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64 Cards in this Set
- Front
- Back
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What is selective permeability?
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A membrane that allows some substance to cross more easily than others.
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What are the staple ingredients of membranes?
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Lipids & Proteins.
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What is an amphipathic molecule?
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A molecule having both a hydrophobic region and a hydrophillic region.
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What membrane is a fluid structure with a mosaic of various proteins embedded in or attached to a bilayer of phospholipids?
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Fluid Mosaic model.
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What preperation splits a membrane along the middle of the phospholipid bilayer?
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Freeze-fracture preperation for electron microscopy.
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A membrane is primarily held together by what?
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Hydrophobic interactions.
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The temperature at which a membrane solidifies depends on what?
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The types of lipids it is made of.
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A membrane will remain fluid at lower temperatures if it is rich in what?
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Phospholipids with unsaturated hydrocarbon tails.
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Why can unsaturated hydrocarbons not pack closely together, like saturated hydrocarbons?
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Because of kinks in the tails where double bonds are located.
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What steroid can be thought of as a temperature buffer for the membrane, resisting changes in membrane fluidity that can be caused by changes in temperature?
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Cholesterol.
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How many types of proteins have been found so far in the plasma membrane of red cells?
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More than 50.
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What type of proteins penetrate the hydrophobic core of the lipid bilayer?
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Integral proteins.
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The hydrophobic regions of an integral protein consist of one or more stretches of what?
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Nonpolar amino acids, usually coiled into alpha helices.
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What protein is not embedded into the lipid bilayer at all, yet they are appendages loosley bound to the surface of the membrane, often to exposed portions of integral proteins?
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Peripheral proteins.
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What are the six major functions performed by proteins of the plasma membrane?
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1.) Transport
2.) Enzymatic activity 3.) Signal Transduction 4.) Cell-cell recognition 5.) Intercellular joining 6.) Attachment to the cytoskeleton and extracellular matrix (ECM) |
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Briefly describe the transport function of a membrane.
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Proteins can provide hydropphilic channels across the membrane that is selective for particular solutes. Other proteins can shuttle substances from one side of the membrane to the other by changing shape. Some of the proteins hydrolize ATP as an energy source to actively pump substances across the membrane.
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Briefly describe the Enzymatic activity function of a membrane.
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A protein built into the membrane may be an enzyme with its active site exposed to substances in the adjacent solution. In some cases, several enzymes in a membrane are organized as a team that carries out the sequential steps of a metabolic pathway.
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Briefly describe the Signal transduction funtion of a membrane.
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A membrane protein may have a binding site with a specific shape of a chemical messenger, such as a hormone. The external messenger (signal) may cause a conformational change in the protein (receptor) that relays the message to the inside of the cell.
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Briefly describe the Cell-cell recognition function of the membrane.
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Some glyco-proteins serve as identification tags that are specifically recognized by other cells.
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Breifly describe the Intercellular joining function of the membrane.
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Membrane proteins of adjacent cells may hook together in various kinds of junctions, such as gap junctions or tight junctions.
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Briefly describe the attachment to the cytoskeleton ECM function of the membrane.
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Microfilaments or other elements of the cytoskeleton may be bonded to membrane proteins, a function that helps maintain cell shape and stabalizes the location of certian membrane proteins. Proteins that adhere to the ECM can coordinate extracellular and intracellular cahnges.
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Carbohydrates that are covalently bonded to lipids are known as what?
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Glycolipids.
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Carbohydrates that are covalently bonded to proteins are known as what?
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Glycoproteins.
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What is an example of carbohydrates on erythrocytes?
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Blood type (ABO/Rh).
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What types of molecules cross the lipid bilayer with ease & without the aid of membrane proteins?
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Hydrophobic (nonpolar) molecules, i.e. hydrocarbons, CO2, & O2.
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What impedes the direct passage of ions and polar molecules, which are hydrophillic, through the membrane?
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The hydrophobic core of the membrane.
