Membranes and Transport pt 2. Transport- how things get through membranes Flashcards
What is simple diffusion?
gasses- CO2 and O2
lipid soluble molecules- steroid hormones and fatty acids maybe
What is facilitated diffusion?
Facilitate diffusion of polar or charged solutes down a concentration gradient: channels (ions) or carriers (larger molecules)
delta G is negative
no energy required
What is a channel?
proteins that form pores that allow small ions and polar molecules to pass, usually non-saturable
often regulated: ligand gated ion channels and voltage gated ion channels
What is a carrier?
another form of facilitated diffusion, usually saturable, allow passage of larger solutes; glucose, amino acids, lactate etc.
What do amphipathic helices form for glucose?
a polar pore which allows glucose to go through
How is glucose transport regulated?
rate of glucose transport is proportional to the number of glucose transporters in the membrane
What is active transport?
solutes transported against a concentration gradient, delta G is positive, energy is required, there is two types:
What are the two types of active transport?
Primary- energy released by ATP hydrolysis drives solute movement abasing an electrochemical gradient
Secondary- gradient of X established by primary transport, movement of X down concentration gradient provides energy for “uphill” transport of S
What is an example of primary active transport?
Na+-K+ ATPase
In most cells:
[K+] high [Na+] low, maintained by sodium pump, energy from ATP hydrolysis
Na+ out and K+ in
What is an example of secondary active transport?
active glucose transport:
What is receptor-mediated endocytosis?
certain molecules bind to specific receptors on the cell surface, receptors cluster and pinch off as vesicles, transport to lysosome for processing
ex: cholesterol and transferrin
What is the LDL receptor?
functions in cholesterol uptake in liver cells
intergal membrane protein
How does cholesterol enter cells?
receptor-mediated endocytosis
What is an aquaporin?
water is a highly polar solvent, needs aqauporins to get through membranes
found in all organisms
extremely high rates
highly specific- won’t transport H3O+
form small pores that allow water molecules to flow in single file
