Biology Exam Study Guide: Cell Membrane, Transport, Systems, Cytoskeleton, and Energetics

Vocabulary flashcards covering cell membrane composition, transport mechanisms, endomembrane pathways, cytoskeleton structures, cell energy, thermodynamics, and enzyme kinetics.

Cell membrane

A thin, flexible barrier around the cell made mostly of a phospholipid bilayer and proteins that maintains homeostasis and controls what enters and leaves.

Selectively permeable

A property of a membrane that allows certain substances to pass through more easily than others.

Phospholipid

The main building block of the cell membrane, consisting of a hydrophilic head and two hydrophobic tails.

Amphipathic

Having both a water-loving (hydrophilic) part and a water-avoiding (hydrophobic) part.

Integral proteins

Proteins embedded within the phospholipid bilayer whose hydrophobic parts interact with fatty acid tails and hydrophilic parts face watery environments.

Transmembrane proteins

Integral proteins that extend all the way across the entire membrane.

Channel proteins

Membrane proteins that form passageways allowing specific substances, such as water through aquaporins, to cross the membrane.

Carrier proteins

Membrane proteins that bind to a particular substance and change shape to move it across the membrane, such as GLUT-1 for glucose.

Pump proteins

Membrane proteins that use energy to move substances against their concentration gradient, such as the sodium-potassium pump.

Glycoproteins and glycolipids

Proteins or lipids with attached carbohydrate chains that help with cell recognition and identification.

Concentration gradient

The difference in the concentration of a substance between two areas.

Passive transport

The movement of substances across a membrane down their concentration gradient without the cell using ATP.

Simple diffusion

Passive movement of small nonpolar molecules directly through the membrane without requiring transport proteins.

Facilitated diffusion

Passive transport of specific substances across a membrane down their concentration gradient using channel or carrier proteins without ATP.

Osmosis

The diffusion of water across a selectively permeable membrane toward the side with a higher concentration of solute.

Hypertonic solution

A solution with a higher solute concentration outside the cell, causing water to leave the cell and animal cells to shrink.

Isotonic medium

A medium equally concentrated in solute and solvent compared to the cell cytoplasm, resulting in no net shift of water and cell size maintenance.

Hypotonic solution

A solution with a lower solute concentration outside the cell, causing water to diffuse into the cell so animal cells swell and may burst.

Active transport

The movement of substances against their concentration gradient (from low to high concentration) requiring transport proteins and energy from ATP.

Sodium-potassium pump

An active transport protein mechanism that uses ATP to move sodium ($\text{Na}^+$) and potassium ($\text{K}^+$) ions against their concentration gradients.

Nuclear Localization Signal (NLS)

A short amino acid sequence on a protein that directs it toward and into the nucleus.

Endomembrane system

A network of membranes and organelles—including the rough ER, Golgi apparatus, vesicles, lysosomes, and plasma membrane—that make, modify, sort, transport, and recycle cellular materials.

Rough Endoplasmic Reticulum (Rough ER)

An organelle covered with ribosomes that synthesizes proteins containing an ER signal sequence for processing and secretion.

Golgi apparatus

An organelle that receives proteins at its cis face from the ER, modifies them, sorts them, and packages them into vesicles for transport to their destinations.

Glycosylation

The process of adding carbohydrate groups to a protein or lipid within the Golgi apparatus.

Pulse-chase experiment

A research method using a brief exposure to labeled building blocks followed by unlabeled ones to track the pathway and timing of molecules moving through cell structures.

Mannose-6-phosphate (M6P)

A carbohydrate sorting tag attached to enzymes that targets them for delivery to lysosomes.

Lysosomes

Membrane-bound compartments containing digestive enzymes that break down materials and recycle useful building blocks.

Receptor-mediated endocytosis

A cellular intake process where specific molecules bind to receptors on the cell surface, causing the membrane to fold inward and bring the selected materials into the cell.

Phagocytosis

A process where a cell engulfs large particles or whole cells into a compartment that fuses with a lysosome for digestion; informally termed 'cell eating'.

Autophagy

An internal recycling process where a cell encloses damaged organelles or internal components and delivers them for breakdown; informally termed 'self-eating'.

Cytoskeleton

A network of protein filaments inside the cell that gives the cell shape, structural support, aids transport, and helps separate chromosomes during cell division.

Actin filaments

The smallest cytoskeleton filaments, built from actin protein subunits with plus and minus ends, that function in cell shape, muscle contraction (interacting with myosin), cytokinesis, and cell movement.

Intermediate filaments

Middle-sized, stable cytoskeletal fibers made of fibrous proteins (such as keratin and nuclear lamins) that provide structural strength and resistance to mechanical stress.

Microtubules

The largest cytoskeleton filaments, formed as hollow tubes from tubulin heterodimers, that serve as transport tracks, form the mitotic spindle to separate chromosomes, and support cilia and flagella.

Kinesin

A motor protein that uses ATP to carry cargo along microtubule tracks, typically moving toward the plus end.

Metabolism

All chemical reactions happening inside an organism, consisting of anabolism and catabolism.

Anabolism

Metabolic pathways that build larger molecules from smaller ones, often requiring an energy input.

Catabolism

Metabolic pathways that break larger molecules into smaller ones, often releasing usable energy.

Enthalpy ($\Delta H$)

The heat-related energy change in a chemical reaction from reactants to products.

Exothermic reaction

A reaction that releases heat to its surroundings, resulting in products with lower enthalpy than reactants and a negative enthalpy change ($\Delta H < 0$).

Endothermic reaction

A reaction that absorbs heat from its surroundings, resulting in products with higher enthalpy than reactants and a positive enthalpy change ($\Delta H > 0$).

Entropy ($\Delta S$)

A measure related to how energy and matter are dispersed among possible arrangements, often simplified as disorder.

Gibbs free energy ($\Delta G$)

A thermodynamic measure given by $\Delta G = \Delta H - T\Delta S$ used to determine whether a reaction is thermodynamically spontaneous under specific conditions.

Exergonic reaction

A thermodynamically spontaneous reaction where $\Delta G < 0$, releasing free energy.

Endergonic reaction

A nonspontaneous reaction where $\Delta G > 0$ that requires an energy input or coupling to proceed.

Energy coupling

The process of using energy released by a favorable (exergonic) reaction to drive an unfavorable (endergonic) reaction.

Oxidation

The loss of electrons by a substance during a chemical reaction.

Reduction

The gain of electrons by a substance during a chemical reaction.

ATP (Adenosine triphosphate)

The major immediate energy carrier in cells, composed of adenine, ribose, and three phosphate groups, which releases usable energy upon hydrolysis.

Enzyme

A biological catalyst that speeds up a chemical reaction by lowering its activation energy without altering the overall $\Delta G$ or equilibrium.

Active site

The specific region of an enzyme where the substrate binds and the reaction is catalyzed.

Denaturation

A process in which an enzyme or protein loses its functional shape and active site structure due to factors like high temperature or extreme pH.

Competitive inhibition

Enzyme inhibition where an inhibitor directly occupies the active site and blocks substrate binding, an effect that can often be reduced by increasing substrate concentration.

Allosteric inhibition

Noncompetitive enzyme inhibition where an inhibitor binds to a separate site (allosteric site) on the enzyme, altering its shape and activity.