Ch 12 How do membranes control chemical compositions of cells Flashcards
the epithelial cells that line the gut have glucose-Na+ symport proteins that actively take up glucose from the lumen of the gut after a meal, creating a high glucose concentration in the cytosol. How do these cells release that glucose for use by other tissues in the body?
the cell have glucose uniport in their plasma membrane
When the glucose-Na+ symport protein is in its outward-open state, which is more likely to occur?
Na+ binds to its binding site, bc concentrations are high outside the cell, Na+ readily binds to the transporter in its outward-open state.
apical plasma membrane of kidney and intestinal cells
Na+ gradient is the energy source
active import of glucose
Na+ driven symport protein are coupled transporters
to pass though the pore of an ion channel, what must be true of an ion?
they show ion selectivity and are not continuously open
it alters the probability that the channel will be found in its open conformation
the depolarization of the nerve terminal plasma membrane triggers the secretion of neurotransmitters by opening which of the following?
the resulting increase in Ca+ concentration in the cytosol triggers the fusion of vesicles with the plasma membrane, which releases neurotransmitters into the synaptic cleft
when transmitter-gated ion channels in the membrane of a postsynaptic cell open in response to neurotransmitter binding, what happens?
the channels open transiently in response to the binding of the neurotransmitter, thus changing the ion permeability of the postsynaptic membrane and in turn causing a change in the membrane potential; this encourages another action potential.
describes Lipid bilayers of cell membrane cells
highly permeable to small, non polar molecules such as O, C
highly impermeable to most large, water-soluble molecules and to all ions
transfer of nutrients, metabolites, and inorganic ions across cell membranes depends on
Membrane transport proteins
which of the following statements is correct? explain.
a. the plasma membrane is highly impermeable to all charged molecules
b. channels have specific binding pockets for the solute molecules they allow to pass
c. transporters allow solutes to cross a membrane at much faster rates than do channels
d. certain H+ pumps are fueled by light energy
e. the plasma membrane of many animals cells contain open K+ channels, yet the K+ concentration in the cytosol is much higher than outside the cell
f. a symport would function as an antiport if its orientation in the membrane were reversed
g. the membrane potential of an axon temporality becomes more negative when an action potential excites it.
D. is true. the bacteriorhodopsin of some photosynthetic bacteria pumps H+ out of the cell using energy captured from visible light
E. is true. most animal cells contain K+ leak channels in their plasma membrane that are predominately open. The K+ concentration inside the cell still remains higher than outside bc the membrane potential is negative and therefore inhibits the positively charged K+ from leaking out. K+ is also continually pumped into the cell by the Na+ pump.
list the following compounds if order of decreasing lipid bilayer permeability: RNA, Ca+, glucose, ethanol, N2, water
n2( small and nonpolar), ethanol (small and slightly polar), water (small polar), glucose (large and polar), Ca2+ (small and charged), RNA (very large and charged)
Name at least one similarity and at least one difference between the following
a. symport and antiport
b. active and passive transport
c. membrane potential and electrochemical gradients
d. pump and transporter
e. axon and telephone wire
f. solute and ion
A. Symport and anti port both couple the movement of two different solutes across a cell membrane.
symports transport both solutes in the same direction, whereas antiports transport the solutes in opposite directions.
B. Active and passive transport both are mediated by membrane transport proteins.
passive transport of a solute occurs downhill, in the direction of its concentration or electrochemical gradient, whereas active transport occurs uphill and therefore needs an energy source.
active transport can be medicated by transporters but not by channels, whereas passive transport can be mediated by either
C. Membrane potential and electrochemical gradients both terms describe gradients across a membrane.
D. a pump is a specialized transporter that uses energy to transport a solute uphill- against an electrochemical gradient for a charged solute or a concentration gradient for an uncharged solute.
E. Axon and telephone wire both transmit electrical signals by means of electrons in ire and by ion movements across the plasma membrane in axons.
F. Solute and ion both affect the osmotic pressure in a cell. an ion is a solute that bears a charge.
Name three ways in which an ion channel can be gated
ion channels can be ligand-gated, voltage-gated, or mechanically gated
Amino acids are taken up by animals using symport in the plasma membrane. what is the most likely ion whose electrochemical gradient drives the import? is ATP consumed in the process? if so, how?
animal cells drive most transport processes across the plasma membrane with the electrochemical gradient of Na+. ATP is needed to fuel the Na+ pump to maintain the Na+ gradient.
1.how do enzymes maximize the energy harvested from the oxidation of molecules?
enzymes allow cells to carry out the oxidation of sugars in a tightly controlled stepwise series of reactions. these reactions pay out energy in small packets to activated carriers, which allows cells to capture much of the energy released by the oxidative breakdown of glucose in the high-energy bonds of ATP and other activated carriers.
- which of the following generated the largest number of ATP molecules?
glycolysis
citric acid cycle
gluconeogenesis
electron transport chain
electron transport chain in the inner mitochondrial membrane generates a large amount of ATP from electrons donated by the active carries produced during glycolysis and the citric acid cycle.
- in step 6 of glycolysis, glyceraldehyde 3-phosphate, which has one phosphate group converted into 1,3-biphosphate, which has two. where does the extra phosphate group come from?
ATP
NADH
fructose 1,6-biphosphate
a free phosphate molecule
free phosphate molecule.
this is the only substrate level phosphorylation in glycolysis that creates a high energy phosphate linkage directly from a free phosphate
How would the dynamics of microtube polymerization change if cells were incubated with a nonhydrolyzable analog of GTP?
A. microtubules would polymerize and grow longer
B. Microtubules would depolymerize and shrink
C. Dynamic instability would increase as microtubules switch more frequently between growing and shrinking states.
D. Microtubules dynamics would not change
A. is correct the microtubules would have permanent GTP caps and would continue to grow and not shrink
