1. 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
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.
2. 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.
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.
3. 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
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.
4. 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
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.
5. 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
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.
6. Single can encode multiple proteins.
a) False
b) True
Explanation: The above statement is true. It is estimated that the human genome comprises between 20,000 and 25,000 genes, while, the total number of proteins in the human proteome is estimated at over 1 million. These estimations demonstrate that single genes encode multiple proteins.
7. Which of the following is not a mechanism that can generate different mRNA transcripts from a single gene?
a) Alternative splicing
b) Transcription initiation at alternative promoters
c) Genetic recombination
d) Recombinant DNA technology
Explanation: Recombinant DNA technology is not a mechanism that can generate different mRNA transcripts from a single gene. Alternative splicing, transcription initiation at alternative promoters, and genetic recombination are mechanisms that can generate different mRNA transcripts from a single gene.
8. Which of the following is not a post-translational modification?
a) Lipidation
b) Protein phosphorylation
c) Proteolytic processing
d) DNA methylation
Explanation: DNA methylation is not a post-translational modification. It is a biological process in which DNA molecules are methylated. Lipidation, protein phosphorylation, and proteolytic processing are proteolytic processing.
9. In O-linked glycosylation, monosaccharides bind to the hydroxyl group of which of the following amino acids?
a) Histidine or glycine
b) Alanine or tryptophan
c) Aspartic acid or glutamic acid
d) Serine or threonine
Explanation: In O-linked glycosylation, monosaccharides bind to the hydroxyl group of Serine or threonine amino acids. It does not bind to alanine, tryptophan, aspartic acid, glutamic acid, histidine, or glycine. O-linked glycosylation takes place entirely in the Golgi complex.
10. The human proteome is dynamic.
a) false
b) true
Explanation: The above statement is true. The human proteome is dynamic and changes in response to a legion of stimuli, and post-translational modifications are commonly employed to regulate cellular activity. Post-translational modifications occur at distinct amino acid side chains or peptide linkages, and they are most often mediated by enzymatic activity.