Biology of the Cell: Structure and Function

A comprehensive set of vocabulary flashcards covering cell structure, plasma membrane function, transport mechanisms, organelles, and the cellular life cycle based on Chapter 4 of the lecture notes.

Cytology

The study of cells, which requires microscopes and uses micrometers as the standard unit of measurement.

Micrometer

A unit of measurement used for cells, equal to $1/10,000\,cm$ ($\mu m$).

Erythrocyte

A red blood cell, which typically measures between $7\text{--}8\,\mu m$ in diameter and has a biconcave disc shape.

Human oocyte

A female germ cell with a diameter of approximately $120\,\mu m$.

Plasma membrane

The outer, limiting barrier that forms the boundary separating the internal contents of the cell from the external environment.

Nucleus

The largest structure in the cell, enclosed by a nuclear envelope, which contains genetic material ($DNA$) and nucleoplasm.

Cytoplasm

The cellular contents located between the plasma membrane and the nucleus, consisting of cytosol, organelles, and inclusions.

Cytosol

The viscous, intracellular fluid of the cytoplasm that has a high water content and contains dissolved macromolecules and ions.

Membrane-bound organelles

Complex, organized structures enclosed by a membrane that separates their contents from the cytosol, including the endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, and mitochondria.

Non-membrane-bound organelles

Organelles composed of protein that are not enclosed within a membrane, including ribosomes, the cytoskeleton, centrosomes, and proteasomes.

Inclusions

Temporary storage molecules in the cytosol, such as pigments, glycogen, and triglycerides, which are not considered organelles.

Phospholipids

The basic structure of the plasma membrane framework, organized as a bilayer with polar, hydrophilic heads and nonpolar, hydrophobic tails.

Cholesterol

A lipid scattered within the phospholipid bilayer that strengthens and stabilizes the membrane against temperature extremes.

Glycocalyx

A "coating of sugar" on the cell's surface formed by glycolipids and glycoproteins.

Integral proteins

Proteins embedded within and extending across the phospholipid bilayer, often acting as glycoproteins.

Peripheral proteins

Proteins that are not embedded in the lipid bilayer but are loosely attached to the external or internal surfaces of the membrane.

Transport proteins

A functional category of membrane proteins including channels, carriers, pumps, symporters, and antiporters that regulate movement across the membrane.

Ligands

Molecules, such as neurotransmitters, that bind to cell surface receptors to initiate cellular responses.

Identity markers

Proteins that communicate to other cells that they belong to the body, distinguishing healthy cells from those to be destroyed.

Passive processes

Membrane transport mechanisms that require no expenditure of cellular energy, as substances move down their concentration gradient.

Active processes

Membrane transport mechanisms that require cellular energy expenditure to move a substance up its concentration gradient or involve vesicles.

Diffusion

The net movement of a substance from an area of greater concentration to an area of lesser concentration until equilibrium is reached.

Simple diffusion

The unassisted movement of small, nonpolar solutes (such as $O_2$, $CO_2$, fatty acids, and urea) between phospholipid molecules of the plasma membrane.

Facilitated diffusion

Transport for small charged or polar solutes that requires assistance from plasma membrane proteins, either as channel-mediated or carrier-mediated diffusion.

Channel-mediated diffusion

The movement of small ions through specific water-filled protein channels, which can be continuously open (leak channels) or gated.

Carrier-mediated diffusion

The movement of small polar molecules across the membrane assisted by a carrier protein that changes shape, such as a uniporter.

Osmosis

The passive movement of water through a selectively permeable membrane in response to differences in water concentration.

Aquaporins

Integral protein water channels that allow for the movement of water across the plasma membrane.

Osmotic pressure

The pressure exerted by the movement of water across a semipermeable membrane due to a difference in solution concentration.

Hydrostatic pressure

The pressure exerted by a fluid on the inside wall of its container.

Tonicity

The ability of a solution to change the volume or pressure of a cell by osmosis.

Isotonic solution

A solution with the same relative concentration of solutes as the cytosol, such as $0.9\%\,NaCl$, resulting in no net movement of water.

Hypotonic solution

A solution with a lower concentration of solutes (higher water) than the cytosol, causing water to enter the cell and potentially leading to lysis.

Hypertonic solution

A solution with a higher concentration of solutes (lower water) than the cytosol, causing water to leave the cell and resulting in crenation (shrinking).

Primary active transport

Transport that uses energy directly from the breakdown of $ATP$ to move a solute against its concentration gradient.

Sodium-potassium ($Na^+/K^+$) pump

An exchange ion pump that uses $ATP$ to continuously export three $Na^+$ out of the cell and move two $K^+$ into the cell.

Secondary active transport

Transport that uses the kinetic energy from a second substance (usually $Na^+$) moving down its gradient to power the movement of another substance up its gradient.

Symport

A type of secondary active transport where two substances are moved in the same direction.

