Protein Sorting And Transport Flashcards
(14 cards)
Explain ‘central dogma’.
The flow of genetic information from DNA to RNA to protein.
Explain what happens in protein synthesis?
1) In the nucleus, gene encoding specific protein is transcribed into mRNA.
2) mRNA is translated by ribosomes in the cytoplasm.
3) Ribosomes read the mRNA strand and join the AA’s together to make a PP chain.
What are signal sequences?
Short stretches of AA’s in a pp chain which act as a postal code that directs proteins to their specific destination.
OR
A short peptide that directs the ribosomes to the ER
What kind of signal sequence does a protein meant for ER have?
Proteins meant for ER have a N-terminal signal sequence which consist of hydrophobic AA’s.
Explain the steps for signal sequences.
1) SRP binds to signal sequence whilst the protein is being synthesised by ribosomes. This causes translation to halt temporarily.
2) Ribosomes-SRP complex docks at the SRP receptors on the ER membrane, positioning the ribosomes near a protein channel known as translocon.
3) Once the ribosomes are secured, the pp chain is fed through the translocon into the ER lumen. Signal sequence is then cleaved off.
Describe nuclear localised signals (NLS).
It directs proteins to the nucleus. It is rich in +ve AA’s like lysine and arginine.
Describe the target signals for the proteins meant for the mitochondria.
The target signals contain alternating hydrophobic and +ve residues.
Where does the secretory pathway begin and what happens there?
It begins in the ER. Proteins for secretion and membrane localisation is synthesised and folded. Protein undergo initial modifications.
Give 2 initial modifications proteins go through in the ER.
- Disulphure bond formation, for stabilisation of structure.
- Glycosylation, sugar chains attach for better stability and function.
After proteins undergo initial modifications in the ER, what happens?
2) proteins packaged into vesicles coated in COPII protein which facilitates their transport to the Golgi apparatus.
3) further modifications in the Golgi by glycolysation and tagged for final destination. Eg. Proteins for lysosome are embedded with mannos-6-phosphate ensuring they are recognised and directed to the lysosome.
4) vesicles bud off from the trans-Golgi network then guided to their target by molecular motors travelling along cytoskeleton filaments.
5) when vesicles reach destination, SNARE’s (protein) mediates fusion between vesicles and membrane.
Explain palade’s experiment.
He used radio labelled AA’s to trace movements by Newley made proteins which showed that proteins are 1st made in the ER to Golgi apparatus to secretory vesicles.
Give 3 example of disorders to do with protein sorting and transport.
1) Cystic fibrosis - a mutation in the CFTR gene leads to the production of misfolded chloride channel proteins. This protein stays in ER and never reaches cell surface resulting in impaired ion transport.
2) Lysosome storage disorders - deflect in the sorting of enzymes needed for degrading of cellular waste. Without enzyme substrate build up in lysosome causing cellular dysfunction and disease.
3) Alzheimer’s disease - misfolded amyloid beta protein build up and form plaque which disrupts neural function.
What is glycosylation?
The addition of carbohydrate groups/sugars to proteins. For stability and structure.
What is vesicles transport?
The process of transporting proteins between organelles in membrane-bound vesicles.
