lect 10: intracellular membrane traffic Flashcards
what are the learning objectives of this lecture?
-explain the steps involved in vesicle transport and target membrane fusion
-explain the functions of lysosomes
-describe how proteins are taken up by mitochondria, and peroxisomes
-YOUR HOMEWORK: describe how proteins are transported into the nucleus (into nuclear envelope)
what is the graph of exocytosis and endocytosis?
vesicle budding is driven by __________________
the assembly of a protein coat
what is the graph of clathrin-coated vesicles transport?
transport SELECTED cargo molecules (very specifically bringing in molecules)
-dynamin and friends=constricts and detaches vesicle from plasma membrane
what is the table of some types of coated vesicles? what is the role of clathrin?
the role of clathrin is to induce curvature of plasma membrane and start bud formation
what is the role of adaptins?
- associating clathrin molecules
- bind to cargo receptor (cargo selection)
what are the steps of targeting vesicles to a particular compartment?
- move vesicle toward specific target compartment
-become associated with microtubules and motor proteins - tether vesicles to target compartment
- dock vesicles with target compartment
- fusion between vesicle and target membrane
vesicle tethering depends on….
vesicular transport has high specificity
-Rab proteins
-tethering proteins
-both of which are molecular markers
-complement and recognize one another to allow for fusion
tethering=bring things closer together
what is tethering?
vesicle docking depends on…..
SNAREs
what is docking?
SNAREs
-family of integral membrane proteins
-localized to specific subcellular compartments
-bring vesicle and target compartment in close contact (close enough to fuse)
-v-SNAREs=vesicle (green)
-t-SNAREs=target (purple, orange)
what is the docking and fusion of neurons?
neuron plasma membrane (2 t-SNAREs)
-syntaxin (red) (only 1 involved)
-SNAP-25 (green) (2 involved)
synaptic vesicle membrane (1 v-SNARE)
-synatobrevin (blue)
t and v SNAREs interact
-4-stranded bundles (alpha-helices)
-parallel orientation
-“zip” together
yellow=transmembrane domain (syntaxin doesnt have one)
what is exocytosis?
vesicle membrane orientation
-luminal part=extracellular surface of plasma membrane
-cytosolic part=intracellular surface
what are the two basic processes of endocytosis?
- bulk-phase endocytosis (pinocytosis)
-non-specific uptake extracellular fluid - receptor-mediated endocytosis (clathrin-mediated endocytosis)
-specific extracellular macromolecules
what is the endocytic pathway?
moving membrane and materials into cell interior
1. endocytosis
-internalization cell surface receptors/bound extracellular ligands
2. phagocytosis
-special type of endocytosis
-large particle e.g. bacterium
what are lysosomes in endocytic pathways?
lysosomes are the principal sites of intracellular digestion
-endocytic pathway is the main destinations for lysosomes
50 different hydrolytic enzymes found in lysosomes
-acid hydrolases (break down)
-optimal activity in acidic lumen
-pH is 4.6 (acidic, need sequestrated environment)
-pH maintained by protein pump in lysosome membrane (H+ ATPase)
what is the graph of endocytosis, phagocytosis and autophagy?
autophagy=organelles that aren’t functioning correctly
what is the posttranlational uptake of proteins by peroxisomes, mitochondra?
-peroxisomes are small, membranous organelles which contain enzymes for variety of metabolic reactions
organelles that import proteins through outer boundary membrane(s)
-nucleus, mitochondria, chloroplasts, peroxisomes
like RER
-proteins have signal sequences recognized by receptors on organelle outer membrane
unlike RER
-imported post translationally (i.e. NOT co-translationally) (entire polypeptide is synthesized and then moved)
-synthesis on free ribosomes
what is the uptake of proteins into peroxisomes?
peroxisomes have 2 subcompartments (result in translocation)
-boundary membrane (mPTS)
-internal matrix (PTS)
-peroxisomal targeting signals (see above)
-PTS receptors bind to peroxisome-destined proteins (cytosol)
-proteins shuttled to surface of peroxisome which is uptaked into organelle
what is the uptake of proteins into the mitochondria?
