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25 Cards in this Set
- Front
- Back
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what is membrane transportability based on? |
1. Size 2. Polarity |
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what is the ranking of molecules that can get through the barrier? |
1. small molecules like O2, N2, etc. 2. large hydrophobic molecules like benzene 3. small polar molecules like water ____ then the following cannot enter normally 5. large polar molecules (sugars, amino acids) 6. charged ions |
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how were transport proteins discovered? |
the specificity of transport proteins was discovered through Lactose Permease mutant. e.g., Humans Cystinuria mutant wouldn't transport certain membrane proteins, which led to kidney stones. |
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how do transmembrane proteins act? |
as specific, selective entries to the cell |
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what are the 2 types of protein membrane transports? |
1. Passive: transports down a gradient 2. Active: goes up a gradient |
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how do you classify protein transports? |
1. Passive, down a gradient, such as ion channels and carriers 2. Active, up a gradient and requires energy, such as a pump |
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What is the electrochemical gradient and how does it affect transmembrane import? |
The inside is purposefully charged negative, while the outside is more positive. If an ion channel opens, positively charged ions will rush in |
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what is the average internal charge of the cell? |
-50 mV to -100 mV. The average is around -70 mV. That's about 200,000 V/cm! |
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What ions are favored entry into the cell, which are not? why? |
Na+ ions are favored to enter because they are + charged and the inside of the cell is negative. Cl- are not favored because that is up a concentration gradient |
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What is the Na+K+ATPase and how/why does it work? |
1. It sets up 10% of the ECG 2. Function: It pumps 3NA+ out for every 2K+ in 3. Result: more Na+ outside and K+ inside, creating both electro and chemical gradient |
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What does NA+K+ATPase control? |
1. electrochemical gradient 2. controls ion concentration of cell 3. membrane potential across PM 4. controls cell volume 5. drives active transport of amino acids, sugars, nucleotides |
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how much of the cells energy fuels the Na+K+ ATPase? |
1/3 for normal cell 2/3 for brain |
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how does ATPase drive transport? |
1. It has two subunits; a 100 kDa and 45 kDa 2. 100 kDa units has many binding sites for Na+, K+, ATP, oubain 3. Oubain is an inhibitor and it binds to the K+ site 4. ATP and ADP splits |
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How does ATPase set up gradient? |
1. 3 Na+ bind to pump. 2. ATP attaches and ATP>ADP, leaving Phos. 3. Pump opens on other side, 3Na+ release 4. 2K+ bind to pump 5. autophosphorylates with Phosphate group 6. changes conformation, 2K+ enter cell |
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how does ATPase control volume of cell? |
normally, Na+ is kept at a low volume due to the pump. however, if oubain blocks, then Na+ concentration grows and water floods cell until it bursts |
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How does ATPase control import of amino acids, nucleotides, and sugars? |
The energy stored in the Na+ gradient is used to push across cell. |
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how does 2Na+ - 1 glucose transport work? |
there's a Na+ driven symport which allows Na+ in, K+ out and glucose binds to enter with Na+. |
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how is oubain used? |
1. by monarch butterflies: consume plants with oubain to become poisonous 2. on blow darts for hunters 3. used as a heart contractility drug- but if misdosed it's poisonous |
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what is the P-type ATPase transport family? |
they autophosphorylate themselves in their mechanism. e.g.: specific Ca+ pump keeps concentration ~10^-7mM |
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Active Carrier Proteins/ABC transports- what do they do? |
They have multiple transmembrane domains and bind multiple ATP |
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What are some examples of ABCs? |
1. Flippases 2. P-glycoprotein 3. trypanosome protein that resists malaria drugs (chloroquine) 4. cystic fibrosis mutation |
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What are the 3 types of gated ion channels? |
1. Voltage gated (opens when electro gradient changes) 2. intra-cellular ligand-binding (opens when ligand binds inside) 3. extra-cellular ligand binding (opens when ligand binds outside) 4. mechanically gated (something else opens it) |
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How are ion channels selective? |
1. There's a selective pore size that only allows the right-sized ion through 2. alpha helix in transmembrane domains and selectivity loop form the filter 3. for K+ to enter it must lose its hydration shell. This becomes favorable because it interacts with carbonyl oxygens 4. Na+ cannot enter because it's too small and will not interact |
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How long are channels open? How many ions enter in that time? How does that compare to ATPase?
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Approximately 1 millisecond; about 30,000 ions/msec Compared to ATPase: 300 Na+/sec 200 K+/sec 100 ATP cleaved in a second |
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How does an action potential work? |
1. action potential moves down via a series of sequential depolarizations allowing ion channels to open and Na+ to flood in 2. at nerve terminal causes Ca++ channel to open, concentration increase causes vesicles to leave 3. neurotransmitter in vesicles moves across synaptic cleft to bind to ligand-gated ion channel, cycle repeats. |
