Week 4 Flashcards
Why is cholesterol important in a cell?
Cholesterol is important for merane integrity
Cholesterol sits next to an unsaturate fatty acid
A source for the production of hormones, bile acids and vitamin D
How does fluidity effect a membrane?
Fluidity-Flexibilty maintained so that the membrane can fucniton properly
What happens if a membrane is too fluid?
The membrane will be leaky
What happens is a membrane is not fluid enough?
No movement or solute passage
What effect does heat have on a membrane?
HEAT = lipids move more, arranging/rearranging; more fluid membrane
How does cold effect membrane fluidity?
COLD = lipids laterally orders.organisaes, lipid chains pack togehter tightly
What other factors effect a memrbanes fluidity?
- Fatty acid length
- Long= stiff
- Short = less stiff
- Double bonds
- Satureated = more stiff
- Unsaturated = less stiff
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How does cholesterol dampen the effect of temperature?
- Cholesterol and heat = stabilizes the membrane and raises its melting point
- Cholestoer and cold = intercolated between phospholopids; prevents clusterind and stiffening
What are teh different types of membrane transport?
- Dissusion
- Facilitated diffusion
- Active transport
- Secondary active transport
What are the two different types of diffusion? And waht are their differences?
- Simple diffusion through the phopholipid bilayer
- E.g. O2 and CO2 and lipid-soluble substances cross membrane by simple diffusion
- Molecules move b engaging in random collisions with other like molecules
- From high conc to low conc - Factilitated diffusion through channel porteins or carrier proteins
- Facilitated diffusion requires teh transported molecuels to bind to a specific carrier protein
- Energy is not required
How can water pass through into and out of a cells?
Aquaporins
- Aquaporins are channel proteins
- Water molecules move in a single file through a hydrophilic cahnnel
- Water passively pours through aquaporins by osmosis, moving from low to high concentrations
- This is facilitated diffusion (part of passive)
What are symporters and antiporters?
They are ‘coupled transporters’ because tehy move two substances at once
Symporters = simultaneously transport a sugar (or amino acid) and an ion (usually Na+ of H+ ion) across a membrane. E.g.Na+/glucose symporter: couples transmembrane movement of 1 glucose molecule to teh transport of 2 Na+ ions.
Antiporters = Transport one solute in one direction while transporting a second solute in the opposite direction. Exchange of one solute for another, and one is expelled at the expense of the import of one. E.g. Na+/Ca+ antiporter.
What is active transport? And what are the different types and example?
Transporters that use energy.
- Energy concentrates the compound on one sidde of the membrane
1. [rimary active transport = energy applied to teh transporter (e.g. ATP hydrolysis by Na, K-ATPase; and Ca2+-ATPase) ATPase is an enzyme that catalyze hydrolysis of ATP to yield ADP and inorganic phosphate with release of free energy
2. Secondary active transport = energy establishes ion gradient (e.g. teh Na+ gradient), ad the gradient is used to concentrate another compound
How does the Sodium/potassium ATPase (Na/K-ATPase) pump work?
Energy from ATP hydrolysis phosphorylates an internal domaina nd cahnge the transporter’s conformation.
Na+ are released to the outsie, and two external K+ bind adn trigger hydrolysis of the bound phosphate group and a reture to teh original conforation, accompanied by release of K + inside the cell.
Cells can maintain a much lower intracellular [Na+] anc much higher intracellular [K+] than present in serum.
How does secondary active transport work?
A sodium symporter brings molecules into cells
Sodium moves down its gradient and this drives teh uphill transport of a cotransporter substrate (glucose)
Does not hydrolyze ATP but depends on maintenace of the sodium gradient by the sodium/potassium pump.