BIOL 230 - Chapt. 15 Protein Transport Pt. 2

What type of signal sequence do proteins imported to the mitochondria and chloroplasts have? 

N-terminus 

What does a protein have to do to enter mitochondria or chloroplasts? 

unfold

What is the N-terminus recognized by?

complex of import receptor and translocator of outer membrane

The protein diffuses laterally of complex until it is recognized by what?

translocator of inner membrane

What do both translocators do once protein is recognized by inner membrane translocator?

transport protein across both membranes unfolding the protein in the process

What cleaves off the signal sequence after translocation through both inner and outer membrane? 

signal peptidase 

What helps pull proteins across membranes and helps refold the proteins and requires ATP?

chaperones

Where do proteins enter from in peroxisomes?

the cytosol and the ER

How do proteins from the cytosol enter peroxisomes?

the import signal being recognized by the receptor protein in the cytosol that escorts protein into the peroxisome

How do proteins from the ER enter peroxisomes? 

arrive via vesicles that bud from ER that fuse with preexisting peroxisomes 

Can proteins reenter the cytosol after being inside ER lumen or being embedded in the ER membrane?

NO

What types of proteins are transferred from the cytosol to the ER?

water soluble proteins, prospective transmembrane proteins

Where are water soluble proteins destined for? 

secretion, or the lumen of an organelle of endomembrane system 

Where are prospective transmembrane proteins destined for?

the membrane of organelles of endomembrane system or in the plasma membrane

What directs ribosomes to the ER membrane?

ER signal sequence

TRUE or FALSE? Proteins enter the ER while being synthesized

TRUE 

What directs a ribosome to the ER membrane?

ER signal sequnce and SRP

What is the function of the signal reception particle (SRP)?

binds the ER signal sequence and the ribosome

What protein embedded in the membrane recognizes SRP?

SRP receptor, releases SRP from ribosome

Where does the SRP receptor pass the ribosome to?

protein translocator

What does the ER signal sequence open? 

protein translocator 

What work together to embed double-pass membranes in the bilayer?

start transfer signal and stop transfer sequence

What is vesicular transport? 

the movement of material between members of the endomembrane system via transport vesicles 

What is an endocytic pathway?

ingestion or degradation of molecules via endosome/lysosome

What is a secretory pathway?

synthesis of proteins begins on ER membrane and their entry into ER to golgi to cell surface

What do transport vesicles carry? 

soluble proteins and membrane components between organelles 

What are in the contents of a transport vesicle?

contents or cargo, membrane itself, membrane components

What is the best studied vesicle coating?

clahtrin

What is the function of adaptins? 

recognizes molecules for transport 

What does clathrin do?

binds adaptin and forms basketlike cages that help shape membranes into vesicles

What does dynamin do?

form a ring around the neck of each invaginated section of the membrane and constricts until the vesicle is pinched off

What does vesicle docking depend on?

tethers and SNAREs

What happens during tethering? 

Rab proteins (GTPases) recognized by tethering proteins 

What happens during docking?

v-SNARE binds t-SNARE

What happens during fusion?

SNARE proteins catalyze fusion of membranes by winding together and squeezing any water that remains between layers

What do disulfide bonds do? 

stabilize structure of proteins that will encounter degradative enzymes 

where are most proteins covalently modified?

in the ER

What is glycosylation?

conversion of some proteins that enter ER to glycoproteins

What does oligosaccharyl transferase do? 

transfer proteins to glycoproteins 

What is the function of glycosylation?

protects protein from degradation, holds it in the ER until properly folded, aids in cell recognition

What is preformed oligosaccharide attached to?

specialized lipid, dolichol

What does oligosaccharyl transferase do? 

transfers oligosaccharide to amino group of an asparagine side chain of protein 

Where does oligosaccharide processing continue?

in the Golgi

What is constitutive secretion?

supplies plasma membrane with newly made lipids and proteins and carries soluble proteins to cell surface to be released outside, occurs continuously

What is regulated secretion?

occurs in cells specialized for secretion, large amount of product, stored in secretory vesicle for later release, release is regulated, stimulated by signal

Where is most extracellular material taken up by pinocytosis delivered to? 

endosomes

What do endosomes do?

sort endocytosed material

What is the function of an acidic endosome interior?

causes receptors to release their cargo

What happens to receptor proteins?

recycled, degraded via lysosome, or transcytosis

What is LDL (low density lipoprotein)?

a protein that transports cholesterol 

What provides a specific route into animal cells?

receptor-mediated endocytosis