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During an action potential, which of the following actions DOES NOT help return a depolarized membrane to its resting membrane potential? (*when I ask a "does not" question, first make a list of all the things that DO help return a depolarized membrane to its resting membrane potential) The flow of K+ OUT of the cell The inactivation of voltage-gated Na+ channels The opening of voltage-gated K+ channels The opening of voltage-gated Na+ channels ---------CORRECT ANSWER----------------- The opening of voltage-gated Na+ channels Following excitation in a nerve membrane, the region goes through a brief period during which it cannot be stimulated again. What takes place during this period? the membrane potential remains unchanged ligands bind to voltage-gated Ca2+ channels voltage-gated Na+ channels in the nerve cell membrane are inactivated ligand-gated Na+ channels in the nerve cell membrane are inactivated --------- CORRECT ANSWER-----------------voltage-gated Na+ channels in the nerve cell membrane are inactivated
What is the role of the Na+-K+ pump in an action potential? After the action potential, the pump re-establishes the electrochemical gradients of ions Depolarization is caused by the flow of Na+ through the Na+-K+ pump Repolarization begins when Na+ flows through the Na+-K+ pump The Na+-K+ pump triggers the release of neurotransmitters The Na+-K+ pump is a voltage-gated channel that opens in response to a neurotransmitter ---------CORRECT ANSWER-----------------After the action potential, the pump re-establishes the electrochemical gradients of ions The creation of an action potential on the post synaptic cell is highly regulated. Often several different neurotransmitters are released in a synapse. A neurotransmitter that is referred to as "inhibitory" means: it is a chemical that blocks the binding of a ligand it is a ligand that makes it harder for a post synaptic neuron to reach action potential threshold it is a competitive inhibitor for excitatory ligand targets it stops an action potential from propagating in the pre-synaptic neuron --------- CORRECT ANSWER-----------------it is a ligand that makes it harder for a post synaptic neuron to reach action potential threshold Which of the following are true of inhibitory neurotransmitters? They make post-synaptic neuron depolarization LESS likely to happen They can lead to the entry of anions ( - ions) into cells
Opening the transmitter-gated ion channel changes the electrical potential of the membrane, which can result in depolarization The transmitter-gated ion channel releases vesicles that fuse with the presynaptic cell ---------CORRECT ANSWER-----------------Opening the transmitter-gated ion channel changes the electrical potential of the membrane, which can result in depolarization When a neuron is activated by a stimulus, the membrane potential of a portion of its plasma membrane will increase until it reaches a peak around +40 mV. What is special about this value? This value is the membrane potential at which the electrochemical gradient for K+ is zero. This value is the membrane potential at which the electrochemical gradient for Na+ is zero. The resting membrane potential will become permanently changed when the membrane potential reaches this value +40 mV is the threshold potential at which voltage-gated Na+ channels open ------ ---CORRECT ANSWER-----------------This value is the membrane potential at which the electrochemical gradient for Na+ is zero. Which of the following explains why Ouabain, a chemical derived from a plant found in some regions of the world, is capable of killing a massive mammal like a hippo? the molecule leads to an increase in extracellular sodium the molecule prevents heart muscle cells from maintaining the sodium gradient ouabain directly blocks the coupled pump for calcium
ouabain prevents facilitated diffusion of sodium up its gradient ---------CORRECT ANSWER-----------------the molecule prevents heart muscle cells from maintaining the sodium gradient Ion channels have different gating mechanisms. Which of the following is NOT an example of how these mechanisms work? voltage gated ion channels open in response to a change in water distribution across the membrane a mechanically gated potassium channel opens in response to physical stimulus ligand gated ion channels require the binding of a molecule that causes a conformation shift in the channel protein voltage gated ion channels can be affected by the concentration gradients of positive or negatively charged ions ---------CORRECT ANSWER-----------------voltage gated ion channels open in response to a change in water distribution across the membrane As long as a channel is open, it will allow selective diffusion of a particular solute DOWN its gradient. True False ---------CORRECT ANSWER-----------------true Most proteins that transport hydrophilic molecules across the membrane contain one alpha helix that crosses the plasma membrane a single time. True
