Biology Chapters 04-06: Cell Structure, Membranes, and Energy & Metabolism

Vocabulary practice flashcards covering eukaryotic and prokaryotic cell structures, plasma membrane components and transport mechanisms, thermodynamics, ATP, and enzyme kinetics.

Cell Theory

The fundamental biological principle stating that all organisms are made of cells, the cell is the simplest collection of matter that can be alive, and all cells arise only from pre-existing cells.

Unicellular Organism

A single-celled living organism, such as bacteria or archaea.

Multicellular Organism

An organism composed of a collection of many cells working together.

Bright-Field Microscope

A light microscope where light is transmitted directly through a specimen, giving little natural contrast unless stained (which requires cell fixation/death).

Dark-Field Microscope

A light microscope that directs light at an angle toward the specimen so only reflected light enters the condenser lens, producing a bright specimen against a dark background.

Phase-Contrast Microscope

A light microscope that brings light waves out of phase to produce differences in contrast and brightness in live, unstained specimens.

Differential-Interference-Contrast Microscope

A microscope that splits polarized light into two beams with slightly different paths through the sample, producing enhanced contrast especially at structural edges.

Fluorescence Microscope

A microscope in which fluorescent stains absorb light at one wavelength and emit it at another, using filters to transmit only the emitted light.

Confocal Microscope

A microscope that focuses laser light to a point and scans across a fluorescently stained specimen, excluding out-of-focus light to generate clear images of a single plane or 3-D reconstructions.

Transmission Electron Microscope (TEM)

An electron microscope that passes an electron beam through a specimen section to reveal internal cellular ultrastructure based on electron scattering.

Scanning Electron Microscope (SEM)

An electron microscope that scans an electron beam across a specimen's surface to knock off electrons, revealing detailed 3-D surface topography.

Surface-Area-to-Volume Ratio

The relationship between a cell's outer surface area and its inner volume; critical because as a cell grows larger, its volume increases faster than its surface area, limiting transport.

Prokaryotic Cell

A simple type of cell lacking a membrane-bound nucleus and membrane-bound organelles, with cytoplasm bound by the plasma membrane and DNA located in an unbound nucleoid region.

Eukaryotic Cell

A complex cell characterized by having a membrane-bound nucleus and other membrane-bound organelles within cytoplasm bound by the plasma membrane.

Nucleoid

The unbound central region in a prokaryotic cell where its single circular DNA chromosome is located.

Nucleus

The spherical organelle in eukaryotic cells that contains chromosomes, stores genetic information, and directs protein synthesis and cell reproduction.

Nuclear Envelope

The double membrane structure perforated by nuclear pores that surrounds the eukaryotic nucleus.

Nucleolus

A dense structure within the eukaryotic nucleus that serves as the site of genes for rRNA synthesis and ribosome assembly.

Chromatin

Long threads composed of a complex of DNA and protein (histones) found in eukaryotic cells.

Ribosomes

Small, complex assemblies of protein and RNA consisting of large and small subunits that serve as the sites of protein synthesis.

Endomembrane System

A network of internal eukaryotic membranes—including the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vesicles, and plasma membrane—that regulates protein traffic and performs metabolic functions.

Rough Endoplasmic Reticulum

A membrane network studded with ribosomes on its outer surface that synthesizes proteins destined for membranes, organelles, or extracellular secretion.

Smooth Endoplasmic Reticulum

A tubular, ribosome-free membrane network involved in lipid and steroid synthesis and drug detoxification in liver cells.

Golgi Apparatus

Stacks of flattened vesicles (cisternae) with cis and trans faces that receive, modify, package, and ship proteins for secretion or organelle transport.

Lysosome

A membrane-bound digestive vesicle derived from the Golgi apparatus containing hydrolytic enzymes to break down old/damaged organelles (autophagy) or phagocytized particles.

Peroxisome

A microbody containing oxidative enzymes that isolate metabolic reactions and detoxify the cell by converting hydrogen peroxide ($H_2O_2$) to water ($H_2O$) and oxygen ($O_2$).

Central Vacuole

A large single membrane-bound organelle in plant cells that stores water and nutrients and maintains cellular turgor pressure.

