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What are the functions of cellular membranes?
- -Structural backbone
- -selectively permeable membrane
Which three types of macromolecules are found in
the cellular membranes and which one is responsible for the majority of
- lips, proteins and carbohydrate groups
- Proteins-•Enzymes, anchors, transporters,
In terms of weight, rank the three macromolecules
in decreasing order of their relative abundance in most cellular
membrane. Is the protein/lipid ratio always the same between different
types of membranes? (see Table 7-1)
- Protein, lipids, carbohydrates
- No, different
What are the three types of membrane lipids?
phospholipids, glycolipids, sterols
a phospholipid found in animal plasma membranes and absent in plants and bacteria
they are glycolipids found in brain and nerve cells
they are glycolipids found in brain and nerve cells
What is the main sterol found in animal, plant,
fungal, or prokaryotic cell membranes respectively?
- •Main one in animal cell membranes
- is cholesterol
•Phytosterols in plants
•Ergosterols in fungi
•Hopanoids in some bacteria
How does thin-layer chromatography separate
different types of lipids?
- Chromatography separates lipids according to their polarity or relative
- affinities for the polar plate and the less polar solvent.
How would phospholipids molecules organize
themselves when they are in water?
- Phopholipids form a bilayer (about 6-8nm thick)
- to shield hydrophobic tails from water
- -energetically favorable
- they self seal
In what ways can cellular membranes in various
organelles, cell types, or species of organisms differ?
- Membranes differ in
- the types of lipids, the types of fatty acid chains (length and number of
- double bonds), and the R or head groups.
The current model of membrane structure is the fluid-mosaic
model, explain this model. What do “fluid” and “mosaic” mean? Describe
how lipids can move within a membrane.
- Fluid means they care constantly moving
- Mosaic means the lipids have proteins bound in a certain way.
- lipids move by –Free movement within monolayer (lateral diffusion)
–Free rotation along long axis
–Flip-flops (transverse diffusion) are rare
In which organelle are new phospholipid
molecules synthesized and how are they added to the growing membranes?
- •New phospholipids are made in the ER and added
- to the cytosolic side of the bilayer.
- They are added by vesicles
What are flippases?
They flip phospholipids from the inner membrane to the outer.
In what ways is the lipid bilayer asymmetric?
–Have different kinds of lipids
- –Differ in the degree of
- saturation of the fatty acids
- –Glycolipids of the plasma membrane are only
- in the outer monolayer
- –Proteins are embedded with a
- specific orientation
Be able to follow the
cytosolic and noncytosolic/extracellular sides of the membrane as a
vesicle fuses with the plasma membrane.
What is Tm for a lipid bilayer? What
happens to the Tm when membrane fluidity increases or
- 28 degrees
- if it increases it turns fluid
- if it decreases it turns gel/solid
What are some factors that influence membrane
–Temperature (warmer → more fluid)
–Fatty acid chains
•Length (shorter → more fluid)
- •Degree of saturation (more
- unsaturated → more fluid)
•Decrease fluidity at T > Tm (rigid intercalation)
- •Increase fluidity at T < Tm (prevent tight packing of
- fatty acid chains)
How does the presence of sterols in membranes
affect its permeability?
- Sterols are in both bilayers but each sterol is
- on one side.
- Decrease the fluidity
- of the membrane at high temps but increase fluidity at low temps.
- Sterols decrease
- membrane permeability.
What are the three main classes of membrane
- Integral membrane proteins - transmembrane
- peripheral membrane proteins - surface only
- lipid anchored membrane proteins- On the surfaces of the bilayer but covalently bound to lipids embedded within the bilayer.
How does each class associate with the lipid
How is each class removed/solubilized/isolated
from the lipid bilayer?
- integral- use of detergents
- pH or ionic strength (e.g. high-conc. salt solutions) of the solution
- lipid anchored- Covalent
- bonds to the lipid must be cleaved before removal of these proteins
What types of secondary structures are found in the
transmembrane/membrane-spanning region of membrane proteins? How are the amino
acid side chains (what types) arranged?
alpha helices, beta barrels
What are some characteristics of detergent
molecules? What is SDS?
- Dissolve membranes and separate proteins from lipids.
- –Single hydrophobic tail
- –Aggregate into micelles in water
What is a micelle?
they selfseal into spheres
In which four ways can lateral movement of
proteins within membranes be restricted?
- Membrane proteins tethered to proteins inside the cell .
- Membrane proteins tethered to extracellular matrix
- molecules outside the cell.
- Membrane proteins tethered to proteins on the surface of
- another cell.
- Tight junctions
- restrict proteins to particular membrane domain
Know how these three membrane domains differ:
apical, lateral, basal.
What is glycosylation?
- is the addition of a
- carbohydrate side chain to a protein.
- Glycosylation occurs in the ER and Golgi and usually appears
- on the noncytosolic side of the membrane protein.
In which direction do carbohydrates attached to
membrane lipids or proteins face?
Describe and sketch the
pathway taken by glycolipids or glycoproteins as they are synthesized,
glycosylated, and inserted into the plasma membrane (include the
organelles in which each process occurs).
What functions does the external carbohydrate
- •Protects cell surface from
- mechanical and chemical damage
•Lubricates and hydrates the cell
What are glycolipids, glycoproteins, proteoglycans,
- they form Glycocalyx: the carbohydrate
- coat on many animal cells
- Recovery After Photobleaching (FRAP)
- •Can be used to measure lipid mobility within membranes
, hydropathy analysis
- membrane-spanning regions by looking at the DNA sequence of the protein &
- identifying regions with hydrophobic amino acids
, radioactive labeling
- Radioactive labeling
- with lactoperoxidase and 125I
- determines protein orientation. (Use of galactose oxidase and 3H-BH4
- labels carbohydrate side chains.)
cell fusion with fluorescent staining.
What information can each of these methods
provide? Understand how each method works. You may be asked to interpret
- Most membrane
- proteins are mobile in the membrane; their mobility can be measured by
- •Cell fusion via a
- virus & fluorescent antibody labeling
- •Methods used to determine protein orientation
- –Radioactive labeling
- –Antibody binding / Affinity
- Hydropathic Analysis-
- Predicts membrane-spanning regions by looking at the DNA sequence of the
- protein & identifying regions with hydrophobic amino acids