Lecture 9. Synthesis and Packaging of Signaling Molecules for Release Flashcards
How does the secretory system function ?
Through the use of vesicular transport
What is vesicular transport ?
When transport vesicles carry soluble proteins and membranes between compartments
What did Pallad show us ?
How proteins move through at a subcellular level
What is sec 1 protein essential for ?
Vesicles fusing with a membrane which is called Munc 18
What can vessels with sec 1 do ?
Carry a full cargo intended for the cell surface but cannot merge with it and releases their contents
What does sec 7 do ?
Causes a huge swelling in the golgi network that prevents vesicles from forming
What happened when sec 1 and sec 7 are crossed ?
The swellings still formed but vesicles were not produced.
This tells us that vesicles production was downstream or later in the process than swelling formation
What do proteins destined for the membrane or secretory pathway have ?
A signal sequence on the nascent polypeptide
What does having a signal sequence on the nascent peptide target the proteins for ?
Binding with the protein signal recognition particle
How many particles does the signal recognition particle contain ?
6
What is the function of the signal recognition particle ?
Binds to the signal sequence and take it to the endoplasmic reticulum
What happens once the signal recognition particle has bound the signal sequence ?
It is recognised by the signal recognition particle receptor protein which is in the membrane of the rough endoplasmic reticulum
What happens when the signal recognition receptor protein complex binds ?
It directs the nascent protein into the lumen of the endoplasmic reticulum
Where does the signal peptide go through ?
The translocator complex
What happens when the signal peptide goes through the translocator complex ?
The signal peptidase cleaves off the signal peptide which is left in the membrane and the mature protein is cleaved off and liberated into the endoplasmic reticulum
What is the function of sugars that bind to the protein as it emerges into the endoplasmic reticulum ?
Regulate protein folding
What are the chaperone proteins that recognise the sugar binding ?
Calnexin and calreticulin
What are calnexin and calreticulin specialised to do ?
Recognise when the sugars are being cleaved off and therefore retain the protein in the endoplasmic reticulum until the protein is correctly folded
What is the signal that protein folding is complete ?
Once the sugar residues have been cleaved off
What do exit signal proteins do ?
Recognise the released proteins with some specificity and begin to form vesicles
What is the function of coat protein complex coated vesicles ?
They are structurally important in organising the form of the vesicle
What can the vesicle coated with COPII do once it forms the vesicular tubule structure ?
Can bud off
How does the vesicle coated with COPII travel ?
In an antergrade fashion along the microtubule
What do vesicles coated with COPII use to walk and carry the cargo ?
Motor proteins like kinesin
What is vesicle coated with COPII targeted according to ?
What they are coated in to move towards the golgi network
In the golgi apparatus, what are vesicles sorted into ?
Cis-cisterna, trans-cisterna and the trans-golgi network
What labels the layers in the stack in the golgi ?
Different enzymes or substances
What happens to the vesicles after they have gone through several processes in the golgi?
Proteins are sorted into new vesicles which bud off from the trans golgi network to the final destination in the cell
How does insulin messenger RNA go from the ribosome to the endoplasmic reticulum ?
Translator complex
What is insulin synthesised as ?
Pre pro insulin
What does pre pro insulin have that targets it to the signal recognition complex ?
A signal sequence
What part of the pre pro insulin gets cleaved off in the endoplasmic reticulum ?
The signal sequence
Once the signal sequence is cleaved from the pre pro insulin how many amino acids remain ?
76
What happens after pre pro insulin cleavage ?
It starts to fold but three disulphide bonds form which keep the a and b parts of the peptide together