Anatomy Topic 2: Cells - The Living Units

Comprehensive vocabulary flashcards covering cell parts, plasma membrane structure, transport mechanisms, organelle functions, cytoskeletal elements, nuclear structures, and the stages of the cell cycle and mitosis.

Plasma Membrane

The outer boundary of a cell that separates intracellular fluid from extracellular fluid and selectively controls the movement of substances into and out of the cell.

Phospholipid

The primary lipid constituent of cell membranes, featuring a polar, hydrophilic phosphate head and a nonpolar, hydrophobic tail consisting of two fatty acid chains.

Hydrophilic

Describing charged or polar molecules or molecular groups (such as phosphate heads) that readily interact with water.

Hydrophobic

Describing nonpolar molecules or molecular groups (such as fatty acid chains) that lack charge and avoid interaction with water.

Cholesterol

A plasma membrane lipid that stabilizes the lipid bilayer, making it more rigid and increasing its impermeability to water and solutes.

Integral Proteins

Proteins firmly embedded in the membrane bilayer, either extending partially into the lipid layer or spanning clear across it as transmembrane proteins.

Peripheral Proteins

Proteins that are not embedded within the lipid bilayer itself, but are loosely attached to either its inner or outer surface.

Glycocalyx

A sticky carbohydrate coating on the outer surface of the plasma membrane, composed of the sugar chains of glycolipids and glycoproteins, that helps cells bind together and provides cell identification.

Simple Diffusion

The unassisted passive movement of small, uncharged, or fat-soluble molecules directly through the lipid bilayer down their concentration gradient without energy expenditure.

Facilitated Diffusion

The passive transport of water-soluble or charged molecules down their concentration gradient across the plasma membrane via integral protein channels or carriers.

Active Transport

An energy-requiring membrane transport process in which integral proteins consume ATP to move substances across the plasma membrane against their concentration gradient.

Membrane Transport Mechanisms

The collection of passive processes (simple diffusion, osmosis, facilitated diffusion) and active processes (active transport, vesicular transport) by which substances cross the plasma membrane.

Endocytosis

A bulk vesicular transport mechanism by which large particles or macromolecules are brought into the cell by being enclosed in a membrane-bound vesicle.

Phagocytosis

A form of endocytosis in which a cell engulfs large particles or debris by extending pseudopods around them, forming an intracellular vesicle called a phagosome.

Pinocytosis

A non-specific type of endocytosis where an infolding of the plasma membrane carries a droplet of extracellular fluid and its dissolved solutes into the cell inside a vesicle.

Receptor-Mediated Endocytosis

A selective bulk transport mechanism in which specific extracellular substances bind to membrane receptor proteins, triggering their ingestion within coated vesicles.

Exocytosis

An active transport process by which intracellular substances contained within secretory vesicles are released outside the cell following vesicle fusion with the plasma membrane via v-SNARE and t-SNARE binding.

Cytosol

The viscous fluid portion of the cytoplasm consisting of water, ions, enzymes, nutrients, and dissolved solutes in which cellular structures are suspended.

Ribosomes

Non-membrane-bound cytoplasmic complexes consisting of proteins and ribosomal RNA (rRNA) that serve as the sites of translation and protein synthesis.

Rough Endoplasmic Reticulum

A membranous organelle composed of flattened sacs (cisterns) studded with ribosomes that manufactures proteins destined for cell secretion, lysosomal inclusion, or plasma membrane insertion.

Smooth Endoplasmic Reticulum

A network of membranous tubules lacking ribosomes that is involved in lipid metabolism, toxic compound breakdown, and intracellular calcium ion storage.

Golgi Apparatus

An organelle consisting of a stack of $3$ to $10$ disc-shaped cisterns that sorts, modifies, and packages proteins received from the rough ER.

Mitochondria

Double-membrane organelles containing inner foldings called cristae and an internal matrix that generate cellular ATP via the citric acid cycle and electron transport chain.

Lysosomes

Spherical, membrane-bound organelle vesicles containing acid hydrolase enzymes that break down worn-out organelles, foreign debris, and macromolecules.

Peroxisomes

Membrane-bound vesicles containing oxidase enzymes that convert free radicals into hydrogen peroxide, and catalase enzymes that break down hydrogen peroxide into water and oxygen.

Cytoskeleton

An elaborate network of protein rods throughout the cytosol—including microfilaments, intermediate filaments, and microtubules—that supports cell structure and facilitates movement.

Microfilaments

Thin cytoskeletal strands measuring $7\,nm$ in diameter made of actin protein subunits that generate contractile forces and assist in cell movement.

Intermediate Filaments

Tough, insoluble protein fibers measuring $10\,nm$ in diameter that resist tension forces acting upon the cell.

Microtubules

Hollow cytoskeletal tubes measuring $25\,nm$ in diameter constructed from tubulin protein subunits that maintain cell shape and form centrioles, cilia, and flagella.

Centrosome

A spherical region near the nucleus comprising a matrix cloud and a pair of centrioles that acts as the primary microtubule-organizing center.

Centrioles

Cylindrical structures formed by microtubule triplets located within the centrosome matrix that organize the mitotic spindle during cell division.

Glycosomes

Non-membrane-bound cytoplasmic inclusion bodies that store glycogen and contain enzymes for glycogen synthesis and degradation.

Nuclear Envelope

A double-membrane barrier enclosing the nucleus that is lined by the nuclear lamina and penetrated by protein-ringed nuclear pores.

Nucleolus

A dense body within the nucleus containing chromosomal regions that encode ribosomal RNA and serve as the assembly site for ribosome subunits.

Chromatin

Structures in the nucleus composed of double-stranded DNA wrapped around complexes of histone proteins.

Nucleosome

The basic repeating subunit of chromatin, consisting of a length of DNA coiled twice around a cluster of eight histone proteins.

Deoxyribonucleic Acid (DNA)

A double-helical nucleic acid composed of a sugar-phosphate backbone and paired nucleotide bases (Adenine, Thymine, Cytosine, Guanine) that encodes genetic information.

Interphase

The non-dividing stage of the cell cycle consisting of $G_1$ (growth), S (DNA replication), and $G_2$ (final preparation for division) subphases.

Prophase

The first phase of mitosis, characterized by chromatin condensation into visible chromosomes, nucleoli disappearance, mitotic spindle assembly, and nuclear envelope breakdown.

Metaphase

The second phase of mitosis, during which chromosomes align precisely along the midline equator (metaphase plate) of the cell.

Anaphase

The shortest mitotic phase, wherein centromeres split and sister chromatids are pulled apart toward opposite cell poles by kinetochore microtubules.

Telophase

The final stage of nuclear division, during which chromosomes uncoil into chromatin, nuclear envelopes reform, nucleoli reappear, and the mitotic spindle disassembles.

Mitosis

The process of nuclear division in which replicated DNA is divided equally between two daughter nuclei through four continuous phases: prophase, metaphase, anaphase, and telophase.

Cytokinesis

The division of the cytoplasm at the end of the cell cycle, accomplished by a cleavage furrow containing a contractile ring of actin microfilaments and myosin that pinches the cell into two daughter cells.