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Flashcards in Protein embedded in the membrane Deck (32):

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?



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.


Each transmembrane domain is inserted into the membrane individually in a multiple transmembrane domain protein?

Yes. Of course yes. Can you imagine the amount of energy it would take to shove 8 alpha helices at the same time through the hydrophilic portion of the membrane?


Transmembrane alpha helixes can slide relative to each other, beta barrels are rigid. How does this effect function?

The alpha helices are providing a machine which maintains mobility, the beta sheets are a machine with no moving parts. Still useful, but it has lost some versatility.


Attachment of oligosaccharides and formation of disulfide bonds occurs exclusively in the _____. Which is topologically equivalent to the _____. So these two features are distinctive to which monolayer?

Lumen of the Endoplasmic reticulum and the golgi apparatus.

Extracellular space.

The extracellular monolayer.


What is another term for the glycocalyx?

The cell coat.


What is the glycocalyx? What is it made out of? What does it do?

It is a combination of glycoproteins and glycolipids that coat the extracellular monolayer of the plasma phospholipid bilayer. It provides protection, and allows for distinctive cell recognition. In other words specific cell types will have specific glycocalyx's.


Detergents form micelles, whereas phospholipids form liposomes/lipid bilayers. Why is there this difference?

Detergents have a single nonpolar tail. Phospholipids have two. This extra area extends them to form bilayers. Detergents break these bilayers by acting like micelles.


Understand the nature of how detergents break apart phospholipid bilayers. Google it now.

I was serious.


A belt can be made out of HDL (high density lipoproteins. How does this connect to detergents and transmembrane proteins?

This belt can take both the transmembrane protein and the lipid environment it was found in.


Transmembrane domains have specificity for both the other transmembrane domains in a multi-transmembrane protein and for specific phospholipids/membrane lipids which will form a specific environment around them (or the protein will migrate to a specific environment which is ideal for it). True or false.

Oh so true!


Glycolipid lipids form covalent or ionic interactions between lipid and carbohydrate?



In the plasma membrane glycolipids are found on which monolayer?



What are Lectins?

Lectins are proteins which bind carbohydrates. They can bind to the carbohydrate portion of a glycolipid. This can mediate cell to cell interactions.


What are glycolipids synthesized from?



What is a ganglioside?

The most complex glycolipid. The contain sialic acid (NANA). Sialic acid has a single negative charge, which attracts extracellular calcium 2+ (which is in abundance outside of a cell but scarce inside) this association between a -1 charge and a +2 results in an increased + charge to the outside of the cell. When we consider phosphatidylserine we realize the cytosolic monolayer is negatively charged. This contributes to membrane potential.


Which cell type is NANA most common in?

Nerve cells, since they need a strong membrane potential.


What is another name for sialic acid? Which molecule has at least one sialic acid?

NANA. A ganglioside (which is a type of glycolipid).


Caveolae is a special type of lipid raft which is involved in?

Endocytosis. Cavoelae are where the invagination which becomes the endosomes originates in the plasma membrane.