Cell bio-Membrane Proteins
MHC proteins of the immune system
Some membrane proteins can serve as recognition proteins, distinguishing self from nonself; give an example
function as 1. enzymes 2. receptors 3. adhesion 4. recognition 5. transport
What are the five functions of membrane proteins
Can be purified by gentle methods that disrupt noncovalent interactions
What is useful about peripheral membrane proteins (protein associated membrane proteins)
beta barrel
a few membrane channels are formed by a beta sheet that is curved into a cylinder; what is this called
single pass alpha helix=receptor protein multi-pass alpha helix=channel forming protein curved beta sheet=channel forming protein
classify the following proteins as a receptor protein or a channel forming protein: single pass alpha helix multi pass alpha helix curved beta sheet
protein associated membrane proteins
these are entirely outside of the membrane and are noncovalently associated with other transmembrane or membrane associated proteins
lipid linked proteins
these are entirely outside the membrane and are covalently attached to a membrane lipid
membrane associated proteins
these proteins are located in the cytoplasm and are anchored to the inner layer of the plasma membrane via an amphipathic alpha helix
transmembrane proteins
these span the entire bilayer
1. resistance to phagocytosis by WBC 2. resistance to flushing 3. attachment to surfaces and to other bacteria
three functions of the glycocalyx in prokaryotes
hydrophobic amino acids
transmembrane alpha helices are composed almost exclusively of ?
kyte-doolitle hydropathy plot
transmembrane domains can be identified by analyzing the amino acid sequence of a protein; useful way to do this?
integral membrane proteins
transmembrane proteins membrane associated proteins and lipid linked proteins all of these are classified as peripheral or integral membrane proteins?
-sodium dodecyl sulfate (SDS)-strong, ionic -triton X-100- mild, nonionic
two common detergents
they have a hydrophobic tail and a hydrophilic head and can form detergent micelles
what does it mean that detergents are amphipathic
positive value goes to a hydrophobic AA negative value goes to a hydrophilic AA
when assigning a hydrophobicity value to AA for a hydropathy plot, which AA get the + value and which the - value
streptococcus mutans which initiates dental cavities by : 1. breaking down sucrose into fructose and glucose 2. breaking down glucose into dextran (which sticks to tooth enamel) using glucosyltransferase
example of prokaryotes using the glycocalyx
that would indicate two membrane spanning alpha helices
if a hydropathy plot indicated two regions of hydrophobicity; what would that indicate
it is composed of secreted carbs rather than carbs covalently attached to a lipid or protein
in prokaryotes, the glycocalyx, or cacpsule, is composed of ?
the free energy required to transfer that amino acid from a nonpolar solvent to water
in step one of hydropathy plot, you assign a hydrophobicity value to each amino acid; what is a hydrophobicity value
1. transmembrane proteins 2. membrane associated proteins 3. lipid linked proteins 4. protein associated membrane proteins
membrane proteins associate with lipid bilayers in what ways
enzymes for : oxidative phosphorylation light dependent reactions of photosynthesis adenylate cyclase enzyme to generate cAMP
membrane proteins can function as enzymes; give examples
Gap junctions-specialized intercellular connection between a multitude of animal cell-types. They directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regulated gate between cells.
membrane proteins can serve as adhesion proteins; an example includes connexons; what is this proteins function
integrins-link extracellular matrix to cytoskeleton
membrane proteins can serve as adhesion proteins; an example includes integrins; what is this proteins function
desmosomes-a cell structure specialized for cell-to-cell adhesion. A type of junctional complex, they are localized spot-like adhesions randomly arranged on the lateral sides of plasma membranes
membrane proteins can serve as adhesion proteins; an example is a cadherin; what is this proteins function
claudins and occludins provide tight junction
membrane proteins can serve as adhesion proteins; an example is claudins and occludins; what are the functions of these proteins
insulin receptor EPO receptor nerve growth factor receptor
membrane proteins can serve as receptors, binding extracellular messengers and generating intracellular signals; give examples
1. assign a hydrophobicity value to each amino acid 2. plot each amino acid in the polypeptide chain vs its hydrophobicity value 3. predict the membrane topography of the polypeptide
steps of conducting a hydropathy plot
true
t or f all eukaryotic cells have carbs attached to the plasma membrane
true
t or f cell membranes may be as much as 50% protein by weight
-h. phobic amino acid side groups exposed on outside of helix -polar peptide bonds in polypeptide backbone form H-bonds with each other inside helix
Explain the hydrophobic and hydrophilic anatomy of a membrane spanning alpha helix
porins; these are channel forming proteins in bacteria and the outer mitochondrial membrane
Give an example of a protein that can form a beta barrel
NaK and Ca pump
some membrane proteins provide transport, moving molecules across a lipid bilayer; give an example
glycolipid glycoprotein
carbs covalently attached to membrane lipids?carbs covalently attached to membrane proteins?
1. water-soluble complexes of transmembrane proteins and detergent molecules 2. water soluble mixed lipid-detergent micelles
disruption of a cell membrane by a detergent begins with combining a membrane protein in a lipid bilayer and detergent micelles -what are the results
leukocyte rolling
eukaryotes can use the glycocalyx for cell migration as in the migration of WBC out of the blood vessels; this is called ?
1. protection from mechanical and chemical damage 2. lubrication (in blood cells) 3. specific uses of carbs: -cell migration -cell cell recognition -communication -adhesion -immune responses -blood clotting -molecular targeting
functions of the glycocalyx in eukaryotes
this forms a carb layer around cells called a glycocalyx
glycoproteins and glycolipids almost exclusively face outside the cell, forming ?
face outside of the cell
glycoproteins and glycolipids almost exclusively face which direction in the cell membrane
membrane associated proteins are anchored to the inner layer of the plasma membrane by an amphipathic alpha helix
how are membrane associated proteins anchored to the inner layer of the plasma membrane
These proteins can only be purified by disrupting the ENTIRE membrane with a detergent
how are transmembrane proteins, membrane associated proteins and lipid linked proteins purified
They are peripheral membrane proteins
protein associated membrane proteins are classified as which type of proteins