Channels use the energy from ATP hydrolysis to move ions UP (against) their electrochemical gradient. True False ---------CORRECT ANSWER-----------------false The energy for secondary active transport is supplied by ATP phosphorylation of the coupled transporter An ATP hydrolysis reaction performed by the coupled transporter An electrochemical gradient of another ion Moving glucose from high to low concentration ---------CORRECT ANSWER----------- ------An electrochemical gradient of another ion True or False: In secondary active transport, solutes are transported across the membrane in tandem with another molecule, with both moving from lower concentration to higher concentration. True False ---------CORRECT ANSWER-----------------false Which statement about a cell's resting membrane potential is TRUE? (reminder: "resting" membrane potential is the overall charge difference between inside and outside the cell when the cell is at "rest" or in standard conditions)
The resting membrane potential for most animal cells is 0 mV, because the positive and negative ions are in balance The resting membrane potential for most animal cells is positive, because Na+ ions are so plentiful inside cells. The resting membrane potential for most animal cells is negative, because the inside of the cell is more negatively charged than the outside of the cell. At the resting membrane potential, no ions enter or exit the cell because they are at equilibrium. ---------CORRECT ANSWER-----------------The resting membrane potential for most animal cells is negative, because the inside of the cell is more negatively charged than the outside of the cell. Tight junctions found between the cells in our intestines PREVENT Small, non-polar molecules from using simple diffusion to cross the plasma membrane Membrane proteins from showing lateral movement through the entire plasma membrane of a cell The formation of a membrane domain The tethering of proteins in the membrane to proteins in the cytoskeleton The import of glucose into intestinal cells ---------CORRECT ANSWER----------------- Membrane proteins from showing lateral movement through the entire plasma membrane of a cell The voltage difference across a membrane is called: Depolarization The threshold potential
Which of the following is NOT a function of human plasma membrane proteins? Allow specific ions to cross the plasma membrane Serve as receptors to convey extracellular signals to the cell interior Catalyze the production of small molecules used for cell signaling Generate energy required for lipids to diffuse through the membrane --------- CORRECT ANSWER-----------------Generate energy required for lipids to diffuse through the membrane The fluidity of the plasma membrane depends upon which phospholipids it contains. You've learned that phospholipids with unsaturated hydrocarbon tails contain ____________. Lipid bilayers with a large proportion of unsaturated tails are ________. Double bonds between adjacent carbon atoms; MORE fluid Double bonds between adjacent carbon atoms; LESS fluid Only single bonds between adjacent carbon atoms; MORE fluid Only single bonds between adjacent carbon atoms; LESS fluid ---------CORRECT ANSWER-----------------Double bonds between adjacent carbon atoms; MORE fluid In eukaryotic cells, new phospholipids are made by enzymes found _________________. on the cytosolic side of the ER membrane within the lumen (interior) of the ER
on the cytosolic side of the golgi membrane on the cytosolic side of the plasma membrane on the extracellular side of the plasma membrane ---------CORRECT ANSWER-------- ---------on the cytosolic side of the ER membrane How does cholesterol affect the lipid bilayer of animal cells? Cholesterol makes the bilayer less amphipathic Cholesterol makes the bilayer more hydrophilic Cholesterol makes the lipid bilayer more permeable to small, polar molecules Cholesterol makes the lipid bilayer more fluid Cholesterol makes the lipid bilayer less fluid ---------CORRECT ANSWER----------------
- Cholesterol makes the lipid bilayer less fluid A bacterium leaves a human host and is deposited into the cold external world. Which of the following would allow the bacterium to maintain a constant level of membrane fluidity when introduced into the cold environment? Decrease the amount of glycolipids in the membrane Produce phospholipids that have longer fatty acid tails Produce phospholipids that have shorter fatty acid tails Produce phospholipids that are more saturated and therefore more hydrophobic - --------CORRECT ANSWER-----------------Produce phospholipids that have shorter fatty acid tails
Within the Golgi, sugars are added to some phospholipids Which of the following statements describe the phospholipids found in the plasma membrane? Select all that are true. Each phospholipid contains three fatty acid tails Portions of these molecule are hydrophilic, while other portions contain nonpolar covalent bonds Their fatty acid tails interact with each other through a large network of hydrogen bonds The hydrocarbon tails of the phosopholipids form alpha helical structures Different phospholipids can very in the length of their hydrocarbon tails --------- CORRECT ANSWER-----------------Portions of these molecule are hydrophilic, while other portions contain nonpolar covalent bonds Different phospholipids can very in the length of their hydrocarbon tails What is the role of carbohydrates in the plasma membrane? Sugars increase hydrophobic interactions between phosopholipids Attachment of sugars to lipids and proteins affects cell-cell interactions Sugars fill in the gaps within the interior of the lipid bilayer Sugars make up a large structural support network on the cytosolic side of the membrane Sugars are the major factor in influencing the fluidity of the lipid bilayer --------- CORRECT ANSWER-----------------Attachment of sugars to lipids and proteins affects cell-cell interactions
