The Endomembrane System and Membrane Trafficking
What is the function of Dynamin?
Once clathrin coats the membrane and causes it to invaginate, Dynamin comes in at the branch connecting the almost formed vesicle to the rest of the membrane and squeezes it until the vesicle is released from the membrane.
What is the function of the ER Signal Sequence?
The sequence on a protein that the SRP binds to allowing it to drag it to the ER, this sequence is then cut off as the partially translated protein is being threaded through the translocon
Define and Explain Regulated Secretion
The signals cluster in vesicles, they're bound for the plasma membrane (so they can released into the ECF), but they are only secreted when you receive the proper signal (insulin). There are only one type of secretory signal produced in a cell at a given time (ex: cells in the Islets of Langerhans produce only insulin) and the signal for fusion of the vesicle containing the secretion with plasma membrane is a rise in intracellular Calcium
What is the function of Endocytosis/Autophagy?
The things lysosome munch on on is wrapped inside of a membrane (the source of the membrane isn't known) and that fuses with the lysosome
What is opsonization?
when complement coats a microbe and provides binding sites for phagocytes to engulf the invader
What does N-Linked Glycosylation do?
Polysaccharides attach to asparagine (N), this aides in protein folding, slows the rate of degradation of secreted/membrane proteins, and makes up recognition domains.
What happens if a misfolded protein was sent out into the body?
Pretty much can lead to cystic fibrosis
What happens if the GTP hydrolyzes before the SNARE binds to the RABs?
RAB will release from the tethering protein and will need to be rebound to another GTP to try again
Describe Cystic Fibrosis
A certain Cl- ion channel in the cells lining the respiratory tract are slightly misfolded so BiP doesn't allow them out of rER. Leads to no enough Cl- leaving the cell=increase in osmolarity of the cell=sucks up the water from the ECF= the ECF becomes thick and raps bacteria leading to chronic lung infections
What is the function of Receptor-mediated endocytosis?
A form of pinocytosis where the cell absorbs metabolites, hormones, proteins, and viruses (way viruses enter cell). Occurs when clathrin-coated sections of the membrane that contain the receptor for the ligand turn into vesicles. (process of LDL internalization)
What is the function of the "Eat me" signaling protein?
A special signal used to coat anything that is destined to be eaten by a lysosome.
What is role of Mannose-6-phosphate (M6P) signal in targeting newly synthesized lysosomal hydrolyses to lysosome?
ALL LYSOSOMAL HYDROLASES receive a special signal as they travel through rER and the Golgi called M6P signal and this signal TARGETS THESE PROTEINS TO LYSOMES. In the trans Golgi there's the M6P receptor than binds all of the lysosomal hydrolyses and clusters them in vesicles, clathrin then clusters the receptors and it buds off and forms a primarily lysosome.
What is an important "Eat me" signal in the human body?
Antibodies
What are secondary lysosomes?
Are the primary lysosomes that fusee with a vesicle containing cargo to be digested
What is BiP?
Binding Protein
What is function of SRP?
Binds to proteins being translated in the cytoplasm by free ribosomes and stops translation. From there the SRP translocates the protein + ribosome complex
What is the function of Phagosomes?
Cell engulfed a solid particle (ex: bacteria) and the particle is placed inside of a vesicle, that vesicle fuses with lysosome but only after the vesicle is covered with the "eat me" signal (opsinizied).
What is the function of Phagocytosis?
Cell uses pseudopodia formed by actin polymerization to engulf a particle, that particle is now inside of vesicle headed towards the lysosome BUT it needs to be seasoned before its eaten which is where the "eat me" signaling molecules come in to play. The ligand is opsonized (in humans we opsonize using antibodies) and then vesicle fuses with a lysosome and particle is digested to the best of the lysosomes abilities.
What is function of Translocon?
Channel on the ER membrane, SRP drags protein to the translocon, feeds the protein through the hole, the protein is now inside of the ER
What is the function of BiP (Binding Protein)?
Chaperone protein found in the lumen of rER and it binds to the hydrophobic regions of proteins that should be folded properly (but since they have hydrophobic regions show they are obviously not folded properly) and try to refold them. If the refolding just isn't happening the BiP takes messed up protein and drags it out of the ER through protein translocator and lets ubiquitin bind to it; leads to proteasome shredding the messed up protein BiP is the biggest party stopper, if a protein isn't folded perfectly it will not release it
What is the function of the clathrin coated vesicles?
Clathrin binds to membrane via the adaptor proteins and induces an invagination of that membrane which then cut off from the rest of the membrane by Dynamin Clathrin are required for a vesicle to bud off
What is the purpose of RABs?
Contribute to the specificity of docking reaction, found on a vesicle that binds to a tethering protein which gets the vesicle close to the membrane allowing SNARE to bind and fuse the two of them.
