Membrane Transport, Cell Signaling, and Enzymes (3-4)

Vocabulary practice flashcards covering membrane structure, transport mechanisms across the cell membrane, bioenergetics, ATP cycling, and enzyme function and inhibition.

Fluid Mosaic Model

A model of cell membrane structure depicting a fluid lipid bilayer embedded with a mosaic of proteins, phospholipids, cholesterol, and glycolipids.

Integral Proteins

Proteins embedded directly within the lipid bilayer of the cell membrane, spanning or partially penetrating the hydrophobic core.

Peripheral Proteins

Proteins located on the inner or outer surface of the plasma membrane rather than embedded within the hydrophobic core.

Passive Transport

The diffusion of a substance across a biological membrane without any energy investment from the cell.

Active Transport

The transport of solute molecules across a cell membrane against their concentration gradient, requiring cellular energy in the form of ATP.

Diffusion

The movement of molecules from a region of higher concentration to a region of lower concentration until equilibrium is reached.

Concentration Gradient

The region across which the concentration of a chemical substance transitions from high to low concentration.

Osmosis

The diffusion of water across a selectively permeable or differentially permeable membrane.

Tonicity

The strength of a solution in relationship to osmosis, determining whether water flows into or out of a cell.

Isotonic Solution

A solution having an equal concentration of solutes compared to the inside of a cell, resulting in no net gain or loss of water.

Hypertonic Solution

A solution with a higher solute concentration than the cell, causing a net movement of water from the inside to the outside of the cell.

Hypotonic Solution

A solution with a lower solute concentration than the cell, causing a net movement of water from the outside into the inside of the cell.

Lysis

The bursting of an animal cell caused by excessive water entry when placed in a hypotonic solution (termed hemolysis in red blood cells).

Crenation

The shriveling of an animal cell that occurs when water leaves the cell in a hypertonic solution.

Turgor Pressure

Internal hydrostatic pressure that develops in a plant cell as its central vacuole fills with water in a hypotonic solution, pushing chloroplasts against the cell wall.

Plasmolysis

The shrinking of a plant cell's cytoplasm away from the cell wall when vacuoles lose water in a hypertonic solution.

Facilitated Diffusion

A form of passive transport where substances that are not lipid soluble (such as glucose and amino acids) cross the plasma membrane down their gradient with the assistance of a carrier protein.

Sodium-Potassium Pump

A membrane carrier protein that hydrolyzes ATP to move $3\text{ Na}^+$ out of the cell and $2\text{ K}^+$ into the cell against their respective concentration gradients.

Exocytosis

A form of membrane-assisted transport in which a cell secretes macromolecules via the fusion of intracellular vesicles with the plasma membrane.

Endocytosis

A process of bulk transport where a cell takes in macromolecules and particulate matter by forming new vesicles that bud inward from the plasma membrane.

Phagocytosis

A type of endocytosis in which a cell engulfs a large particle by wrapping pseudopodia around it and packaging it into a vacuole.

Pinocytosis

A type of endocytosis in which a cell takes in droplets of extracellular fluid and dissolved solutes by pinching off tiny vesicles.

Receptor-Mediated Endocytosis

A specific endocytic process wherein extracellular ligands bind to receptors concentrated at a coated pit, which then pinches off to form an intracellular coated vesicle.

Kinetic Energy

Energy associated with motion.

Potential Energy

Stored energy capable of performing work based on position or structure.

First Law of Thermodynamics

The principle stating that the energy of the universe is constant; energy cannot be created or destroyed, only transformed from one form to another.

Second Law of Thermodynamics

The principle stating that energy cannot be converted from one form to another without a loss of usable energy, typically dissipated as heat.

Entropy

A measure of molecular disorder or randomness, toward which the universe is continually increasing according to thermodynamic laws.

Free Energy ($\Delta G$)

The amount of energy available to perform work after a chemical reaction has taken place.

Exergonic Reaction

A spontaneous chemical reaction that releases energy, characterized by products having less free energy than reactants (negative $\Delta G$).

Endergonic Reaction

A non-spontaneous chemical reaction that requires an input of energy, in which the products possess more free energy than the reactants.

Coupled Reactions

The pairing of an energy-releasing exergonic reaction (such as ATP breakdown) with an energy-requiring endergonic reaction to drive cellular processes.

ATP (Adenosine Triphosphate)

The primary energy currency of cells, composed of adenine, ribose, and three phosphate groups.

Chemical Work

A category of cellular work that uses ATP energy to synthesize macromolecules that construct the cell.

Transport Work

A category of cellular work where ATP energy is used to pump substances across the plasma membrane against concentration gradients.

Mechanical Work

A category of cellular work where ATP powers physical movements, such as muscle contraction, vesicle transport along microtubules, and the beating of cilia and flagella.

Metabolic Pathway

A series of linked, multistep chemical reactions within a cell where reactants are sequentially converted into final products.

Enzyme

A catalytic protein that accelerates the rate at which chemical reactions approach equilibrium without being altered or consumed in the process.

Substrate

The specific reactant molecule that binds to an enzyme and undergoes a chemical reaction.

Active Site

The specific physical pocket or cleft on an enzyme where substrate molecules bind to form an enzyme-substrate complex.

Activation Energy

The initial energy barrier that must be surmounted for a chemical reaction to occur, which is lowered by enzymes.

Denaturation

The alteration and loss of an enzyme's functional three-dimensional shape, often resulting from unfavorable shifts in temperature or pH.

Cofactor

An inorganic ion (such as copper, zinc, or iron) or an organic molecule required by an enzyme to achieve proper catalytic function.

Coenzyme

A non-protein organic cofactor, such as a vitamin, that aids in enzyme function.

Competitive Inhibitor

An inhibitor that structurally resembles the normal substrate and competes directly for binding at the enzyme's active site; overcome by increasing substrate concentration.

Noncompetitive Inhibitor

An inhibitor that binds to an allosteric site on an enzyme rather than the active site, inducing a conformational shape change that prevents substrate binding.