Transport Across the Membran BIOL 160 Sphack Lecture 6
Transport Across the Membran BIOL 160 Sphack Lecture 6 Biol 160
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This 4 page Class Notes was uploaded by Anushree Kumar on Monday March 7, 2016. The Class Notes belongs to Biol 160 at University of Tennessee - Knoxville taught by Dr. Shpak in Spring 2016. Since its upload, it has received 12 views. For similar materials see Cellular and Molecular Biology in Biology at University of Tennessee - Knoxville.
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Date Created: 03/07/16
BIOL 160 Sphack Transport Across Membrane Important point key term learning objective Plasma Membranes - Selective permeability o Allows compounds inside that cell needs o Keeps band compouds out - allows cell to maintain homeostasis o environment inside cell can be different from outside of cell - allows compartmentalization o chemical reactions are more efficient o reactions that don’t go well together can be separated Fluid Mosaic Model – a model that shows how proteins are imbedded in the membrane - model includes phospholipids and proteins o integral proteins – inside the hydrophobic bilayer amphipathic – part hydrophilic and part hydrophobic can span a membrane can have segments facing the inside and outside of cell o peripheral proteins - on the outsides of the bilayer/hydrophilic sides found only on the side of the membrane peripheral proteins are usually attached to integral proteins - proteins in general can be amphipathic o the hydrophilic amino acids will be towards the end o hydrophobic amino acids will stay in the middle Freeze Fracture proteins – experiment that figured out proteins were imbedded in the membrane - scientist froze a cell in ice - broke off a section of the ice o this peeled some of the membrane off so that half of the lipid bilayer was still intact - they noticed bumps were jutting out even though the top half of the bilayer was removed - concluded these were proteins imbedded in the membrane Fluidity of Membrane - phospholipids are in constant lateral motion o weak hydrophobic reactions make this possible o p.lipids usually never switch sides Electrochemical gradient - the concentration (of atoms) and charge gradient across a membrane - Na+/Cl- gradient o more Na+ outside cell o more Cl- inside cell Passive Transport/Simple Diffusion - moves down concentration gradient - no energy input required - no type of transport protein involved - movement of substances through channels and carriers are passive - passive transport - Transport Proteins – integral proteins that transport molecules and affect membrane permeability - Channel proteins o Facilitated diffusion down/along chemical gradient o Channel has specific structure for 1 or 2 particular ions/molecules o Helps molecules get across more efficiently aquaporin is a common channel protein – it helps water molecules across the membrane - Gated channels o Regulates movement across membrane o Opens and closes in response to a signal Example: potassium channel in membrane. When inside of membrane has a negative charge (relative to outside) then channel is closed. If the charges reverse(inside becomes more positive), the channel opens to restore the original charge state Example: if a molecule binds to the channel, it can stay open for as long as the molecule is binded (extracellular) ligand gated channel o This is still passive transport - Carrier proteins/transporters o Interact with their “cargo” heavily o Physically change shape to allow bigger molecule Still passive transport Factors that affect the rate of facilitated diffusion - Solute concentration on either side of membrane - Number of carrier proteins available in membrane - Affinity of carrier proteins for ions/molecules Pumps -membrane proteins that actively transport molecules across membrane o Uses active transport! o Pushes molecules against electrochemical gradient o Requires ATP to function Against gradient isn’t natural, that’s why it needs energy to do this How ATP Actually Works - P-groups have 2 negative charges - 1 P group leave ATP o Makes 1 ADP and 1 lone P - Lone P interacts with the charged amino acids in the protein (pump) - This makes the protein’s potential energy increase o The protein changes shape because of it - when lone P leaves, protein changes shape again o returns to original shape and process starts again ATP is an example of an activated nucleotide How the Na+/K+ pump works - Empty (unbound protein: 3 empty slots in protein that have a strong attraction for Na+ ions - 3 Na binds to sites o 3 NA+ ions from the inside bind to these spots. o ATP approaches the pump - ATP makes pump change shape o A phosphate from ATP binds to the protein, making the protein change shape - Na+ ions release o Once protein changes shape, the Na+ ions leave the cell o The lone P is still attached to the protein - Empty (unbound) protein o After Na+ ions leave, there are 2 slots in the protein that have a high attraction for 2 K+ ions o Lone P is still attached - 2 K+ bind to sites o 2 K+ ions from outside the cell bind to these spots o Lone P is still attached - P leaves and changes shape o The lone P finally leaves, making the protein change back to its original shape (in shape 1) - K+ ions release o Once protein changes shape again o The K+ ions leave the protein and go inside the cell - The process repeats Secondary Active Transport/Cotransporter - Cotransporter – transmembrane protein that helps diffuse and ion down its gradient, while simultaneously transporting another ion against its gradient - Two types of cotransporters o Symporters – Uses energy from transporting ion A down gradient to transport ion B in the same direction, against its gradient o Antiporters – transports ion A down gradient while transporting ion B in the opposite direction, against its gradient Primary Active Transport vs. Secondary Active Transport - Primary – requires hydrolysis of ATP to drive movement. Different molecules that are being transported move one molecule type at a time o Example: Na+/K+ pump - Secondary – molecule transport that transports two molecules/ions. One with gradient, one against. Doesn’t require ATP because secondary transport utilized gradients Cystic Fibrosis - can be caused by improper flow of chloride ions
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