which of the following method make protein precipitated keep biological activity( )
A. strong acid
B. salting-out
C. room temperature alcohol
D. alkaloid reagent
E. heavy metal ions
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The basic unit of composing nucleic acid is ( )
A. ribose and deoxyribose
B. phosphate and ribose
C. base
D. mononucleotide
E. Polynucleotide
in certain DNA molecule, the content of adenine is 30%,then, the content of guanine is ( )
A. 15%
B. 20%
C. 30%
D. 60%
E. 80%
Which of the following is true about the composition of DNA bases ()
A. DNA is mainly composed of four bases: A, G, C and U
B. In DNA, (A+T)/(C+G) = (A+C)/(G+T).
C. In DNA, (A+G)/(T+C) =1
D. The base composition of DNA is species-specific and organ-specific
E. none of the above
The secondary structure of DNA is ( )
A. α-helix
B. Β-pleated sheet
C. Β-turn
D. supercoil
E. double helix
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