Biology Forums - Study Force

My AP  BIO book says each DNA molecule is made up of two long chains arranged into what is called a double helix. Each link of a chain is one of four kinds of chemical building blocks called nucleotides.

My question is what's a link of a chain? Is it a segment of a double helix chain? If So, is ONE segment/link just one type of the four kinds of nucleotides (Adenine, Guanine, Cytosine and Thymine), or is each segment/link made up of multiple nucleotides?


I never fully understood this, and now it has come back to haunt me.

Hey NeedsAPbiohelp...

Don't get confused.  :P

DNA is made up of nucleotides. A single nucleotide is composed of a nucleobase (adenine, guanine, cytosine, thymine), a 5-carbon ring (called deoyxribose sugar), and a phosphate group.

There are four types of nucleotides: dAMP (has an adenine nucleobase), dGMP (has a guanine nucleobase), dCMP (has a cytosine nucleobase), and finally dTMP (has a thymine nucleobase).

These nucleotides are connected with one another by their phosphate groups (pay attention to the attached picture). A phosphate of one nucleotide connects to the sugar of another nucleotide, so on and so forth. This is what makes up the first link of chains (remember: a complete DNA molecule consists of two "links of chains"). Now, in order to connect one link of chains with the other link of chains to make a complete dna molecule, the nucleobases of the first link of chains have to chemically bind to the nucleobase of the 2nd link of chains. This is done by hydrogen bonds (represented as H's in the attached picture). The rule is Adenine binds with thymine (or vice versa) and cytosine binds with guanine (or vice versa).

Makes sense?

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