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BIO Cellular Transport
Terms in this set (24)
What can pass through the cell membrane? and Why does selective permeability helps the cells?
gases and small uncharged particles(ethanol, urea) that way they can regulate cells membrane potential, the rate of simple diffusion is dependent on the concentration gradient and hydrophobicity
What is electrochemical gradient?
It is the diffusion gradient of an ion, which is affected by both the concentration difference of an ion across a membrane (a chemical force) and the ion's tendency to move relative to the membrane potential (an electrical force).
3 main types of transport proteins
1. channels: movements of specific ions or water down the electrochemical gradient(passive transport to facilitated diffusion)
2. transporters: use energy stored in the electrochemical gradient, goes through conformational change
-uniporter: moves one molecule down its concentration gradient (glucose, and amino acids)
-symporter: moves both things in the same direction but one is moving against their concentration gradient
-antiporter: both molecules move in different direction but one of them are moving against their concentration gradient
3. Atp powered pumps: are ATPases( enzyme that catalyze the hydrolysis of phosphoanhydride bond (active transport) against their electrochemical gradient
GLUT 1 in erythrocytes
-accounts for 2% of the protein in the membrane
-after glucose in transported in, it is immediately phosphorilated into G3P thus it cannot leave the cell, so intracellular glucose concentration is kept low, GLUT
-goes through 2 conformational change: one substrate binding sites faces outward and one binding site faces inward
-Diffusion of water through a selectively permeable membrane
-In plants, rigid cell wall prevent the cell from bursting, animals have contractile vacuoles that pushes water out when osmotic pressure increases
-turgor pressure: water pressure generated by the entry of water into the cytosol then vacuole(higher solute concentration)
-A transport protein in the plasma membrane of a plant or animal cell that specifically facilitates the diffusion of water across the membrane
-water forms hydrogen bond with the hydrophilic amino acid side chains, several water molecules can go through the time thus pushes each other down stream
-does not go through conformational change thus faster than GLUT 1
-the formation of H-bond between oxygen of water and amino groups of side change and narrow diameter ensures only water pass through
hyposecretion of ADH, absence of aquaporin 2 thus not being able to conserve water in the body and excrete large volumes of dilute urine
Resting cell potential in animal, plants and bacteria
-animals cell potential is due to NA+/K+ pumps which establish concentration gradient
-plants negative cell membrane potential is generated by pumping protons out of the cell by ATP pumps leaving a negative Cl ion
-Bacteria cell membrane potential is generated by electron transport chain
K+ channel specificity
- 2 conserved helices and shorter pore segment
-has water filled cavity and selectivity filter
-K+ loses 8 waters of hydration and bound in the same geometric to 8 carbonyl oxygen atoms of the amino sequence of the channel
Why can't Na+ or Ca+2 pass through a K+ channel?
-Because once Na+ is dehydrated it is too small to bind with the carbonyl oxygen in the selectivity filter
-dehydrated Ca+2 is small and the +2 charge binds to the water oxygen more tightly thus more energy to strip not favored
Glucose transport in kidney tubules&intestinal cell lining
Glucose concentration is very large inside of the cell and importing it requires a lot of energy thus the ratio fo Na:glucose is very high
Mechanism of CHF
-increase in Ca+2 concentration initiates muscle contraction, then Ca+2 acts like a second messenger allows the Ca+2 in the sarcoplasmic reticulum to release
-increased Ca+2 concentration initiate muscle contraction
-3 Na+ out, 1 Ca+ in
hydrolysis of the phosphate group allows conformational change in the Na/K pumps to let the Na in and K out, but with the medicine, you cannot dephosphorilate the P thus K+ gets stuck so that the pumps to get Na+ out stops thus indirectly inhibits Na/Ca+2 pumps
Cotransporters regulating cytosolic pH
-anaerobic metabolism of glucose yield lactic acid and aerobic yields CO2 which combines with water to form carbonic acid.
- carbonic acid dissociates and lowers the cytosolic pH
- Cells remove it by importing Na+ HCO3-/ Cl- anti-porters
-carbonic anhydrase will consume cytosolic H+ and also Na+/H+ antiporters will move Na in and export H+ to raise cytosolic pH
- To lower pH when too high: Cl-/ HCO3- (OH- and CO2) anti porter import Cl to lower pH in the cytosol
Transport of CO2 by erythrocytes
In systemic capillaries waste Co2 released from cells into the capillary blood freely diffuse across the erythrocyte membrane. In erythrocyte carbonic anhydrase combines CO2 with OH- (comes from splitting the water) to form HCO3- (water soluble). The red cell antiporter AE1(anion exchanger) cytosolic HCO3- is transported out of the erythrocyte in exchange for an entering Cl- anion. Additionally, the release of the oxygen initiate a conformational change in the histidine residue of the hemoglobin to bind to a proton(comes from the split water)
In pulmonary capillaries, the CO2 is released,
What is trancellular transport?
