Cell Biology: Cell Structure, Membranes, and Energy & Metabolism Flashcards

Vocabulary flashcards generated from chapters 4, 5, and 6 covering cell structure, membrane transport mechanisms, thermodynamics, and enzyme function.

Cell Theory

The foundational biological principle stating that all organisms are composed of cells, cells are the smallest living things, and cells arise only from pre-existing cells.

Resolution

The minimum distance two points can be apart and still be distinguished as two separate points.

Light Microscope

A type of microscope that uses magnifying lenses with visible light to resolve structures that are $200\,nm$ apart.

Electron Microscope

A type of microscope that uses a beam of electrons to resolve structures as close as $0.2\,nm$ apart.

Nucleoid

The region in a prokaryotic cell where its DNA is located, lacking a surrounding membrane.

Peptidoglycan

A protein-polysaccharide complex that composes the strong cell wall encasing most bacterial cells.

Compartmentalization

The cellular organization in eukaryotic cells achieved through the use of membrane-bound organelles and the endomembrane system.

Nucleolus

A specialized region within the eukaryotic nucleus where ribosomal RNA (rRNA) synthesis takes place.

Chromatin

The complex of linear DNA and proteins that forms eukaryotic chromosomes.

Rough Endoplasmic Reticulum (RER)

A membrane network studded with ribosomes that functions in the synthesis of proteins destined to be secreted, sent to lysosomes, or embedded in the plasma membrane.

Smooth Endoplasmic Reticulum (SER)

A membrane network with relatively few bound ribosomes involved in lipid synthesis, $Ca^{2+}$ storage, and detoxification.

Golgi Apparatus

Flattened stacks of interconnected membranes (cisternae) featuring cis and trans faces that package and distribute molecules synthesized in the cell.

Lysosomes

Membrane-bounded digestive vesicles arising from the Golgi apparatus containing hydrolytic enzymes that catalyze the breakdown of macromolecules and engulfed foreign matter.

Peroxisomes

A type of microbody containing enzymes involved in the oxidation of fatty acids, producing $H_2O_2$ as a by-product which is rendered harmless by catalase.

Tonoplast

The membrane that encloses the central vacuole in plant cells.

Cristae

Infoldings of the inner mitochondrial membrane that house proteins carrying out oxidative metabolism.

Thylakoids

Membranous disk-like sacs within the chloroplast inner membrane, organized into stacks called grana.

Endosymbiosis

The evolutionary theory proposing that eukaryotic organelles such as mitochondria and chloroplasts originated as free-living prokaryotes engulfed by ancestral cells.

Microfilaments (Actin Filaments)

Cytoskeletal elements composed of two loosely twined protein chains involved in cellular movements like contraction, crawling, and pinching.

Microtubules

The largest cytoskeletal elements, formed from dimers of $\alpha$- and $\beta$-tubulin subunits, facilitating cell motility and intracellular transport.

Centrosome

The microtubule-organizing center surrounding the centrioles in animal cells that nucleates microtubule assembly.

Integrins

Transmembrane proteins that link the extracellular matrix (ECM) to the cell's cytoskeleton to influence cellular behavior.

Tight Junction

A cell connection that connects the plasma membranes of adjacent cells in a sheet to prevent leakage between them.

Anchoring Junction (Desmosome)

A cell connection that mechanically attaches the cytoskeletons of neighboring cells together.

Communicating Junction (Gap Junction)

A cell connection formed by connexons in animal cells that allows chemical or electrical signals to pass directly from one cell to an adjacent cell.

Plasmodesmata

Specialized openings in plant cell walls through which the cytoplasm of adjoining cells is connected, functioning similarly to gap junctions.

Fluid Mosaic Model

The model of cell membrane structure describing a mosaic of globular proteins floating in or on a fluid lipid bilayer.

Phospholipid Bilayer

A two-layered membrane structure where hydrophobic nonpolar fatty acid tails face inward and hydrophilic polar phosphate heads face outward.

Fatty Acid Desaturases

Enzymes that introduce double bonds into membrane fatty acids to maintain membrane fluidity under cold temperature conditions.

Diffusion

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

Facilitated Diffusion

Passive transport of molecules across a selectively permeable membrane mediated by channel or carrier proteins down a concentration gradient.

Aquaporins

Specialized membrane channel proteins that facilitate the rapid passage of water molecules during osmosis.

