This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Gene Expression – Genetic Code Properties”.
1. Who elaborated on the significance of codons?
a) George Gamow
b) Thomas Morgan
c) H. J. Muller
d) James Watson
View Answer
Explanation: George Gamow proposed that a group of three nucleotides, called codons, are responsible for encoding an amino acid in the polypeptide chain. The process of protein synthesis is referred to as translation.
2. The genetic code is degenerate.
a) True
b) False
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Explanation: The genetic code is degenerate because one amino acid can be encoded by more than one codon. A codon is a group of three nucleotides and amino acid is a constituent of the polypeptide chain.
3. How many codons do not code for amino acids?
a) 3
b) 5
c) 9
d) 11
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Explanation: There are 64 possible codons because each codon consists of 3 nucleotides and there are 4 types of nucleotides. Out of the 64 codons, 3 have a special function of being termination codons.
4. The degeneracy of code was originally predicted by __________________
a) Charles Darwin
b) Francis Crick
c) Robert Hooke
d) James Watson
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Explanation: The degeneracy of codon was predicted by Francis Crick, he considered the great range in base composition of various bacteria. The G + C content of the genomes varied from 20 to 74 percent, whereas the amino acid composition of the proteins from these organisms showed little variation.
5. First artificially synthesized gene sequence was _________________
a) poly(U)
b) poly(A)
c) poly(G)
d) poly(C)
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Explanation: First artificial genetic message was synthesized by Marshall Nirenberg and Heinrich Matthaei, composed of uridine residues called poly(U). They were able to synthesize bacterial proteins using the poly(U), ribosomes, amino acids and soluble factors.
6. Which was the first artificially synthesized polypeptide?
a) polyphenylalanine
b) tyrosine
c) valine
d) polyisoleucine
View Answer
Explanation: The first artificially synthesized protein is polyphenylalanine, synthesized using the poly(U) genetic sequence. After the successful synthesis of polyphenylalanine, it was confirmed that the codon UUU specifies phenylalanine.
7. UGA is a universal stop codon.
a) True
b) False
View Answer
Explanation: The UGA is a stop codon in all organisms with one exception, the codons of mitochondrial messenger RNA. UGA is read as tryptophan rather than a translation stop.
8. Which of the following is a stop codon in mitochondrial mRNA?
a) AUG
b) UUU
c) AGG
d) UGA
View Answer
Explanation: There are a few exceptions to the universality of genetic code that are found to occur in codons of mitochondrial messenger RNAs. AGG and AGA are read as stop codons rather than as arginine.
9. A change in nucleotide sequence that does not affect the amino acid sequence is called _____________ change.
a) insignificant
b) significant
c) synonymous
d) nonsynonymous
View Answer
Explanation: Changes in the genome occur throughout the evolution and among all the species. A change in the nucleotide sequence of the gene that does not affect the amino acid sequence of the polypeptide is called a synonymous change.
10. Which types of changes participate in the process of natural selection?
a) nonsynonymous
b) phenotypic
c) allotypic
d) synonymous
View Answer
Explanation: Nonsynomous are the changes that cause a change in the amino acid sequence when there is a change in the nucleotide sequence. Such changes affect the phenotype of an individual and are hence selected for or against in the process of natural selection.
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