Answers
Answer: C
Difficulty: 2
Section: The Universal Features of Cells on Earth
Feedback: All living organisms are made of cells. However, only a minority of them are eukaryotes with defined cell nuclei. Not all cells obtain their energy directly from sunlight. However, regardless of the energy source, the main energy currency used by all known living cells is ATP. Some prokaryotic genomes contain only a few hundred genes.
Answer: E
Difficulty: 1
Section: The Universal Features of Cells on Earth
Feedback: All living cells replicate their DNA by the same overall mechanism of templated polymerization. They also transcribe the genetic information into RNA form using the same mechanism. Translation of this information into protein form is mediated by the ribosome in all cells. Additionally, all cellular membranes have membrane transport proteins that control the flow of material through the membranes.
Answer: B
Difficulty: 3
Section: The Universal Features of Cells on Earth
Feedback: There are 64 (that is, 43) nucleotide triplets or codons using four types of nucleotide monomers, whereas each codon encodes one out of only 20 amino acids. Therefore, some sequence information is lost when translating from mRNA to protein sequences, such that it is not usually possible to deduce the original mRNA sequence given a translated polypeptide sequence.
Answer: C
Difficulty: 2
Section: The Universal Features of Cells on Earth
Feedback: Diffusion is a spontaneous process driven by the thermal energy of randomly moving molecules, and normally does not require energy expenditure by the cell. For the other mentioned processes, free energy is required. If a cell “dies,” these processes would stop or get out of control, but small molecules would still diffuse.
Answer: C
Difficulty: 2
Section: The Diversity of Genomes and the Tree of Life
Feedback: Bacterial cells do not have membrane-enclosed organelles such as mitochondria.
Answer: D
Difficulty: 2
Section: The Diversity of Genomes and the Tree of Life
Feedback: Highly conserved genes that code for optimized, essential, protein or RNA molecules should be studied to trace family relationships across distant taxa. Mutations in these regions (such as the genes that code for ribosomal RNAs) are usually eliminated, making the sequence recognizable even after billions of years of evolutionary history.
Answer: E
Difficulty: 2
Section: The Diversity of Genomes and the Tree of Life
Feedback: Horizontal gene transfer is common in bacteria and can result in the acquisition of new antibiotic-resistance genes by pathogenic bacteria.
Answer: D
Difficulty: 1
Section: The Diversity of Genomes and the Tree of Life
Feedback: Viruses are not living cells, but use the cellular machinery of their hosts to replicate their genetic material, which is made of DNA or RNA. They can act as vectors for horizontal gene transfer between cells of the same or different species. Infection is followed by either lysis (killing of the host cell) or the persistence of the viral genome in the host cell (which can last for many cell generations).
Answer: D
Difficulty: 2
Section: The Diversity of Genomes and the Tree of Life
Feedback: Introduction of genes into bacteria or eukaryotes by viral infection or artificially in the laboratory are examples of horizontal gene transfer, as is sexual reproduction between members of the same eukaryotic species. A great deal of horizontal gene transfer has occurred during the evolution of eukaryotic cells, such as in the process that led to the development of mitochondria (see Figure 12–3).
Answer: C
Difficulty: 2
Section: The Diversity of Genomes and the Tree of Life
Feedback: Gene duplication within a single genome results in paralogous genes (such as human ACTB and ACTC1 genes), whereas other homologous genes that share direct ancestry are called orthologs (in this case, some ancestor of MreB is presumably a distant actin ortholog). These genes all belong to the actin family.
Answer: C
Difficulty: 2
Section: The Diversity of Genomes and the Tree of Life
Feedback: A significant fraction of the ubiquitous gene families across the three domains of life is involved in translation and amino acid metabolism and transport. Other metabolic processes such as carbohydrate and coenzyme metabolism and transport also constitute a large subset. This is only a rough sketch of the core ancestral gene set, but is nevertheless informative. Please refer to Table 1–1 for details.