Expert: Joy Ramos - 4/25/2006

Question
the nucleotides in one strand of DNA are held together by what?

a base pair is a unit of dna that consists of what?

What happens to the strands of dna molecule that gets replicated?

the two strands of a double helix of dna are linked by what kind of bonds?
if the sequence TCGTA was used as a template in DNA replication, what would the sequence of bases be on the newly synthesized strand?


Answer
Hi, Jai. DNA nucleotides in each strand of DNA are held together by phoshpodiester bonds found between 3'O(H) of the preceding nucleotide and the 5' phosphate group of the succeeding nucleotide.

Since DNA is double-stranded, a base pair is a pair of nucleotides that are bound to each other on opposite sides of the DNA ladder. Because of the particular conformation of the different nucleotides, the only possible pairs are between Adenine (A) and thymine (T)  and between guanine (G) and cytosine (C).

DNA replication involves opening up this double-strand and polymerases come in to put up the corresponding, matching nucleotide that can base-pair with the single-stranded template strand. Once replication is complete, you'll end up with two exact double-stranded copies of your original DNA. Each "daughter" DNA will have one strand from the original DNA and one strand that's completely new.

The two strands of a DNA double helix are held together by hydrogen bonds between the nucleotides. An A-T pair would have two hydrogen bonds between them and a G-C pair would have three.

Convention dictates that sequences are written in the 5'-3' direction. So I assume that "TCGTA" is from 5'-3'. DNA is "anti-parallel", that is one strand is in the 5'-3' orientation while the other opposite strand is in the 3'-5' oriention. I've also mentioned A can only pair with a T and G can only pair with a C. So, the partner of "TCGTA" is AGCAT in the 3'-5' orientation. If you were to write it in the 5'-3' convention, that would be "TACGA".

Hope this helps! If you need any more clarification, please let me know. This is exactly in my line of work!