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Ch. 5

Molecular Biology

QuestionAnswer
cellular membranes are fluid mosaics of _____ & _______. lipids, proteins
In the fluid mosaic model ______ proteins are embedded in the phospholipid bilayer. amphipathic
phospholipids and some ______ move laterally within the membrane. the unsaturated hydrocarbon tails of some phospholipids keep membranes fluid at lower temps. while ______ helps membranes resist changes in fluidity caused by temperature changes. proteins, cholesterol
what is the role of phospholipids in the structure and function of biological membranes? phospholipids form a selectively permeable structure
why is the plasma membrane referred to as the "fluid mosaic"? The fluid aspect of the membrane is due to the lateral and rotational movement of phospholipids, and embedded proteins account for the mosaic aspect.
which cell structure exhibits selective permeability between a cell and its external environment? the plasma membrane
Consider the currently accepted fluid mosaic of the plasma membrane. Where in the plasma membrane would cholesterol be found? in the interior of the membrane
which functional processes are a result of the consequence of the association of proteins with biological membranes? enzymatic activity, cell-cell recognition, intercellular joining, & cell to cell communication
Carbohydrates associate with the plasma membrane in what way? membrane carbohydrates function primarily in cell to cell recognition.
Consider the currently accepted fluid mosaic of the plasma membrane. Where in the plasma membrane would carbohydrates be found? on the outside (external) surface of the membrane
which molecule is most likely to passively diffuse across the plasma membrane? carbon dioxide
which molecule would be least likely to diffuse through a plasma membrane without the help of a transport protein? a large polar molecule
what is passive transport? it permits the solute to move in either direction, but the net movement of the population of solute occurs down the concentration gradient of the molecule.
cells A & B are the same size, shape, & temperature, but cell A is metabolically less active than cell B; cell B is actively converting oxygen to water in cellular respiration. Oxygen will diffuse more rapidly into cell ____ because____. b; the diffusion gradient in cell B is steeper.
true or false? Diffusion is a passive process. True
the internal solute concentration of a plant cell is about 0.8M. To demonstrate plasmolysis, it would be necessary to suspend the cell in what solution? 1.0M
A single plant cell is placed in an isotonic solution. Salt is then added to the solution. Which of the following would occur as a result of the salt addition? water would leave the cell by osmosis, causing the volume of the cytoplasm to decrease.
True or false? Facilitated diffusion of solutes may occur through channel or transport proteins in the membrane. True
True or false? Facilitated diffusion requires the hydrolysis of ATP. False
The concentration of solutes in a red blood cell is about 2%, but RBCs contain almost no sucrose or urea. Sucrose can't pass through the membrane, but water and urea can. Osmosis would cause RBCs to shrink the most when immersed in which solution? a hypotonic solution
green olives may be preserved in a brine, which is 30% salt solution. How does this method of preservation prevent microorganisms from growing in the olives? a 30% salt solution is hypertonic to the bacteria, so they lose too much water and plasmolyze.
true or false? active transport requires an input of energy and can also generate voltages across a membrane due to the sodium/potassium pump hydrolyzing ATP & resulting in a net charge of +1 outside the cell membrane. True
what is the difference between active transport and facilitated diffusion? Activbe transport requires energy from ATP and facilitated diffusion does not.
describe a general property of all electrogenic pumps They create a voltage difference across the membrane
a cell has a membrane potential of -100mV and has 1,000 times more calcium ions outside than inside. describe a mechanism by which Ca2+ enters the cell. facilitated diffusion of Ca2+ into the cell down its electrochemical gradient.
true or false? Cotransport proteins allow a single ATP-powered pump to drive the active transport of many different solutes. True
What enables a cell to pick up & concentrate a specific kind of molecule? Receptor-mediated endocytosis
which process & organelles accounts for the replacement of lipids & proteins lost form the plasma membrane? exocytosis and smooth and rough ER
true of false? In mother's milk, molecules enter the cells lining the baby's digestive tract via endocytosis True
What is the primary function of the membrane transport process? Pinocytosis....the uptake of water and small solutes into the cell by formation of vesicles at the plasma membrane.
When a platelet contacts a damaged blood vessel, it is stimulated to release thromboxane A2. Thromboxane A2 in turn stimulates vascular spasm & attracts additional platelets to the injured site. In this example thromboxane A2 is acting as a ___. local regulator
Early work on signal transduction and glycogen metabolism by Sutherland indicated that ____. the signal molecule did not interact directly with the cytosolic enzyme, but required and intact plasma membrane before the enzyme could be activated.
