Fossils of Lystrosaurus, a dicynodont therapsid, are most common in parts of modern-day South America, South Africa, Madagascar, India, South Australia, and Antarctica. It apparently lived in arid regions, and was mostly herbivorous. It originated during the mid-Permian period, survived the Permian extinction, and dwindled by the late Triassic, though there is evidence of a relict population in Australia during the Cretaceous. The dicynodonts had two large tusks, extending down from their upper jaws; the tusks were not used for food gathering, and in some species were limited to males. Food was gathered using an otherwise toothless beak. Judging from the fossil record, these pig-sized organisms were the most common mammal-like reptiles of the Permian.Which of Lystrosaurusʹ features help explain why these organisms fossilized so abundantly?

I. the presence of hard parts, such as tusks

II. its herbivorous diet

III. its persistence across at least two geological eras

IV. its widespread geographic distribution

V. its mixture of reptilian and mammalian features

#Question id: 621

#SCPH05 I Biotechnology

Michaelis and Menten assumed that the overall reaction for an enzyme-catalyzed reaction could be written as Using this reaction, the rate of breakdown of the enzyme-substrate complex can be described by the expression:

#Question id: 622

#SCPH05 I Biotechnology

An enzyme-catalyzed reaction was carried out with the substrate concentration initially a thousand times greater than the Km for that substrate.  After 9 minutes, 1% of the substrate had been converted to product, and the amount of product formed in the reaction mixture was 12 micromol.  If, in a separate experiment, one-third as much enzyme and twice as much substrate had been combined, how long would it take for the same amount (12 micromol) of product to be formed?

#Question id: 623

#SCPH05 I Biotechnology

Which of these statements about enzyme-catalyzed reactions is false?

#Question id: 624

#SCPH05 I Biotechnology

The following data were obtained in a study of an enzyme known to follow Michaelis-Menten kinetics: The Km for this enzyme is approximately:

#Question id: 625

#SCPH05 I Biotechnology

For enzymes in which the slowest (rate-limiting) step is the reaction Km becomes equivalent to:

#Question id: 626

#SCPH05 I Biotechnology

A metabolic pathway proceeds according to the scheme, R -> S -> T -> U -> V -> W.  A regulatory enzyme, X, catalyzes the first reaction in the pathway.  Which of the following is most likely correct for this pathway?