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Cell/Molec
Membrane Structure and Compartments and Protein Structure
| Question | Answer |
|---|---|
| What is a cell membrane? | Separate the inside and outside of the cell. Function of the membrane is that of a barrier (not strength) |
| What is a plasma membrane? | Lipid bi-layer with hydrophilic phospho-head groups and hydrophobic lipid tails |
| What is the consistency of the membrane? | Fluid |
| What are the four parts of the phospholipid phosphatidylcholine? | A polar head group, a phosphate group, glycerol, and the non-polar fatty acid tails |
| What makes a molecule polar? | Where there is an uneven distribution of electrons (most likely with the presence of oxygen) |
| What is the kink in the fatty acid tail attributed to? | A cis-double bond (promotes cylindrical shape for arrangement of lipid bi-layer). A cis-double bond makes the tails shorter, and causes the membrane to be thinner. |
| Why do polar molecules dissolve in water? | Oxygen and hydrogen atoms have a perfect arrangement for interaction and partial charge distribution. |
| What conformation is favorable in the case of liposomes? | A lipid bi-layer sphere is energetically favorable because the edges are less exposed to the polar water environment. |
| Why are liposomes useful? | In a test tube, you can determine what atoms and molecules can easily pass through a lipid bi-layer membrane. |
| What movements can individual phospholipids make in the membrane? | Phospholipids can only move laterally (flip-flops rarely occur and must utilize an enzyme). |
| What are the names of the parts of the membrane when referring to a cell? | The outside is the extracellular layer. The inside is the cytosolic layer. |
| What characterizes a soap or detergent? | A large molecule where one part is polar and another region is non-polar. Can invade and break up membrane of a cell. |
| What are lipid rafts? | Lipid rafts are thicker pieces of membrane with special phospholipids. Can select for specific proteins that are different from the rest of the membrane. |
| What is cholesterol and why is it important? | Cholesterol is a steroid that is not soluble in water. Has an tiny hydrophilic head group (OH-), steroid rings, and one fatty acid tail. Is a major component of animal cell membranes (between phospholipids) |
| What are four important types of phospholipids? | Phosphotidyl-enthanolamine (+), Phosphotidylcholine (+), Phosphotidylserine (-), and Sphingo-myelin (lipid in enriched lipid rafts) |
| Where are phosphotidylserine and glycolipids usually present in a membrane? | Phosphotidylserine is usually present in the cytosolic layer and glycolipids are usually present in the extracellular layer. |
| What conformation of amino acids do proteins usually cross the membrane as? | An alpha-helix. (Helices enriched with hydrophobic non-polar side chains of amino acids usually span the membrane). About 20% of proteins in humans span in an alpha-helix. |
| What are the four ways proteins can be associated with the membrane? | Spanning the membrane, embedded in the membrane (peripheral proteins), attached to a lipid or glycolipid, or attached to another membrane protein. |
| What is significant about the hydrophobic regions of amino acids? | The non-polar hydrophobic side chains of amino acids interact with the inside of the lipid bilayer (characteristic of membrane spanning proteins). |
| What is a hydropathy plot and what is it used for? | A hydropathy plot predicts transmembrane helices from amino acid sequences. At least 20 amino acids in a row with hydrophobic side chains indicate transmembrane portion. |
| What is a basic amino acid composed of? | Contain an amine group (NH3+), a carboxylic acid group (COO-), and a varying side-chain group (characterizes amino acid). About 22 different types found in eukaryotes. |
| How are beta-barrels stabilized in the membrane? | Hydrogen-bonding. The inside of a beta-barrel is completely polar. Derived from the secondary protein structure of the beta-pleated sheet. |
| How are membrane proteins studied? | Use of a detergent and injection into a liposome, Freeze Fracture Electron Microscopy, SDS-Page Gel, and FRAP |
| What are two popular detergents used for protein analysis? | Sodium Dodecyl Sulfate (SDS), and Triton X-100 |
| How do you study proteins using SDS-Page (Polyacrylamide Gel Electrophoresis) Gel? | After applying a current to the gel, heavier molecules take longer to move through the membrane (sorts and indicates protein movement abilities) |
| What is the function of glycophorin in red blood cells that a SDS Page gel would confirm? | Gylcophorin binds sugars and is part of the cytoskeleton, wouldn't move as much as a free-floating protein. (BAND 3 is an anion transporter used in the pH buffer system involving carbonic acid (HCO3-) |
| What is the significance of Freeze Fracture Electron Microscopy? | A cell membrane is frozen in buffer and sliced to cytosolic and extracellular layers of membrane are divided. Analysis of proteins indicates which layer they are more associated with. |
| What layers of a membrane would glycophorin and BAND 3 associate with from the use of Free Fracture Electron Microscopy? | Glycophorin associates with the extracellular layer of the membrane (E face). BAND 3 associates with the cytosolic layer of the membrane (E face). |
| How does FRAP (Florescence Recovery After Photobleaching) aid in protein analysis? | After GFP (green fluorescence protein) is inserted into a proteins plasmid, a laser bleaches a small area of a cell to deactivate GFP. If a protein is mobile in membrane, cell will fluoresce in area that was bleached. |
| What are three reasons why proteins do not move in membrane? | It is part of a big complex in the membrane, it is bound to other proteins outside cell (cytoskeleton or EC matrix), or is bound to membrane protein of other cell (cell junction) |
| What molecules can move across the membrane fairly easily? | Hydrophobic molecules (O2, CO2, N2, benzene, steroids, hormones) and Small Uncharged Polar Molecules (H2O, urea, glycerol). |
| What molecules have trouble moving across the membrane? | Large Uncharged Polar Molecules (Glucose, Sucrose) and Ions (H+, Na+, HCO3-, K+, Ca2+) |
| What are two types of proteins used in molecular transport? | Carrier Proteins and Channel Proteins |
