Unit 2: Topic 9 - Mechanisms of Transport Flashcards
Describe the two general categories of cell transport across the cell membrane.
The two types of transport are passive and active transport. Passive transport is diffusion of a substance across a membrane from an area of high concentration of the subtance to an area with a low concentration. This type of transport does not require metabolic energy, but it may need channel or carrier proteins. The other type of tranpsort is active transport, which does require metabolic energy. The substance in this type of transport travels against its concentration gradient, meaning that it travels from an area of low concentration to an area of high concentration.
What are the differences between simple and facilitated diffusion? Be sure to explain when facilitated diffusion would be needed rather than simple diffusion.
Diffusion is the random movement of molecules that results in an even distribution of molecules and a net movement of molecules from an area of high concentration to an area of low concentration. Simple diffusion is diffusion that does not require energy or carrier proteins. Molecules that are lipid-soluble (meaning they are small, non-polar, and uncharged) usually undergo simple diffusion across the cell membrane. On the other hand, facilitated diffusion requires a specific carrier protein for the molecule being diffused to be transported across a membrane. This type of diffusion usually occurs with molecules that are hydrophilic/non-soluble in lipids (these molecules are usually large, polar, or charged).
What are the different types of proteins that could be used for facilitated diffusion?
The two major types of proteins that could be used for facilitated diffusion are channel proteins and carrier proteins. Channel proteins are transmembrane proteins that form an aqueous passageway across the membrane to allow specific molecules to pass through. These proteins can always be open or gated. Gated channel proteins need a ligand to bind to it to change their structure and open the passageway. They could also be voltage-gated, meaning they open and close according to changes in the electric membrane potential (essentially, the difference in ion concentrations between the inside and outside of the cell). Some examples of channel proteins include ion channels (channel proteins specific to a particular ion) and aquaporins (channel proteins specific to water). The other type of protein used in facilitated diffusion is carrier protein. These proteins bind to specific molecules and transport them across the membrane.
What is osmosis?
A) The movement of solutes from low to high concentrations
B) The moment of water from low to high concentrations
C) The movement of water from high to low concentrations
D) The movement of solutes from high to low concentrations
C) The movement of water from high to low concentrations
Osmosis is the facilitated diffusion of water across a membrane through aquaporins (channel proteins specific to water).
Define each of the following terms: hypertonic, hypotonic, and isotonic.
Hypertonic: The solution being described has a higher solute concentration than the other solution.
Hypotonic: The solution being described has a lower solute concentration than the other solution.
Isotonic: Both solutions have equal solute concentrations.
What is the difference between primary and secondary active transport?
Primary active transport involves using energy from the direct hydrolysis of ATP to generate energy to move a molecule against its concentration gradient. On the other hand, secondary active transport uses energy supplied by an ion concentration gradient (which is usually set up using primary active transport) to move the molecule.
Explain the role of transport pumps in active transport.
Transport pumps are transmembrane proteins that actively (using energy from ATP) move ions or solutes across the membrane and against their concentration gradient.
How does the active transport of large molecules differ from the active transport of small molecules?
While small molecules can be transported using transport pumps, large molecules need to be transported through exocytosis or endocytosis. Exocytosis is the process in which a vesicle inside the cell (which can contain either large molecules or proteins that will be secreted) merges with the cell membrane and releases its contents to the outside of the cell. Endocytosis is the process in which the cell membrane pinches inward and forms a vesicle inside the cell containing materials brought in from outside the cell. This process usually depends on receptors on the cell membrane (these receptors are integral membrane proteins located on the outside of the cell membrane), meaning that when a certain molecule binds to the receptors, it triggers the pinching in of the cell membrane and the internalization of the receptors, the ligands that bound to them, and other substances near the site of invagination (the site where the cell membrane pinched in). Two specific types of endocytosis include pinocytosis (the endocytosis of a liquid containing dissolved substances) and phagocytosis (the endocytosis of a large particle or another cell).
