Final Exam Flashcards
Cytosol compartment function
contains many metabolic pathway; protein synthesis; the cytoskeleton
Nucleus compartment function
contains main genome; DNA and RNA synthesis
Endoplasmic Reticulum (ER) compartment function
synthesis of most lipids; synthesis of proteins for distribution to many organelles and to the plasma membrane
Golgi Apparatus compartment function
modification, sorting, and packaging of proteins and lipids for either secretion or delivery to another oganelle
Lysosomes compartment function
intracellular degradation
Endosomes compartment function
sorting of endocytosed material
Mitochondria compartment function
ATP synthesis by oxidative phosphorylation
Chloroplasts (in plant cells) compartment function
ATP synthesis and carbon fixation by photosynthesis
Peroxisomes compartment function
oxidative breakdown of toxic molecules
what is the fate of each protein after synthesis?
Protein Sorting
Protein Sorting
Energy-dependent mechanisms for protein entry into an organelle from the cytosol
Proteins are transported into organelles by three mechanisms
- Transport through nuclear pores
- Transport across membranes
- Transport by vesicles
What do Signal sequences do?
The signal sequence is a “flag” bound to an amino acid terminus and directs proteins to the correct compartment
Signal sequences are ___________________ to direct a
protein to an organelle
necessary and sufficient
Necessary (signal sequences)
removing a signal peptide from a protein that should go to the ER, the
protein remains in the cytosol (default location)
Sufficient (Signal Sequences)
adding an ER signal peptide to a cytosolic protein, makes it move to
the ER
Small molecules can freely diffuse through the nuclear pore but large
molecules like proteins cannot pass without _________________________
an appropriate sorting signal
To pass through the nuclear pore
_________ need to present
proteins
nuclear localization signal
(short stretch of lysines/arginines,
positive charges)
nuclear transport receptors
recognize the nuclear transport
signal and help the protein
through by disrupting the gel-like
meshwork of nuclear fibrils
Proteins remain in their fully
folded conformation (as they were in the ribosome)
throughout the _________ _________
transport process
What drives nuclear transport?
Energy supplied by GTP hydrolysis
Ran-GTP
high affinity for Nuclear Import Receptor; Nuclear
Ran-GDP
low affinity for Nuclear Import Receptor; Cytoplasmic
True or False: Proteins must be unfolded during transport.
true
What helps re-fold the protein after transport
Chaperone Protiens
What do N terminal signal sequences target?
proteins to specific site within the organelle
What is the most extensive membrane in the cell that is also the entry point for proteins destined for several other organelles and the cell exterior?
The ER
What kinds of proteins are transferred by the cytosol to the ER?
- Soluble Protein
- Transmembrane Protein
Soluble Proteins
-Transferred completely to the ER lumen
-Destined for secretion out of the cell or to the lumen of another organelle (not mitochondria or plastid)
Transmembrane Proteins
-Partly translocated into ER, embedded in the membrane
-Destined to reside in ER or the membrane of another organelle or plasma membrane
What is happening while the proteins enter the ER?
While being synthesized
What do the Membrane-bound ribosomes do?
make proteins that are translocated to the ER
What makes all the other proteins?
Free ribosomes
Steps of Signal Recognition in the cytosol
- ER signal sequence on the growing polypeptide chain
- Signal Recognition Particle (SRP)
- SRP receptor in the ER membrane
- Translocation channel