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What functions by having a hydrophillic channel, so that certian molecules or atomic ions can use a tunnel to get through the membrane?
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Transport Proteins.
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The passage of water molecules through the membrane in certian cells is facilitated by channel proteins know as what?
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Aquaporins.
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What protein changes shape in a way that shuttles them across the membrane?
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Carrier Proteins.
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What is a result of thermal motion by molecules?
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Diffusion.
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A simple rule of diffusion states that in the abscence of outside forces, what will ahppen to a solution?
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A substance will diffuse from where it is more concentrated to where it is less concentrated. (substances diffuse down their concentration gradient).
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Diffusion across a biological membrane in which the cell does not havbe to expend energy is known as what?
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Passive Transport.
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What is the diffusion of water across a selectively permeable membrane known as?
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Osmosis
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The ability of a solution to cause a cell to gain or lose water is known as what?
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Tonicity
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In an isotonic environment, in which direction does the water move across the membrane?
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There is no net movement.
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In a hypertonic environment, in which direction will the water move, and what is the effect on the membrane?
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The cell will lose water to its environment, probably resulting in cell death as a result of shriveling.
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In a hypotonic environment, in which direction will the water move, and what is the effect on the membrane?
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Water will enter the cell faster than it can leave, and the cell will swell and lyse.
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What is the control of water balance known as?
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Osmoregulation
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What is it known as when a plant becomes very firm from backpressure, as a result to refusing osmosis?
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Turgid
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When a plant is limp from their surrondings being isotonic this is known as what?
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Flaccid
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What is it known as when a cell is immersed into a hypertonic environment and begins to lose water to its surrindings and shrivel?
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Plasmolysis
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What is it known as when polar molecules and ions impeded by the lipid bilayer diffuse passively with the help of transport proteins spanning the membrane?
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Facilitated Diffusion.
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What are the two types of transport proteins?
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Channel proteins & Carrier Proteins.
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What type of channel is activated by electrical or chemical stimulus?
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Ion channels.
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What is a gated channel?
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A channel that opens and closes when presented with a stimulus.
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What proteins undergo a subtle change in shape that somehow translocates the solute-binding site across the membrane?
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Carrier Proteins.
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Pumping a molecule across a membrane against its gradient, in whic energy is expended is known as what?
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Active Transport
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All proteins that move solutes against a gradient are what types of proteins?
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carrier proteins.
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What supplies the energy for most active transport?
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ATP
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What charge does the cytoplasm carry?
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A negative charge.
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The extracellular fluid has what type of charge?
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An unequal charge because of the distribution of anions and cations.
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The voltage across a membrane is known as what?
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Membrane Potential.
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Memrbane Potential has a range of what?
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-50to -200 millivolts
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What are two forces that drive the diffusion of ions across a membrane?
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Chemical force (the ions concentration gradient)
Electrical force (the effect of the membrane potential on the ions movement. |
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The combination of electrical & chemical forces on the ion is called what?
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electrochemical gradient.
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What is a trasnport protein that generates voltage across a membrane known as?
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electrogenic pump.
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What is the main electrogenic pump in animal cells?
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Na-K pump.
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What is the main electrogenic pump of plants, fungi, and bacteria?
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proton pump.
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A single ATP powered pump that transports a specific solute can indirectly drive the active transport of several other solutes in a mechanism called what?
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Cotransport
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How do large molecules such as proteins and polysaccharides, and even larger molecules cross the membrane?
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Using vesicles.
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When the cell secretes macromoleculs by the fusion of vesicles with the plasma membrane this is known as what?
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Exocytosis.
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When a cell takes in macromolecules and particulate matter by forming new vesicles from the plasma membrane this is known as what?
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Endocytosis
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What are the three types of endocytosis?
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1.Phagocytosis
2.Pinocytosis 3.Receptor-mediated |
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What is a general term used for any molecule that binds specifically to a recptor site of another molecule?
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Ligands.
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