Sec61/SecY Protein review
• Sec61 protein is important for the movement of proteins across the cell membrane?
• A signal sequence guides the protein to the Sec61 protein?
• A plug model was put into play by this paper?
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Lipid Membrane
More characteristics
• Driving Force of formation of lipid bilayer are Hydrophobic Interactions
Kinds of lipids in membrane
• Phospholipids
• Glycolipids
• cholesterol
Phospholipids
• PE- phosphatidyl ethanolamine
• PC- phosphatidyl choline
• SM- sphingomyleine
• PS- phosphatidyl serine
Can serve as different markers for cell
Kyte Dolittle
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K+ Channel
• Selective filter for moving potassium out of the cell
• Has four identical transmembrane subunits
• Each subunit has 2 transmembrane helices and a third shorter helix called the pore helix
• These subunits form a central pore
K+ channel
• Channel tilts outwards
• Has a loop that forms in channel and is going to make the selectivity filter, which will only allow K+ out
• Filter formed by carbonyl oxygens of the peptide backbone
• K+ is 1.95 A NA+ is 0.95 A
• In the cell potassium will be hydrated with water and so will sodium
• Bonding between these elements and water will be a specific length
• Water needs to be shed in order for K+ to go through
• Carbonyl oxygen will act as the surrogate water
• The dehydration of the ion takes energy but it is immediately made up by interactions with carbonyl oxygen
• Na is too small for this mechanism and therefore is not transported out
Porin
• Made by up and down barrel• Either 16 are 18 beta strands make up
the porin• Porin channel has a loop region in the
middle of it which will act as a selective filter. 8 A in diameter
• Only certain small molecules will be able to transverse the membrane
• Porin is made up of three channels as described
Bacteriarhodopsin
• 7 transmembrane alpha helices
• This protein is used for transforming light to chemical energy
• Proton pump
Retinol
• Bound in the pocket of the protein
• Undergoes isomerization when light hits it from trans to cis
• Bound covalently to lysine 216
The mechanism
• Light at a certain wavelength cause change from trans to cis of retinal
• Then Asp transfers proton to schiff base
• This proton is then transferred to Asp 85 and then out to the extracellular space
Result
• Form an electrochemical gradient which is important for bacteria survival
• Use for generation of energy
Photosynthetic Reaction Center
• L, H, M and cytochrome subunits
• L and M subunits each have 5 hydrophobic transmembrane helices
• H subunit has one transmembrane helice
What is taking place
• Transfer of light to generate energy
• Players in the reaction must be arranged in a way that ensures the forward movement of the reaction
• Photons absorbed by chlorophylls