This set of Protein Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Ribosomes”.
1. Which of the following is the site of protein synthesis in a cell?
a) Nucleus
b) Cell membrane
c) Vacuole
d) Ribosomes
View Answer
Explanation: Ribosome is the site of protein synthesis in a cell. They are small organelles present inside the cell in two forms, which are membrane-free ribosomes and ER membrane-bound ribosomes.
2. What does the ribosome consist of?
a) Two subunits of equal sizes
b) Two large and two small subunits
c) Two large and one small subunit
d) One large and one small subunit
View Answer
Explanation: Ribosomes are small organelles that are known to synthesize protein. In all organisms, they are composed of two subunits, one large and one small subunit. In prokaryotes, the sizes of the small and large subunits are the 30S and 50S respectively. In eukaryotes, the sizes of the small and large subunits are the 40S and 60S respectively.
3. Which of the following was used by Carl Woese to build the prokaryotic phylogenetic tree?
a) 5.8S rRNA gene
b) 5S rRNA gene
c) 23S rRNA gene
d) 16S rRNA gene
View Answer
Explanation: The 16S rRNA gene was used by Carl Woese to build the prokaryotic phylogenetic tree. This gene is present in all prokaryotic cells. Apart from this gene, there are few other genes like 5S rRNA, 23S rRNA gene which is present in prokaryotic cells.
4. There is no difference between prokaryotic and eukaryotic ribosomes.
a) True
b) False
View Answer
Explanation: The above statement is false. There are differences in prokaryotic and eukaryoticribosomes in terms of size and composition. The eukaryotic ribosome is the 80S and the prokaryotic ribosome is 70S in size.
5. Which of the following represents the correct constituents of a prokaryotic ribosome?
a) 16S, 23S, and 5.8S rRNA
b) 23S, and 5.8S rRNA
c) 16S and 5S rRNA
d) 16S, 23S, and 5S rRNA
View Answer
Explanation: The correct constituents of a prokaryotic ribosome are 16S, 23S, and 5S rRNA. A prokaryotic ribosome has a size of 70S. It is composed of a larger subunit (the 50S) and a smaller subunit (30S).
6. Which of the following represents the correct constituents of a eukaryotic ribosome?
a) 16S, 28S, and 5S rRNA
b) 16S, 28S, and 5.8S rRNA
c) 18S, 28S, and 5.8S rRNA
d) 18S, 28S, 5S, and 5.8S rRNA
View Answer
Explanation: The correct composition of a eukaryotic ribosome is 18S, 28S, 5S, and 5.8S rRNA. The size of the eukaryotic ribosome is the 80S. 16S rRNA is not a constituent of the eukaryotic ribosome.
7. Find the odd one out.
a) 18S rRNA
b) 28S rRNA
c) 5.8S rRNA
d) 16S rRNA
View Answer
Explanation: 18S, 28S, and 5.8S rRNA are part of a eukaryotic ribosome. 16S rRNA is a constituent of the prokaryotic ribosome. Hence, 16S rRNA is the odd one out.
8. Proteins that are to be incorporated into cytoplasmic organelles are synthesized on ER membrane-bound ribosomes. Whereas, proteins that are to be imported into the ER-Golgi system are synthesized on free ribosomes in the cytosol.
a) True
b) False
View Answer
Explanation: The above statement is false. Proteins that are to be incorporated into cytoplasmic organelles are synthesized on free ribosomes in the cytosol. Whereas, proteins that are to be imported into the ER-Golgi system are synthesized on ER membrane-bound ribosomes.
9. Find the odd one out.
a) ER proteins
b) Lysosomal proteins
c) Golgi complex proteins
d) Soluble cytosolic proteins
View Answer
Explanation: ER proteins, lysosomal proteins,and Golgi complex proteins are synthesized by ER bound ribosomes. Whereas, soluble cytosolic proteins are synthesized by free ribosomes in the cytosol.
10. Which of the following protein is not synthesized by membrane-free ribosomes?
a) Chloroplast proteins
b) Peroxisomal proteins
c) Extrinsic membrane proteins localized to the cytoplasmic surface
d) Extrinsic membrane proteins localized to the extra-cytoplasmic surface
View Answer
Explanation: Extrinsic membrane proteins localized to the extra-cytoplasmic surface are not synthesized by membrane-free ribosomes. ER membrane-bound ribosomes synthesize the extrinsic membrane proteins that are localized to the extra-cytoplasmic surface. Chloroplast proteins, peroxisomal proteins, and extrinsic membrane proteins localized to the cytoplasmic surface are synthesized by membrane-free ribosomes.
11. Which of the following protein is not synthesized by ER membrane-bound ribosomes?
a) Integral plasma membrane proteins
b) Golgi complex proteins
c) Extrinsic membrane proteins localized to the extra-cytoplasmic surface
d) Extrinsic membrane proteins localized to the cytoplasmic surface
View Answer
Explanation: Extrinsic membrane proteins localized to the cytoplasmic surface is not synthesized by ER membrane-bound ribosomes. Free ribosomes in the cytosol synthesize the extrinsic membrane proteins that are localized to the cytoplasmic surface. Integral plasma membrane proteins, Golgi complex proteins, and extrinsic membrane proteins localized to the extra-cytoplasmic surface are synthesized by ER membrane-bound ribosomes.
12. Which of the following statement is incorrect?
a) Ribosome catalyzes peptide bond formation
b) A ribosome is made up of two unequal subunits
c) Ribosome contains only rRNA and many small proteins
d) The ribosome does not include specific binding sites for tRNA molecules.
View Answer
Explanation: The ribosome includes specific binding sites for tRNA molecules. Thus, it helps in proper attachment of tRNA to the complementary mRNA. Hence, the statement “Ribosome does not include specific binding sites for tRNA molecules” is incorrect.
13. Identify the incorrect statement.
a) A prokaryotic ribosome consists of two subunits, which are the 50S and 30S
b) Ribosomal RNAs have complicated secondary structure
c) The ribosome has a complex three-dimensional structure
d) The distribution of proteins in the two ribosomal subunits is uniform
View Answer
Explanation: The distribution of proteins in the two ribosomal subunits is not uniform. Most of the proteins are concentrated on the sides opposite to where the two subunits interact with each other. The part of the ribosome which interacts with mRNA mostly consists of rRNAs.
14. Which of the following is not a feature of the larger subunit of the eukaryotic ribosome?
a) 60S size
b) Contains both 5.8S and 5s rRNA
c) Catalyzes peptide elongation
d) mRNA binding
View Answer
Explanation: The larger subunit is mainly involved in mediating tasks such as catalyzing the reaction of polypeptide elongation. The smaller subunit acts in the recognition process, such as mRNA and tRNA binding. The size of the larger subunit of eukaryotic ribosomes is the 60S and it contains both 5.8S and 5S rRNA.
15. Ribosomes contain three functionally distinct tRNA binding sites. Which of the following is not one of them?
a) A site
b) P site
c) E site
d) O site
View Answer
Explanation: The O site is not one of the three functionally distinct tRNA binding sites. Those three sites are A or aminoacyl site, P or peptidyl site, and E or exit site. These three sites are responsible for correct tRNA binding on ribosomes.
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