对一双链DNA而言,若一条链中(A+G)/(T+C)=0.7,则:(1)互补链中(A+G)/(T+C)=? (2)在整个DNA分子中(A+G)/(T+C)=? (3)若一条链中(A+T)/(G+C)=0.7,则互补链中(A+T)/(G+C)=? (4)在整个DNA分子中(A+T)/(G+C)=?
正确答案:(1)设DNA的两条链分别为α和β,那么:
A=βT,Tα=Aβ,Gα=Cβ,:Cα=Gβ,
因为,(Aα+Gα)/(Tβ+Cβ)=(Aα+Gα)/(Aβ+Gβ)=0.7
所以,互补链中(Aβ+Gβ)/(Tβ+Cβ)=1/0.7=1.43
(2)在整个DNA分子中,因为A=T,G=C,
所以,A+G=T+C,(A+G)/(T+C)=1
(3)假设同(1),则
Aα+Tα=Tβ+Aβ,Gα+Cα=Cβ+Gβ,
所以,(Aα+Tα)/(Gα+Cα)=(Aβ+Tβ)/(Gβ+Cβ)=0.7
(4)在整个DNA分子中
(Aα+Tα+Aβ+Tβ)/(Gα+Cα+Gβ+Cβ)=2(Aα+Tα)/2(Gα+Cα)=0.7
A=βT,Tα=Aβ,Gα=Cβ,:Cα=Gβ,
因为,(Aα+Gα)/(Tβ+Cβ)=(Aα+Gα)/(Aβ+Gβ)=0.7
所以,互补链中(Aβ+Gβ)/(Tβ+Cβ)=1/0.7=1.43
(2)在整个DNA分子中,因为A=T,G=C,
所以,A+G=T+C,(A+G)/(T+C)=1
(3)假设同(1),则
Aα+Tα=Tβ+Aβ,Gα+Cα=Cβ+Gβ,
所以,(Aα+Tα)/(Gα+Cα)=(Aβ+Tβ)/(Gβ+Cβ)=0.7
(4)在整个DNA分子中
(Aα+Tα+Aβ+Tβ)/(Gα+Cα+Gβ+Cβ)=2(Aα+Tα)/2(Gα+Cα)=0.7
答案解析:有
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