| What are the characteristics of carrier proteins? | Carrier proteins have a solute binding site, transport molecules across the bilayer, and change shape while transporting molecules (passive or active transport) |
| What are the characteristics of channel proteins? | Channel proteins have an aqueous pore to allow movement, do not change shape, and only do passive transport |
| What is passive transport? | A simple diffusion, channel or carrier-mediated transport that does not require energy. Moves molecules from areas of high to low concentration (probability) |
| What is active transport? | Carrier-mediated transport that requires energy and occurs from low to high concentrations (against gradient). |
| What are three ways to drive active transport? | Coupled Carrier, ATP-Driven Pump, and Light-Driven Pump |
| How does coupled-carrier transport work? | The energy needed to transport against a concentration gradient is stored in the gradient used to transport another molecule in the other direction (example= Sodium-Glucose Transporter Na+ goes high to low into cell, glucose goes low to high into cell) |
| What is an electrochemical gradient? | A difference in the amount of charged molecules across a membrane (Na+ outside vs. inside cell) and difference in membrane potential |
| What is a membrane potential? | A difference in charge across a membrane due to phospholipids( such as phosphotidylcholine in cytosolic layer of membrane) |
| What are three types of Carrier-Mediated Transport? | Uniport, Symport, and Antiport (symport and antiport are coupled transport) |
| Where is the Sodium-Glucose Transporter found in the body? | Located in the intestinal epithelial cells (microvilli of the lumen of the gut) where glucose must be transported from the lumen into the cell, and from the cell to the extracellular fluid. |
| How does the Sodium-Glucose Transporter work? | First, Na+ binds to protein from outside of cell and increases affinity for glucose bind. Na+ and glucose are then dumped into the membrane (energy as coupled carrier and symport transport) |
| How do mobile glucose transporters stay in the correct area of the membrane? | Tight junctions prevent proteins from moving away from part of the membrane where they need to be. |
| What other proteins exist in the intestinal epithelial cells to maintain homeostasis? | The symport Na+/Glucose transporter, the antiport Na+/K+ pump (ATP), and the Passive Glucose Transporter (uniport) |
| Where is Calcium found and what concentrations occur in cells? | Ca2+ reservoirs occur in mitochondria, the ER, and the sarcoplamsic reticulum (muscle cells). Ca2+ has a high concentration outside of the cell, and a low concentration in the cytosol |
| What does the Sodium-Potassium Pump regulate and work? | The Na+/K+ pump uses ATP to pump Na+ and K+ against their concentration gradients (pumps 3 Na+ outside cell and 2 K+ inside cell). 1 ATP is hydrolyzed and protein becomes phosphorylated |
| If a cell is placed in a hypertonic solution, what will occur? A hypotonic solution? | In a high salt environment, the water will follow the salt and the cell will shrivel (pump will slow). In a low salt environment, cell will swell (pump will activate to release ions) |
| What are some characteristics of the Potassium Ion Channel? | A passive transport channel that has a pore and does not change shape. K+ ions diffuse outside the cell. A selectivity filter allows K+ to pass by interaction with oxygen molecules (vestibule allows Na+ and K+ to enter but not pass) |
| What is the Potassium Ion Channel made of? | The channel consists of four subunits and the inside pore is lined with polar carbonyl groups. |
| How do passive ion channels close? | Alpha-helices become closer together to close the channel (do not change shape while transporting molecules) |
| What are three types of gated ion channels? | Voltage gated (membrane potential), Ligand gated (bound ligands/neurotransmitters), and Mechanically gated (vibrations/pressure) |
| What are the three parts of a typical neuron? | A cell body (with dendrites), an axon, and terminal branches |
| What is an action potential? | A signal( wave of changes in membrane potential) that travels down a neuron |
| What type of channels line an axon to propagate an action potential? | Na+ voltage channels open when membrane potential changes. 3 conformations can be open, closed (large potential -70 mVolts), or inactivated. Allows Na+ into the cell. |
| What conformation is the channel when the membrane is polarized? Depolarized? | When membrane is polarized, channel is closed. When depolarized, channel is open (smaller membrane potential) and then inactivated. |
| What do Patch-Clamp Recordings tell us? | While a pipette tip takes a part of a membrane and a current runs through, a reading will tell if the channel is open or closed. |
| Approximately how long does it take to open, inactivate, and close Na+ voltage channels? | About 2 milliseconds. |
| What is the refractory period? | The time it takes for an inactivated channel to return to the closed conformation |
| What is myelin and what cell secretes it? | Myelin is a fatty insulator that allows propagation of an action potential along an axon. A Schwann cell wraps myelin sheath around an axon. |
| What is the space between myelin sheaths called? | node of Ranvier |
| What types of channels occur on the post-synaptic target cell? | A ligand-gated ion channel (Na+) |
| Where is neurotransmitter stored at in a chemical synapse? | In vesicles of the pre-synaptic terminal branches |
| What promotes release of neurotransmitter at the synaptic cleft? | As the action potential reaches terminal branches, Ca2+ voltage ion channels allow Ca2+ into cell, and promotes fusion of vesicle to membrane and promotes exocytosis |
| What would release of acetylcholine into a neuromuscular synapse cause in the post-synaptic cell? | Acetylcholine would bind to Na+ ligand ion channel, and allow Na+ into cell to begin action potential in new cell. |
| What happens to neurotransmitter left in the synapse? | Most neurotransmitter is taken back up by presynaptic cell, but some is degraded by enzymes. |
| How does a muscle contract in the post-synaptic cell of a neuromuscular junction? | When Ca2+ voltage channel opens Ca+ release channel in sarcoplasmic reticulum and causes contraction from concentration in cytosol |
Created by:
jgk25
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