Chapter 4: Inside the Cell

Vocabulary flashcards covering cell structure, microscopy, prokaryotic and eukaryotic organelles, membrane proteins, the cytoskeleton, and intercellular junctions from Chapter 4 of Essentials of Biology (7th edition).

Light microscope

An instrument invented in the seventeenth century used to view cells that is limited by the physical properties of light.

Electron microscope

An instrument invented in the 1930s that overcomes the resolution limitations of light microscopes by utilizing a beam of electrons.

Surface-area-to-volume ratio

A biological principle dictating that small cells have more surface area relative to their volume, ensuring adequate exchange and passage of materials into and out of the cell.

Microvilli

Cellular adaptations located in the small intestine that increase surface area for the absorption of nutrients.

Fluid mosaic model

The model describing the structure of the plasma membrane as a phospholipid bilayer with embedded proteins, in which hydrophilic polar heads face outward into watery medium and hydrophobic nonpolar tails face inward toward each other.

Channel proteins

Membrane proteins that form an open tunnel through the membrane allowing specific molecules to pass.

Transport proteins

Membrane proteins involved in the movement of molecules through the plasma membrane, sometimes requiring the input of cellular energy.

Cell recognition proteins

Membrane glycoproteins that enable the immune system and body to distinguish between its own cells and the cells of other organisms.

Receptor proteins

Membrane proteins with specific shapes that bind signaling molecules, triggering a specific cellular response.

Enzymatic proteins

Membrane-bound proteins that directly participate in and catalyze metabolic reactions.

Junction proteins

Membrane proteins that form connections between adjacent cells to assist with cell-to-cell adhesion and intercellular communication.

Cell theory

The foundational biological theory stating that all organisms are composed of cells and that all cells come only from preexisting cells.

Prokaryotic cells

Structurally simple, smaller organisms belonging to the domains Bacteria and Archaea that lack a membrane-bounded nucleus.

Eukaryotic cells

Complex, compartmentalized cells comprising protists, fungi, plants, and animals that contain organelles and a membrane-bounded nucleus housing DNA.

Capsule

A protective, gel-like coating found on the exterior of the cell wall in certain bacterial cells.

Nucleoid

The non-membrane-enclosed region inside a prokaryotic cell where the single circular, coiled chromosome is located.

Conjugation pili

Tubular appendages in bacteria that facilitate the transfer of DNA from one cell to another.

Fimbriae

Small, bristle-like protein appendages that allow bacterial cells to attach to surfaces.

Chromatin

A diffuse network of DNA, protein, and some RNA in the nucleus that condenses and compacts into chromosomes prior to cell division.

Nucleolus

A dark region within the eukaryotic nucleus where ribosomal RNA ($\text{rRNA}$) is synthesized.

Nuclear envelope

A double membrane perforated with nuclear pores that encloses the nucleus and regulates the passage of substances between the nucleus and the cytoplasm.

Ribosomes

Organelles composed of two subunits made of proteins and $\text{rRNA}$ that carry out protein synthesis in the cytoplasm according to mRNA instructions.

Endomembrane system

A cellular compartmentalization network consisting of the nuclear envelope, endoplasmic reticulum membranes, Golgi apparatus, and transport vesicles that restricts specific enzymatic reactions to localized regions.

Rough endoplasmic reticulum

A membranous network studded with ribosomes on its cytoplasmic surface that modifies newly synthesized polypeptides in its lumen and packages them into transport vesicles.

Smooth endoplasmic reticulum

A continuous system of membranous channels lacking ribosomes that synthesizes lipids, produces testosterone, and detoxifies drugs.

Golgi apparatus

A stack of flattened saccules functioning as a transfer station that receives transport vesicles from the ER, modifies their contents, and sorts and repackages them for destination transport.

Lysosomes

Digestive vesicles produced by the Golgi apparatus containing hydrolytic enzymes that break down macromolecules and old cell parts, and are defective in Tay-Sachs disease.

Vacuoles

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

Mitochondria

Double-membrane-bounded organelles responsible for cellular respiration, breaking down carbohydrates to synthesize ATP while utilizing oxygen and producing carbon dioxide.

Cristae

The folded convolutions of the inner mitochondrial membrane that expand surface area for ATP-generating metabolic reactions.

Matrix

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

Chloroplasts

Three-membrane energy-converting organelles found in plants and algae that capture solar energy to synthesize carbohydrates via photosynthesis.

