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31 Cards in this Set
- Front
- Back
list 4 main functions of plasma membrane
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communication, intercellular connection, physical barrier, selective permeability,
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which molecules cna readily diffuse across lipid bilayer?
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- small non polar molecules, oxygen, CO2, Nitrogen
- small uncharged molecules, water, ethanol, |
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list main ntracellular ions
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K = 140 mM
CL= 5mM Na = 10 mM Ca = 0.1 nM |
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list main exttra cellular ions
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Na = 145 mM
Cl = 125 mM K= 4mM Ca = 1.6mM |
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what is the difference between transporter and channel?
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Transporter has moving parts, transfers moleules from one side of the membrane to teh other by changing its shape
Channel forms hydrophilic pores in the membrane that allows passage of small molecules ( ions) |
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what is different name of passive transport ?
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facilitated diffusion
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describe passive transport
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molecules move down their concentration gradient from high to low,
does not require energy |
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describe active transport
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molecules move against their concentration gradient,
requires energy referred as pumps |
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describe two states of passive transporter
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state A - binding site for the solute are exposed to the outside membrane
state B - the binding sites are exposed to the inside of the membrane These transitions occur randomly and independent of whether solute is bound, |
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give example of passive transporter
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glucose uniporter GLUT
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what are 3 methods of active transport?
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coupled transport
ATP-driven pumps light -driven pumps |
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what is coupled transport?
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couples the transport of one molecule down its concentration gradient with the transport of another molecule up its concentration gradient
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describe ATP driven transport
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couples transport of molecules up
its concentration gradient with ATP hydrolysis |
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what are two types of coupled transport?
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symport and antiport
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give example of symporters
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SGLT1 in small intestine and
SGLT2 in proximal tubules of nephron couples transport of Na+ ions down its concentration gradient with transport of glucose against its concentration gradient |
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describe glucose absorption in the small intestine
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enterocytes have 2 different transporters
apical surface has sodium dependent glucose transporter and basal surface - has passive glucose transporter(uniporter) |
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give example of antiporters
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Na+Ca2+ Exchanger
found in plasma membrane helps regulate intracellular Ca level uses energy of the Na movement down its gradient to move Ca out of the cell against gradient |
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how the resting potential is maintained?
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due to Na-K pump found in plasma membrane of all cells
requires energy from ATP responsible for one third of cells energy expenditure and even 2/3 in neurons |
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how Na -K pump works?
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transport 3 Na out and 2 K in per cycle
maintains net negative charge near the inner side of the plasma membrane |
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what are the 2 mechanisms by which intracellular Ca concentration is kept low?
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1) sodium-calcium exchanger (NCX)
2) Ca pumps both are examples of active transport - NCX uses energy from electrochemical gradietns and Ca pump from ATP |
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what are characteristics of ion channels?
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- posses ion selectivity
- gated |
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what does it mean that channel is gated?
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normally closed but open for a brief time in response to a specific stimulus
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what are the types of gated channels?
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voltage gated
ligand gated stress gated |
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where can we find voltage-gated channels?
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neurons,
muscles egg cells |
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describe voltage gated channels
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opening of voltage gated ion channels is controled by membrane potential.
Changes above a certain threshold produce enough force to cause a conformation change in the channel resulting in opening it or closing |
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what is role of voltage gated Na channels?
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responsible for creation and propagation of action potential
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what is role of voltage gated Ca channels?
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muscle excitation and contraction
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what is role of voltage gated K channels?
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involved in repolarization following action potential
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describe ligand - gated channels
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opening of this channels is controlled by binding of molecule ( ligand) to the channel ( receptor)
The ligand binding site can face either the outside or the inside - they convert chemical signal into electrical signal |
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where can we find ligand gated channels?
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on the surface of some neurons and at the postsynaptic side of neuromuscular junction
- binds acetylcholine, and this opens the channel and allow for influx of Na and outflow of K along their electrochemical gradients |
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describe stress-gated channels
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auditory hair cells of the inner ear have projectionsc called sterocilia
- stress gated ion channels on one stereocilia are connected to those on adjacent stereocilia through a linking filament sound vibrations cause the basilar membrane to vibrate , the stereocila tilt , opening fo stress gated channels , causing ions to flow into the hair cells , this results in electrical signal that is transmitted to the auditory nerve |