Class notes
week 5 lecture 1 notes
- Course
- Institution
cell biology 2b03 lecture notes, exam review 2022
[Show more]
Seller
Follow
notetaker12345
Content preview
WEEK 5LECTURE 1: PROTEIN PROCESSING AND TRAFFICKING IN THE RER
ROUGH ER + SMOOTH ER FUNCTIONS
• RER
o Many ribosomes
o Co-translational transport
o Protein modification
o Formation of vesicles to transport proteins from ER to Golgi
• SER
o No ribosomes
o Fatty acid + phospholipid synthesis
o Carb metabolism
o Calcium sequestering to regulate Ca+ concentration in cytosol
POST TRANSLATIONAL MODIFICATIONS (PTMS) IN THE ER
1. Glycosylation
2. protein folding
3. disulphide bond formation
4. proteolytic cleavage
• modifications occur in luminal part of membrane, not on transmembrane domain or
cytosolic part
1. PROTEIN GLYCOSYLATION: N-LINKED
• covalent addition of polysaccharides
• on proteins. Secreted from cell + embedded in
cell membrane
• needed for proteins that mediate cell interactions with extracellular matrix +
receptor-ligand recognition
• N-linked glycosylation:
o Add sugar to NH2 of R-group of asparagine
• Further modifications to the sugar can occur in ER and Golgi
• Required for proper transport of proteins, folding + stability, function (influences
substrates)
, 2. PROTEIN FOLDING IN THE ER
• Recognize amino acids carrying N-linked sugars
• Lectins recognize modified proteins + help fold (similar to chaperones)
o Calnexin + calreticulin
§ Calnexin in ER membrane
BIP
• ER resident HSP70 chaperone
• Function depends on ability to recognize + bind to
unfolded proteins
• Co-chaperones Hsp40 + nucleotide exchange factor
• Transfer proteins from ER through translocon by
binding to proteins as soon as they appear on luminal
side of membrane during co-translational transport
• Initiates unfolded protein response in ER
3. DISULPHIDE BOND FORMATION IN ER
• Disulphide bond: covalent linkage between sulfhydryl groups of 2 cysteine residues
• In proteins secreted from cell + on outer leaflet of membrane
o Helps maintain folds of protein
• Can occur within a single protein (intramolecular) or 2 different proteins
(intermolecular)
• In eukaryotic cells: oxidative rxn to form disulphide bond only in ER
• Lumen of ER: oxidizing environment (favours reverse rxn)
• Cytoplasm: reducing environment
DISULPHIDE BONDS IN RNASE A
• Pancreatic ribonuclease A contains 4 disulphide bridges
• Secreted into intestine
• Digestion of RNA by cleaving it into small pieces
• Acidic condition of small intestine normal cause proteins to denature
• Prevented by disulphide bonds
PROTEINS DISULPHIDE ISOMERASE (PDI)
• Resident ER protein that promotes oxidation
• Forms intermediate with 2 cysteine residues to
accelerate rate of rxn
• Oxidized PDI contains a disulphide bridge
• PDI intermediate with 1 cysteine residue in a
protein to form intramolecular cysteine bond
• PDI spontaneously converted back to oxidized
form
• Can correct inappropriate disulphide bridges
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller notetaker12345. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $5.99. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
78834 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now