}$ to pump $3\,\text{Na}^+$ ions out of the cell while transporting $2\,\text{K}^+$ ions into the cell.

Salty Banana Analogy

A biological memory aid for neuronal ion distribution indicating high potassium ($\text{K}^+$) inside the cell like the fruit and high sodium ($\text{Na}^+$) outside like salt on the peel.

Exocytosis

A form of bulk active transport where an intracellular vesicle fuses with the plasma membrane to secrete its cargo outside the cell.

Phagocytosis

A form of endocytosis ('cell eating') in which the plasma membrane surrounds and internalizes large, solid particles or entire microorganisms.

Pinocytosis

A form of endocytosis ('cell drinking') where the cell membrane invaginates to take up small liquid droplets and dissolved solutes.

Receptor-Mediated Endocytosis

A selective type of endocytosis where specific target molecules bind to receptor proteins on the plasma membrane before vesicle internalization.

Extracellular Matrix (ECM)

A complex network of fibrous proteins and polysaccharides (including collagen, elastin, and integrins) located outside animal cells that provides mechanical and biochemical support.

Desmosomes (Adhesion Junctions)

Intercellular junctions that mechanically fasten adjacent cells together by connecting to cytoskeletal filaments, found in tissues prone to mechanical stretching like the heart and bladder.

Tight Junctions

Intercellular connections formed by zipper-like membrane proteins that seal spaces between adjacent cells to create a waterproof barrier (e.g., in the bladder and kidneys).

Gap Junctions

Intercellular communication channels ('tunnels') formed by membrane proteins that allow ions and small signaling molecules to pass directly between adjacent animal cells.

Plasmodesmata

Narrow, membrane-lined cytoplasmic channels spanning the plant cell wall that allow direct transport and communication between adjacent plant cells.

Endosymbiotic Theory

The evolutionary theory proposing that eukaryotic organelles such as mitochondria and chloroplasts originated from free-living prokaryotes engulfed by ancestral host cells.

Nucleolus

A dense, dark-staining region within the eukaryotic nucleus dedicated to the synthesis of ribosomal RNA (rRNA) and assembly of ribosome subunits.

Nuclear Pores

Protein complexes that span the nuclear envelope to regulate the bidirectional transit of macromolecules such as ribosomal subunits, mRNA, and proteins.

Chromatin

The uncoiled, diffuse complex of DNA and associated proteins located within the eukaryotic nucleus that condenses into visible chromosomes during cell division.