Hypertonic Solution

A solution with a higher solute concentration compared to the inside of a cell, causing water to flow out of the cell.

Hypotonic Solution

A solution with a lower solute concentration compared to the inside of a cell, causing water to flow into the cell.

Isotonic Solution

A solution that has the same solute and osmotic concentration as the interior of a cell.

Turgor Pressure

The internal hydrostatic pressure created in plant cells as water enters, pushing the plasma membrane tightly against the cell wall.

Active Transport

The movement of substances across a membrane against their concentration gradient using selective carrier proteins and requiring ATP.

Uniporter

A membrane transport protein that carries a single type of molecule at a time.

Symporter

A membrane transport protein that moves two different molecules or ions across the membrane in the same direction.

Antiporter

A membrane transport protein that moves two different molecules or ions across the membrane in opposite directions.

Sodium–Potassium ($Na^+–K^+$) Pump

A direct ATP-driven active transport antiporter that pumps $3\,Na^+$ out of the cell and $2\,K^+$ into the cell against their concentration gradients.

Coupled Transport

Indirect active transport that uses the energy released from one molecule diffusing down its concentration gradient to drive the transport of another molecule against its gradient.

Phagocytosis

A form of endocytosis in which a cell engulfs discrete particulate matter or whole bacterial cells.

Pinocytosis

A form of endocytosis in which a cell takes in liquid droplets and dissolved solutes from the extracellular fluid.

Receptor-Mediated Endocytosis

Specific bulk transport in which target molecules bind to cell-surface receptors concentrated in clathrin-coated pits before being internalized in vesicles.

Exocytosis

The bulk transport process by which secretory vesicles fuse with the plasma membrane to discharge materials out of the cell.

Thermodynamics

The branch of chemistry concerned with energy changes and transformations in physical and biological systems.

Kinetic Energy

The energy possessed by an object due to its motion.

Potential Energy

Stored energy that has the capacity to do work.

Calorie

The amount of heat required to raise the temperature of $1\,g$ of water by $1\,^\circ C$.

Oxidation

The loss of an electron by an atom or molecule, resulting in a lower energy state.

Reduction

The gain of an electron by an atom or molecule, resulting in a higher energy state.

First Law of Thermodynamics

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

Second Law of Thermodynamics

The law stating that entropy (disorder) in the universe is continuously increasing during spontaneous energy transformations.

Entropy

A quantitative measure of the degree of disorder or randomness in a system ($S$).

Free Energy

The energy available in a molecule or system to do work at constant temperature and pressure ($G$), expressed as $G = H - TS$.

Endergonic

A non-spontaneous chemical reaction that requires an input of energy and has a positive change in free energy ($\Delta G > 0$).

Exergonic

A spontaneous chemical reaction that releases energy and has a negative change in free energy ($\Delta G < 0$).

Activation Energy

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

Catalyst

A substance that lowers the activation energy of a chemical reaction to increase its rate, without being consumed or altering the final ratio of reactants to products.

Adenosine Triphosphate (ATP)

The chief energy currency of all cells, composed of ribose, adenine, and a triphosphate chain.

Active Site

The specific pockets or clefts on an enzyme where substrates bind to form an enzyme–substrate complex.

Induced Fit

The conformational change in an enzyme's active site upon substrate binding that applies stress to distort specific bonds and lower activation energy.

Multienzyme Complex

An assembly of several enzyme subunits working sequentially to pass products directly from one enzyme to the next, preventing unwanted side reactions.

Ribozymes

Biological catalysts composed of RNA molecules rather than proteins.

Competitive Inhibitor

An inhibitor that competes directly with the substrate for binding to an enzyme's active site.

Noncompetitive Inhibitor

An inhibitor that binds to an enzyme at a site other than the active site, altering its shape so that it can no longer bind the substrate.

Allosteric Site

A specific regulatory binding site on an enzyme away from the active site that acts as an chemical on/off switch when bound by an effector.

Anabolism

Metabolic reactions that expend energy to build up complex molecules from simpler ones.

Catabolism

Metabolic reactions that harvest energy by breaking down complex molecules into simpler ones.

Feedback Inhibition

A regulatory mechanism where the end-product of a biochemical pathway binds to an allosteric site on the enzyme catalyzing the first reaction, shutting down the pathway.