Cell Structure and Function: Subcellular Components and Compartmentalization

Comprehensive vocabulary flashcards covering cell theory history, prokaryotic versus eukaryotic structure, the endomembrane system, energy organelles, the endosymbiont theory, cytoskeleton filaments, and cell size dynamics.

Anton Van Leeuwenhoek

The naturalist who made microscopic observations in $1676$ documenting white blood cells, red blood cells, yeast cells, sperm cells, and bacteria cells.

Matthias Schleiden

Botanist who concluded in $1838$ that all plants are composed of cells.

Theodor Schwann

Zoologist who determined in $1839$ that all animals are composed of cells.

Rudolf Virchow

Physician who proposed in $1855$ that every cell arises from a pre-existing cell ("Omnis cellula e cellula").

Classical Cell Theory

The foundational biological principle developed by Schleiden ($1838$), Schwann ($1839$), and Virchow ($1855$) establishing that all living organisms are made of cells and all cells come from pre-existing cells.

Basic Features of All Cells

Four common cellular structures present in every organism: a plasma membrane, cytosol, chromosomes, and ribosomes.

Prokaryotic Cells

Single-celled organisms (Bacteria and Archaea) typically $0.5\text{--}10\,\mu\text{m}$ in length that lack internal membrane-bound organelles and possess a nucleoid, plasmids, and $70\text{S}$ ribosomes.

Eukaryotic Cells

Complex cells (protists, fungi, plants, and animals) measuring $30\text{--}150\,\mu\text{m}$ that contain a membrane-bound nucleus, linear chromosomes, $80\text{S}$ cytosolic ribosomes, and membrane-bound organelles.

Plasmids

Small, circular accessory DNA molecules found floating in the cytoplasm of prokaryotic cells.

Endomembrane System

A coordinated network of subcellular components including the nuclear envelope, endoplasmic reticulum, Golgi complex, lysosomes, vesicles/vacuoles, and plasma membrane that modify, package, and transport polysaccharides, proteins, and lipids.

Energy Organelles

Mitochondria and chloroplasts; specialized eukaryotic structures that convert environmental or stored energy into usable forms to perform cellular work.

Compartmentalization

The division of the eukaryotic cell interior into distinct membrane-bound compartments, increasing surface area for enzymatic reactions and isolating incompatible biochemical processes.

Nuclear Envelope

A double membrane enclosing the nucleus, perforated by nuclear pores regulating entry and exit of molecules, and continuous with the endoplasmic reticulum membrane.

Nucleolus

A dense non-membrane region within the nucleus responsible for synthesizing ribosomal RNA (rRNA) and assembling large and small ribosomal subunits.

Ribosomes

Subcellular complexes synthesized from ribosomal RNA (rRNA) and proteins that translate genetic instructions in mRNA into polypeptide chains.

Free Ribosomes

Ribosomes suspended in the cytosol that synthesize proteins functioning predominantly within the cytosol, such as metabolic enzymes.

Bound Ribosomes

Ribosomes attached to the endoplasmic reticulum or nuclear envelope that synthesize membrane-inserted proteins, lysosomal enzymes, or secretory proteins destined to leave the cell via transport vesicles.

Rough Endoplasmic Reticulum (RER)

A network of membranous sacs and tubules studded with ribosomes that compartmentalizes protein synthesis and provides intracellular transport.

Smooth Endoplasmic Reticulum (SER)

A ribosome-free membranous network of tubules dedicated to lipid synthesis, carbohydrate metabolism, and cell detoxification.

Golgi Complex

A membrane-bound organelle consisting of flattened sacs (cisternae) that chemically modifies, sorts, tags with molecular markers, and packages ER products into vesicles for secretion via exocytosis or delivery within the cell.

Cis Face of the Golgi

The receiving side of the Golgi apparatus oriented toward the endoplasmic reticulum that fuses with incoming transport vesicles.

Trans Face of the Golgi

The shipping face of the Golgi apparatus that buds off transport vesicles directed to other organelles or the plasma membrane for secretion.

Lysosomes

Membranous animal cell sacs filled with hydrolytic enzymes that digest macromolecules, clear debris, recycle organelle parts, and trigger apoptosis.

Autophagy

A recycling process where lysosomes fuse with damaged or malfunctioning organelles to break them down and enable cellular renewal.

Apoptosis

Programmed cell death occurring when lysosomal membranes break down, releasing hydrolytic enzymes into the cytoplasm to degrade cellular components.

Peroxisomes

Membrane-bound metabolic compartments separate from the endomembrane system that oxidize fatty acids, produce $H_2O_2$ via oxidases, and convert harmful $H_2O_2$ to water and oxygen via catalase.

Central Vacuole

A large single vacuole in plant cells that stores water and inorganic nutrients, maintains cellular turgor pressure, and can carry out hydrolytic digestion.

Plasmodesmata

Cytoplasmic channels perforating plant cell walls that connect adjacent plant cells, allowing direct intercellular transport and communication.

Mitochondria

Double-membrane energy organelles in eukaryotic cells that generate ATP through the Krebs cycle and electron transport chain during aerobic cellular respiration.

Cristae

Infoldings of the inner mitochondrial membrane that expand surface area for ATP synthesis and divide the organelle into the intermembrane space and mitochondrial matrix.

Chloroplasts

Photosynthetic organelles in plants and algae that capture light energy using chlorophyll to manufacture carbohydrates from carbon dioxide and water.

Thylakoids

Flattened membranous sacs inside chloroplasts organized into stacks called grana, serving as the location for the light-dependent reactions of photosynthesis.

Stroma

The fluid-filled space within the inner chloroplast membrane surrounding thylakoids, containing chloroplast DNA, $70\text{S}$ ribosomes, and the enzymes that carry out the Calvin cycle.

Endosymbiont Theory

The evolutionary model proposing that mitochondria and chloroplasts originated as free-living prokaryotic cells engulfed by an ancestral host cell, evolving into mutualistic endosymbionts.

Cytoskeleton

A network of protein fibers extending through the cytoplasm that anchors organelles, preserves cell shape, and cooperates with motor proteins to facilitate intracellular movement and whole-cell motility.

Microtubules

Hollow rods measuring $25\,\text{nm}$ in diameter formed from tubulin dimers that grow from centrosomes, position organelles, separate chromosomes during cell division, and form the core of cilia and flagella.

Microfilaments

Thin, solid cytoskeletal rods measuring $6\,\text{nm}$ in diameter made of the globular protein actin that support cell tension, power muscle contraction with myosin, and form the contractile ring during animal cell division.

Intermediate Filaments

Cytoskeletal fibers with an intermediate diameter of $10\,\text{nm}$ composed of fibrous protein subunits (such as keratin) that reinforce cell shape, anchor the nucleus, and form the nuclear lamina.

Nuclear Lamina

A net-like array of intermediate filaments lining the inner surface of the nuclear envelope that mechanically maintains nuclear structural integrity.

Cell Size Constraints

Physical limitations imposed by surface area-to-volume ratios, where increasing volume diminishes relative membrane surface area, limiting diffusion rates for nutrient intake, waste removal, and thermal dissipation.