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?

QuickTime™ and aCinepak decompressor

are needed to see this picture.

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

QuickTime™ and aCinepak decompressor

are needed to see this picture.

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