Thylakoids

Disc-shaped membranous sacs formed from the third membrane of a chloroplast containing light-capturing pigments, which stack together to form grana.

Stroma

The homogeneous fluid-filled matrix within the inner chloroplast membrane surrounding the thylakoid system.

Cytoskeleton

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

Motor proteins

Cellular proteins—including myosin, kinesin, and dynein—that utilize energy from ATP hydrolysis to generate cell motility and transport intracellular components.

Microtubules

Small, hollow cylinders assembled under the regulation of the centrosome that maintain cellular architecture and act as tracks for organelle transport.

Intermediate filaments

Ropelike cytoskeletal assemblies intermediate in size that extend between the nuclear envelope and the plasma membrane.

Actin filaments

Structural protein filaments composed of two chains of globular monomers twisted into a helix, forming a supporting web beneath the plasma membrane.

Centrioles

Short, barrel-shaped organelles found in pairs at right angles within animal centrosomes, each composed of nine sets of microtubule triplets.

Cilia and flagella

Eukaryotic cellular projections constructed from a $9+2$ pattern of microtubules that move cells or propel extracellular fluids.

Plasmodesmata

Membrane-lined channels passing through plant cell walls that link adjoining plant cells for the direct exchange of water and small solutes.

Extracellular matrix (ECM)

A nonliving network of fibrous proteins—including collagen and elastin—and polysaccharides situated outside animal cells that provides support and resilience.

Adhesion junctions

Intercellular junctions formed by internal cytoplasmic plaques joined by intercellular filaments that create a sturdy but flexible sheet of cells.

Tight junctions

Intercellular connections where proteins zipper adjacent plasma membranes together, forming an impermeable fluid barrier between cells.

Gap junctions

Intercellular junctions consisting of joined membrane protein channels that allow direct passage of ions and signaling molecules between adjacent cells.

Stem cells

Cells that can develop into a wide variety of cell types because they contain all of the genetic information and internal structures needed to become almost any other type of cell in the body.

Electron microscopes

Microscopes that utilize beams of electrons instead of beams of light as their illumination source.

Light microscope (LM)

An optical microscope that uses visible light to magnify specimens.

Transmission electron microscope (TEM)

An electron microscope that transmits a beam of electrons through an ultra-thin specimen to form an image.

Scanning electron microscope (SEM)

An electron microscope that scans a focused electron beam over a specimen surface to create detailed three-dimensional images.

Ovum

The largest human cell, with a size of approximately $.1\,\text{mm}$.

Sperm cell

The smallest human cell, measuring approximately $1/20\text{th}$ the size of the ovum.

Nerve cell (Animal)

The largest animal cell, reaching up to $14\,\text{meter}$ in length.

Surface-area-to-volume ratio

A critical physical constraint on cell size; higher ratios provide increased surface area for the same volume, allowing for increased nutrient absorption.

Plasma membrane

The outer cellular boundary that regulates the entry and exit of substances to maintain internal homeostasis.

Phospholipid bilayer

A double-layered membrane structure composed of phospholipids with hydrophilic heads facing outward toward aqueous environments and hydrophobic tails facing inward.

Cholesterol (in plasma membrane)

A lipid component embedded in the plasma membrane that regulates membrane fluidity across varying temperatures.

Channel proteins

Plasma membrane proteins that provide open pores allowing specific molecules or ions to pass freely across the membrane.

Transport proteins

Membrane proteins that actively move specific substances across the plasma membrane by altering their shape.

Cell recognition proteins

Membrane glycoproteins that act as unique ID tags allowing the immune system to distinguish between self and foreign cells.

Receptor proteins

Membrane proteins that bind specific extracellular signaling molecules to trigger targeted cellular responses.

Enzymatic proteins (Membrane)

Plasma membrane proteins that catalyze specific metabolic and biochemical reactions directly at the membrane surface.

Junction proteins

Membrane proteins that establish intercellular connections to tightly bind adjacent cells together.

Cell Theory

The unifying biological principle stating that all organisms are composed of cells, cells are the basic units of life, and all cells arise from pre-existing cells.

Universal cellular features

The three fundamental structures common to all cells: the plasma membrane, cytoplasm, and DNA.

Prokaryotic cells

Small, simple cells that lack a membrane-bound nucleus and membrane-bound organelles.

Eukaryotic cells

Larger, complex cells characterized by the presence of a true membrane-bound nucleus and specialized membrane-bound organelles.

