Chapter 4: Inside the Cell

Vocabulary practice flashcards covering cellular structure, microscopy, organelles, the endomembrane system, cytoskeleton, and intercellular junctions from Chapter 4 of Essentials of Biology (7th Edition).

Light microscope

An optical instrument invented in the seventeenth century that is limited by the physical properties of light.

Electron microscope

A high-resolution microscope invented in the 1930s that overcomes the resolution limits of light by utilizing a beam of electrons.

Surface-area-to-volume ratio

A physical relationship that limits cell size, dictating that smaller cells have proportionally more surface area relative to their volume for exchanging nutrients and waste.

Plasma membrane

A phospholipid bilayer with embedded proteins that marks the boundary between the outside and inside of a cell, regulating the passage of materials in and out.

Fluid mosaic model

The structural model describing the dynamic plasma membrane, consisting of a fluid phospholipid bilayer embedded with a mosaic of diverse proteins.

Channel protein

A membrane protein that forms an open tunnel spanning the bilayer to permit the passage of specific molecules.

Transport protein

A membrane protein involved in the passage of molecules across the plasma membrane, which sometimes requires an input of cellular energy.

Cell recognition protein

A membrane glycoprotein that enables the immune system and body to distinguish between self cells and foreign cells.

Receptor protein

A membrane protein possessing a binding site shaped specifically for signal molecules, initiating a cellular response upon binding.

Enzymatic protein

A membrane protein that directly participates in and catalyzes specific metabolic chemical reactions.

Junction protein

A membrane protein that joins neighboring cells together to facilitate cell-to-cell adhesion and intercellular communication.

Cell theory

A foundational biological concept stating that all organisms are composed of cells and that all cells originate only from preexisting cells.

Prokaryotic cells

Relatively small, simple unicellular organisms belonging to the domains Bacteria and Archaea that lack a membrane-bounded nucleus.

Eukaryotic cells

Complex, compartmentalized cells containing a membrane-bounded nucleus housing DNA and specialized organelles; comprises protists, fungi, plants, and animals.

Nucleoid

The region within a prokaryotic cell where the single circular, coiled bacterial chromosome is located; not surrounded by a membrane.

Capsule

A gel-like protective coating found outside the cell wall in certain bacteria.

Fimbriae

Small, hairlike bacterial appendages that function in adhering cells to environmental surfaces.

Conjugation pili

Tubular bacterial surface appendages utilized for the horizontal transfer of DNA between cells.

Chromatin

A diffuse network of DNA, associated proteins, and RNA within the nucleus that condenses into chromosomes prior to cell division.

Nucleolus

A dense, specialized region within the eukaryotic nucleus where ribosomal RNA (rRNA) is synthesized.

Nuclear envelope

A double membrane perforated by nuclear pores that encloses the nucleus and regulates molecular traffic between the nucleoplasm and cytoplasm.

Ribosome

A cytoplasmic structure composed of two subunits of rRNA and proteins that translates mRNA into a polypeptide chain during protein synthesis.

Endomembrane system

A compartmentalized network of internal membranes consisting of the nuclear envelope, endoplasmic reticulum, Golgi apparatus, and various vesicles.

Rough endoplasmic reticulum (Rough ER)

A system of membranous channels and flattened saccules studded with ribosomes that modifies newly synthesized proteins and packages them into transport vesicles.

Smooth endoplasmic reticulum (Smooth ER)

A continuous extension of the rough ER that lacks ribosomes; functions in synthesizing lipids such as phospholipids and steroids, producing testosterone, and detoxifying drugs.

Golgi apparatus

A stack of flattened saccules functioning as a cellular transfer station that receives, modifies, sorts, and repackages ER products into transport or secretory vesicles.

Lysosomes

Membrane-bound digestive vesicles produced by the Golgi apparatus that contain enzymes to break down foreign molecules or recycle old cell parts; associated with Tay-Sachs disease.

Vacuoles

Large membranous storage sacs that rid cells of excess water, perform digestion, or store plant pigments and lipids in animal adipocytes.

Mitochondria

Double-membrane-bound energy organelles present in plants and animals that perform cellular respiration, breaking down carbohydrates to synthesize ATP.

Cristae

Inward folds of the inner mitochondrial membrane that significantly increase the surface area available for cellular respiration and ATP synthesis.

Mitochondrial matrix

The fluid-filled inner space enclosed by the inner mitochondrial membrane containing respiratory enzymes, mitochondrial DNA, and ribosomes.

Chloroplasts

Three-membrane photosynthetic organelles found in plants and algae that capture solar energy to synthesize carbohydrates; contain their own DNA and ribosomes.

Stroma

The fluid-filled matrix enclosed within the double membrane of a chloroplast surrounding the thylakoids.

Thylakoids

Disc-shaped membranous sacs stacked into grana inside chloroplasts whose membranes contain light-capturing photosynthetic pigments.

Cytoskeleton

A network of interconnected protein filaments and tubules extending from the nucleus to the plasma membrane that maintains eukaryotic cell shape and enables organelle transport.

Actin filaments

Cytoskeletal elements consisting of two chains of globular monomers twisted into a helix that form a dense supporting web beneath the plasma membrane.

Intermediate filaments

Ropelike cytoskeletal assemblies intermediate in size that extend from the nuclear envelope to the plasma membrane, providing mechanical strength.

Microtubules

Small, hollow cylinders assembled under the control of the centrosome that maintain cell shape and provide structural tracks along which motor proteins travel.

Centrioles

Paired, barrel-shaped organelles found in animal centrosomes composed of nine sets of microtubule triplets arranged at right angles; absent in plant cells.

Cilia and flagella

Motile hairlike or whiplike eukaryotic cell surface projections constructed in a characteristic $9+2$ pattern of microtubules; cilia are shorter and more numerous than flagella.

Plasmodesmata

Membrane-lined channels perforating adjacent plant cell walls that connect the cytoplasm of adjacent cells for rapid exchange of water and small solutes.

Extracellular matrix (ECM)

A meshwork of fibrous proteins (such as collagen and elastin) and polysaccharides secreted outside animal cells that provides support, tensile strength, and resilience.

Adhesion junctions

Intercellular junctions consisting of internal cytoplasmic plaques linked across intercellular space by filaments, creating sturdy yet flexible sheets of tissue.

Tight junctions

Impermeable intercellular junctions formed by proteins that closely fuse adjacent plasma membranes, preventing extracellular fluids from leaking across cell sheets.

Gap junctions

Communicating junctions formed when adjacent plasma membrane channel proteins align, allowing ions and small molecules to flow directly between neighboring cells.