Lecture 7 - Membrane Transport Flashcards
what is the difference between simple diffusion and facilitated diffusion?
- simple diffusion: requires membrane permeability and favourable gradient conditions
- facilitated diffusion: requires a protein to help get the molecule across the membrane
what is the difference between passive transport and active transport?
- passive transport: down a concentration gradient, no energy needed, transport proteins may or may not be needed
- active transport: against a concentrations gradient, requires energy input, transport protein “pumps” are required
what is a uniporter?
carrier that transports a single solute
what is an antiporter?
carrier that transports two solutes in the opposite direction across the membrane
what is a symporter?
carrier that transports two solutes in the same direction across the membrane
def: transporter that alternates between two conformations, bind one or more solute molecules, undergoes a conformational change that transfers the solutes to the other side
carrier protein
def: water filled pore thorough which specific ions or small molecules can diffuse, form hydrophilic channels through
transmembrane channel
def: highly specific channel that can conduct almost a million ions per second, bidirectional, flow determined by electrochemical gradient
ion channel
def: passage of a variety of hydrophilic solutes, determined by pore size; some antibiotic resistance has been linked to mutations in certain bacterial porins
porin
def: water flows through this channel at a rate of several billion per second, amino acid residues discriminate against other ions of similar size
aquaporin
what ions are ion channels normally selective for?
Na+, K+, Ca2+, Cl-
def: open and close in response to changes in membrane potential
voltage-gated
def: triggered by the binding of specific substances to the channel protein
ligand-gated
def: respond to mechanical forces that act on the membrane
mechanosensitive-gated
what structural features make a channel a specific to a particular ion?
- ion specific associations (amino acid side chains and the polar backbone)
- constriction in the centre to serve as a size filter
which kind of body cells have aquaporins?
specialized cells in the kidney
what does the Glucose transporter GLUT1 do?
facilitated diffusion of glucose by a uniport carrier protein
where is GLUT1 found?
on all mammalian plasma membranes
GLUT1 process is __________ - can function in either direction depending on the ____________ ________
reversible, concentration gradient
T or F: Glucose is rapidly phosphorylated inside the cell which keeps the intracellular concentration of glucose low and this maintains a concentration gradient
True
intracellular or extracellular = higher potassium concentration
intracellular
where is the highest concentration of Ca2+?
extracellular
where is the highest concentration of Na+?
extracellular
where is the highest concentration of Cl-?
extracellular
def: solute accumulation is coupled directly to an exergonic chemical reaction (such as ATP hydrolysis)
direct (primary) active transport like ATPases or ATPase pumps
what do ATPases do?
- harness the energy of ATP hydrolysis to move ions or small molecules against a concentration gradient/electrical potential
- active transport
where are P type ATPases mostly found?
on the plasma membrane
which class of P type ATPases are found in all organisms?
P1
Which classes of P type ATPases are found only in eukaryotes?
P2-P5
what do P1, P2, P3, P5 transport?
cations or heavy metals
what does P4 transport?
- lipids
- acts as a flippase to help maintain membrane asymmetry
what do all types of ATPase pumps have in common?
they all have one or more ATP binding sites on the cytosolic membrane leaflet
P-Type ATPases are members of a large family and are ____________ Phosphorylated by ATP on a specific ____________ acid residue
reversibly, aspartic
what is most energy consumed by the brain (2/3) used to do?
maintain Na+/K+ that maintains the membrane potential required for the transmission of nerve impulses
what do V-type ATPase pumps do?
pump protons(H+) into organelles
what’s an example of a V-type ATPases?
- vacuoles
- vesicles
- lysosomes
- endosomes
- Golgi complex
what are V-type ATPases like structurally?
- 2 multi-subunit components
- integral component embedded in the membrane
- peripheral component that juts out from the membrane surface
where are v-class proton pumps in animal cells?
endosomal and lysosomal membranes
what do F-type ATPases do?
transport protons in bacteria, mitochondria, and chloroplasts
F-type ATPases: __________ flow of H+ up their concentration gradient _______ ATP
endergonic, hydrolysis
F-type ATPases: _________ flow of H+ down their concentration gradient is used to _________ ATP
exergonic, synthesize
T or F: can F-type ATPases act in the reverse direction
true
where are F-type proton pumps found in eukaryotes?
inner mitochondrial membrane
what does the ABC in ABC type ATPases stand for?
ATP binding cassette transporters
what were the first kind of ABC type ATPases discovered?
importers, involved in the uptake of nutrients
what do all ABC type ATPases have?
- 2 nucleotide (ATP) binding domains
- 2 transmembrane domains
why are ABC transporters medically important?
some of them pump antibiotics or drugs out of cells and render the cell resistant to the drug
tumours that are resistant to growth inhibiting drugs have a high concentrations of what kind of transporter?
ABC transporter: MDR transport protein
unlike most ABC transporters, MDR protein transports a _______ ______ of ________ ________ drugs
wide range of chemically dissimilar drugs
T or F: Does indirect active transport rely on ATP ?
Yes, because the Na+ or H+ concentration gradient necessary for this process is generated by ATPase pump
in co transport, can a molecule move on its own?
no, the favoured reaction is coupled with the unfavourable reaction in order to drive the unfavourable reaction against a concentration gradient