-transcellular transport: molecules are imported throughout the plasma membrane on the apical(surface) of the cell and exported through the basolateral side of the cell
simple diffusion (passive transport)
-Nonpolar small lipid soluble substances diffuse directly through
-down a concentration gradient and energetically favorable
-rate limiting step is the movement of polar molecule into the hydrophobic interior
- Large proteins like antibody and reactive ions all require cell surface receptor proteins
2 major function of integral proteins
transport polar molecules and move molecules against their concentration gradient
Kinetics of glucose transport
-GLUT 1 in erythrocytes face high selective pressure because they cannot make glucose thus it has very low Km (high affinity)
-vmax is maximal rate of transport when all transporters are bound
Gc vs Gm
-Gc is the delta G involving the concentration of the gradient(chemical)
-Gm is the delta G involving the membrane potential (charges)
- delta Gc is always the larger factor because the K channels are always open thus K+ can move out anytime to maintain membrane potential
- Na+ import and K+ export always have -deltaGc
-K+/Na+ import has -deltaGm
You're growing mammalian cells in an incubator set at 37°C. Someone mistakenly removes them and places them in an incubator set at 42°C. What (if anything) do you predict will happen in these cells to enable them to maintain the same plasma membrane fluidity at 42°C that they had at 37°C? That is, can cells compensate for temperature-dependent changes in membrane fluidity to maintain a constant fluidity irrespective of that temperature change.
The plasma membranes of cells grown at 42°C will have increased amounts of saturated FAs relative to unsaturated FAs and an increased amount of cholesterol relative to when the cells were grown at 37°C
Plasma Membrane Slides #4 & 7. Cells maintain a constant fluidity in response to limited changes in the external temperature they are grown at. If cells did not do this, then the plasma membranes of cells grown at 42°C will become more fluid than the same cells grown at 37°C. They compensate at the higher temperature by increasing the amount of saturated fatty acids relative to unsaturated FAs & by increasing the amount of cholesterol. They could also achieve the same effect by increasing the amount of long chain fatty acids relative to short chain FAs and by increasing the amount of cholesterol.
The opposite effect would be observed if cells were initially grown at 37°C & shifted to a lower temperature of 32°C. In this case, in order for the cells grown at 32°C to maintain the same fluidity they had at 37°, they would increase the relative amount of unsaturated FAs relative to saturated FAs (and/or increase the relative amount of short-chain FAs relative to long chain FAs) and they would reduce the amount of cholesterol.
Phosphatidylcholine (PC), shown below, is sold as a dietary supplement of unsubstantiated benefit to improve cognitive function and to reduce the risk of dementia. It is also the active ingredient contained in cosmetic injection products used to "dissolve" fat although there is no reliable evidence that it does so. What covalent bond(s) is/are the most important in forming PC from its 4 primary constituents?
Ester bonds. Plasma Membrane Slide #5. Phospholipids such as PC do not contain mixed acid anhydride bonds. Van der Waals interactions are non-covalent. The 2 fatty acids are esterified to glycerol; glycerol is esterified to phosphate; phosphate is esterified to a small polar molecule, in this case choline.
Which statement(s) correctly describe functions of the indicated Glycophorin proteins?
-The Dantu hybrid GPA/B prevents binding of Plasmodium falciparum to the erythryocyte plasma membrane.
-GYPA & GYPB interact with a specific proteins on Plasmodium falciparum to enable its binding to the erythrocyte plasma membrane.
-GYPA is required to attach the erythrocyte plasma membrane to the underlying cytoskeleton to increase its flexibility and enables erythrocytes to be reversibly compressed in capillaries.
-most abundant protein in the erythrocytes
group of lipid soluble compounds which facilitate the transport of ions across the cell membrane like a instant artificial non-gated ion channels
K+ valinomycin: crown like structure which creates holes for K+ to pass through, can easily kill the cell because cell membrane potential gets very negative
Ca+2 A23197: instant calcium used to determine if certain cellular process is Ca+2 dependent
Which of the following pairs of transport processes both have a negative ΔGm in a typical non-neuronal mammalian cell?
Because Ecell is -70mV, ΔGm is always negative for cation import and anion export. Conversely, ΔGm is always positive for cation export and anion import. ΔGm for the transport of uncharged molecules such as glucose or H2O = 0.
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