Protein Localization Flashcards
Membrane-enclosed organelles often have characteristic positions in the cytosol
Protein pathway from nucleus
Nucleus
ER
Transport vesicle
Golgi Apparatus (Cis face)
Golgi Apparatus (Trans face)
Secretory vesicle
Protein expelled
Function of proteins are determined by their localizations in cells
- Cytosolic Protein Synthesis
Proteins are synthesized by ribosomes in the cytosol.
Some proteins remain in the cytosol as they lack specific localization signals.
- Endoplasmic Reticulum (ER) Targeting
Proteins with an ER signal sequence are directed to the rough ER.
The signal sequence allows entry into the ER lumen, where they undergo folding and modifications.
- Golgi Complex Processing
Proteins from the ER are transported to the Golgi apparatus.
The Golgi further processes and sorts proteins for their final destinations.
- Secretory Pathway
Some proteins are sent to the plasma membrane for secretion or become integral membrane proteins.
Others are targeted to lysosomes for degradation functions.
- Peroxisomal Targeting
Proteins with a peroxisomal targeting sequence are directed to peroxisomes.
Peroxisomes play roles in lipid metabolism and detoxification.
- Mitochondrial and Chloroplast Targeting
Proteins meant for mitochondria or chloroplasts contain specific targeting sequences.
These sequences allow them to be imported into their respective organelles, where they function in energy metabolism (e.g., ATP production in mitochondria, photosynthesis in chloroplasts).
Conclusion
The localization of proteins is determined by specific signal sequences within their structure.
Proper localization is essential for cellular function, as proteins need to be in the correct organelles or membranes to perform their roles efficiently.
4 ways proteins are transported:
1.Protein translocation
*Protein translocators transport proteins
*E.g. cytosol-ER lumen, mitochondria, ER
2.Gated transport
*Involves selective gates
*E.g. nuclear transport
3. Vesicular transport
*Involves transport vesicles
4. Engulfment/autophagy
*involves of formation of compartments
PGVE
A simplified “roadmap” of protein traffic
Identify which type of protein transport:
Nucleus <-> Cytosol
Gated transport
A simplified “roadmap” of protein traffic
Identify which type of protein transport:
Cytosol -> Plastids
Protein translocation
A simplified “roadmap” of protein traffic
Identify which type of protein transport:
Cytosol -> Mitochondria
Protein translocation
A simplified “roadmap” of protein traffic
Identify which type of protein transport:
Cytosol -> ER
Protein translocation
A simplified “roadmap” of protein traffic
Identify which type of protein transport:
Cytosol -> Peroxisomes
Protein translocation
A simplified “roadmap” of protein traffic
Identify which type of protein transport:
ER -> Peroxisomes
Vesicular transport
A simplified “roadmap” of protein traffic
Identify which type of protein transport:
ER <-> Golgi Body
Vesicular transport
A simplified “roadmap” of protein traffic
Identify which type of protein transport:
Golgi Body <-> Late Endosome
Vesicular transport
A simplified “roadmap” of protein traffic
Identify which type of protein transport:
Golgi Body <-> Early Endosome
Vesicular transport
A simplified “roadmap” of protein traffic
Identify which type of protein transport:
Golgi Body -> Plasma membrane and Cell exterior
Vesicular transport
A simplified “roadmap” of protein traffic
Identify which type of protein transport:
Golgi Body <-> Secretory vesicles
Vesicular transport
A simplified “roadmap” of protein traffic
Identify which type of protein transport:
Late Endosome -> Lysosome
Vesicular transport
A simplified “roadmap” of protein traffic
Identify which type of protein transport:
Secretory Vesicles -> Plasma membrane and Cell exterior
Vesicular transport
A simplified “roadmap” of protein traffic
Identify which type of protein transport:
Cytosol -> Lysosome
Engulfment
A simplified “roadmap” of protein traffic
Identify which type of protein transport:
Early Endosome -> Late Endosome
Vesicular transport
A simplified “roadmap” of protein traffic
Identify which type of protein transport:
Plasma membrane and Cell exterior <-> Early Endosome
Vesicular transport
2 ways in which sorting signals can be built into a protein:
Signal sequence
Signal patch
- a continuous stretch of amino acid sequence, typically 15-60 residues long that resides in a single discrete stretch of amino acid sequence
- used to direct proteins from the cytosol into the ER, mitochondria, chloroplasts, and peroxisomes, and nucleus to the cytosol and from the Golgi apparatus to the ER
- Recognized by sorting receptors
Signal sequence
Where is the signal sequence located in an amino acid:
Amino group or Carboxyl group?
Amino group
- 3D arrangement of amino acids formed by the juxtaposition of amino acids from regions that are physically separated before the protein folds.
- Cytosol-nucleus
Signal patch