Membrane Transport Flashcards
Define Uniport
Carrier transports only one substance
Ex: facilitated transport/carrier-mediated diffusion of glucose (GLUT 1)
Define Symport
Two or more substances transported in same direction. Also called co-transport.
- Secondary active transport
Define Antiport
Two or more transported substances move in opposite directions through membrane. Also called exchange transport or countertransport
- secondary active transport
Describe factors affecting rate of simple diffusion
- Lipid solubility = increased lipid solubility; increased permeability
- Molecular size = Decrease in size; increase in diffusion
- Cell Membrane thickness = decrease in thickness; increase in diffusion
- Conc gradient = greater difference; the faster diffusion
- Membrane surface area = greater surface area; greater diffusion
- composition of lipid bilayer
Describe factors affecting rate of diffusion through channels
Permeability: # of channels, percentage of open channels
Selectivity: structure of channel and distribution of charges
Concentration gradient: electrochemical conc gradient in case of ions.
Describe Osmosis
Example of diffusion through channel.
- water goes from area of high conc to low conc.
- rate is affected by the # of aquaporins in the membrane (can be regulated by insertion or remobal of aquaporins)
Define Nephrogenic diabetes insipidus
Caused by a mutation in aquaporins causing lack of water channels in membrane.
- results in production of large amounts of dilute urine and excess thirst
- Unable to reabsorb enough water for kidney collecting ducts.
Describe the factors affecting the rate of transport of GLUT 1
- Glucose conc. gradient: After glucose is transported into the cell, it is rapidly phosphorylated forming glucose-6-phosphate.
- Glucose transporter #: Insulin incrases the number of glucose transport proteins in cell membrane
- Affinity of glucose binding to transporter: smaller Km, higher affinity, higher rate of glucose transport.
Define Diabetes mellitus type I
- immune mediated destruction of the Beta cells that produce insulin.
- lack of insulin causes decreased numbers of glucose channels and hyperglycemia since they cannot use glucose quickly enough to prevent its buildup in the blood.
Describe key features of facilitate diffusion/uniport
- rate of substrate movement is far higher than simple diffusion.
- Maximum rate of diffusion depends on # of uniporters in membrane.
- Speed of diffusion depends on conc gradient
- Transport direction is REVERSIBLE.
Define primary active transport
NA+/K+ pump
- Maintain normal sodium and potassium gradients
- energy stored in the sodium/potassium gradients for secondary transport
Describe ABC transporters
Primary active transport:
- ex: CFTR = Cl- channel and regulator of other channels.
- Opening and closing of the channel is controlled by binding of ATP.
- Mutations in the gene cause cystic fibrosis.
Give example of Symporter
Sodium co-transporter = sodium ions moves down conc. gradient and the energy generated is used to drive another molecule against its conc. gradient (e.g sodium co-transport of glucose into epithelial cells of kidney tubule)
Give example of Antiporter
- Na+/Ca+ exchanger = Sodium moves into the cell down its conc gradient and pumps Ca+ out of the cells against its conc. gradient.
- Na/H exchanger = 1:1 exchange of sodium for hydrogen utilizing sodium’s conc. gradient.
Define Fluid Phase Endocytosis
- Uptake of materials that are dissolved in the extracellular fluid (material NOT bound to receptors)
- Utilize clathrin, coat protein, that is attached to membrane via interactions with adaptin proteins.
- The adherent membrane invaginates into the CLATHRIN CAGE forming a COATED PIT.
- clathrin cage formation is spontaneous and energetically favorable
- Once Clathrin cage is COMPLETED the CLOSED VESICLE detaches from the cell membrane and cytoplasmic enzyme disassemble the clathrin cage via ATP.
- * INEFFICIENT WAY TO TRANSPORT SPECIFIC SUBSTANCES**
