What happens after double-stranded DNA is heat denatured（）
A. Decreased viscosity
B. Decreased settlement coefficient
C. Decreased buoyancy density
Decreased UV absorption
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8 Which of the following related statements is correct（）
A. The 1st carbon atom of pentose is connected to the 9th nitrogen atom of purine to form a l,9-glycosidic bond
B. Dehydration between the free hydroxyl group of pentose sugar in nucleoside and phosphoric acid generates nucleotides through condensation of phosphoester bond
C. Both deoxyribonucleoside and ribonucleoside can form 2′-3′- or 5′-ribonucleotide
D. 5′-nucleotides are mostly free in organisms
The characteristics of the secondary structure of tRNA molecules are（）
A. There is poly A at the 3’end
B. C-C-A at the 5’end
C. There is a password ring
D. Has an amino acid arm
Which of the following methods can be used to isolate DNA（）
A. Salt extraction
B. Cesium chloride density gradient centrifugation
C. Electrophoresis
D. Heating precipitation
Regarding the tertiary structure of DNA, which of the following statements are correct（）
A. The tertiary structure of A DNA is a supercoiled structure formed on the basis of secondary structure
B. The double-stranded DNA of B prokaryotic DNA is entangled in histones to form nucleosomes
C. Histones involved in the formation of nucleosomes include five subunits: H1, H2A, H2B, H3, and H4
D. The formation of supercoiled structure compressed the length of DNA in the nucleus by nearly ten thousands time
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