Lipids in a lipid bilayer rapidly exchange positions with one another in their own monolayer. True False ---------CORRECT ANSWER-----------------true Many transmembrane proteins contain a single alpha helix. What chemical properties of an alpha helix are important for its interaction with membrane phospholipids? All covalent bonds in the alpha helix are nonpolar, which allows the helix to interact with the hydrophobic fatty acid tails The backbone of every polypeptide is hydrophobic, which means that an alpha helix can interact with the hydrophobic fatty acid tails Amino acids within an alpha helix can have hydrophobic side chains that interact with the hydrophobic fatty acid tails An attraction occurs between the positively charged alpha helix and the negatively charged phospholipids ---------CORRECT ANSWER-----------------Amino acids within an alpha helix can have hydrophobic side chains that interact with the hydrophobic fatty acid tails Select all of the following options that would give you the MOST fluid membrane: 26 hydrocarbon phospholipid tail 14 hydrocarbon phospholipid tail saturated tails
If the sodium potassium pump stopped function in the intestinal cells, which of the following would occur? The sodium gradient would reach an equilibrium with the intestinal lumen the sodium inside the cell would decrease in concentration glucose symport from the intestinal lumen would stop the high glucose gradient in the cell would decrease ---------CORRECT ANSWER----- ------------The sodium gradient would reach an equilibrium with the intestinal lumen glucose symport from the intestinal lumen would stop the high glucose gradient in the cell would decrease Ion channels have different gating mechanisms. Which of the following is NOT an example of how these mechanisms work? voltage gated ion channels open in response to a change in water distribution across the membrane a mechanically gated potassium channel opens in response to physical stimulus ligand gated ion channels require the binding of a molecule that causes a conformation shift in the channel protein voltage gated ion channels can be affected by the concentration gradients of positive or negatively charged ions ---------CORRECT ANSWER-----------------voltage gated ion channels open in response to a change in water distribution across the membrane
Imagine that the opening of voltage-gated Na+ channels in a neuron's membrane is blocked by a toxin. Which step of the action potential will be blocked first when this toxin is applied? The entry of K+ ions into cells The threshold will not be reached The release of synaptic vesicles by the pre-synaptic cell The opening of voltage-gated Ca2+ channels The repolarization of the cell ---------CORRECT ANSWER-----------------The threshold will not be reached The direction and rate at which Na+, Cl-, K+ and other ions cross the membrane through a channel is determined by: (select all that apply) The concentration gradient The membrane potential The molecule's binding pocket The molecule's size ---------CORRECT ANSWER-----------------The concentration gradient The membrane potential The propagation of an action potential is due to many sodium ions diffusing through the cytosol of the nerve axon to the axon terminal. True False ---------CORRECT ANSWER-----------------false
The signal sequence of the protein would NOT be removed inside the mitochondria ---------CORRECT ANSWER-----------------The signal sequence of the protein would NOT be removed inside the mitochondria How is the transport of proteins into mitochondria different from the transport of proteins into the nucleus? Mitochondrial proteins are transported through the mitochondrial membrane while fully folded Mitochondrial proteins must cross two translocator proteins Mitochondrial proteins do not require a signal sequence Mitochondrial proteins must cross two membranes, while nuclear proteins only cross one Mitochondrial proteins require ER-bound ribosomes for translation --------- CORRECT ANSWER-----------------Mitochondrial proteins must cross two translocator proteins Proteins that lack a sorting signal remain as permanent residents of which part of a eukaryotic cell? The Golgi The smooth ER None of these: The protein would be secreted from the cell The cytosol The lysosome ---------CORRECT ANSWER-----------------The cytosol
True or False: Proteins are imported into mitochondria while translation is in progress. True False ---------CORRECT ANSWER-----------------false Which organelle cannot receive proteins directly from the cytosol? Endoplasmic reticulum Nucleus Mitochondria The Golgi ---------CORRECT ANSWER-----------------The Golgi Which of the following is NOT a step in the import of a protein into the nucleus? The protein travels in a vesicle from the ER to the Golgi A protein is bound by a nuclear import receptor The amino acid sequence of a protein contains a nuclear localization signal The protein must cross through the gel-like center of the nuclear pore --------- CORRECT ANSWER-----------------The protein travels in a vesicle from the ER to the Golgi What is the function of the signal-recognition particle (SRP) in protein sorting? SRP cleaves the ER signal sequence from the polypeptide chain
