Eukaryotic and Prokaryotic Cell Biology, Membrane Transport, and Metabolism

Flashcards covering key terms and concepts in eukaryotic and prokaryotic cell biology, membrane transport mechanisms, thermodynamics, enzyme kinetics, and viral replication cycles.

Cytosol

The semifluid substance present within all cells in which subcellular components are suspended.

Cytoplasm

The cellular contents between the plasma membrane and nucleus, comprising the cytosol together with membrane-bound organelles.

Eukaryotic Cell

A type of cell characterized by having a nucleus enclosed within a double membrane and containing distinct membrane-bound organelles.

Plasma Membrane

A selective phospholipid bilayer boundary that regulates the passage of oxygen, nutrients, and waste into and out of the cell.

Nuclear Envelope

A double membrane structure consisting of two lipid bilayers and associated proteins that encloses the nucleus and separates it from the cytoplasm.

Nuclear Pores

Protein-lined openings approximately $100\,\text{nm}$ in diameter where the inner and outer nuclear envelopes fuse, serving to regulate molecular entry and exit.

Nuclear Lamina

A net-like array of intermediate filaments lining the inner surface of the nuclear envelope that maintains nuclear shape and provides attachment sites for genetic material.

Chromatin

The complex of cellular DNA bound to proteins that organizes genetic material into eukaryotic chromosomes.

Nucleolus

A prominent structure within the nucleus formed by loops of chromosomes that encodes rRNA and assembles ribosomal subunits.

Ribosome

A cellular complex composed of ribosomal RNA and proteins, divided into large and small subunits, responsible for conducting protein synthesis.

Smooth Endoplasmic Reticulum

A region of the endoplasmic reticulum that lacks attached ribosomes and functions in lipid synthesis, carbohydrate metabolism, calcium ion storage, and drug detoxification.

Rough Endoplasmic Reticulum

A region of the endoplasmic reticulum studded with ribosomes on its cytoplasmic surface, involved in processing secretory and membrane-bound proteins.

Golgi Apparatus

An organelle consisting of flattened membranous sacs called cisternae with distinct cis and trans faces, responsible for modifying, sorting, and shipping cell products.

Lysosome

A membrane-bound sac of hydrolytic enzymes that operates optimally at an acidic pH of $\le 5$ to digest ingested substances, macromolecules, and worn-out organelles.

Phagocytosis

A type of endocytosis where a cell engulfs solid food particles or microorganisms to form a food vacuole that fuses with a lysosome for digestion.

Autophagy

A cellular recycling process wherein a lysosome fuses with a double-membraned vesicle containing damaged organelles to break them down with hydrolytic enzymes.

Central Vacuole

A large membrane-bound organelle in plant cells enclosed by the tonoplast that stores water, organic compounds, inorganic ions, pigments, and toxins.

Mitochondria

Double-membraned eukaryotic organelles with an inner membrane folded into cristae that act as the primary sites of cellular respiration and ATP generation.

Chloroplast

A specialized photosynthetic plant and algal organelle containing stroma and thylakoid membranes stacked into grana.

Peroxisome

A single-membrane metabolic organelle containing enzymes that transfer hydrogen to oxygen, producing hydrogen peroxide ($H_2O_2$) and subsequently converting it to water.

Microtubules

Hollow cytoskeletal rods $25\,\text{nm}$ in diameter composed of tubulin dimers that shape the cell, guide organelle transport, and separate chromosomes during cell division.

Centrosome

A region near the nucleus that acts as a microtubule-organizing center, containing a pair of perpendicular centrioles in animal cells.

Axoneme

The internal structural core of eukaryotic cilia and flagella, consisting of a $9 + 2$ arrangement of outer microtubule doublets and two central singlet microtubules.

Dynein

A motor protein powered by ATP that attaches to microtubule doublets and generates the sliding forces required for ciliary and flagellar movement.

Microfilaments

Solid cytoskeletal rods $7\,\text{nm}$ in diameter formed by two intertwined strands of actin that bear tension, maintain cell shape, and facilitate cellular motility.

Intermediate Filaments

Fibrous cytoskeletal proteins $8\text{--}12\,\text{nm}$ in diameter made of keratin family subunits that provide structural stability and anchor the nucleus and organelles.

Extracellular Matrix (ECM)

An elaborate meshwork external to animal cell membranes composed of glycoproteins like collagen, fibronectin, and proteoglycans linked to cell-surface integrins.

Tight Junctions

Intercellular connections where neighboring cell membranes are bound tightly together by specific proteins to form continuous seals preventing fluid leakage across cell layers.

Desmosomes

Anchoring intercellular junctions that fasten cells together into strong sheets, secured into the cytoplasm by keratin intermediate filaments.

Gap Junctions

Communicating intercellular junctions consisting of pore-forming membrane proteins that allow ions, sugars, and small molecules to pass directly between adjacent animal cells.

Plasmodesmata

Membrane-lined channels penetrating plant cell walls that connect the cytoplasm of adjacent cells to allow passage of water and solutes.

Metabolism

The totality of chemical reactions performed by an organism, emerging from molecular interactions within cells.

