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