Chapter 12 Cell Bio
inability to import sugar into cell
A hungry yeast cell lands in a vat of grape juice and begins to feast on the sugars there, producing carbon dioxide and ethanol in the process: C6H12O6 + 2ADP + 2Pi + H+ → 2CO2 + 2CH3CH2OH + 2ATP + 2H2O Unfortunately, the grape juice is contaminated with proteases that attack some of the transport proteins in the yeast cell membrane, and the yeast cell dies. Which of the following could account for the yeast cell's demise?
negative to positive
During an action potential, the membrane potential changes from
concentration gradient
For an uncharged molecule, the direction of passive transport across a membrane is determined solely by
chemical to electrical
Ligand-gated ion channels in nerve cell membranes convert _____ to _______
postsynaptic
Many neurotransmitter receptors are ligand-gated ion channels that open transiently in the
ligand gated
Many receptors for neurotransmitters are _______ ion channels.
K+-coupled
Active transport requires the input of energy into a system so as to move solutes against their electrochemical and concentration gradients. What is not one of the common ways to perform active transport?
Cl-
Although the extracellular environment has a high sodium ion concentration and the intracellular environment has a high potassium ion concentration, both must be neutralized by negatively charged molecules. In the extracellular case, what is the principal anion?
in the muscles sarcoplasmic reticulum
Ca++ pump is found where
preventing Ca2+ from altering the activity of molecules in the cytosol
Ca2+ pumps in the plasma membrane and endoplasmic reticulum are important for _____________.
dendrites
Neurons chiefly receive signals at their highly branched
active transport
Pumps are transporters that are able to harness energy provided by other components in the cells to drive the movement of solutes across membranes, against their concentration gradient. This type of transport is called _____________.
action potential will be larger
Studies on the squid giant axon were instrumental in our current understanding of how action potentials are generated. You decide to do an experiment on the squid giant axon yourself. You add NaCl to the extracellular fluid and effectively double the amount of extracellular Na+ cation. How does this affect the action potential?
more negative
Studies on the squid giant axon were instrumental in our current understanding of how action potentials are generated. You decide to do an experiment on the squid giant axon yourself. You remove the cytoplasm in an axon and replace it with an artificial cytoplasm that contains twice the normal concentration of K+ by adding KOAc, where OAc- is an anion that is impermeable to the membrane. In this way you double the internal concentration of K+ while maintaining the bulk electrical balance of the cytoplasmic solution. Will this make the resting potential of the membrane more or less negative?
the action potential will be smaller
Studies on the squid giant axon were instrumental in our current understanding of how action potentials are generated. You decide to do an experiment on the squid giant axon yourself. You replace half of the NaCl in the extracellular fluid with choline chloride. (Choline is a monovalent cation much larger than Na+. Note that the presence of choline will not impede the flow of Na+ through its channels.) How will this affect the action potential?
The pump is phosphorylated
The Na+-K+ ATPase is also known as the Na+-K+ pump. It is responsible for maintaining the high extracellular sodium ion concentration and the high intracellular potassium ion concentration. What happens immediately after the pump hydrolyzes ATP?
-53.7 mV
The Nernst equation can be used to calculate the membrane potential based on the ratio of the outer and inner ion concentration. In a resting cell, membrane potential is calculated taking only K+ ions into account. What is V when Co = 15 mM and Ci = 106 mM?
ligand gated
The acetylcholine receptor in skeletal muscle cells is a(n) _______ ion channel.
electrochemical gradient
The net driving force for a charged molecule across a membrane therefore has two components and is referred to as the
acetylcholine
The stimulation of a motor neuron ultimately results in the release of a neurotransmitter at the synapse between the neuron and a muscle cell. What type of neurotransmitter is used at these neuromuscular junctions?
stress-gated
The stimulation of auditory nerves depends on the opening and closing of channels in the auditory hair cells. What type of gating mechanism do these cells use?
hydrophilic pathway through the membrane for specific polar solutes or inorganic ions
Transporter proteins and ion channels function in membrane transport by providing a _____
a gating mechanism
Transporters, in contrast to channels, work by ________________.
True
True or False: Cells expend energy in the form of ATP hydrolysis so as to maintain ion concentrations that differ from those found outside the cell.
False
True or False: Gap junctions are large pores that connect the cytosol to the extracellular space.
True
True or False: Most ion channels are gated, which allow them to open and close in response to a specific stimulus rather than allowing the constant, unregulated flow of ions.
True
True or False: Neurotransmitters are small molecules released into the synaptic cleft after the fusion of synaptic vesicles with the presynaptic membrane.
True
True or False: The Na+-K+ pump helps to keep both Na+ and Cl- ions out of the cell.
False
True or False: The differences in permeability between artificial lipid bilayers and cell membranes arise from variations in phospholipid content.
False
True or False: The ion selectivity of a channel completely depends solely on the charge of the amino acids lining the pore inside the channel.
False
True or False: The net negative charge on the cytosolic side of the membrane enhances the rate of glucose import into the cell by a uniporter.
