Before DNA was established as the genetic material, proteins were considered the most likely molecules to serve this role. In part this belief was based on the fact that there are 20 building blocks (20 different kinds of amino acids) for proteins versus
4 building blocks (4 different nucleotides) for DNA. If proteins stored a code, there would be a far greater number of code words possible for a protein of a given number of amino acids than for a DNA molecule of the same number of nucleotides. For example, there are 16 different sequences (42 ) possible for a DNA two nucleotides long and 400 (202 ) different sequences possible for a protein two amino acids long. For a sequence three nucleotides or three amino acids in length, the number of distinct DNA sequences is ________, and the number of distinct protein sequences is ________.
A) 20; 420 B) 64; 8,000 C) 800; 8,000 D) 30; 800 E) 64; 800
Answer: B
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The special kind of fault along where different ocean plates are moving laterally away from each other is called:
a. trench. b. midocean. c. transform. d. arc. e. convergent.
The zygote is
a. diploid. b. tetraploid. c. polyploid. d. triploid. e. haploid.
Greenhouse gases act primarily to ____
a. warm Earth's surface b. cool the atmosphere c. block out ultraviolet radiation d. contribute to acid rain e. increase carbon monoxide concentrations
What would happen to a plant cell in a hypertonic environment?
A. There would be no change. B. It would swell and burst. C. Its turgor pressure would increase. D. It would shrink.