Antiport

A type of secondary active transport where two substances move in opposite directions.

Exocytosis

A form of vesicular transport where large substances or macromolecules are secreted from the cell after a vesicle fuses with the plasma membrane.

Endocytosis

The cellular uptake of large substances from the external environment through the formation of a vesicle via invagination.

Phagocytosis

"Cellular eating"; a type of endocytosis where a cell engulfs large particles using pseudo-podia.

Pinocytosis

"Cellular drinking"; the internalization of droplets of interstitial fluid containing dissolved solutes into small vesicles.

Receptor-mediated endocytosis

Vesicular transport that uses specific membrane receptors to bind and internalize bulk quantities of substances, such as low-density lipoproteins ($LDL$).

Rough Endoplasmic Reticulum (Rough ER)

A membrane network with attached ribosomes that produces proteins for secretion or membrane insertion and helps form peroxisomes.

Smooth Endoplasmic Reticulum (Smooth ER)

A membrane network without ribosomes that functions in lipid synthesis, carbohydrate metabolism, and detoxification.

Golgi apparatus

An organelle composed of cisternae that exhibits polarity (cis-face and trans-face) and functions to modify, package, and sort proteins.

Lysosomes

Small membranous sacs containing digestive enzymes formed by the Golgi that participate in the digestion of unneeded substances.

Peroxisomes

Small membrane-enclosed sacs formed from the rough ER that contain enzymes for chemical digestion, beta oxidation, and lipid synthesis.

Endomembrane system

An extensive array of membrane-bound structures, including the $ER$, Golgi, lysosomes, peroxisomes, nuclear envelope, and plasma membrane, that provides interior transport.

Mitochondria

The "powerhouses" of the cell; oblong organelles with a double membrane that perform aerobic cellular respiration to synthesize $ATP$.

Ribosomes

Non-membrane-bound organelles composed of protein and $RNA$ that synthesize proteins; they can be bound to the $ER$ or free in the cytosol.

Cytoskeleton

An intracellular network of microfilaments, intermediate filaments, and microtubules that supports the cell, organizes organelles, and facilitates movement.

Microfilaments

The smallest cytoskeleton components, made of actin, which maintain cell shape, support microvilli, and facilitate muscle contraction.

Microtubules

Hollow cylinders made of tubulin that maintain cell shape, move organelles, form cilia/flagella, and separate chromosomes during cell division.

Centrosome

An organelle containing a pair of centrioles that organizes microtubules and directs the formation of the mitotic spindle during cell division.

Proteasomes

Large, barrel-shaped protein complexes that degrade damaged or unneeded proteins marked with a ubiquitin tag.

Cilia

Hair-like extensions of the plasma membrane that contain microtubules and move substances, such as mucus, along the cell surface.

Flagella

Long, solitary membrane extensions used to propel a cell; the only human example is the sperm cell.

Microvilli

Microscopic, densely packed extensions of the plasma membrane supported by microfilaments that increase surface area for absorption.

Nucleolus

A dark-staining, non-membrane-bound body in the nucleus that produces ribosome subunits.

Chromatin

A mass of genetic material composed of $DNA$ wound around histone proteins, present when the cell is not dividing.

Chromosomes

Tightly coiled masses of chromatin formed during cell division.

Gene

A segmental unit of nucleotides that provides instructions for the synthesis of a specific protein, containing promoter and terminator regions.

Transcription

The process occurring in the nucleus where a copy of a gene is formed from $DNA$ to create $RNA$ using $RNA$ polymerase.

Translation

The process occurring at ribosomes in the cytoplasm where $mRNA$ is read to synthesize a protein from amino acids.

Codon

A three-base unit of nucleotides on $mRNA$ that codes for a specific amino acid or a start/stop signal.

Transfer RNA (tRNA)

A cloverleaf-shaped molecule that brings specific amino acids to the ribosome, matching its anticodon with the $mRNA$ codon.

Mitosis

Cell division occurring in somatic cells (all cells except sex cells) to produce two identical daughter cells.

Cell Cycle

The series of steps in replication consisting of Interphase (approximately $23\,hours$) and the Mitotic Phase (approximately $1\,hour$).

S phase

The synthesis phase of interphase during which $DNA$ replication occurs, overseen by $DNA$ polymerase.

Prophase

The first stage of mitosis where chromatin supercoils into chromosomes, the nucleolus breaks down, and the nuclear envelope dissolves.

Metaphase

The stage of mitosis where chromosomes align along the equatorial plate of the cell.

Anaphase

The stage of mitosis where spindle fibers pull sister chromatids apart toward opposite poles of the cell.

Telophase

The final stage of mitosis where chromosomes uncoil back into chromatin, new nucleoli form, and nuclear envelopes reappear.

Cytokinesis

The division of the cytoplasm, resulting in a cleavage furrow and the final separation of the mother cell into two daughter cells.