Midterm 3 Flashcards
(107 cards)
Why are membranes important to organisms?
- Surround cells, organelles, and other structures
- Gatekeeper for entry and exit of molecules
- Transmits signals from outside to inside of cells
- Location of key reactions in cells
- mitochondrial membrane site of ATP
What is the composition of membranes?
mixed with lipids and proteins
What are the Lipids involved in the membrane?
- Major Phospholipids = Glycerophospholipids and Sphingolipids
Glycerophospholipids includes:
Phosphatidylcholine and Phosphatidylethanolamine - Sterol = major sterol is cholesterol
What are the proteins involved in the membrane?
- mostly containing proteins
- often contain carbohydrates that are glycosylated
- makes up 75% = more than the lipid bilayer — packed proteins
Membrane lipids form a bilayer
polar head group = faces out
fatty acids = faces in
two layers = fatty acids are not exposed to water
Why does the bilayer fold into a sphere?
- fatty acids are not exposed to water
- it creates inner aqueous cavity (cytosol) which holds the cell contents
Lipids can also form micelles, what are micelles?
- single layer that does not contain an aqueous cavity
- formed by fatty acids (not phospholipids)
- wedge shape of fatty acids encourages the formation - micelles are formed during the digestion of fats
Membranes are asymmetric, what does this mean?
- leaves of the bilayer are asymmetric = one leaf may have the components while the other leaf does not.
Examples of membranes being asymmetric.
ER and Golgi
- starts symmetric in the ER and becomes asymmetric in the Golgi
Plasma Membranes are also asymmetric
What is added to the Golgi that makes it asymmetric?
Sphingolipids
What are the 3 types of protein?
Integral
Peripheral
Amphitrophic
What are integral proteins?
- embedded in the bilayer
two types:
- monotopic ( one leaflet)
- polytopic (both leaflets (top and bottom))
- can only be removed chemically in the lab with detergents
What is the structure of an integral protein?
- hydrophobic = non polar = embedded in the membrane
- hydrophilic = polar = not embedded in the membrane
What does it mean when the hydropathy index is higher/positive
Amino acid is more hydrophobic
What is the hydropathy index?
- it measures how hydrophobic an amino acid is
_______ define the different regions
Amino Acids
Hydrophobic regions have
amino acids that have high hydropathy index
Regions with high hydropathy index will likely to be
integral proteins
__________ are common in regions embedded in membrane
certain protein structures
– ∂ helix
– ß barrel ( r groups are facing outwards)
What are the amino acids that are common at the outer edge of the membrane
Tyr and Trp
Tyr and Trp have
r groups that have intermediate hydropathy index = nonpolar or neither polar (good for this environment)
- Large R groups = better for stability and serves as an anchor
What are peripheral proteins?
- can be chemically removed in the lab via high ph and carbonate (used too purify the protein)
- peripheral proteins are attached to integral proteins via hydrogen bonds and electrostatic interactions
- attached to integral but not embedded in the membrane
What is amphitropic proteins?
- Proteins that are 50/50 when attaching to membranes (sometimes attached sometimes not)
- the attachment is regulated biologically by the cells
- can attach end detaches which is controlled by cells (enzymes)
Example of amphitropic proteins?
- GPI anchor proteins
- linked to membrane lipid through an oligosaccharide
- releases when an enzyme (phospholipase C cleaves oligosaccharides
from lipids)