Testosterone and estrogen are lipid-soluble signal molecules that cross the plasma membrane by simple diffusion. If these molecules can enter all cells, why do only specific cells respond to their presence? Nontarget cells lack the intracellular receptors that, when activated by the signal molecule, can interact with genes in the cells's nucleus.
Steroid hormones can enter a cell by a simple diffusion. Therefore steroids____. do not initiate cell signaling by interacting with a receptor in the plasma membrane.
True or false? Steroid hormones can enter a cell by simple diffusion. Therefore steroids move through a channel, down a gradient, and are nonpolar. False
Receptors for signal molecules ______. may be found embedded in the plasma membrane, or found within the cytoplasm or nucleus.
Testosterone does not affect all cells of the body because _____. Not all cells have cytoplasmic receptors for testosterone.
Nitric oxide is unusual among animal signal molecules in that it ____. is a gas
A G protein is active when _____. GTP is bound to it
What event would activate a G protein? Replacement of GDP with GTP
Ras, a small G protein located at the plasma membrane, is often mutated in different types of cancer.Ras normally signals to a cell that it should divide.Cancer cells divide uncontrollably. what change to Ras would you expect? a mutation that means Ras cannot hydrolyze GTP to GDP
The cellular response of a signal pathway that terminates at a transcription factor would be ____. the synthesis of mRNA
What did Sutherland discover about glycogen metabolism in liver cells? the hormone epinephrine binds to specific receptor on the plasma membrane of the liver cell.
True or false? Sutherland discovered that glucose is produced from glycogen when epinephrine binds to a cytoplasmic protein. False
the general name for an enzyme that transfers phosphate groups from ATP to a protein is _________. protein kinase
ATP gammaS is a form of ATP that can't be hydrolyzed by enzymes. If this compound was introduced to cells so that it replaced the normal ATP present in the cell, what would you predict? A decrease in phosphorylated proteins in the cell
phosphorylation can _____________________________. either activate or inactivate a protein
the source of phosphate for a phosphorylation cascade is _____. ATP
second messengers tend to be water-soluble and small. this accounts for their ability to _______. rapidly move throughout the cell by diffusion.
cAMP usually directly activates ________. protein kinase A
A mutation in the active site of adenylyl cyclase that inactivates it would most likely lead to ______. Lower activity of protein kinase A.
In eukaryotic cells, name a second messenger that is produced as a response to an external signal such as a hormone? cyclic AMP
T or F? Parts of proteins that are exposed to the cytoplasmic side of the ER are also exposed to the cytoplasmic side of the plasma membrane. True
In the plasma membrane, the asymmetrical distribution of membrane proteins, lipids, & carbohydrates across the plasma membrane are determined as the _____ __ ____ _____. membrane is being constructed.
T or F? In a plasma membrane, the 2 lipid layers may differ in specific lipid composition True
T or F? not every membrane protein has a specific orientation In the plasma membrane. False
membrane structure results in _______ _______. selective permeability
______ ________ is diffusion of a substance across a membrane with no energy investment. passive transport
____ ______ uses energy to move solutes against their gradients. active transport
Bulk transport across the plasma membrane occurs by _____ and ______. exocytosis, endocytosis
the plasma membrane plays a key role in most ___ ____. cell signaling
amphipathic a molecule containing both a hydrophobic and hydrophilic region.
T or F? Unsaturated hydrocarbon tails (kinked) prevent packing. enhancing membrane fluidity. True
member protein functions transport, enzymatic activity, attachment to the cytoskeleton & extracellular matrix, cell-cell recognition, intercellular joining, & signal transduction
proteins that penetrate the hydrophobic interior of the lipid bilayer integral proteins
proteins that are loosely bound to the surface of the membrane. peripheral protein
a lipid with one or more covalently attached carbohydrate glycolipid
a protein with one or more covalently attached carbohydrate glycoprotein
the 4 human blood types, A, B, AB, O reflect variation in the carbohydrate part of _______ on the surface of red blood cells. glycoproteins
inorganic ions sodium (Na+), potassium (K+), calcium (Ca2+), chloride (CI-)
nonpolar molecules that are hydrophobic and can dissolve in the lipid bilayer of the membrane and cross it easily, without the aid of member proteins. hydrocarbons, carbon dioxide, and oxygen
2 molecules that can cross a lipid bilayer without help form membrane proteins are O2 and CO2. what property allows this to occur? O2 and CO2 are both small nonpolar molecules that can easily pass through the hydrophobic interior of a membrane.
