Question

what does dna look like?
as you can see in the figure below, a strand of dna looks like a twisted ladder. this spiral shape is called a double helix. the two sides of the ladder are made of the sugar and phosphate parts of nucleotides. the sugars and phosphates alternate along each side of the ladder. the rungs of the dna ladder are made of pairs of bases.
the bases in dna can only fit together in certain ways, like puzzle pieces. adenine on one side of a dna strand always pairs with thymine on the other side. guanine always pairs with cytosine. this means that adenine is complementary to thymine, and guanine is complementary to cytosine. because the pairs of bases in dna are complementary, the two sides of a strand of dna are also complementary.

1. identify what are the sides of the dna \ladder\ made of?

critical thinking

1. apply concepts imagine that you are a scientist studying dna. you measure the number of cytosines and thymines in a small strand of dna. there are 45 cytosines and 55 thymines. how many guanines are there in the strand? how many adenines are there?

take a look

1. identify give the ways that dna bases can pair up.

each side of a dna molecule is complementary to the other side.

Explanation:

The problem is about DNA base - pairing. In DNA, adenine (A) pairs with thymine (T) and guanine (G) pairs with cytosine (C). For the number of guanines, since G pairs with C, the number of guanines is equal to the number of cytosines. For adenines, since A pairs with T, the number of adenines is equal to the number of thymines.

Answer:

There are 45 guanines and 55 adenines.