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BIOL 200 Exam Review Verified Questions And Answers With Latest Quizzes
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BIOL 200 Exam Review Verified Questions AndAnswers With Latest Quizzes
Explain the structural and functional relationships between the different compartments of the
endomembrane system, and identify them on micrographs ANS
Describe how proteins are targeted and imported into the ER and compare these mechanisms to
protein targeting and import into the nucleus ANS
Predict the signal sequences required to insert a protein into the ER membrane in any orientation, and
predict protein topology from a corresponding domain map ANS
Discuss the role of chaperones in protein folding and the role of proteasomes in quality control of
misfolded proteins in the secretory pathway ANS
Describe and interpret the results of different experimental tools studying the secretory pathway ANS
Functions of the ER
(6) ANS 1. Entry point for proteins into the secretory pathway
- co-translational transfer across RER membrane then transported by vesicular traffic to Golgi etc.
2. Site of post-translational modifications of proteins
- Ex. protein disulfide isomerase forms disulfide bonds here
- Glycosylation starts here
3. Site of protein folding by chaperone proteins
- Ex. BiP (binding protein) prevents hydrophobic domains of proteins from aggregating and promotes
proper folding
4. Quality control site
,- Checks for defective proteins (proteins are not exported from ER if they are not properly
assembled)
5. Site of membrane lipid biosynthesis (sterols and glycerolipids)
- Cells producing large amount of lipids have abundant sER
6. Controls calcium levels in cytoplasm by acting as a calcium store
- cell signalling, muscle contraction
Which are false?
1. RER are sites of secretory protein synthesis
2. SER are site of lipids and steroid synthesis
3. RER have ribosomes docked on them while SER do not
4. RER and SER are separate and discrete membrane systems in the cell
5. ER occur at discrete places in the cell and ribosomes have to travel miles to get to them
6. ER is the starting point for proteins traveling in the endomem system ANS 4, 5
Which types of proteins would you expect to be sent to the ER?
(3) ANS 1. Soluble proteins destined for secretion
2. Mem proteins that are inserted into mem of the ER as they are synthesized during the translation
process
3. Resident proteins: ER, Golgi, Lysosome etc.
Proteins that are destined to live their entire lives in the cytosol do not need any targeting sequence
encoded in their primary sequence
T or F
why? ANS True
- Since the site of translation is the cytosol, a protein does not need any kind of targeting sequence to
enter the cytosol. However it always needs a targeting sequence to leave the cytosol
,Properties of the signal sequence for import into ER ANS chain of non-polar amino acids
- ER targeting sequences are short (approx. 10aa) hydrophobic domains
Properties of the signal sequence for retention in lumen of ER?
What is this sequence called? ANS KDEL sequence
- contains charged (+ & -) aa along with non-polar aa
Properties of the signal sequence for import into mitochondria ANS - positively charged aa
dispersed throughout the sequence
Properties of the signal sequence for import into the nucleus?
What is this called? ANS - NLS (nuclear localization signal)
- 5 positively charged aa in a row
Properties of the signal sequence for export from nucleus?
What is this called? ANS non-polar amino acids dispersed throughout the sequence
Protein targeting ANS A fundamental cellular process
The cell uses 3 main ways to enter a compartment ANS 1. Nuclear pore
- nuclear entry/exit
2. Membrane translocators
- ER, mitochondria, chloroplast
3. Via vesicle traffic
, - Keeps cargo from having to re-enter the cytosol
- used inside endomem system
What are the requirements for protein import into an organelle?
1. A specific aa 'targeting sequence'
2. A specific protein receptor on the organelle of interest
3. Energy input (ex. ATP)
4. A fully translated protein
5. A fully folded protein ANS 1,2
Proteins that have a specific destination have what? ANS A sorting signal in their sequence
Sorting signals ANS 1. Direct the protein to a specific organelle
2. Must be present for the protein to leave the cytosol compartment
Post translational trafficking of proteins ANS - Ribosomes remain "free" in the cytosol
- Complete polypeptide goes to its functional destination depending on its sorting signal
- Polypeptide may be folded or unfolded
Co-translational trafficking of proteins ANS - Ribosomes attach to ER membrane
- Protein is threaded through ER membrane as its being translated
- Proteins either stay in ER, or continue to other compartments of the endomembrane system
All proteins are processed once they are translated
T or F
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