Because cell walls consist of a cross-linked network of long filaments embedded in a stiff surrounding material, they can be called __________.
The most abundant protein found in the extracellular matrix of animal cells is _____.
The type of cell-cell attachment that resembles quilting, with proteins acting as stitches, is _____.
What role do plasmodesmata play in plant cells?
-They prevent the plant cell from losing water in desert conditions.
-They allow the plant cell to withstand extreme temperatures.
-They serve as sites of protein production in the cell.
-They serve as communication portals between neighboring plant cells, allowing the passage of substances between the two cells.
They serve as communication portals between neighboring plant cells, allowing the passage of substances between the two cells.
Why does a hormone only act on specific cell types in an organism and not others?
-Hormones are prevented from entering the bloodstream, and thus only act on the releasing cell itself.
-Hormones only act on cells that are adjacent to the releasing cell.
-A cell must have the appropriate receptor before it can bind to the hormone.
-All cells will take up the hormone and process it, but not all cells will elicit a response.
A cell must have the appropriate receptor before it can bind to the hormone.
The long and complex series of events that occurs when a signal binds to the cell surface and is converted from one form to another is called _____.
How can a hormone that is present in very small quantities within the bloodstream elicit such a large response within a cell?
-Cells degrade the hormone into many tiny molecules, and then each piece creates a response within the cell.
-The hormone is only taken up by the largest cells in the body, and thus it can elicit a large response.
-The hormone is always an extra large macromolecule even though it is present in minute quantities.
-The message from the hormone is amplified many times within the cell.
The message from the hormone is amplified many times within the cell.
How is phosphorylation important in a signal transduction cascade?
-Phosphorylation will shut down a signal transduction cascade, thus leading to an end of the signal.
-A hormone will phosphorylate the entire cell, thus causing the cell to be marked for destruction.
-Phosphorylation will turn an inactive protein into an active one, which triggers another response in the cell.
-When the hormone itself becomes phosphorylated, it travels to all nearby cells and activates them to release more hormones of that same type.
Phosphorylation will turn an inactive protein into an active one, which triggers another response in the cell.
A common GTP-binding messenger that links the receipt of an extracellular signal to the production of an intracellular one is _____.
Why is it important for signal transduction systems to trigger a rapid response within a cell and be able to be shut down quickly?
-All signal transduction cascades are shut down immediately so as to prevent the cell from mounting a response.
-Cells are unable to respond quickly to hormones, and therefore signal transduction cascades always occur over a long time.
-Cells have to be able to function alone, because they are unable to work together in a coordinated fashion.
-Cells often have to respond very quickly to changes in their internal and external environments.
Cells often have to respond very quickly to changes in their internal and external environments.
Which of these cell junctions form a barrier to the passage of materials?
-desmosomes (anchoring junctions)
-gap (communicating) junctions
The primary role of _____ is to bind animal cells together.
-gap (communicating) junctions
_____ aid in the coordination of the activities of adjacent animal cells.
-Gap (communicating) junctions
Gap (communicating) junctions
Which of these is a logical signal transduction pathway?
-A receptor tyrosine kinase activates adenylyl cyclase, which activates phospholipase C, which converts ATP into cyclic AMP, which binds to an intracellular enzyme that carries out a response.
-An ion-channel receptor opens, allowing a steroid hormone to enter the cell; the steroid hormone then activates protein kinases that convert GTP to GDP, which binds to an intracellular enzyme that carries out a response.
-A G-protein-linked receptor activates G protein, which activates phospholipase C, which cleaves a membrane lipid to form IP3, which binds to a calcium channel on the ER, which opens to release calcium ions into the cytoplasm, which bind to an intracellular enzyme that carries out a response.
-An intracellular receptor activates phospholipase C, which cleaves a membrane protein to form IP3, which then activates the opening of an ER channel protein, which releases cyclic AMP into the cytoplasm, where it binds to an intracellular enzyme that carries out a response.
A G-protein-linked receptor activates G protein, which activates phospholipase C, which cleaves a membrane lipid to form IP3, which binds to a calcium channel on the ER, which opens to release calcium ions into the cytoplasm, which bind to an intracellular enzyme that carries out a response.
The cleavage of glycogen by glycogen phosphorylase releases _____.
-nothing: glycogen phosphorylase cannot cleave glycogen
Epinephrine acts as a signal molecule that attaches to _____ proteins.
-receptor tyrosine kinase
Which of these is a receptor for calcium ions?
Which of these is NOT correct?
-Kinases are enzymes that phosphorylate other molecules.
-Ion channels are found on both the plasma membrane and the endoplasmic reticulum.
-Cyclic AMP binds to calmodulin.
-Phospholipase C catalyzes the formation of IP3.
-Tyrosine-kinase receptors consist of two polypeptides that join when activated by a signal molecule.
Cyclic AMP binds to calmodulin.
A toxin that inhibits the production of GTP would interfere with the function of a signal transduction pathway that is initiated by the binding of a signal molecule to _____ receptors.
-receptor tyrosine kinase
A signal transduction pathway is initiated when a _____ binds to a receptor.
Which of these is the second of the three stages of cell signaling?
-binding of a neurotransmitter to a plasma membrane receptor
Which of these extracellular signal molecules could diffuse through a plasma membrane and bind to an intracellular receptor?
A(n) _____ is an example of a signal molecule that can bind to an intracellular receptor and thereby cause a gene to be turned on or off.