chap 4- transport (b1- foundation) Flashcards
what types of transport require energy from ATP?
- primary
- secondary active transport (co-transport & counter transport)
- endocytosis
- exocytosis
- phagocytosis
active transport definition
movement of substances against the electrochemical gradient
- requires energy which is obtained mainly by breakdown of high energy compounds like ATP
diffusion vs active transport
diffusion: random molecular movement of substances molecule by molecule
- energy that causes diffusion is energy of normal kinetic motion of matter
active transport: movement of ions or other substances across membrane w/ carrier protein such that substances move AGAINST their concentration gradient
- requires additional source of energy
an important difference b/w simple diffusion & facilitated diffusion
simple diffusion: no carrier
- as conc. of diffusing substrate increases, rate of diffusion just keeps increasing proportionately
facilitated diffusion: carrier- mediated
- as conc. of diffusing substrate increases, rate of diffusion cannot rise higher than the Vmax
- bc carrier proteins just cant open and close fast enough to allow it to keep increasing
what is simple diffusion & what factors does it depend on?
simple diffusion no carrier proteins needed, movement of molecules/ions occurs through membrane openings of intermolecular spaces
rate of diffusion depends on:
- amount of substance available
- velocity of kinetic motion
- # & size of openings in membrane through which molecules/ions can move
simple diffusion: lipid soluble substances through the lipid bilayer
rate of diffusion of lipid soluble substances is directly proportional to its lipid solubility (how non polar it is, the more nonpolar = faster it will go through)
highly lipid soluble substances: O2, CO2, fatty acids, steroids
(how O2 gets in so easily - its so needed too)
2 ways that simple diffusion occurs
-
Lipid solubility of substance through lipid bilayer (just goes in depending on whether or not its nonpolar- mostly for O2/CO2)
- for nonpolar things
aquaporins are simple
-
Protein channels - extend throughout membrane and allow water to come in rapidly
- aquaporins, K+/Na+ channels
- for polar things
how do water soluble (polar) substances get through the cell membrane?
through protein channels
- such as Na+, K+, & Ca2+
what are aquaporins/what do they do?
selectively permit rapid passage of water through the membrane
- very selective, however; can sometimes also let molecules like urea & glycerol pass through (but at a MUCH smaller rate)
2 distinguishing characteristics of protein channels
-
selectively permeable to certain substances
- based on: diameter, shape, electrical charges, chemical bonds (inside surface) - opened/closed by gates/chemical (voltage-gated or ligand-gated channels)
structure of potassium channels
- tetrameric structure (4 identical proteins subunits; purple coils that make like a V, 2 of these helixes are transmembrane)
- 4 subunits surround a central pore that has pore loops at the top
- Pore loops form a selectivity filter that has carbonyl oxygens lining it - carbonyl oxygens dehydrate potassium (pull the water) to allow potassium to pass
- This makes it selective and only lets K+ through even though Na+ is smaller
potassium channels vs potassium gates (for own knowledge)
K+ channel: full protein structure that allows K⁺ to move
- always includes the selectivity filter
K+ gate: the movable part of the channel that opens or closes
- found in voltage-gated or ligand-gated channels
how is the sodium channel highly selective for passage of sodium ions?
selectivity filter on these channels are lined with strongly negatively charged amino acid residues
- the charge pulls small Na+ molecules away from their water, dehydrates them, and lets them pass (they don’t get fully dehydrated though)
opening/closing of the gates of protein channels are controlled by what 2 factors?
-
voltage gating: responds to electrical potential across cell membrane
- ex. strong (-) charge on inside of cell membrane causes outside sodium gates to remain closed, but when gains (+) charge, gates suddenly open -
chemical (ligand) gating: opened by binding of chemical substance (ligand) with protein = causes conformational change in protein molecule that opens/closes gate
- ex. acetylcholine ligand-gated ion channel that’s gates only open when ACh binds to receptors
what is facilitated diffusion? and what are the 3 important characteristics of it?
facilitated diffusion: requires carrier protein to aid passage of molecules/ions by binding with them chemically
- specificity: each carrier only transports 1 specific substance (or very similar ones)
- saturation: if all carriers are full, rate of transport reaches maximum (the Vmax thing)
- competition: similar substances may compete for the same carrier
molecules can be transported in either direction
important example of facilitated diffusion
GLUT-4: glucose transporter that is activated by insulin which can increase the rate of facilitated diffusion of glucose by 10-20x
(how insulin regulates glucose levels in the body)
mainly through facilitated diffusion: glucose & amino acids
how is osmosis different from aquaporins? (for own knowledge)
water can short of cross through the membrane but really really slowly so aquaporins exist to speed up this process
“While osmosis is the underlying process of water movement, aquaporins act as specialized protein channels to speed up and regulate this process.”
what is osmosis?
type of passive transport- doesn’t require energy (ATP)
net movement of water across a semipermeable membrane caused by conc. difference
- membrane allows water to pass through, but not solutes (like salt or sugar)
- usually net water conc. doesnt exist, its sort of just at 0, maintained, but sometimes can happen and then osmosis starts
water moves from area of low conc. to higher conc.
what is osmotic pressure?