Describe Hypercholesterolemia (FH)
Defective LDL receptor =LDL can't bind to it= no clustering into the clathrin-coated section of the membrane= no vesicle with LDL inside of it= LDL floats around within the serum= Cardiovascular disease in the patients 30s and 40s (assuming the patient only has one ****ed up allele that codes for this stuff (heterozygous)). IF the patient is homozygous for the ****ed allele the cardiovascular disease might start in childhood.
Describe Botox
Degrades SNARES (proteins that allow vesicle to fuse with a membrane) found inside of the axon terminals in the face, this results in no acetylcholine being able to cross int he synapse = prevents muscle contraction. Tetanus toxin causes lockjaw by the same mechanism
What happens when there is no adaptin or messed up adaptin?
Hypercholesterolemia cardiovascular disease at an early age
What is the function Glycocalyx?
Is a kind of 'sugar rim' made of carbohydrates bound to lipids and proteins on the outside of cell 'glass' Serves a protective function (since it absorbs water it becomes kind of spongy) and is very important in cellular recognition
What is the function of HSP70?
Known as "chaperone" protein because it aids in correct protein folding by binding to the hydrophobic domains present in the newly translated protein for an amount of time (however long it takes HSP70 to Hydrolyze its ATP) the time bought allows for another hydrophobic region to be translated and for the two hydrophobic regions to interact with each other
What is the function of LDL Pathway?
LDL (low-density lipoproteins (balls of cholesterol and fats that come from the liver)) binds to adapting which causes receptors to cluster in clathrin-coated pits. From there clathrin and dynamin do their things and the vesicles with LDL inside of it is formed
What is the function of Adaptins?
LDLs bind to this receptor and it causes the receptors to all congregate in the clathrin-coated section of the membrane and become a vesicle within the cell.
What are the steps of the Secretory Pathway?
Secreted proteins are translated by the ribosomes in the rER and then travel from rER to the Golgi apparatus by a vesicle Vesicle from rER contain the newly translated proteins fuses with the cis face of the Golgi and dumps the proteins inside the cisternae of the Golgi The proteins move from the list to eh medial to the trans region of the Golgi where it is bagged, tagged and shipped in vesicles out of the cell (only contains perfectly folded membrane/soluble proteins)
What is an important N-linked sugar?
Sialic acid, its negatively charged and its what gives the plasma membrane an overall negative charge on the extracellular side
What is the function of M6P?
Signal that all of the lysosomal hydrolyses receive as they travel through the rER and the Golgi that targets these proteins to the lysosome. The receptor on the trans side of the Golgi binds M6P and cluster them so they can all be in a vesicle together. When that vesicle buds off it is considered to be a primary lysosome
What is one way to treat Hypercholesterolemia?
Statin
What is the function Rough Endoplasmic Reticulum (rER)?
Synthesizes and modifies secretory/membrane/Golgi/ ER proteins (basically any proteins that doesn't work inside of the cytoplasm or the mitochondria)
What is the function of Pinocytosis?
Taking things outside of the cell and putting them inside of vesicles/vacuoles inside of the cell. Caveolae and clathrin-coated vesicles are some of the types of vesicles that can carry out pinocytosis
Define and Explain Constitutive Secretion (bulk flow)
Vesicles containing things you want to secrete at all times (ex: membrane proteins) travel to and fuse with the plasma membrane directly after leaving the Golgi. There is no signal needed to cluster into a vesicle and no signal needed to fuse with the plasma membrane
What are the modifications that occur to proteins and lipids as they pass through the rER and Golgi?
While the secretory protein is being synthesized inside of the rER it is being modified in a few major ways partially due to the that of the lumens of the ER and Golgi are more oxidative than the cytosol and they have different enzymes than the cytosol. (MODIFICATIONS ONLY OCCUR TO THE SIDE OF THE PROTEIN FACING THE LUME OF THE ER/GOLGI). This difference will allow cysteine to form disulfide bridges with other cysteine= helps in folding and stabilization Signal peptidases (SRP (binding proteins that stops cytosomal translation and carries the ribosome and the partially translated protein into the sER)) are cut off so that translation can continue. (ONLY OCCURS IN THE ER) Protein Folds: Aided by BiP and HSP 70, important for quality control
What is the function of Clathrin?
type of protein that binds to certain membrane proteins and causes receptor-mediated invagination of cell membrane. This is a major player in pinocytosis/endocytosis (works with dynamin)
What is the function of SNARES?
v-SNARE located on the membrane of the Vesicle t-SNARES are located on the Target membrane SNARES interact with each other which results in vesicle fusing with the target membrane
What does the addition of the GPI anchor help in for proteins?
~40 membrane proteins get cut in such a way that they lose their transmembrane proteins to peripheral membrane proteins. These GPI's cluster in the caveolae and serve as signaling proteins