This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Cytoplasmic Membrane Systems – Post-translational Uptake”.
1. Eough endoplasmic reticulum imports its proteins posttranslationally.
Explanation: Rough endoplasmic reticulum imports the proteins cotranslationally i.e. while they are being synthesized. Organelles like peroxisomes and mitochondria import the proteins posttranslationally, after their complete synthesis on free ribosomes in the cytosol.
2. For which of the following organelles, the proteins to be imported remain in their native folded state?
d) Endoplasmic reticulum
Explanation: Proteins carrying a peroxisomal targeting signal (PTS) bind to the PTS receptors, present on the membrane surface, which escort the protein through the boundary membrane to the internal matrix, in its native folded state.
3. Most of the proteins of mitochondria are synthesized in the ______________
a) mitochondrial matrix
b) mitochondrial membrane
d) medial cisternae
Explanation: Few of the integral membrane polypeptides of the mitochondria are synthesized in mitochondria itself. Most of its proteins (99%) are synthesized in the cytosol and then imported posttranslationally.
4. Mitochondrial matrix proteins have a target sequence, called presequence located at __________
c) interstitial site
d) center of the sequence
Explanation: Mitochondrial matrix proteins contain a removable sequence (presequence) containing a number of positively charged residues, located at the N-terminus.
5. Hsp 70 and Hsp 90 are ____________ involved in the mitochondrial uptake of proteins.
Explanation: For uptake into the mitochondria, proteins must be presented to it in an unfolded state. Molecular chaperones Hsp 70 and Hsp 90 prepare the proteins for mitochondrial uptake by unfolding them.
6. Following its entry into the mitochondrial matrix, the peptide is _______________
b) converted to phagosome
c) folded to its native conformation
Explanation: Following its entry into the mitochondrial matrix, the unfolded peptide is converted back to its original folded state followed by the enzymatic removal of its presequence.
7. In how many subcompartments of the chloroplasts, can the proteins be delivered?
Explanation: Proteins can be delivered to the following six subcompartments of a chloroplast: inner nd outer envelope membrane, intermembrane space, stroma, thylakoid membrane and thylakoid lumen.
8. Most proteins destined for uptake by the chloroplasts are synthesized with a ________________
a) removable C-terminal sequence
b) removable N-terminal sequence
c) removable hydrophobic tail
d) removable hydrophilic tail
Explanation: Similar to the proteins taken up by mitochondria, proteins destined for chloroplast are also synthesized with a removable N-terminal sequence, termed the transit peptide.
9. ‘Stroma targeting domain’ is located in the ________________
d) transit peptide
Explanation: The ‘stroma targeting peptide’ is located in the transit peptide sequence of the protein taken up by the chloroplast. This domain ensures the delivery of the protein to stroma of the chloroplast.
Sanfoundry Global Education & Learning Series – Cell Biology.
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