Catabolic Pathways

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

Anabolic Pathways

Metabolic pathways that consume energy to build complex macromolecules from simpler molecular building blocks.

First Law of Thermodynamics

The principle of conservation of energy stating that energy can be transferred and transformed, but cannot be created or destroyed.

Second Law of Thermodynamics

The physical law stating that every energy transfer or transformation increases the entropy (disorder) of the universe.

Free Energy

The portion of a system's energy that can perform work when temperature and pressure are uniform throughout the system.

Exergonic Reaction

A spontaneous chemical reaction that releases free energy, denoted by a negative change in Gibbs free energy ($\Delta G < 0$).

Endergonic Reaction

A non-spontaneous chemical reaction that absorbs free energy from its surroundings, denoted by a positive change in Gibbs free energy ($\Delta G > 0$).

Activation Energy

The initial amount of energy ($E_a$) required to break existing chemical bonds and start a reaction.

ATP (Adenosine Triphosphate)

An adenine-containing nucleoside triphosphate with three phosphate groups that functions as the primary energy currency for cellular work.

Phosphorylated Intermediate

A recipient molecule that receives a phosphate group directly transferred from ATP, making the molecule less stable and more reactive.

Enzyme

A biological macromolecular catalyst that accelerates specific chemical reactions by lowering the activation energy barrier ($E_a$) without being consumed.

Active Site

The specific region or pocket on an enzyme where a substrate molecule binds and undergoes a catalytic reaction.

Induced Fit

The conformational change of an enzyme's active site upon substrate binding to enfold the substrate and catalyze the reaction.

Competitive Inhibitor

A substance that reduces enzyme productivity by binding directly to the active site in direct competition with the substrate.

Noncompetitive Inhibitor

An inhibitor that binds to an allosteric site away from the active site, inducing a conformational change that decreases enzymatic activity.

Allosteric Regulation

A mode of enzymatic control where a regulatory molecule binds noncovalently to a protein at one site and affects its activity at another site.

Feedback Inhibition

A metabolic regulation mechanism in which the final end product of a pathway inhibits an early enzyme in that same pathway to halt overproduction.

Fluid Mosaic Model

The structural model depicting biological membranes as fluid phospholipid bilayers containing embedded protein mosaics and surface carbohydrates.

Amphipathic Molecule

A molecule possessing both hydrophilic polar regions and hydrophobic nonpolar regions.

Transmembrane Proteins

Integral membrane proteins that completely span the hydrophobic core of the lipid bilayer, commonly via nonpolar $\alpha$-helices.

Selective Permeability

The fundamental characteristic of cell membranes allowing specified substances to pass through while preventing others.

Facilitated Diffusion

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

Aquaporins

Specialized channel proteins that facilitate the rapid passive movement of water molecules across biological membranes.

Osmosis

The diffusion of free water across a selectively permeable membrane from a region of lower solute concentration to one of higher solute concentration.

Tonicity

The capacity of a surrounding solution to cause a cell to gain or lose water depending on relative solute concentrations.

Plasmolysis

The shrinking of a plant cell's cytoplasm away from its cell wall when exposed to a hypertonic solution.

Active Transport

The movement of solutes across a membrane against their concentration gradient, requiring energy input (such as ATP) and carrier proteins.

Sodium-Potassium Pump

A primary electrogenic active transport protein in animal cells that hydrolyzes ATP to export three $Na^+$ ions and import two $K^+$ ions.

Electrochemical Gradient

The combined driving force of concentration gradients and electrical membrane potentials influencing ion transport across membranes.

Cotransport

A process where the downhill diffusion of one solute, established by primary active transport pumps, drives the uphill transport of a second solute.

Endocytosis

An active bulk transport process in which a cell takes in extracellular materials by forming new vesicles invaginated from the plasma membrane.

Exocytosis

An active bulk transport mechanism where intracellular transport vesicles fuse with the plasma membrane to secrete contents into the extracellular space.

Bacteriophage

A virus that infects bacterial cells, typically consisting of a complex protein capsid head, a tail sheath, and tail fibers.

Lytic Cycle

A viral reproductive pathway that results in the synthesis of new viruses and culminates in the lysis and death of the host cell.

Lysogenic Cycle

A viral reproductive cycle in which the viral genome incorporates into the host chromosome as a prophage and replicates without destroying the host.

Prophage

A viral genome that has integrated into the circular DNA chromosome of a host bacterium during a lysogenic cycle.

Nucleoid

The non-membrane-bounded cytoplasmic region in prokaryotic cells where the circular bacterial chromosome is concentrated.

Peptidoglycan

A polymer network composed of modified sugars cross-linked by short polypeptides found in the cell walls of bacteria.

Gram-Negative Bacteria

Bacteria with a thin peptidoglycan layer bounded by an outer membrane containing lipopolysaccharides that stain pink or red in Gram staining.

Binary Fission

The method of asexual reproduction in prokaryotes where the chromosome replicates and the cell divides into two identical daughter cells.

Horizontal Gene Transfer

The movement of genetic material between unicellular organisms via transformation, transduction, or conjugation.

Archaea

A domain of prokaryotic organisms distinct from bacteria that lack peptidoglycan in their cell walls and frequently inhabit extreme environments.