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BIL 255 EXAM 3 QUESTIONS AND VERIFIED ANSWERS
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BIL 255 EXAM 3 QUESTIONS AND VERIFIED ANSWERS....
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Every membrane has different _____________. - ANSWER transportersMembrane Transport Proteins Types - ANSWER • *Transporters* (moving
parts)- change their shape to allow molecules to pass though
through
• *Channels* (hydrophilic pores)- do not change their shape, are little holes in
the membrane
What would a membrane without proteins be able to pass through? - ANSWER
*Small nonpolar molecules* could pass through relatively easily, then *small
uncharged polar molecules* to *larger uncharged polar molecules*, and *ions*
cannot pass through at all
Ion concentrations inside the cell are the same as those outside. (True/False) -
ANSWER False, they are different. Membranes can selectively accept ions.
The pH of the cell is slightly acidic (more H+ protons). There are more Na+
outside cells and more K+ in cells.
Does ion diffusion occur with cell membranes? - ANSWER No, membranes
are impermeable to ions by themselves.
Membrane potential - ANSWER • The voltage across a cell's plasma
membrane. The high concentration of positive sodium outside of the cell is
balanced by the positive charge of potassium inside. And then those positive
charges are balanced by negatively charged molecules on their sides, for
instance the large amount of K+ is balanced by the negatively charged DNA,
while Cl- balances the Na+ outside. So the charges are *counterbalanced*
• Despite this, there is still a slight positive charge outside the cell and slightly
negative inside.
•The voltage across a cell's plasma membrane; can either be in *resting
potential* or *action potential*
Channels - ANSWER •Regulate water flow and solutes through membrane
,•Do not change their conformation
•*Passive transport*
•They are highly selective and only allow one type of molecule to go through
(ex. aquaporins have channels the size of a single water molecule and have an
aspargine which prevents other protons from getting in)
Transporter - ANSWER •Specifically bind to a substrate and *change
conformation* to allow transport (can be passive transport)
•*Pump* is a type of transporter (active transport)
Pump - ANSWER •A *type of transporter* (since they bind to a substrate) that
requires energy
•*Active transport*
•Can use light or ATP as a source of energy
Active transport - ANSWER •Energy-requiring process that moves material
across a cell membrane *against a concentration* difference
•Pumps use active transports, they can be gradient-driven, ATP-driven, or light-
driven
Passive transport - ANSWER •The movement of materials through a cell
membrane *without* using *energy*
•Electrochemical gradient when voltage and concentration gradients work in the
same direction
•Can be channel-mediated or transporter-mediated (*facilitated diffusion*)
Electrochemical gradient - ANSWER •The diffusion gradient of an ion,
representing a type of potential energy that accounts for both the concentration
difference of the ion across a membrane and its tendency to move relative to the
membrane potential.
•An ion is driven by *BOTH* the concentration gradient and the charge (ex. a
proton will be be attracted to a negative charge and to the area with less
protons)
•Both forces can also counteract each other and lead to reduced movement (ex.
K+ would want to diffuse to the outside since it has a lower concentration in
that area, but the positive charge that is outside will reduce this movement)
,Sodium Potassium Pump (Active Transport) - ANSWER •A transport protein
in the plasma membrane of animal cells that actively transports sodium out of
the cell and potassium into the cell
•Against the gradient since there is more sodium outside the cell, and the pump
transports even more (same thing for potassium, but for the inside of the cells)
•Steps: Na+ first binds to the pump, the the pump phosphorylates itself by
hydrolyzing ATP. This triggers a conformation change where Na+ is released to
the outside and now K+ can fit. It then dephosphorylates itself and the K+ is
released into the inside of the cell.
•The actual stoichiometry is *3 Na+ outside for every 2 K+* inside for every
ATP
•It *used to maintain osmotic pressure*
•It establishes a membrane potential and creates a very steep sodium
concentration gradient, which provides energy to other pumps (coupled
transport)
What three things does the Na+-K+ pump do? - ANSWER *1.* Establishes
membrane potential
*2.* Maintains osmotic balance
*3.* Creates a very steep sodium concentration gradient, which provides energy
to other pumps (coupled transport)
Coupled transport - ANSWER •The movement of a substance against its
electrochemical gradient (from lower to higher concentration, or from opposite
charge to like charge) using the energy provided by the simultaneous movement
of a different chemical down its electrochemical gradient
•Usually coupled with Na+ since it traveling back into the cell follows both it's
electrical and concentration gradient (highly spontaneous)
•There is a *symport* (require energy), *antiport* (require energy), and a
*uniport* (don't require energy)
Symport - ANSWER •A membrane transport process that carries *two
substances in the same direction* across the membrane.
•Is a pump (active transport)
Antiport - ANSWER •A membrane transport process that *carries one
substance in one direction and another in the opposite direction*.
•Is a pump (active transport)
, Uniport - ANSWER •A membrane transport process that carries a *single
substance.*
•A type of passive transport and is NOT a pump
Transport of glucose across gut epithelia. - ANSWER •A type of coupled
transport that is unidirectional
•The glucose concentrations is much higher inside the cell, so glucose is
coupled with Na+ going back inside the cell and ultimately travels against its
gradient (*symport*)
•The reaction is rarely reversible, since there is less Na+ in the cell that can
coupled with glucose to go outside the cell
Bacteriorhodospin - ANSWER •Pigmented protein found in abundance in the
plasma membrane of the salt-loving archaeon Halobacterium halobium
•Pumps protons out of the cell in response to light.
•Light activates retinol that is inside the protein which then triggers a bunch of
conformational changes which leads to H+ being pumped outside of the cell for
every photon
Channels are ion-selective and gated: - ANSWER •*Ion selective*: let some
ions pass but not others (ex. aquaporin being a small size)
•*Gated*: can switch between open and closed states
-Can react to stimuli very quickly and lead to an influx of ions at opening
Patch-Clamp recording - ANSWER •Technique used to monitor the activity of
ion channels in a membrane; involves the formation of a tight seal between the
tip of a glass electrode and a small region of cell membrane, and manipulation
of the membrane potential by varying the concentrations of ions in the electrode
(measure the flow of the current to determine when the ion channels are open or
close).
What types of stimuli can cause the gates on ion channels to open or close? -
ANSWER •*Voltage-gated*- voltage changes during membrane potentials can
open or close channels (ex. depolarization)
•*Ligand-gated* (extracellular ligand)- when bound to specific ligand, a
channel opens or closes (signal molecule)
•*Ligand-gated* (intracellular ligand)
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