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NadiaA

Transmembrane Transport
LO:
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Describe membrane protein and function e
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Facilitated diffusion
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Receptor-mediated uptake
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g
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g
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So it may have 75% proteins and 25% lipids
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Protein channels form the selective permeability characteristic of membranes
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g
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Mutation causes
dwarfism, achondroplasia
Phospholipase C- phosphatidyl inositol will be converted to head group and acyl chains
which are secondary messengers which will trigger other events

Channel proteins
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Selective- if the channel protein is negatively charged, it will only attract positively charged
ions and not negatively charged ions
It can be regulated, it opens and closes
It is a continuous pore that spans the membrane
Only works downhill- solute moves down its electrochemical gradient to reach equilibrium
Passive transport- doesn’t require ATP
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NadiaA
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Channel proteins facilitate a lot of bulk transport

Transporter protein
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Have a specific shape of binding site for a specific molecule
Undergoes a conformational change to allow the molecule through to the other side
Down concentration gradient to reach equilibrium
Low capacity- does not allow bulk transport of molecules, usually allows one or two
molecules at a time
Facilitated diffusion
Passive

Active transport (efflux transporter)
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High affinity solute binding site is exposed to cytosol
Solute binds
The solute binding causes ATP binding
Conformational change to allow solute to other side
Low affinity binding site is exposed to extracellular space
Against concentration gradient/electrochemical gradient
(diagram showing difference between passive and active transport)
ATP- primary active pump, the net efflux depends on ATP, ATP is the universal energy
currency

Electrochemical gradient
Only applies when there are charged solutes
(Notes referring to diagram)
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This is still an electrochemical gradient as the ion is charged- there is both a
concentration gradient and electrochemical gradient, it’s just that it is not working with or
against a membrane potential
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More energy for transport proteins to help in their function
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As long as an ion is involved, there is an electrochemical gradient
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youtube
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SGLT1 brings in glucose, and cotransports 2Na+
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It goes into the bloodstream
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ATP8B1- transports phosphatidyl serine
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ABCB11- transports bile salts
Know the process;
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Bile salts made from cholesterol
ABCB11 transports bile salt to canaliculus
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ABCB4 transports phosphatidyl choline
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Bile excreted into gut, emulsifies fat that we got from the diet
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Hepatic portal vein transports Bile salts back to hepatocyte, from enterocyte
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ASBT-secondary active symport
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NadiaA
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If ATP is being broken down, it is usually a primary active transporter
OST alpha beta- facilitated diffusion
NA+K+ ATPase- primary active ATPase you can identify it is primary as ATP is the source of
energy
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This
increases the risk of the patient suffering from coronary heart disease and atherosclerosis
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Drugs can treat this;
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Potentiators- effective against mutation at position 551
 Bind to transport protein (channel) to increase its ability to open
 Drug approved by the FDA

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