Protein Trafficking Flashcards
What determines protein cellular destination?
Destination is encoded in the proteins amino acid sequence known as sorting signals,
Continuous or discontinuous sequences.
Recognised by receptors proteins.
Eg-KDEL for ER retention and nuclear localisation signals for import into nucleus
What are the main pathways of protein transport within cells
Gated transport- movement between equivalent spaces, nucleus and cytosol via nuclear pore complex’s.
Transmembrane transport- movement across membrane using translocators eg cytosol to er
Vesicular transport-transport within membrane-enclosed vesicles between organelles.
Describe the secretory pathways for proteins
Co-translational transport into the ER
Exit ER and entry into the Golgi
Passage through Golgi for processing
Exit Golgi via secretory vesicles.
Exocytosis- fusion of vesicles with the plasma membrane for secretion
What modifications occur to proteins during the secretory pathway
In ER: N- linked glycoslylation , folding and quality control by chaperones.
In Golgi: o-linked glycosylation, extensive trimming and processing of glycoproteins.
Role of vesicular transport in cells?
Vesicles carry proteins,
Between ER, Golgi and plasma membrane
Using membrane budding and fusion process
Key differences between constitutive and regulated secretion
Constitutive: continuous secretion without external signals
Regulated: requires specific signals (for hormones) for vesicle fusion and content release
What are the main types of endocytosis
Pinocytosis- uptake of fluid and small molecules
Receptor-mediated endocytosis: uptake via specific receptors
Phagocytosis: ingestion of large particles by specialised cells like macrophages
What is the endosomal pathway for endocytosed material?
Plasma membrane -> early endosome sorting-> late endosome ->lysosome for degradation
Alternatively- early endosome-> recycling endosome-> plasma membrane
Role of early endosome play in vesicular trafficking
Act as sorting hubs determines whether cargo,
Progresses to late endosomes for degradation,
Returns to the plasma membrane via recycling endosomes
Signals within the cell
Role of protein coats in vesicular transport
Protein coats (eg. Clathrin , COPI, COPII),
Shape the membrane into vesicles
Capture specific cargo molecules
Clathrin- involved in endocytosis
COPI-mediates Golgi to ER retrograde transport
COPII- directs transport from ER to Golgi
Coat disassembly occurs after vesicle budding to allow fusion
What is the function of Rab GTPases in vesicular transport
Rab GTPases-ensures specificity in vesicle targeting by tethering donor and target compartments via Rab effector
How do SNAREs mediate vesicle fusion
V-SNAREs and t-SNAREs
Interact and wind together to bring membranes close
Facilitate membrane fusion by overcoming energy barriers
Proteins ,ice NSF dissassemble SNARE complexes post fusion
What are the key steps in vesicle fusion
Tethering by Rab GTPases and effectors
Docking via snare complex formation
Fusion of vesicle and target membranes
Lipid bilayers rearrange to for a continuous membrane
Why are SNAREs critical for intracellular transport
Provide specificity in vesicle fusion
Ensure preside delivery of cargo to the correct
Regulate processes such as neurotransmitters release and membrane recycling
What happens when vesicular trafficking pathways are disrupted
Mislocalisation of proteins
Accumulation of vesicles
Potential cellular dysfunction, contributing to disease like neurodegeneration
