π Universal genetic code (DNA) (12 MCQs)
π From Campbell Biology β’ 1. Evolution and the theme of Biology and Scientific Inquiry β’ 12 questions available
What is Universal genetic code (DNA)?
Definition:
The universal genetic code is the set of rules by which information encoded in DNA or RNA sequences is translated into proteins, where triplets of nucleotides (codons) specify the 20 standard amino acids, and this code is nearly identical across all known organisms, from bacteria to humans, providing powerful evidence for common ancestry and serving as the fundamental language of life.
Working:
This code works during transcription and translation, where DNA is transcribed into mRNA, and ribosomes read the mRNA in codons, each codon corresponding to a specific amino acid or a stop signal, and the degeneracy of the code (multiple codons for one amino acid) is described by the equation , which codes for 20 amino acids plus stop codons, ensuring that even with a single nucleotide change, the protein sequence may remain functional.
Example:
A simple example is the codon AUG, which codes for methionine and also serves as the start signal for protein synthesis in all organisms, and the codon UAA, UAG, and UGA are stop codons that terminate translation, and this same code is used to produce insulin in a human cell or in a genetically engineered bacterium, demonstrating its universality.
Reason:
The universal genetic code is essential for understanding molecular biology, genetic engineering, and evolution, as it allows genes from one organism to be expressed in another (e.g., human insulin in bacteria), and its universality is a cornerstone of the theory of common descent, underpinning all genetic and biotechnological applications.
π All Universal genetic code (DNA) MCQs
Q1. Which observation most strongly supports the idea that DNA-based genetic information is broadly shared among organisms?
π Explanation: The strongest evidence is functional compatibility across organisms. Because DNA information can sometimes be transferred and interpreted by different organisms to produce a related functional protein, the underlying information system is highly conserved despite differences in DNA sequences.
Q2. A researcher compares DNA from bacteria, plants, and animals. Their sequences differ substantially, but all use the same four basic DNA bases to encode hereditary information. What conclusion is best supported?
π Explanation: Different organisms can have highly different DNA sequences while retaining the same fundamental molecular language. This supports the conclusion that hereditary information is encoded through a broadly conserved DNA-based system rather than separate systems for each lineage.
Q3. A laboratory inserts a bacterial gene into a plant cell, and the plant produces the corresponding bacterial protein. Which reasoning best explains this result?
π Explanation: The result indicates that the information contained in the bacterial DNA can be read by the plant's molecular machinery. This cross-organism compatibility is evidence for conservation of the genetic information system.
Q4. A scientist changes several DNA bases in a gene but observes no change in the resulting protein. Which interpretation is most scientifically reasonable?
π Explanation: Not every change in DNA necessarily changes the resulting protein because multiple nucleotide combinations can correspond to the same amino acid. Therefore, an unchanged protein does not demonstrate that the DNA change had no molecular effect.
Q5. A student argues: "Humans and bacteria cannot share a genetic code because their DNA sequences are very different." What is the main flaw in this reasoning?
π Explanation: The student confuses sequence differences with differences in the underlying coding system. Organisms can have very different DNA sequences while using the same fundamental rules for translating genetic information into biological molecules.
Q6. Two genes from different organisms contain different nucleotide sequences but produce proteins with similar functions. Which explanation is most consistent with evolutionary reasoning?
π Explanation: Evolution can modify nucleotide sequences while preserving important functional properties. Different sequences may therefore encode proteins with similar structures or functions, especially when biological constraints favor conservation of particular molecular activities.
Q7. A biotechnology company tests whether a DNA sequence from species X can function in species Y. The transferred sequence is transcribed and a functional protein is produced. Which additional observation would provide the strongest evidence that the compatibility results from a conserved genetic system rather than coincidence?
π Explanation: Successful expression of several unrelated genes would make coincidence much less plausible. Repeated cross-species compatibility would indicate that the molecular machinery of species Y consistently recognizes and interprets DNA information using a conserved biological system.
Q8. A graph shows the percentage of functional protein produced after transferring the same gene between organisms: Organism A = 92%, B = 88%, C = 15%, D = 90%. Which conclusion is most justified?
π Explanation: The pattern shows strong functional compatibility in three organisms but poor expression in one. The low result for C does not necessarily disprove a conserved genetic system because transcription, translation, regulation, or protein stability could create organism-specific barriers.
Q9. A researcher finds that a gene works in another organism only after its regulatory region is replaced, while the protein-coding region remains unchanged. What does this result suggest?
π Explanation: Replacing only the regulatory region restores expression, suggesting that the coding information can still be interpreted by the recipient. The failure was more likely caused by differences in gene regulation than by incompatibility of the coding system.
Q10. Consider this reasoning: "Because DNA is found in many organisms, all organisms must have identical genomes and therefore identical traits." Which correction is most appropriate?
π Explanation: The conservation of DNA as an information-storage molecule does not mean organisms possess identical sequences. Differences in genes, nucleotide sequences, regulation, and interactions with environments contribute to the enormous diversity of biological traits.
Q11. A researcher compares three organisms. Organism P has a DNA sequence of 1000 bases, Q has 1000 bases, and R has 1500 bases. The researcher concludes that P and Q must be more closely related because their DNA lengths are equal. Why is this conclusion weak?
π Explanation: Genome or gene length alone provides little evidence about relatedness. Two organisms may have DNA molecules of equal length but very different sequences, whereas organisms with different lengths can still share substantial evolutionary and functional similarities.
Q12. A hypothetical organism uses DNA bases normally, but its cells interpret every codon according to a completely different amino-acid assignment. If its DNA is transferred into a typical laboratory organism, what outcome would most strongly reveal this difference?
π Explanation: If the donor organism truly used a different coding system, the recipient's translation machinery would interpret the same nucleotide sequence differently from the donor's machinery. Comparing predicted and observed protein sequences could therefore reveal incompatibility in the coding assignments.