Mitochondria

Double-membrane organelles containing cristae and a matrix that function as the sites of oxidative metabolism and ATP production ('power plants' of the cell).

Chloroplast

A double-membrane organelle in plant and algal cells containing thylakoids stacked into grana surrounded by stroma; contains chlorophyll and serves as the site of photosynthesis.

Endosymbiotic Theory

The evolutionary theory stating that mitochondria and chloroplasts originated when an ancestral eukaryotic cell engulfed oxygen-using nonphotosynthetic and photosynthetic prokaryotic cells.

Cytoskeleton

A network of protein filaments (microtubules, microfilaments, intermediate filaments) extending throughout the cytoplasm that maintains cell shape, anchors organelles, and enables cell motility.

Microtubules

Hollow protein tubes ($25\,nm$ diameter) composed of tubulin dimers (\alpha- and \beta-tubulin) that resist compression, guide organelle transport, move chromosomes during cell division, and form centrioles, cilia, and flagella.

Centrosome

A microtubule-organizing center near the nucleus in animal cells containing a pair of centrioles, each formed by nine microtubule triplets arranged in a ring.

Microfilaments (Actin Filaments)

Two intertwined strands of actin ($7\,nm$ diameter) that bear tension, maintain cell shape, and enable muscle contraction, amoeboid movement, and cytoplasmic streaming.

Intermediate Filaments

Fibrous proteins coiled into cables ($8\text{--}12\,nm$ diameter, such as keratins) that maintain cell shape, anchor the nucleus and organelles, and form the nuclear lamina.

Extracellular Matrix (ECM)

A network of glycoproteins (collagen, proteoglycan, fibronectin) secreted by animal cells that binds to cell-surface integrins to provide structural support and influence cell behavior.

Plasmodesmata

Specialized channels through plant cell walls that connect the cytoplasm of adjacent cells to permit transport and communication.

Tight Junctions

Animal cell junctions that press adjacent plasma membranes tightly together to form a watertight seal that prevents fluid leakage between cells.

Desmosomes

Adhesive anchoring junctions in animal cells that use cadherins and intermediate filament plaques to fasten cells together into strong structural sheets.

Gap Junctions

Communicating junctions in animal cells formed by connexon channels that allow ions, sugars, and small molecules to pass directly between neighboring cells.

Fluid Mosaic Model

A structural model depicting cellular membranes as a fluid phospholipid bilayer embedded with a mosaic of proteins, glycolipids, and sterols that move laterally.

Phospholipid Bilayer

A double layer of amphipathic phospholipids with hydrophilic heads facing aqueous environments and hydrophobic tails facing inward, forming the structural foundation of membranes.

Amphipathic Molecule

A molecule containing both hydrophilic (polar) and hydrophobic (nonpolar) regions, such as a phospholipid.

Integral Proteins

Membrane proteins that penetrate or span the hydrophobic core of the lipid bilayer, typically possessing nonpolar hydrophobic \alpha-helices.

Peripheral Proteins

Proteins that are not embedded in the lipid bilayer but are loosely bound to the extracellular or cytoplasmic surface of the plasma membrane.

Selective Permeability

The property of cellular membranes allowing certain substances (e.g., small nonpolar molecules like $O_2$ and $CO_2$) to pass freely while restricting others.

Passive Transport

The movement of substances across a membrane down their concentration gradient without requiring cellular energy expenditure.

Simple Diffusion

The unassisted net movement of particles from an area of higher concentration to an area of lower concentration down a concentration gradient.

Facilitated Diffusion

The passive movement of polar or charged particles across a membrane down their concentration gradient via specific channel or carrier proteins.

Osmosis

The simple diffusion of water across a selectively permeable membrane toward a region of higher solute concentration.

Tonicity

The ability of a surrounding solution to cause a cell to gain or lose water by osmotic flow.

Hypertonic Solution

A solution with a higher solute concentration than the cytoplasm, causing water to leave the cell and leading to animal cell shriveling or plant cell plasmolysis.

