Biol 3140 Exam 2 Flashcards - Iowa State University

Exam 2 for Cellular and Molecular Biology

plasma membrane

The protein-containing lipid bilayer that surrounds a living cell.

lipid bilayer

Thin pair of closely juxtaposed sheets, composed mainly of phospholipid molecules, that forms the structural basis for all cell membranes.

phospholipid

The major type of lipid molecule in cell membranes. Generally composed of two fatty acid tails linked to one of a variety of phosphate-containing polar groups.

phosphatidylcholine

Common phospholipid present in abundance in most cell membranes; uses choline attached to a phosphate as its head group.

amphipathic

Having both hydrophobic and hydrophilic regions, as in a phospholipid or a detergent molecule.

fat droplet

Large cluster of hydrophobic fats or oils that forms inside the cells.

unsaturated

Describes an organic molecule that contains one or more double or triple bonds between its carbon atoms.

saturated

Describes an organic molecule that contains a full complement of hydrogen; in other words, no double or triple carbon–carbon bonds.

cholesterol

Short, rigid lipid molecule present in large amounts in the plasma membranes of animal cells, where it makes the lipid bilayer less flexible.

membrane protein

A protein associated with the lipid bilayer of a cell membrane. Attaches to the membrane by a hydrophobic hydrocarbon chain.

detergent

Soapy substance used to solubilize lipids and membrane proteins.

bacteriorhodopsin

Pigmented protein found in abundance in the plasma membrane of the salt-loving archaeon Halobacterium halo_bium; pumps protons out of the cell, fueled by light energy.

cell cortex

Specialized layer of cytoplasm on the inner face of the plasma membrane. In animal cells, it is rich in actin filaments that govern cell shape and drive cell movement.

membrane domain

Functionally and structurally specialized region in the membrane of a cell or organelle; typically characterized by the presence of specific proteins.

• example: Spectrin: works with membrane proteins to shape red blood cells by forming a mesh network

glycocalyx

Protective layer of carbohydrates on the outside surface of the plasma membrane formed by the sugar residues of membrane glycoproteins, proteoglycans, and glycolipids.

membrane transport protein

Any transmembrane protein that provides a passageway for the movement of select substances across a cell membrane.

membrane potential

Voltage difference across a membrane due to a slight excess of positive ions on one side and of negative ions on the other.

passive transport

The spontaneous movement of a solute down its concentration gradient across a cell membrane via a membrane transport protein, such as a channel or a transporter.

active transport

The movement of a solute across a membrane against its electrochemical gradient; requires an input of energy, such as that provided by ATP hydrolysis.

electrochemical gradient

Driving force that determines which way an ion will move across a membrane; consists of the combined influence of the ion's concentration gradient and the membrane potential.

aquaporin

Channel that facilitates the transport of water, but not ions, across cell membranes; those found in the plasma membrane greatly increase a cell's permeability to water.

osmosis

Passive movement of water across a cell membrane from a region where the concentration of water is high (because the concentration of solutes is low) to a region where the concentration of water is low (and the concentration of solutes is high).

turgor pressure

Force that builds as water flows into plant and yeast cells by osmosis; drives the expansion of cells that underlies plant growth and maintains the rigidity of plant stems and leaves.

transporter

Membrane transport protein that moves a solute across a cell membrane by undergoing a series of conformational changes.

• example: Transporting glucose

pump

Transporter that uses a source of energy, such as ATP hydrolysis or sunlight, to actively move a solute across a membrane against its electrochemical gradient.

Na⁺ pump (or Na⁺-K⁺ ATPase)

Transporter found in the plasma membrane of most animal cells that actively pumps Na⁺ out of the cell and K⁺ in using the energy derived from ATP hydrolysis. Considered a symport because it uptakes Glucose.

