The Living World 8th Edition by George Johnson

تمرين 2

Which of the following lists the purine nucleotide bases?
A) adenine and cytosine
B) guanine and thymine
C) cytosine and thymine
D) adenine and guanine
Chargaff studied the composition of DNA from different sources and found that
A) the number of phosphate groups always equals the number of five-carbon sugars.
B) the proportions of A equal that of C and G equals T.
C) the proportions of A equal that of T and G equals C.
D) the proportions of deoxyribose equal that of ribose.
The Watson-Crick model of DNA suggested that Chargaff's rule reflected the fact that DNA has two complementary strands. Thus, if the base sequence of one strand is AATTCG, then the sequence of the other strand must be
A) AATTCG.
B) TTGGAC.
C) TTAAGC.
D) GGCCGA.
In analyzing DNA obtained from your own cells, you are able to determine that 15% of the nucleotide bases it contains are thymine. What percentage of the bases are cytosine?
From a hospital patient afflicted with a mysterious illness, you isolate and culture cells, then purify DNA from the culture. You find that the DNA sample contains two quite different kinds of DNA: one is double-stranded human DNA and the other is single-stranded virus DNA. You analyze the base composition of the two purified DNA preparations and obtain the following results:
Tube #1 22.1% A : 27.9% C : 29.7% G : 22.1% T
Tube #2 31.3% A : 31.3% C : 18.7% G : 18.7% T
Which of the two tubes contains single-stranded virus DNA?