Escherichia coli (Beneficial)

Symbiotic gut bacterium that aids in food digestion, synthesizes essential vitamins, and prevents colonization by pathogenic bacteria.

Escherichia coli O157:H7

A pathogenic bacterial strain that produces dangerous shiga toxins causing severe abdominal cramps, bloody diarrhea, and kidney failure.

Capsule

A protective outer gelatinous layer surrounding some prokaryotic cells that helps evade the host immune system and adhere to surfaces.

Cell wall

A rigid layer located outside the plasma membrane in plant cells, fungi, algae, and most prokaryotes that maintains shape and provides structural protection.

Nucleoid

The irregularly shaped, non-membrane-bound region within a prokaryote containing its circular DNA.

Prokaryotic Cell Structure

Anatomical organization of a prokaryote containing a capsule, cell wall, plasma membrane, cytoplasm, nucleoid, scattered ribosomes, and a locomotory flagellum.

Organelles

Specialized subcellular membrane-bound compartments within eukaryotic cells that perform distinct biochemical and physiological functions.

Compartmentalization

The division of eukaryotic cells into distinct internal membrane-bound compartments to isolate and optimize different biochemical reactions.

Nucleus

The eukaryotic organelle that stores and protects genetic material (DNA) and directs all cellular activities.

Chromatin

The uncoiled, diffuse complex of DNA and associated proteins found in eukaryotic cells during non-dividing stages.

Chromosomes

Tightly condensed and coiled structures of DNA formed during cell division.

Nucleolus

A dense subnuclear region responsible for the synthesis of ribosomal RNA (rRNA) and the assembly of ribosomal subunits.

Nuclear envelope

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

Ribosomes

Complexes of ribosomal RNA and proteins composed of two subunits that translate messenger RNA (mRNA) into polypeptide chains.

Rough Endoplasmic Reticulum (Rough ER)

A network of membrane-bound tubes and flattened sacs studded with ribosomes dedicated to the synthesis and modification of proteins.

Smooth Endoplasmic Reticulum (Smooth ER)

A tubular network of membranes lacking ribosomes that functions in lipid synthesis and chemical detoxification.

Golgi apparatus

A series of flattened, membrane-bound cisternae that modifies, sorts, and packages proteins and lipids into vesicles for transport.

Lysosomes

Membrane-bound vesicles containing hydrolytic digestive enzymes that degrade waste materials, cellular debris, and engulfed pathogens.

Vacuoles

Large, membrane-bound sacs within cells that store water, nutrients, pigments, and waste products.

Chloroplasts

Double-membrane plant and algal organelles containing thylakoids that capture solar energy to convert $CO_2$ and water into glucose and $O_2$ through photosynthesis.

Mitochondria

Double-membrane eukaryotic organelles with folded inner cristae that generate cellular ATP via cellular respiration.

Adenosine Triphosphate (ATP)

The primary energy currency molecule of the cell, generated during cellular respiration to power endergonic biochemical processes.

Photosynthesis

The biochemical process by which autotrophic plant cells convert solar energy, carbon dioxide ($CO_2$), and water into glucose and oxygen ($O_2$).

Cytoskeleton

A highly dynamic, interconnected network of protein fibers throughout the cytoplasm that maintains cell architecture, supports organelles, and drives motility.

Motor proteins

Specialized proteins that use ATP to move along cytoskeletal filaments to transport cellular cargo and generate movement.

Microtubules

Cylindrical cytoskeletal protein fibers that act as internal transport tracks for organelles and assemble into the mitotic spindle during cell division.

Intermediate filaments

Cytoskeletal elements that provide mechanical strength and preserve cell shape under physical stress.

Actin filaments

Thin cytoskeletal protein fibers that reinforce cell shape, mediate cellular motility, and facilitate muscle contraction.

Centrioles

Cellular structures that organize microtubules and contribute to the formation of the mitotic spindle during cell division.

Cilia

Short, numerous hair-like cell projections that beat rhythmically in unison to move surrounding fluids or propel cells across surfaces.

Flagella

Long, whip-like locomotory appendages that rotate or undulatingly propel cells through liquid media.

Plant Cell Structure (Figure 4.8)

Diagram of a eukaryotic plant cell showing: A. Nucleus, B. Nucleolus, C. Chromatin, D. Nuclear envelope, E. Rough ER, F. Smooth ER, G. Vacuole, H. Ribosome, I. Chloroplast, J. Cell wall, K. Plasma membrane, L. Mitochondria, M. Golgi apparatus, and N. Vesicle.