Biological membranes are about ___% lipid and ___% protein.
Biological membranes are about 50% lipid and 50% protein.
In most naturally occurring triglycerides, the ____ fatty acid molecule is ____.
In most naturally occurring triglycerides, the central fatty acid molecule is unsaturated.
In solution, fatty acids spontaneously form. . .
In solution, glycerolipids spontaneously form. . .
a lipid bilayer
Cholesterol in membranes
If there is no head group, it is phosphatidic acid.
If there is a head group it is phosphatidyl x. (example: if x is a choline, it is phosphatidyl choline).
Types of glycerophospholipid
Types of sphingolipid
glucocerebrosides, unlike phosphatidylinositol, are ___.
glucocerebrosides, unlike phosphatidylinositol, are neutral. They do not carry a phosphate group.
Different membranes have different ____.
Different membranes have different membrane lipid compositions. Different leaflets also have different membrane lipid compositions.
Major Routes of Protein Trafficking
Proteins translated in the cytosol may end up in compartments 1, 2, 3, or 4.
Proteins translated in the ER may end up in 5, 6, 7, 8, or 9.
Proteins from outside the cell may end up in compartments 10 or 11.
Signal sequence for cytoplasm
Signal sequence for nucleus
Nuclear localization sequence
The NLS is a short stretch of basic amino acids arginine (R) and lysine (K)
Signal sequence for mitochondria
Mitochondrial localization sequence
Basic localization flowchart
Signal sequence for peripheral membrane proteins
Must be c-terminal. example: CCIL-Cterm
Signal sequence for integral membrane protein
Must also contain ER signal seq, as it requires ER processing.
SXXS - Hydrophobic span, ~22 amino acids - R and K-rich region, ~6 amino acids
Ecto domain - Transmembrane domain - cytoplasmic domain
Signal sequence for constitutive secretion
Just the ER localization sequence is sufficient to enter the secretory pathway.
Signal sequence for regulated secretion
Various sequences for targeting to specific regulated secretory granules. Often controlled by calcium.
Signal sequence for ER residents
ER localization sequence
C-terminal KDEL sequence
Signal sequence for lysosomal proteins
Architecture of nucleus
Nuclear transport occurs through. . .
Nuclear pores complexes
Attached is an image showing scanning EM of both sides of a nuclear pore. Note the 8-fold symmetry.
The nuclear localization sequence is a binding site for ____.
The nuclear localization sequence is a binding site for importins.
The nuclear pore proteins (nucleoporins) have long tails that have repeats containing hydrophobic amino acids like phenylalanine. These hydrophobic tails stick together due to the hydrophobic effect, creating a meshwork that blocks the passage of moderate- to large-sized proteins. The importin proteins have hydrophobic amino acids on their surface that can interact with the hydrophobic tails of the nucleoporins, allowing them to “melt” the meshwork and pass through it. By binding cargo proteins with NLS’s, the importins can piggyback proteins through the meshwork.
Signal sequence for peroxisome
SKL = Serine-Lysine-Leucine
Anchoring of peripheral membrane proteins
All of these proteins are considered peripheral membrane proteins, but only the proteins on the inside of the cell would be translated by cytosolic ribosomes. The protein on the outside of the cell would be translated by a ribosome attached to the ER.
Cartoon of the secretory pathway
Channel in the ER membrane that binds proteins by the ER localization sequence as they are being translated and facilitates their translation into the ER.