9/2/14 - Intracellular Compartments Flashcards
What is the function of the endosome?
Acts as a sorting center or “checkpoint” between the cell membrane and the lysosome. Some molecules are processed and sent to the lysosome for destruction, and others are recycled.
Which organelle functions in the oxidation of fatty acids and some metabolic intermediates?
Peroxisome
Which organelle is responsible for the breakdown of most biomolecules?
Lysosome
What is the purpose of the Golgi apparatus?
To process and sort various molecules, especially those destined to be secreted by the cell.
What are some functions of the endoplasmic reticulum?
It has several functions, including protein synthesis and protein transport. It is also the site of lipid biogenesis and calcium storage.
What is the difference between a signal peptide and a signal patch?
A signal peptide is normally a sequence at the N-terminal, a signal patch is usually a combination of internal amino acid sequences that contribute to the folding of a protein.
What is the purpose of signal peptides and signal patches?
These “tag” proteins and allow cellular machinery to direct them to the appropriate compartment.
What features of signal peptides and signal patches direct proteins to specific compartments?
Amino acid sequence and folded structure.
Signal peptides with a hydrophobic center are typically directed to which organelle?
Endoplasmic reticulum
Signal peptides that are amphipathic alpha helices are typically directed to which organelle?
Mitochondria
What protein helps regulate transport of macromolecules through the nuclear pore?
Ran
What effect does protein size have on nuclear uptake?
Larger proteins require nuclear import signals or they will not pass through the pore.
Describe how Ran facilitates the transport of proteins across nuclear pores.
RanGEF (guanine nucleotide exchange factor) phosphorylates Ran-GDP to form Ran-GTP inside the nucleus. The Ran-GTP gradient across the nuclear membrane powers transport of proteins across the nuclear pore. In the cytosol, RanGAP converts Ran-GTP to Ran-GDP before being transported back into the nucleus in GDP form.
How does the function of Ran-GTP differ between nuclear export and nuclear import?
- Nuclear import: Ran-GTP stimulates dissociation of cargo from the import receptor.
- Nuclear export: Ran-GTP stimulates the association of cargo with the export receptor.
How can the regulation of nuclear import lead to changes in gene expression?
Transcription factors have to enter the nucleus before they can activate gene expression. A disruption in nuclear import could alter gene expression depending on which TFs were affected.
What are the four main structural elements of the mitochondrion?
- Outer membrane
- Intermembrane space
- Inner membrane
- Matrix space
Which membrane complex facilitates transport of proteins through the outer mitochondrial membrane?
TOM (translocase of outer membrane)
Which membrane complex facilitates transport of proteins into the mitochondrial matrix?
TIM23 (translocase of inner membrane)
What role do cytosolic chaperone proteins play in mitochondrial protein import?
Cytosolic Hsp70 bind to unfolded cargo proteins and “push” them through the mitochondrial membranes when powered by ATP hydrolysis.
How are transported proteins re-folded once inside the mitochondria? (2 related proteins)
- Chaperone Hsp70 stabilizes unfolded regions of a protein while the rest of the protein folds up.
- Chaperone Hsp60 forms a cage around the unfolded protein which protects it while it re-folds.
True/False: Peroxisomes perform most oxidation reactions within the cell.
False. Mitochondia perform the most oxidation reactions.
How are peroxisomes differentiated from mitochondria in EM imaging?
Peroxisomes lack inner cristae (inner folds of the mitochondrion) and have a dense core.
What is the main function of the rough ER?
Contains many ribosomes, therefore involved in protein synthesis.
Proteins translated on the ER typically end up in which two locations?
Membrane or secreted from the cell.
