Microbiology Procedure
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Index >> Deoxyribose Nucleic Acid - DNA >> Single Stranded DNA

Single Stranded DNA

Single Stranded DNA - Although DNA of most organisms consists of two strands, single stranded DNA is present in the bacterio-phage virus ;X174 and in several other bacterial viruses Single stranded DNA differs from double stranded DNA in the following respects.

(1) Ultra violet absorption of double stranded DNA remains constant from 0 to 80C, and then rises rapidly (80C is the critical melting point).

In single stranded DNA ultra-violet absorption increases steadily from 20C to 90C.

(2) Double stranded DNA is resistant to the action of formaldehyde. In single stranded DNA the reactive sites are exposed, and therefore it is not resistant.

(3)In double strand DNA A=T and G=C. In single stranded DNA of ;X174 the proportion of A:T:G:C is 1: 1.33: 0.98: 0.75.

(4) Double stranded DNA is linear while single stranded DNA is circular.

During replication, single stranded DNA becomes double stranded (replicative form)

 

 
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