Protein embedded in the membrane Flashcards
In eukaryotes, what is the most common way to maintain an integral (transmembrane) protein?
Alpha helixes.
Why are alpha helixes used by eukaryotes to maintain integral proteins?
Because the basic carboxyl ammonia skeleton of a protein is hydrophilic. Alpha helixes line up and hydrogen bond all of the backbone of the amino acids in the alpha helix. The only thing facing out is the R groups which can be nonpolar.
Where are beta-barrels found?
In the membranes of prokaryotes.
What effect is achieved if a membrane bound protein is bound by a protein who’s alpha helix has one side hydrophilic and the other hydrophobic.
It causes the protein to only be imbedded in one of the two layers of the phospholipid bilayer.
Myristoyl, palmitoyl, and farnesyl anchors anchor what? By ionic or covalent bonds?
This are lipids, which anchor proteins to a monolayer of the phospholipid bilayer. They are covalently bonded to the proteins at consensus sequences.
Which lipid covalent anchor is reversible? Why might it reverse?
Palmitoyl anchor’s are reversible. They might reverse because of a signaling event.
Myristoyl, palmitoyl, and farnesyl anchors all anchor on which side of the plasma membrane?
Cytosolic layer.
What is glycosylphosphatidylinositol protein anchor structurally? How and where is it synthesized?
Glycosylphosphatidylinositol is a phosphatidylinositol (which is a phospholipid bound to a inositol, which is a six member C ring with 1 OH group at each carbon), that has complexed through phosphate with carbon, has had a small carbohydrate string added, and an amino acid as well. This amino acid sticking out can be bonded to a protein. It is synthesized in the ER.
glycosylphosphatidylinositol are anchored to proteins which were suspended in the membrane by?
A short Amino acid sequence ending in the hydrophilic carboxyl group.
A protein is exposed on the lumenal surface of a phospholipid bilayer in the ER, if sent to the extracellular or cytosolic side of the membrane? What if it was on the lumenal side of the Golgi apparatus? Or a vesicle?
For all three it would arrive on the extracellular side of the membrane.
A 30 amino acid long alpha helix is likely in which area of the plasma membrane? What is the range roughly of alpha helix sizes which can exist transmembrane?
In a lipid raft, since it is thicker. 20-30 is about the range.
What does a hydropathy index plot measure? What does a high number value mean?
A hydropathy index plot measures essentially how energetically efficient it is to have that sequence of amino acids placed in the plasma membrane. It plots in units of four amino acids at a time, the length of a single turn in an alpha helix roughly. A more positive value is more non-polar and therefor more likely.
____ percent of proteins have transmembrane domains according to the hydropathy index plots?
30%
What attribute of transmembrane proteins like aquaporin allows for ion-selective transfer?
Aquaporin has multiple transmembrane domains (alpha helices), these shield two incomplete alpha helices, which each make it a little less then half the membrane towards each other. These allow for their to be a niche in the middle which helps to increase ion flow.
Will the transmembrane domains of a multiple transmembrane protein still interact if they where cut by a protease (in a non transmembrane regions), what if the transmembrane pieces were synthesized apart? What does this imply?
Yes and yes. The fact that transmembrane regions associate with being covalently bonded shows that the transmembrane regions themselves interact strongly with each other. This implies a high level of specificity between transmembrane domains for the fellow transmembrane domains within the same protein.
