Answer: D
Difficulty: 1
Section: The Diversity of Genomes and the Tree of Life
Feedback: E. coli is a prokaryotic model organism; although the discovery of many fundamental molecular mechanisms were aided by studies using E. coli, the eukaryotic process of mitosis is best studied in simple eukaryotic cells. E. coli can be easily cultured in the lab in nutrient media. Its genome of 4.6 million nucleotide pairs codes for about 4300 different proteins. But this number is reported for the K-12 strain. Other strains can be different in up to 50% of their genes, a significant diversity which has been explained by the process of horizontal gene transfer.
Answer: D
Difficulty: 1
Section: The Diversity of Genomes and the Tree of Life
Feedback: Most prokaryotes have small genomes (106 to 107 nucleotide pairs) and code for between 1000 and 6000 genes. Archaea are more similar to bacteria in their metabolism, but more similar to eukaryotes with respect to their DNA replication, DNA repair, and DNA packaging proteins (archaeal histones). Before the comparison of DNA sequences of highly conserved genes placed them in a separate domain, archaeal organisms were classified as bacteria.
Answer: D
Difficulty: 3
Section: The Diversity of Genomes and the Tree of Life
Feedback: Genetic analysis of mutations can give clues about gene functions. For example, if a mutation causes cell-cycle arrest, the affected gene is interpreted to have a role in cell-cycle progression. However, this does not necessarily mean that its product physically interacts with (binds to) another cellular component that is also involved in this process.
Answer: E
Difficulty: 2
Section: Genetic Information in Eukaryotes
Feedback: Membrane-bound organelles such as lysosomes are normally not found in prokaryotes. Please note that using the same names for some structures in both prokaryotes and eukaryotes (e.g., cell wall) does not necessarily mean that these structures share the same molecular structure.
Answer: E
Difficulty: 1
Section: Genetic Information in Eukaryotes
Feedback: Many eukaryotes lack chloroplasts, and some have lost their mitochondria.
Answer: D
Difficulty: 2
Section: Genetic Information in Eukaryotes
Feedback: In this lifestyle analogy, acquiring a symbiont chloroplast allowed cells to transition from hunting to farming. Other cells such as fungi evolved into scavengers instead, while protozoa and animal cells maintained their hunting habits. Fungi contain mitochondria.
Answer: B
Difficulty: 2
Section: Genetic Information in Eukaryotes
Feedback: During the evolution of mitochondria and chloroplasts, many essential organelle genes are thought to have been transferred to the nuclear genome.
Answer: E
Difficulty: 2
Section: Genetic Information in Eukaryotes
Feedback: E. coli has the highest ratio of gene number to genome size among the organisms shown in the graph. The lowest ratio belongs to H. sapiens. The ratio for each organism corresponds to the linear difference in the length of the red and blue bars for that organism. If the graph was not drawn in logarithmic scale, this comparison might not have been as straightforward.
Answer: D
Difficulty: 2
Section: Genetic Information in Eukaryotes
Feedback: The smallest and largest genomes in eukaryotes are found in protozoans. Please refer to Figure 1–32.
Answer: E
Difficulty: 1
Section: Genetic Information in Eukaryotes
Feedback: The eukaryotic genome codes for not only various proteins and RNA molecules, but also regulatory molecules that control the expression of other genes. Noncoding regulatory sequences are used to tune the expression level of the cellular genes. The cell actively exchanges signals with other cells in the organism, which help it decide which genes to express.
Answer: A
Difficulty: 1
Section: Genetic Information in Eukaryotes
Feedback: Protozoa are generally quite complicated in their structure and behavior despite being single-celled, as exemplified by D. nasutum.
Answer: B
Difficulty: 2
Section: Genetic Information in Eukaryotes
Feedback: It is the yeast Saccharomyces cerevisiae.
Answer: E
Difficulty: 2
Section: Genetic Information in Eukaryotes
Feedback: It is the nematode worm Caenorhabditis elegans.
Answer: E
Difficulty: 2
Section: Genetic Information in Eukaryotes
Feedback: It is the fruit fly Drosophila melanogaster.