What catalyzes the unwinding of the DNA double helix during DNA replication?
a. topoisomerase
b. primase
c. DNA polymerase
d. helicase
Ans: d. helicase
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What is the role of pepsin?
a. it begins protein digestion in the stomach. b. it begins starch digestion in the oral cavity. c. it begins lipid digestion in the small intestine. d. it is a cofactor in enzymes that break down toxins. e. it is a cofactor in enzymes that break down hydrogen peroxide
Each of the following is true about homeoviscous adaptation in membranes except
A) maintains membrane viscosity despite changes in environmental temperature. B) may decrease the average length of membrane lipid fatty acid tails. C) may increase the unsaturation of membrane lipid fatty acid tails. D) occurs primarily in homeothermic (warm-blooded) organisms and only rarely in poikilothermic (cold-blooded) organisms. E) may increase the proportion of cholesterol in animal cell membranes.
Proton pumps are used in various ways by members of every domain of organisms: Bacteria, Archaea, and Eukarya. What does this most probably mean?
A) Proton gradients across a membrane were used by cells that were the common ancestor of all three domains of life. B) The high concentration of protons in the ancient atmosphere must have necessitated a pump mechanism. C) Cells of each domain evolved proton pumps independently when oceans became more acidic. D) Proton pumps are necessary to all cell membranes.
In an ecosystem, energy
A) cycles along with chemical nutrients.
B) typically flows from consumers to producers to decomposers.
C) typically flows from producers to a series of consumers.
D) comes ultimately from bacteria.