Which of the following is a lophotrochozoan protostome?
a. arthropods
b. cnidarians
c. mollusks
d. chordates
e. nematodes
C; Lophotrochozoans include the mollusks, annelids, brachiopods, nemerteans, flatworms, and several other phyla not mentioned in the text. Ecdysozoans include the nematodes (choice e), arthropods (choice a), and several other phyla not mentioned in the text. Deuterostomes include the echinoderms, hemichordates, and chordates (choice d). Sponges, cnidarians (choice b), and ctenophores are not classified in any of these groups.
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In female humans and other mammals, dosage compensation is achieved by the inactivation of one of the two X chromosomes in each cell. Which one of the following does not occur in the X-inactivation mechanism of female mammals?
A. X-inactivation begins with a small region of the X chromosome that contains a gene for an X-inactivation specific transcript (Xist). B. Xist is expressed in low levels except when an X chromosome is about to be inactivated. C. When an X chromosome is about to be inactivated, Xist RNA transcripts increase markedly and undergo splicing, but do not encode a protein. D. Xist RNA is attracted to and associates with a protein called the X-chromosome inactivation center (XIC), which becomes entirely coated with Xist. E. Xist RNA recruits factors that promote DNA methylation, histone modification, and other changes associated with transcriptional silencing.
When acetyl-CoA containing radioactively labeled carbon atoms is fed to cells, the CO2 produced is not initially radioactive. However, molecules of citrate and oxaloacetate are radioactive. Only after some time has passed will radioactive CO2 be released. What is the best explanation for this observation?
A. Acetyl groups are not metabolized directly into CO2, but enter a cyclical metabolic pathway. B. Acetyl groups first combine with citrate and oxaloacetate before being metabolized into CO2. C. Acetyl groups are not metabolized directly into CO2, but enter a linear metabolic pathway. D. Acetyl groups are metabolized directly into CO2.
The phenotype of ____ does not develop until adulthood
a. muscular dystrophy b. Marfan syndrome c. cystic fibrosis
d. hemophilia e. Huntington’s disease
The first photosynthetic autotrophs used the energy of the sun to split H2O because it is not very electronegative
______________ Indicate whether the statement is true or false.