16 Membrane transport Flashcards
How are the 2 aqueous phases inside and outside the cell divided?
by membrane, phospholipid bilayer
What 3 parts make up the phospholipid bilayer?
- glycerol
- phosphate group
- 2 fatty acid chain (one saturated, one unsaturated)
How do diff parts of the phospholipid react to water?
Hydrophilic head (glycerol is an alcohol), and hydrophobic tail (FA)
What are the 3 types of membrane proteins?
- intrinsic/integral proteins
- extrinsic/peripheral proteins
- transmembrane proteins
What is the diff between instrinsic/integral and extrinsic/peripheral proteins?
- instrinsic/integral: embedded within the phospholipid bilayer
- e.g. transport protein (ion channel, protein carrier), enzymes (usually near to the cytoplasmic domain)
- extrinsic/peripheral proteins
- mainly located on surface of phospholipid layers, could be extracellular or intracellular
- e.g. antigens
what is an example of transmembrane proteins?
receptors
what are 2 other components found in the membrane other than membrane proteins?
glycolipid
* cell-cell recognition
cholesterol
* prevents the aggregation of phospholipid, increase fluidity of phospholipid bilayers (fluid-mosaic model)
What are 2 features of cell membrane?
- asymmetry: due to glycoprotein and glycolipids (more common in extracellular region)
- selectively permeable: only allow certain types of molecules to directly pass through
what is the criteria to pass through selectively permeable membranes?
small and non-polar
or
lipid-soluble
what are the 2 passive and 2 active modes of membrane transport?
Passive (no energy required, high to low conc)
* diffusion
* osmosis
active (atp required, against conc gradient)
* active transport
* vesicular transport
What are the 2 types of diffusion?
simple and facilitated
what are the 2 types of active transport?
primary and secondary active transport
what are the 2 types of vesicular transport?
endocytosis and exocytosis
What is simple diffusion?
directly through plasma membrane
* small and nonpolar
* or lipid-soluble molecules
* e.g. gases (O2 and CO2), fat soluble vitamins
can water travel through the membrane directly?
yes but is hard and slow with simple diffusion
facilitated diffusion is better
What is facilitated diffusion?
- travel across membrane via specific protein channels or carriers
- lipid-insoluble substances
- e.g. glucose, AA, ions, and water molecules
What is osmosis?
- for water molecules
- from high to low water potential (water molecule conc)
- or low to high osmolarity (total conc of solutes) = osmotic pressure
- much faster through aquaporin (also a protein channel)
- simple diffusion of water is very slow through the lipid bilayer
Why cant solutes (e.g. ions or glucose) diffuse across the membrane directly?
because they are valuable
need them, dont want to lose them, instead change the water for osmosis
What is the relationship between water potential and osmolarity?
higher water potential = lower osmolarity
lower water potential = higher osmolarity
which side has higher osmotic pressure?
bottom
higher osmolarity = higher osmotic pressure
What are the 3 different tonicity of solution?
- isotonic - solution conc is same as the cell
- hypertonic - if solution conc is higher than the cell (higher osmolarity)
- hypotonic - if solution conc is lower than the cell (lower osmolarity)
What is ECF and ICF?
extracellular and intracellular fluid
What is the osmolarity of ECF and ICF?
usually have the same osmolarity
what if the following solutions are individually infused into the ECF, what is the outcome: isotonic, hypertonic, hypotonic
- isotonic solution - nothing happens
- hypertonic - water goes from inside to outside
- hypotonic - water goes from outside to inside
What is primary active transport? what are the 3 different types?
- ion pumps using ATP = ATPase
- P, V, F, type
What is ABC transporter
ABC transporter (ATP binding cassette), e.g. P-glycoprotein & CFTR
* under primary active transport
What is the relative conc of Na+ and K+ in ECF and ICF?
more Na+ in ECF than ICF
more K+ in ICF than ECF
What is the P type ATPase
P type - activated by phosphorylation, e.g. Na+/K+ ATPase
What is the mechanism of Na-K ATPase?
K+ out Na+ in
to build up electrochemical gradient
phosphorylation of ATP-> ADP expels Na+ to outside, then K+ binding triggers release of the phosphate group and goes back to original conformation, Na+ binds, cycle repeats
What is the V-type ATPase?
V type - H+ ATPase in vesicles/vacuoles, e.g. lysosome
* once activated by ATP, moves H+ into lysosome to acidify and activates hydrolytic enzymes
What is F type ATPase?
F type - H+ ATPase in mitochondrial inner membrane
* moves H+ ions into mitochondrial matrix to produce ATP
* also ATP synthase
What are examples of ABC transporters?
ABC (ATP binding cassette) transporter
P-glycoprotein & CFTR
* both have similar mechanisms
* once activated by ATP
* P-glycoprotein removes lipid-soluble drugs out of the cell
* CFTR removes Cl- out of the cell
CFTR - cystic fibrosis transmembrane conductance regulator
What is secondary active transport?
movement of one substance driven by the electrochemical gradient of anothre substance (often Na+ ions)
What are the 2 types of secondary active transport?
- symport (or cotransport) system = 2 substances move across the membrane in the same direction
- antiport (or countertransport) system = 2 substances move across the membrane in opposite directions
What is endocytosis?
uptake of large particles using vesicles
What are the 3 types of endocytosis?
- phagocytosis - (cell eating) uptake of solid molecules, e.g. bacteria
- pinocytosis - (cell drinking) uptake of dissolvable molecules, e.g. DNA, protein
- receptor-mediated endocytosis - uptake of specific molecules when recognized by specific receptors, e.g. cholesterol
What is exocytosis?
secretion of large molecules using vesicles
* like endocytosis, exocytosis requires energy
* e.g. release of hormone or neurotransmitter
Compare primary and secondary active transport