Ca²⁺ pump (or Ca²⁺ ATPase)

An active transporter that uses energy supplied by ATP hydrolysis to actively expel Ca²⁺ from the cell cytosol. Undergos phosphorylation.

gradient-driven pump

A protein that uses energy stored in the electrochemical gradient of ions to actively transport a solute across a membrane. Considered an antiport.

symport

A transporter that transfers two different solutes across a cell membrane in the same direction.

antiport

Type of coupled transporter that transfers two different ions or small molecules across a membrane in opposite directions, either simultaneously or in sequence.

H⁺ pump (or H⁺ ATPase)

A protein complex embedded in a cell membrane that actively transports protons (H+ ions) across the membrane, using energy derived from ATP hydrolysis.

channel

A protein that forms a hydrophilic pore across a membrane, through which selected small molecules or ions can passively diffuse.

ion channel

Transmembrane protein that forms a pore across the lipid bilayer through which specific inorganic ions can diffuse down their electrochemical gradients. Determines its ion selectivity by creating a specific environment that only allows certain ions to pass through based on their size and charge.

selectivity filter

Part of an ion channel that determines which ions the channel can transport; located in the region where the channel is narrowest. Ion channels can be opened or closed by various mechanisms, primarily including changes in membrane voltage (voltage-gated), binding of specific molecules (ligand-gated), mechanical forces (mechanically-gated), and even changes in temperature or pH.

K⁺ leak channel

Ion channel permeable to K⁺ that randomly flickers between an open and closed state; largely responsible for the resting membrane potential in animal cells.

resting membrane potential

Voltage difference across the plasma membrane when a cell is not stimulated.

Nernst equation

An equation that relates the concentrations of an inorganic ion on the two sides of a permeable membrane to the membrane potential at which there would be no net movement of the ion across the membrane.

patch-clamp recording

Technique used to monitor the activity of ion channels in a membrane; involves the formation of a tight seal between the tip of a glass electrode and a small region of cell membrane.

mechanically-gated channel

An ion channel that allows the passage of select ions across a membrane in response to a physical perturbation.

ligand-gated channel

An ion channel that is stimulated to open by the binding of a small molecule such as a neurotransmitter.

voltage-gated channel

Channel protein that permits the passage of selected ions, such as Na⁺, across a membrane in response to changes in the membrane potential. Found primarily in electrically excitable cells such as nerve and muscle cells.

neuron

An electrically excitable cell that integrates and transmits information as part of the nervous system; a nerve cell.

axon

Long, thin extension that conducts electrical signals away from a nerve cell body toward remote target cells.

dendrite

Short, branching structure that extends from the surface of a nerve cell and receives signals from other neurons.

action potential

Traveling wave of electrical excitation caused by rapid, transient, self-propagating depolarization of the plasma membrane in a neuron or other excitable cell; also called a nerve impulse.

depolarization

A shift in the membrane potential, making it less negative on the inside of the cell.

voltage-gated Na⁺ channel

Protein in the plasma membrane of electrically excitable cells that opens in response to membrane depolarization, allowing Na⁺ to enter the cell. It is responsible for action potentials in these cells.

synapse

Specialized junction where a nerve cell communicates with another cell (such as a nerve cell, muscle cell, or gland cell), usually via a neurotransmitter secreted by the nerve cell.

neurotransmitter

Small signaling molecule secreted by a nerve cell at a synapse to transmit information to a postsynaptic cell. Examples include acetylcholine, glutamate, GABA, and glycine.

transmitter-gated ion channel

Transmembrane receptor protein or protein complex that opens in response to the binding of a neurotransmitter, allowing the passage of a specific inorganic ion; its activation can trigger an action potential in a postsynaptic cell.

membrane-enclosed organelle

Any organelle in a eukaryotic cell that is surrounded by a lipid bilayer—for example, the endoplasmic reticulum, Golgi apparatus, and lysosome.

endomembrane system

Interconnected network of membrane-enclosed organelles in a eukaryotic cell; includes the endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, and endosomes.

signal sequence

Amino acid sequence that directs a protein to a specific location in the cell, such as the nucleus or mitochondria.

nuclear envelope

Double membrane surrounding the nucleus. Consists of outer and inner membranes, perforated by nuclear pores.