amount of pressure required to stop osmosis (prevent net movement of water across membrane)
“osmotic pressure pulls water in”
osmolarity vs osmolality + normal osmolarity of ECF (blood plasma)
both measure how concentrated a solution is
osmolarity: # of solute particles in 1 liter of total solution (which includes both solute + solvent)
osmolality: measures # of solute particles in 1 kilogram of JUST SOLVENT (water)
normals osmolality of blood plasma - 300 milliosmoles/kg water (which is basically 300 solute particles/kg water)
net diffusion rate across a membrane is proportional to what? whats the equation?
proportional to concentration difference across membrane
rate of net diffusion into cell is proportional to conc on outside minus conc on inside
what is Nersnt potential? what is the equation?
nersnt potential: electrical voltage/potential that will balance a given concentration difference
- at this voltage, ion is in equilibrium meaning no net movement of that ion across membrane
equation: EMF (in mV) = +_61log(C1/C2)
C1= conc. on side 1, C2= conc. on side 2
balance point b/w chemical force & electrical force is the Nernst potential- when ions no longer wanna move
The principal mechanism by which Insulin controls glucose transport across the cell membrane is:
facilitated diffusion
what type of channels are Acetylcholine receptors?
ligand gated channels
2 types of active transport
primary active transport: energy is directly derived from breakdown of ATP
secondary active transport: energy is derived secondarily from energy from ionic concentration differences
- difference was created originally by primary active transport
both depend on carrier proteins that penetrate through the cell membrane
structure of sodium-potassium pump (Na+-K+ pump)
protein complex of 2 separate globular proteins- 1 is α and 1 is β (smaller)
the smaller one’s function is unknown but the bigger one (α) has 3 specific features:
- has 3 binding sites for sodium on inside portion of cell
- has 2 binding sites for K+ on outside
- inside portion near sodium binding sites has ATP-ase activity
how does the sodium-potassium pump work?
- when 2 K+ ions bind on the outside and 3 Na+ ions bind on the inside, ATPase function of protein gets activated
- activation leads to cleavage of 1 molecule of ATP creating liberated energy
- that energy causes a chemical & conformational gradient in molecule, pushing 3 Na+ to outside & 2 K+ to inside
what are the functions of the sodium-potassium pump?
most important function is that it controls cell volume (b/c if gets too hypertonic or hypotonic, cell can shrivel or burst)
also electrogenic in nature which creates an action potential across the cell membrane
- this action potential is basic requirement in nerve & muscle fibers for transmitting nerve & muscle signals
calcium pump (Ca2+-ATPase)
example of primary active transporters
- normally, calcium levels inside cell are very low & much higher outside cell
two types:
1. In cell membrane: pumps Ca2+ out of cell
2. Pumps Ca2+ into sarcoplasmic reticulum of muscle cells & mitochondria of all cells
this carrier protein has the same ability to cleave ATP like in sodium channels
hydrogen pump (H+ ATPase) + where its found
another ex. of primary active transporters- more or less same role as the calcium one except with just H+ ions
important in 2 parts of the body:
- parietal cells of stomach (gastric glands): to secrete HCl into stomach
- intercalated cells of kidneys (renal tubules): to control blood pH by regulating H+ levels
2 types of secondary active transport
co-transport: diffusion energy of Na+ can pull other substances w it to inside of membrane
- ex. co-transport of glucose & amino acids w/ Na+
counter-transport: diffusion energy of Na+ used to transport another substance outside while Na+ goes inside
- ex. sodium-calcium counter transport, sodium-hydrogen counter transport
both use coupling mechanism- both Na+ & substance have to bind in order for carrier protein to work
co-tranport of glucose & amino acids along w/ sodium (secondary active transport)
2 binding sites on transport protein- 1 for Na+ & 1 for glucose - only starts to work when both of them bind
energy for movement is generated from the concentration gradient of Na+ b/c Na+ just constantly trying to go in
- esp important across renal & epithelial cells to promote absorption of these substances into the blood
counter-transport of calcium & hydrogen ions with sodium (secondary active transport)
this is in addition to the already existing calcium/hydrogen active pumps (counter transport is not nearly as powerful but still helpful)
Na+ moves in, Ca2+ moves out and are bound to the same transport protein (has 2 sides- 1 on outside & 1 on inside)
active transport through cellular sheets
cellular sheet: layer of closely packed cells- connected tightly & have 2 sides: one that faces the inside space & 1 that faces the blood
active transport through cellular sheets is movement across the whole layer of cells
occurs through: epithelium of intestine, renal tubules, exocrine glands, & gallbladder
happens by:
1. active transport through membrane on 1 side of transporting cells
2. simple or facilitated diffusion on opposite side of cell
what is transcytosis?
- receptor-mediated uptake of a ligand on one side of the cell
- then vesicular transport across the cell
- lastly, exocytosis of the vesicle contents on the opposite side
uniport vs. symport vs. antiport
uniport: carries only one substance in a single direction
symport: transports 2 different substances in the same direction
antiport: transports 2 different substances in the opposite direction
which disease is caused by defective Cl- channel?
cystic fibrosis
- body produces abnormally thick mucus
