Biochemsitry Ch 22 - Biological Membranes
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What do the components biomembranes do?
Transport different molecules inside and out of the cell or intracellular organelle
What are the functions of the membrane?
- Maintain cell potential
- Signal transduction
- Cell recognition
- Provide sites for maintaining the intactness of the cells
What are examples of lipid components of biological membranes?
(T/F) Phospholipids in the membrane diffuse freely along the layer.
(T/F) Sphingolipids form the outer leaflet of the plasma membrane.
True. The layer is mechanically and chemicall stable which is belived to play a protective role.
What are lipid rafts?
Cholesterol interacts with fatty acid tails of phingolipids serving as "glue" to hold the raft together. Some proteins associate preferably with lipid rafts and the components are held together by weak interactions, there is rapid exchange of lipids and proteins between lipid rafts and the surrounding membrane.
What does loss of lipid asymmetry across the membrane indicate?
Exposure of phosphatidylerine in the outerpart of the bilayer is a signal for programmed cell death (apoptosis)
In red blood cells, phosphatidylserine is important for blood clot formation.
What are the three types of lipid-translocating proteins?
What are Flippases?
ATP-dependent lipid translocating proteins that catalyze the transport of the lipds from the outer to the inner leaflet against the concentration gradient.
What are floppases?
ATP-dependent lipid-translocating proteins that transport substrates from the inner membrane to the external part of the membrane.
What are scramblases?
- Lipid-translocating proteins that are nonspecific bidirectional lipid translocases.
- They transport along the concentration gradient
- Not ATP-dependent.
What are the three types of lipid-linked proteins?
- Prenylated proteins
- Fatty acid acylated proteins
- Glycosylphosphatidylinositol-linked (GPI-linked) proteins
What are prenylated proteins attached to?
Isoprene units attached to a cystine amino acid.
What are fatty acid acylated proteins attached to?
Myristolyation - amino group of an N-terminal amino acid residue (mostly glycine) of a protein. The myristoyl residue is 14 carbons long.
Palmitoylation is attached to cystine with a total of 16 carbons.
What is contained in the gates and fences model of the cell?
Some proteins are tightly bound to the skeleton and are immobile. Some proteins are limited in their movement by the spectrin. Some proteins are free to move.
What is an example of SRP (signal recognition particle) in protein synthesis?
GDP may also be a SRP receptor on the surface of the rough endoplasmic reticulum.
Once GDP attached to the ribosome attached to the messenger RNA, it converts to ________.
This allows for it to be used as a singaling protein for the SRP receptor on the RER surface.
What the length of two carbons within a fatty acid?
0.28 nm. This includes the angle that the carbon chain forms.
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