4. two double stranded fragments of dna are exactly the same length. at 89 c, fragment a has completely denatured, which means that the two strands have separated. at that temperature, fragment b is still double-stranded. how might these fragments differ to result in different denaturation temperatures?

The correct answer is "Fragment B likely has a higher Guanosine/Citosine content".

Explanation:

Guanosine/Citosine content, or GC content, refers to how many molecules of guanosine and citosine have a DNA fragment, respect to the content of adenine and thymine. The higher the GC content, the higher the temperature needed to denature the fragment of DNA. This happens because guanosine and citosine establish three hydrogen bonds, while adenine and thymine establish two hydrogen bonds when they bind together. Therefore, if fragment A and B are the same length, but at 89 C only fragment A is completely denatured, fragment B likely has a higher GC content.

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.