Week 4: Protein Import/Edport Flashcards
What happens if the protein is water soluble?
Stay in the cytoplasm Go outside the world (secretion) Go to the nucleus Go to other organelles (mitochondria, chloroplasts, peroxisomes)
How is the protein targeted to the membrane?
Need carrier to get the protein across the membrane
What is a bacterial system called?
TAT (twin arginine translocation)
What does TAT do
Take folded proteins across the membrane
What does getting a soluble protein across the membrane mean?
Move charged residues through the hydrophobic interior of the membrane
What are some views of the endoplasmic reticulum?
1) Immunofluoresence 2) scanning EM 3) transmission ER 4) model
Which resolution is higher than immunofluorescence?
Scanning EM
What are ribosomes associated with?
MRNA molecules
What are rough ER defined by?
The presence of ribosomes bound to cytosolic surface
What does polypeptide chain have?
Directionality N terminus and C terminus
What does the secretory protein that contain a signal sequence direct ?
Emerging polypeptide and ribosome to the ER membrane
What is a signal hypothesis?
The polypeptide moves into cisternal space of the ER through a protein-lined aqueous channel in the ER membrane
What does the single recognition particle in mammals consist of?
6 different polypeptides + RNA (7s RNA)
What does the SRP bind?
Both the SS on the nascent polypeptide chain and the ribosome
How does the binding to the ER occur?
1) SRP and SRP receptor (in the RER) 2) Ribosome and Translocon
How is the SRP released form the ER receptor?
SRP-ribosome-nascent-polypeptide binds to the cytosolic surface of the ER membrane
What enzyme cleaves the signal peptide?
Signal peptidase
What helps to fold the protein to pass through the lumen?
Chaperon
What does targeting to the membrane require?
Signal polypeptide ( SRP and SRP receptor)
What is required for protein to cross the membrane?
Translocon
How is crossing the membrane done?
Co-translationally (protein crosses the membrane and at the same time it is synthesised)
What was the matrix?
The cytoplasm of the bacterium
What is the function of mitochondria?
Encodes and produces it’s own proteins
What was the inter membrane space?
Periplasm of a gram negative bacterium
What do mitochondria and chloroplast have in common?
Organelles that originated by endosymbiosis Make their own proteins/ most encoded in the nucleus and synthesised in the cytoplasm
What is the difference between mitochondrial system and RER system?
There is no co-translational translocation across the membrane
What is an example of a chaperone?
Hsp50
What is the machinery that gets the polypeptide across the outer membrane ?
TOM complex
What is TIM?
A hydrophobic protein channel in the IMM
Inside the matrix what does the chaperone interact with ?
Polypeptide - helps to pull it through the membrane and then help it fold correctly
What removes the presequence?
Peptidase
What is the Translocon in outer membrane of chloroplast?
TOC
What is the Translocon in inner membrane?
TIC
What is stop transferase sequence?
Hydrophobic transmembrane segment containing at least 15 amino acids
Where is stop transferase sequence located?
Remain in the membrane and is not passed through to the lumen
What is the role of Translocon?
Responsible for determining the correct orientation of the protein in the membrane
What orientation is the proteins synthesised in the RER ?
Inserted into the lipid bilayer in a predictable orientation determined by its amino acid sequence
Where are carbohydrate chain located?
Cisternal side of the cytoplasmic membrane which become exoplasmic side of the plasma membrane following the fusion of vesicles with plasma membrane
What will be found in the cytoplasm?
Glycerol, fatty acid and head group