nuclear pore

Channel through which selected large molecules move between the nucleus and the cytoplasm.

peroxisome

Small membrane-enclosed organelle that contains enzymes that degrade lipids and destroy toxins.

endoplasmic reticulum (ER)

Labyrinthine membrane-enclosed compartment in the cytoplasm of eukaryotic cells where lipids and proteins are made.

rough endoplasmic reticulum

Region of the endoplasmic reticulum associated with ribosomes and involved in the synthesis of secreted and membrane-bound proteins.

transport vesicle

Membrane vesicle that carries proteins from one intracellular compartment to another—for example, from the endoplasmic reticulum to the Golgi apparatus.

vesicular transport

Movement of material between organelles in the eukaryotic cell via membrane-enclosed vesicles.

coated vesicle

Small membrane-enclosed sac that wears a distinctive layer of proteins on its cytosolic surface. It is formed by pinching-off of a protein-coated region of cell membrane.

clathrin

Protein that makes up the coat of a type of transport vesicle that buds from either the Golgi apparatus (on the outward secretory pathway) or from the plasma membrane (on the inward endocytic pathway).

Rab protein

One of a family of small GTP-binding proteins present on the surfaces of transport vesicles and organelles that serves as a molecular marker to help ensure that transport vesicles fuse only with the correct membrane.

tethering protein

Filamentous transmembrane protein involved in the docking of transport vesicles to target membranes.

SNARE

One of a family of membrane proteins responsible for the selective fusion of vesicles with a target membrane inside the cell.

exocytosis

Process by which most molecules are secreted from a eukaryotic cell. These molecules are packaged in membrane-enclosed vesicles that fuse with the plasma membrane, releasing their contents to the outside.

unfolded protein response

Molecular program triggered by the accumulation of misfolded proteins in the endoplasmic reticulum. Allows cells to expand the endoplasmic reticulum and produce more of the molecular machinery needed to restore proper protein folding and processing.

Golgi apparatus

Membrane-enclosed organelle in eukaryotic cells that modifies the proteins and lipids made in the endoplasmic reticulum and sorts them for transport to other sites.

secretion

Production and release of a substance from a cell.

secretory vesicle

Membrane-enclosed organelle in which molecules destined for secretion are stored prior to release.

endocytosis

Process by which cells take in materials through an invagination of the plasma membrane, which surrounds the ingested material in a membrane-enclosed vesicle. (See also pinocytosis and phagocytosis.)

phagocytosis

The process by which particulate material is engulfed ("eaten") by a cell. Prominent in predatory cells, such as Amoeba proteus, and in cells of the vertebrate immune system, such as macrophages.

phagocytic cell

A cell such as a macrophage or neutrophil that is specialized to take up particles and microorganisms by phagocytosis.

pinocytosis

Type of endocytosis in which soluble materials are taken up from the environment and incorporated into vesicles for digestion. (Literally, "cell drinking.")

receptor-mediated endocytosis

Mechanism of selective uptake of material by animal cells in which a macromolecule binds to a receptor in the plasma membrane and enters the cell in a clathrin-coated vesicle.

endosome

Membrane-enclosed compartment of a eukaryotic cell through which material ingested by endocytosis passes on its way to lysosomes.

lysosome

Membrane-enclosed organelle that breaks down worn-out proteins and organelles and other waste materials, as well as molecules taken up by endocytosis; contains digestive enzymes that are typically most active at the acid pH found inside these organelles.

autophagy

Mechanism by which a cell "eats itself," digesting molecules and organelles that are damaged or obsolete.

FRAP

Fluorescence recovery after photobleaching. Used to measure the rate of lateral diffusion of membrane proteins.

lateral diffusion

Moves freely sideways across the membrane without flipping to the opposite side.

• Can be restricted by: inside the cell cortex, extracellular matrix, proteins on the surface of another cell, or the diffusion barrier 

saccharides/carbohydrate 

biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms - aka SUGAR

• used for ATP