False
True or False: Transporters are similar to channels, except that they are larger, allowing folded proteins as well as smaller organic molecules to pass through them.
True
True or False: Transporters undergo transitions between different conformations, depending on whether the substrate-binding pocket is empty or occupied.
False
True or false: Action potentials are usually mediated by voltage-gated Ca2+ channels.
True
True or false: CO2 and O2 are water-soluble molecules that diffuse freely across cell membranes.
False
True or false: Facilitated diffusion can be described as the favorable movement of one solute down its concentration gradient being coupled with the unfavorable movement of a second solute up its concentration gradient.
True
True or false: The electrochemical gradient for K+ across the plasma membrane is small. Therefore, any movement of K+ from the inside to the outside of the cell is driven solely by its concentration gradient.
False
True or false: Voltage-gated K+ channels also open immediately in response to local depolarization, reducing the magnitude of the action potential.
True
True or false: Voltage-gated Na+ channels become automatically inactivated shortly after opening, which ensures that the action potential cannot move backward along the axon.
some channels remain closed and some remain open
Voltage-gated channels contain charged protein domains, which are sensitive to changes in membrane potential. By responding to a threshold in the membrane potential, these voltage sensors trigger the opening of the channels. Which of the following best describes the behavior of a population of channels exposed to such a threshold?
glucose
We can test the relative permeability of a phospholipid bilayer by using a synthetic membrane that does not contain any protein components. Some uncharged, polar molecules are found to diffuse freely across these membranes, to varying degrees. Which has the lowest rate of diffusion across an artificial membrane?
It opens more frequently in response to a given stimulus.
What best describes the behavior of a gated channel?
voltage-gated Ca2+ channels
What is required for the secretion of neurotransmitters in response to an action potential?
action potential
What membrane characteristic or measurement used to study action potentials is indicated by the arrow?
effect of depolarizing stimulus
What membrane characteristic or measurement used to study action potentials is indicated by the arrow?
resting membrane potential
What membrane characteristic or measurement used to study action potentials is indicated by the arrow?
ethanol
What molecule is likely to diffuse through the lipid bilayer? Cl- or ethanol
O2
What molecule is likely to diffuse through the lipid bilayer? H2O or O2
benzene
What molecule is likely to diffuse through the lipid bilayer? benzene or amino acids
glycerol
What molecule is likely to diffuse through the lipid bilayer? glycerol or RNA
symport
When this transporter moves both ions in the same direction across the membrane, it is considered a(n)
temperature is 37 degrees, at rest the interior of the cell is more negatively charged on exterior and K+ is principal positive ion in cell
When using the Nernst equation to calculate membrane potential, we are making several assumptions about conditions in the cell. Name 3 things that are good assumptions
The plasma membrane is primarily permeable to Na+
When using the Nernst equation to calculate membrane potential, we are making several assumptions about conditions in the cell. Which of the following is not a good assumption?
Ca2+ pumps in the ER membrane keep cystosolic calcium levels low.
You have generated antibodies that recognize the extracellular domain of the Ca2+ pump. Adding these antibodies to animal cells blocks the active transport of Ca2+ from the cytosol into the extracellular environment. What do you expect to observe with respect to intracellular Ca2+?
stress gated
_______ ion channels are found in the hair cells of the mammalian cochlea.
voltage gated
_______ ion channels respond to changes in membrane potential.
transporter proteins
________ are highly selective in the solutes they transport, binding the solute at a specific site and changing its conformation so as to transport the solute across the membrane
ion channels
________ discriminate between solutes mainly on the basis of size and electrical charge.
passive transport
a molecule moves down its concentration gradient by ________
active transport
molecule requires _________ to move up its concentration gradient
synapses
neurons communicate with each other through specialized sites called
depolarization
the action potential is a wave of
presynaptic
to neurotransmitters released by the
less
wave is triggered by a local change in the membrane potential to a value that is _______ negative than the resting membrane potential
they keep the electrochemical gradient for K+ at zero
K+ leak channels are found in the plasma membrane. These channels open and close in an unregulated, random fashion. What do they accomplish in a resting cell?
False
Aquaporin channels are found in the plasma membrane, allowing the rapid passage of water molecules and small ions in and out of cells.
opening Cl- channels
Both excitatory and inhibitory neurons form junctions with muscles. By what mechanism do inhibitory neurotransmitters prevent the postsynaptic cell from firing an action potential?
It becomes more positive
If Na+ channels are opened in a cell that was previously at rest, how will the resting membrane potential be affected?
H+
Ion channels are classified as membrane transport proteins. Channels discriminate by size and charge. In addition to Na+, what ion would you expect to be able to freely diffuse through a Na+ channel?
Ca2+ channels
Neurotransmitter release is stimulated by the opening of voltage-gated _______ in the nerve terminal membrane.
voltage
The action potential is propagated by the opening of
axon
The action potential travels along the neuron's
membrane potential
charged molecule
use the movement of one solute down its gradient to provide energy to rive the uphill transport of a second gradient
coupled transporter proteins
antiport
if the ions move in opposite directions, the transporter is considered a(n)