why is a transport protein needed to move water molecules rapidly and in large quantities across a membrane? water is a polar molecule, so it can't pass very rapidly through the hydrophobic region in the middle of the phospholipid bilayer.
aquaporin a channel protein in the plasma membrane of a plant, animal, or microorganism cell that specifically facilitates osmosis.
osmosis the diffusion of free water across the membrane
____ is the movement of particles of any substance so that they tend to spread out into the available space. diffusion
T or F? Diffusion is a spontaneous process, needing no input of energy. True
what does "ISO" mean? same
what does "hyper" mean? more
what does "hypo" mean? less
the control of solute concentrations and water balance is called _____. osmoregulation
How do you think a cell performing cellular respiration rids itself of the resulting CO2? CO2 is a nonpolar molecule that can diffuse through the plasma membrane. as long as it diffuses away so that the concentration remains low outside the cell, other CO2 molecules will continue to exit the cell in this way.
in the supermarket, produce is often sprayed with water. why does this make the vegetables look crisp? the water is hypotonic to the plant cells, so the plant cells take up water. Thus, the cells of the vegetables remain turgid, and the vegetable remains crisp and does not wilt.
2 forces that drive diffusion of ions across a membrane; a chemical force (the ion's concentration gradient) & an electrical force (the effect of the membrane potential on the ion's movement). this combination of forces acting on an ion is called _ __. electrochemical gradient
The Sodium-potassium pump appears to be a major ____ pump of animal cells. electrogenic
The main electrogenic pump of plants, fungi, & bacteria is a ___ pump, which actively transports protons (hydrogen ions, H+) out of the cell. proton
a single ATP-powered pump that transports a specific solute can indirectly drive the active transport of several other solutes in a mechanism called ______. cotransport
Sodium-potassium pumps help nerve cells establish a voltage across their plasma membranes. Do these pumps use ATP or produce ATP? The pump uses ATP. To establish voltage, ions have to be pumped against their gradients, which requires energy.
Explain why the sodium-potassium pump would not be considered a cotransporter. each ion is being transported against its electrochemical gradient. If either ion were transported down its electrochemical gradient, the process would be considered cotransport.
the cell secretes certain biological molecules by the fusion of vesicles with the plasma membrane; a process called ____. exocytosis
T or F? Although the proteins involved in exocytosis and endocytosis are different, the events of endocytosis look like the reverse of exocytosis. True
name 3 types of endocytosis phagocytosis ("cellular eating"), pinocytosis ("cellular drinking"), and receptor-mediated endocytosis.
as a cell grows, its plasma membrane expands. Does this involve endocytosis or exocytosis? Exocytosis. when a transport vesicle fuses with the plasma membrane, the vesicle membrane becomes part of the plasma membrane.
We learned that animal cells make an extracellular matric (ECM) . describe the cellular pathway of synthesis & deposition of an ECM glycoprotein. the glycoprotein would be synthesized in the ER lumen, move through the Golgi apparatus, & then travel in a vesicle to the plasma membrane, where it would undergo exocytosis and become part of the ECM.
T or F? Both animals and plants use chemicals called hormones for long distance signaling. True
the 3 stages of cell signaling reception, transduction, & response
2 types of local signaling Paracrine signaling, synaptic signaling
Long distance signaling where specialized endocrine cells secrete hormones into body fluids, often blood. Hormones reach virtually all body cells, but are bound only by some cells is called ______ ________. Endocrine signaling
______ is the binding of a signaling protein molecule to a receptor protein. reception
an enzyme that tranfers phosphate groups from ATP to a protein is known as a _____ _____. protein kinase
______ is the regulation of transcription or cytoplasmic activities response
in cell signaling, small molecules and ions are _____ ____. second messengers
how do nerve cells provide examples of both local and long-distance signaling? the secretion of neurotransmitter molecules at a synapse is an example of local. the electrical signal that travels along a very long nerve cell and is passed to the next nerve cell can be considered an example of long-distance.
when a signal transduction pathway involves a phosphorylation cascade, what turns off the cell's response? protein phosphatases reverse the effects of the kinases.
in what way do the membranes of a eukaryotic cell vary? certain proteins are unique to each kind of membrane.
what factors would tend to increase membrane fluidity? a greater proportion of unsaturated phospholipids
phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because they amplify the original signal manifold.
lipid-soluble signaling molecules, such as testosterone, cross the membranes of all cells but affect only target cells because intracellular receptors are present only in target cells
which process includes all of the following: osmosis, diffusion of a solute across a membrane, facilitated diffusion, transport of an ion down its electrochemical gradient passive transport
Created by: KellyClark