Cell Bio Final_Exam 2 Essay_2019 Flashcards
Newly synthesized polypeptides (proteins) on the RER-bound ribosomes are modified co-translationally or post-translationally. Please describe how the proteins can be processed in the RER.
The signal sequence is cleaved by a signal peptidase
- Carbohydrates are added by the enzyme oligosaccharyltransferase
- Molecular chaperones assist in appropriate folding of proteins
- Protein disulfide isomerasecatalyzes formation of disulfide(-SS-) bonds between cysteinesto stabilize proteins
Please list the different functional compartments of Golgi complex and their functions, respectively
Functional compartments
-Cis Golgi network (CGN)
o A sorting station to determine destination of proteins
-Cis cisternae
-Medial cisternae
-Trans cisternae
o Sequentially modification of newly synthesized proteins from ER
-Trans Golgi network (TGN)
o A sorting station for segregating proteins into different types of vesicles for final destination
Please list the 3 major motor proteins inside the cytoplasm of eukaryotic cells, the tracks they use and their moving direction along the track.
Kinesin
- Move along microtubule tracks
- plus end-directed microtubular motor based on its movement
Dyenin
- Move along microtubule tracks
- minus end-directed microtubular motor
Myosin
- Move along microfilament track
- MyosinIImoves along microfilament tracks unidirectionally
- Myosin II move toward the plus end
- Actin filament is moved to the minus end
Please list proteins which are synthesized on the ribosomes bound to rough endoplasmic reticulum.
- Secreted proteins
- Integral membrane proteins
- Soluble proteins of residing in endomembrane system
List the major components of cytoskeleton, their individual composition and major function
Microtubules
- Wall of microtubule is composed of 13 protofilaments
I.To provide mechanical support
II.To maintain the internal organization of cells
III. Microtubules facilitate movement of vesicles between compartments
Microfilaments
- Actin protein is the only component
I. Responsible for motility of cell and intracellular parts
Intermediate filaments
- Composed of heterogeneous proteins
I. Primary structural protein for epithelial cells
II. Tethered to the nuclear envelop and radiate out anchoring at the outer edge of the cell by hemidesmosome and desmosome
III. Serve as a scaffold for organizing and maintaining cellular architecture
IV. Absorbing mechanical stresses applied by the extracellular environment
V. Resistant to tensile strength
Please list the name of the three major types of transport vesicles in the cytoplasm of eukaryotic cells, their individual functions, and how they select their cargos.
COPII-coated vesicles
- transporting cargo from the ER to the Golgi Enzymes that act at later stages in the biosynthetic pathway
o Certain integral membrane proteins of the
ER are selectively captured because they contain “ER export” signals as part of their cytosolic tail.
COPI coated vesicles
- Transporting Escaped Proteins Back to the ER
o COPI-coated vesicles accumulate in the presence of a
nonhydrolyzable GTP analogue because, similar to their
COPII counterparts, the coat contains a small membrane bending GTP-binding protein, called Arf1, whose bound GTP must be hydrolyzed before the coat can disassemble
Clathrin-coated vesicles
- Transports lysosomes and endosomes to the TGN
o Adaptor protein GGA
There are two types of receptors which are used in the endocytic pathway. Please list what they are, their final destination after they deliver the ligands, and what kind of ligands they delivery individually.
Housekeeping receptors:
o Responsible for uptake of materials will be used by the cells: e.g. ions, cholesterol
o Will be recycled back to the plasma membrane after ligand delivery
Signaling receptors:
o Responsible for binding of extracellular ligands that carry messages to change the intracellular activities: e.g. hormones, growth factors
o Will be destroyed after ligand delivery
Microtubule-Organizing Centers play important roles in the control of microtubule. Please list what the role (functions) are.
- Initiation of microtubule initiation
- Control the number of microtubules
- Control the polarity of microtubules
- Control the number of protofilamentsthat make up wall of microtubules
- Control the time and location of microtubule assembly
A scientist isolates two-specific mRNAs. One codes for the enzyme fowlase, an enzyme that is involved in digestion in chickadees; the other codes for the quail enzyme quilase that is involved in cellular carbohydrate metabolism. Both mRNAs are placed in a test tube with RER vesicles stripped of their ribosomes, free ribosomes and precursors for protein synthesis. When the protein synthesis reaction is complete, fowlase is found inside the vesicles; quailase is found in the liquid portion of the test tube outside the vesicles. What can one conclude about the two proteins, i.e. type of the protein, location of the protein, etc.?
We can conclude that the enzyme quailase which is found in the liquid portion will be a cytosolic protein. The translation of this protein occurs on membrane free ribosomes in the liquid portion. It may enter the RER vesicles for post translational modifications and then exit back into the liquid portion equivalent to cytosol.
The enzyme fowlase which is found in the RER will be a protein of the secretory pathway involving RER, Golgi and lysosomes. Since this enzyme is involved in digestion, it may be a lysosomal protein. It will be cotranslationally translocated into RER vesicles. Since there is no Golgi and lysosomes, the protein will remain in the RER vesicles.
You are observing a cell process in which small vesicles continually merge with the cell membrane. A number of different treatments known to influence the secretion of specific materials seems to have no effect on the process. What type of secretion appears to be occurring?
Constitutive secretion since known regulatory treatments have little effect.
You want to determine what functions microtubule can play in the animal cells. You first treated the cells with a microtubule assembly inhibitor, which prevent microtubule production. Then you observed the cells under an electron microscope. To your surprise, in the un-treated cells, you can observe a good amount of Golgi apparatus, but you cannot see any Golgi in the microtubule-inhibitor treated cells. Please explain why this happens.
To maintain the internal organization of cells
-Help keep the membrane organelles in position
E.G.: Golgi complex will disassociated into individual Golgi stacks and scattered throughout the cytoplasm if microtubules are disassembled
You are trying to synthesize actin filaments in the test tube. You added all of the essential components which are required, including the short actin seeding fragments, ATP, actin monomers etc. and kept the reaction in an appropriate temperature. Please describe what happened during the actin filament synthesis procedure. Hint: correlate the ATP- actin monomer concentration and speed of actin assembly on both ends of the filament.
- High ATP-Actin, grow on both ends
- Concentration of ATP-Actin drops to a level where net addition of actin monomer only to plus end
- Concentration of ATP-Actin further drops to a level where net loss to the minus end and net addition to the plus end occur
- Steady state where length of microfilament and free ATP-actin remain constant
