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DE Bio - Ch. 5-6

Membrane Transport and Cell Signaling/Intro to Metabolism

What does the plasma membrane do? Separates the living cell from its surrroundings
What does selective permeability mean? Only allowing certain substances to cross over a membrane
True or False: Phospholipids are the most abundant lipids in membranes? True
What are amphipathic molecules? Molecules that contain hydrophobic and hydrophilic regions
This states that the membrane is a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids Fluid mosaic model
The lateral movement of phospholipids is ______ while the movement of proteins are slow (the lipids and proteins in a membrane can shift laterally) Faster
What happens to membranes at cool temperatures? (the temp. in which a membrane solidifies depends on the type of lipids) They switch from a fluid state to a solid state
When does a membrane remain fluid at a lower temperature? When it is rich in phospholipids with unsaturated carbon tails
True or False: Membranes must be solid to work properly? False. They need to be fluid (like salad dressing)
KNOW!!!!!! Cholesterol reduces membrane fluidity at moderate temperatures, but at low temperatures hinders solidification
What happens to membranes when they have cholesterol and are at a warm temperature? It restrains the movement of phospholipids
At cool temperatures, cholesterol maintains membrane fluidity by ______ Preventing tight packing
What are membranes? A collage of different proteins, grouped together, in a fluid matrix of the lipid bilayer
What determines a membrane's specific function? Proteins
What are integral proteins? Proteins that penetrate the hydrophobic interior of the lipid bilayer
What type of integral proteins span the membrane? Transmembrane proteins
KNOW!!! The hydrophobic regions of an integral protein consist of one or more stretches of nonpolar amino acids, often coiled into  helices
What are peripheral proteins? Proteins that are loosely bound to the surface of the membrane
What are the six major functions of membrane proteins? 1. Transport 2. Enzymatic activity 3. Attachment to the cytoskeleton and extracellular matrix 4. Cell-cell recognition 5. Intercellular joining 6. Signal transduction
KNOW!!!! Cells recognize each other by binding to surface molecules, often containing carbohydrates, on the extracellular surface of the plasma membrane
What happens to membrane carbohydrates that covalently bond to lipids? They form glycolipids
What happens to membrane carbohydrates that covalently bond to proteins? (more common) They form glycoproteins
KNOW!!! The asymmetrical distribution of proteins, lipids, and associated carbohydrates in the plasma membrane is determined when the membrane is built by the ER and Golgi apparatus
True or False: A cell must regulate transport of substances across cellular boundaries? True
What type of hydrophobic (nonpolar) molecules can dissolve in the lipid bilayer of a membrane/dissolve easily? Hydrocarbons
What type of polar molecules cannot dissolve in the lipid bilayer of a membrane/dissolve easily? Sugars
What are transport proteins? Proteins that allow passage of hydrophilic substances across the membrane
KNOW!!!!! transport proteins, called channel proteins, have a hydrophilic channel that certain molecules or ions can use as a tunnel
What are the channel proteins that facilitate the passage of water called? Aquaporins
What do carrier proteins do? Bind to molecules and change shape to shuttle them across the membrane
KNOW!!! A transport protein is specific for the substance it moves
What is diffusion? (it is directional as well) The tendency for molecules to spread out evenly into the available space
KNOW!!!!! At dynamic equilibrium, as many molecules cross the membrane in one direction as in the other
What is a concentration gradient? From where it is more concentrated to where it is less concentrated (requires no work)
What is passive transport? The diffusion of a substance across a biological membrane (no energy is expended by the cell to make it happen)
What is osmosis? The diffusion of free water across a selectively permeable membrane
KNOW ABOUT OSMOSIS!!!! Water diffuses across a membrane from the region of lower solute concentration to the region of higher solute concentration until the solute concentration is equal on both sides
What is tonicity? The ability of a surrounding solution to cause a cell to gain or lose water
What is an isotonic solution? Solute concentration is the same as inside the cell; no net water movement across the plasma membrane
What is a hypertonic solution? Solute concentration is greater than that inside the cell; cell loses water
What is a hypotonic solution? Solute concentration is less than that inside the cell; cell gains water
When a plant cell swells due to excess water, it is ________ Turgid (very firm)
When there is no net movement of water in a cell, the plant becomes ________ Flaccid (limp)
When a plant cell loses water and the membrane pulls away from the wall, it produces a lethal effect called ___________ Plasmolysis
What is facilitated diffusion? When transport proteins speed the passive movement of molecules across the plasma membrane
Channel proteins include what? 1. Aquaporins (for facilitated diffusion of water) 2. Ion channels (open or close in response to a stimulus; gated channels)
KNOW!!!!! Facilitated diffusion speeds transport of a solute by providing efficient passage through the membrane but does not alter the direction of transport. Some transport proteins, however, can move solutes against their concentration gradients.
What is active transport? Moves substances against their concentration gradients (requires ATP)
Example of active transport system Sodium-potassium pump
What is membrane potential? The voltage across a membrane; created by differences in the distribution of positive and negative ions across a membrane
What is an electrochemical gradient? When two combined forces drive the diffusion of ions across a membrane
Examples of an electrochemcial gradient 1. A chemical force (the ion’s concentration gradient) 2. An electrical force (the effect of the membrane potential on the ion’s movement)
What is an electrogenic pump? A transport protein that generates voltage across a membrane; also helps store energy that can be used for cellular work
KNOW!!! The sodium-potassium pump is the major electrogenic pump of animal cells
KNOW!!! The main electrogenic pump of plants, fungi, and bacteria is a proton pump
When does cotransport occur? When active transport of a solute indirectly drives transport of other solutes
KNOW ABOUT PROTON PUMP!!!! Plant cells use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell
How do small solutes and water enter or leave the cell through the lipid bilayer? Through transport proteins
How do large molecules, such as polysaccharides and proteins, cross the membrane? In bulk by vesicles (requires energy)
What happens in exocytosis? Transport vesicles migrate to the membrane, fuse with it, and release their contents (secretory cells use exocytosis to export products)
What happens in endocytosis? The cell takes in molecules and particulate matter by forming new vesicles from the plasma membrane (reversal of exocytosis)
What are the three types on endocytosis? 1. Phagocytosis (“cellular eating”) 2. Pinocytosis (“cellular drinking”) 3. Receptor-mediated endocytosis
What is a type of local signaling? The free passage of substances in the cytosol from one cell to another
What are local regulators? Messenger molecules that travel a short distance; messenger molecules are secreted by a signaling cell
Paracrine signaling Growth factors stimulates nearby cells to grow and divide
Synaptic signaling (animal nervous system) Consists of an electrical signal moving along a nerve cell that triggers secretion of neurotransmitter molecules. These diffuse across the space between the nerve cell and its target, triggering a response in the target cell.
Endocrine signaling Long-distance signaling, plants and animals; hormonal signaling in animals, specialized cells release hormone molecules that travel via the circulatory system
What is a ligand? The binding between a signal molecule
KNOW ABOUT LIGANDS!!!! Ligand binding generally causes a shape change in the receptor
What are the two main types of membrane receptors? 1. G protein-coupled receptors 2. Ligand-gated ion channels
What are G protein-coupled receptors? They are plasma membrane receptors that work with the help of a G protein; G proteins bind to the energy-rich molecule GTP; the G protein acts as an on-off switch: If GTP is bound to the G protein, the G protein is inactive
What does a ligand-gated ion channel receptor do? Acts as a “gate” for ions when the receptor changes shape; when a signal molecule binds as a ligand to the receptor, the gate allows specific ions, such as Na+ or Ca2+, through a channel in the receptor
Created by: savvysparks



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