Hypotonic Solution

A solution with a lower solute concentration than the cytoplasm, causing water to enter the cell and leading to animal cell bursting (lysis) or plant cell turgidity.

Isotonic Solution

A solution with an equal solute concentration relative to the cytoplasm, resulting in no net water movement across the membrane.

Active Transport

The movement of solutes across a membrane against their concentration gradient requiring energy expenditure (usually ATP) and specific transport proteins.

Sodium-Potassium Pump

A primary active transport carrier protein that uses ATP phosphorylation to export $3\,\text{Na}^+$ ions out of the cell and import $2\,\text{K}^+$ ions into the cell.

Coupled Transport

Secondary active transport in which the movement of one molecule (e.g., glucose) against its gradient is driven by the downhill movement of another solute (e.g., $\text{Na}^+$).

Exocytosis

Bulk transport mechanism where intracellular vesicles fuse with the plasma membrane to discharge materials into the extracellular environment.

Endocytosis

Bulk transport mechanism where the plasma membrane invaginates to engulf extracellular substances and pinch off into intracellular vesicles.

Phagocytosis

A form of endocytosis ('cell eating') in which a cell engulfs large particles, bacteria, or cellular debris into a food vesicle.

Pinocytosis

A non-specific form of endocytosis ('cell drinking') in which a cell continuously gulps droplets of extracellular fluid into small vesicles.

Receptor-Mediated Endocytosis

A specific type of endocytosis where target molecules bind to cell-surface receptor proteins clustered in clathrin-coated pits, triggering vesicle formation.

Potential Energy

Stored energy available to do work, such as energy contained in the chemical bonds of glucose.

Kinetic Energy

The energy of motion or movement.

First Law of Thermodynamics

The law of conservation of energy stating that energy cannot be created or destroyed, only transformed from one form to another, maintaining a constant total energy in the universe.

Second Law of Thermodynamics

The law stating that every energy transfer or transformation increases the entropy (disorder) of the universe, as some energy becomes unusable (lost as heat).

Entropy

A quantitative measure of disorder or randomness in a system.

Metabolism

The sum total of all chemical reactions carried out by an organism.

Metabolic Pathway

A sequence of linked chemical reactions where the product of one reaction becomes the substrate for the next, with each step catalyzed by a specific enzyme.

Anabolism

Metabolic pathways that consume energy to build complex molecules from simpler precursors.

Catabolism

Metabolic pathways that release energy by breaking down complex molecules into simpler compounds.

Free Energy ($G$)

The portion of a system's energy available to perform work at constant temperature and pressure ($\Delta G = G_{\text{final state}} - G_{\text{initial state}}$).

Exergonic Reaction

A spontaneous chemical reaction that releases energy ($\Delta G < 0$).

Endergonic Reaction

A nonspontaneous chemical reaction that requires energy input ($\Delta G > 0$).

ATP (Adenosine Triphosphate)

The primary energy currency of cells, composed of adenine, a 5-carbon ribose sugar, and three phosphate groups.

Energy Coupling

The cellular process of using an exergonic reaction (such as ATP hydrolysis) to drive an endergonic reaction.

Enzyme

A biological catalyst (usually a protein) that speeds up chemical reactions by lowering the activation energy barrier without being consumed.

Activation Energy ($E_A$)

The initial energy required to destabilize existing chemical bonds and initiate a chemical reaction.

Substrate

The specific reactant molecule that an enzyme binds to and acts upon.

Active Site

The specific region or pocket on an enzyme where the substrate binds and catalysis occurs.

Induced Fit

The conformational change in an enzyme's active site upon substrate binding that fits the substrate more tightly and enhances catalytic action.

Competitive Inhibitor

An inhibitor molecule that binds directly to the active site of an enzyme, competing with the natural substrate.

Noncompetitive Inhibitor

An inhibitor molecule that binds to an allosteric site (away from the active site), altering the enzyme's shape so the substrate can no longer bind.

Coenzyme

An organic cofactor (such as a vitamin) required by an enzyme to assist in its catalytic function.

Feedback Inhibition

A metabolic regulation mechanism where the final end product of a pathway allosterically inhibits an enzyme early in the pathway to shut it down and prevent waste.