Chapter 6 Exam 4

Voltage-gated ion channels

Ion channels that open or close in response to voltage changes.

Ligand-gated channel

Ion channels that open in response to binding of a ligand.

ATP

The energy currency of the cell, powers active transport.

Sodium/potassium ion pump

An antiporter that pumps 3 Na⁺ out and 2 K⁺ into the cell using ATP.

Symporters

Proteins that transport two substances in the same direction.

Antiporters

Proteins that transport two substances in opposite directions.

Uniporters

Proteins that transport one substance in one direction.

Coupled transporters

Transport systems using the energy from gradients established by primary transport.

Phospholipid

A lipid molecule with a hydrophilic head and two hydrophobic fatty acid tails; forms the bilayer of membranes.

Unsaturated fatty acid

A fatty acid with one or more double bonds; causes kinks in the tail, increasing membrane fluidity.

Saturated fatty acid

A fatty acid with no double bonds; straight chains that pack tightly, reducing membrane fluidity.

Cholesterol

A steroid lipid in membranes that stabilizes the bilayer, especially at varying temperatures.

Glycoproteins

Proteins with attached carbohydrates that function in cell recognition and signaling.

Glycolipids

Lipids with attached carbohydrates that contribute to cell recognition.

Transport protein

Proteins that move substances across the membrane.

Receptor protein

Proteins that receive signals (ligands) and initiate a cellular response.

Transmembrane proteins

Integral membrane proteins that span the entire membrane.

Anchored membrane protein

Proteins attached covalently to lipids in the membrane to anchor them.

Peripheral proteins

Proteins loosely attached to one side of the membrane; not embedded.

Integral proteins

Proteins that are partially or fully embedded in the membrane.

Passive transport

Transport that does not require energy; relies on concentration gradient.

Active transport

Transport that requires energy, usually ATP, to move substances against a gradient.

Diffusion

The movement of particles from high to low concentration.

Equilibrium

The state where molecules are evenly distributed and no net change occurs.

Facilitated diffusion

Movement of substances with the help of transport proteins, no energy required.

Concentration gradient

Difference in concentration of a substance across a space or membrane.

Solute

A substance that is dissolved in a solution.

Solvent

The liquid in which a solute is dissolved.

Osmosis

The diffusion of water across a selectively permeable membrane.

Osmoregulation

The control of water balance in organisms.

Aquaporins

Specialized water channels in membranes that facilitate water diffusion.

Ion channels

Proteins forming channels for ions to cross membranes.

Channel protein

Membrane proteins forming pores for molecule transport.

Carrier protein

Proteins that bind and transport substances across membranes.

Hypertonic

A solution with higher solute concentration compared to another.

Hypotonic

A solution with lower solute concentration compared to another.

Isotonic

A solution with equal solute concentration to another.

Turgor pressure

The pressure exerted by water inside a plant cell against the cell wall.

Plasmolysis

Contraction of plant cells in hypertonic solution due to water loss.

Endocytosis

Uptake of substances into the cell via vesicle formation.

Exocytosis

Secretion of substances from the cell via vesicles.

Pinocytosis

A type of endocytosis where small fluids and dissolved substances are taken in.

Phagocytosis

A type of endocytosis where large particles or cells are engulfed.

Receptor-mediated endocytosis

Highly specific endocytosis using receptors to bind and internalize molecules.

Coated pits (clathrin)

Regions of the membrane coated with clathrin for receptor-mediated endocytosis.

Low density lipoprotein (LDL)

A lipoprotein involved in cholesterol transport, taken up by receptor-mediated endocytosis.

Signal transduction pathway

A series of molecular events by which a signal on a cell's surface is converted into a specific cellular response.

Paracrine

A signaling mechanism where the target cells are near the signal-releasing cells.

Juxtacrine

Signaling between adjacent cells through direct contact or shared cytoplasm.

Autocrine

A type of signaling where a cell targets itself with signals it produces.

Hormonal

Signaling over long distances via hormones that travel through the bloodstream.

Gap junctions

Specialized intercellular connections between animal cells that allow direct communication.

Plasmodesmata

Cytoplasmic channels between plant cells that pass through cell walls and allow molecule exchange.

Signaling networks

Complex interactions between multiple signaling pathways within a cell.

Receptor

A protein that detects a signal molecule (ligand) and performs an action in response.

Connexon

Protein subunits that form gap junctions between cells.

Connexin

The protein that makes up connexons in gap junctions.

Desmotubule

A tube-like structure in plasmodesmata that connects the ER of adjacent cells.

Ligand

A molecule that binds specifically to a receptor site of another molecule.

G protein-coupled receptor

A membrane receptor that works with the help of a G protein to relay signals.

Protein kinase receptor

A receptor that activates its own kinase activity upon ligand binding.

Ion channel receptor

A receptor that acts as a gate for ions when it changes shape.

Intracellular receptors

Receptors located inside the cell that bind to hydrophobic signal molecules.

Agonists

A molecule that mimics a signal and activates a receptor.

Antagonists

A molecule that blocks or dampens a signal by binding to a receptor.

Phosphorylation

The addition of a phosphate group to a molecule, often used to activate proteins.

Kinase

An enzyme that catalyzes phosphorylation by transferring phosphate from ATP.

Tyrosine

An amino acid often targeted in phosphorylation for signal transduction.

Phosphatase

An enzyme that removes phosphate groups from proteins.

G protein

A protein that binds GTP and activates downstream signaling pathways.

Effector protein

A protein activated by a receptor that produces a cellular response.

Adenylyl cyclase

An enzyme that converts ATP to cAMP in response to a signal.

Phosphodiesterase

An enzyme that breaks down cAMP into AMP, terminating the signal.

GDP

A nucleotide that binds to inactive G proteins.

GTP

A nucleotide that activates G proteins when bound.

Phosphorylation cascade

A series of protein activations where each step amplifies the signal.

First messenger

The initial signaling molecule that binds to the receptor.

Secondary messengers

Small molecules like cAMP, Ca²⁺, IP₃ that relay signals from receptors to target molecules.

cAMP

A common secondary messenger involved in activating protein kinases.

Ca²⁺

A calcium ion that acts as a versatile second messenger in many pathways.

Nitric oxide

A gaseous signaling molecule involved in smooth muscle relaxation.

Diacylglycerol (DAG)

A lipid-derived second messenger involved in PKC activation.

Inositol triphosphate (IP3)

A second messenger released from membrane lipids; helps release Ca²⁺ from ER.

Glycogen phosphorylase

An enzyme that breaks down glycogen into glucose-1-phosphate.

Phospholipase

An enzyme that cleaves phospholipids to produce DAG and IP₃.

Phospholipase C

A specific enzyme that cleaves PIP₂ into IP₃ and DAG.

PIP2

A membrane phospholipid cleaved into IP₃ and DAG during signaling.

Nitric oxide (NO) synthase

An enzyme that synthesizes nitric oxide from arginine.