Expert: Florence M Rollwagen - 3/18/2009

Question
I have an extra credit project in my Biology class to come up with 10 questions about DNA and ask an expert from this site or another expert site. These aren't questions I was assigned, I made them up myself:


1.Why is DNA called a "Double Helix"?
2.Why does the structure of DNA twist?
3.How many strands make up a Double Helix?
4.How does a nitrogenous base know to connect with its complimentary base?
5.How do sugars hold so much information?
6.Do the nitrogenous bases have any particular order?
7.Why don't all cells have their own unique DNA?
8.How does DNA know its own job if it holds all the information?
9.What percent of our body is made up of DNA?
10.Why are tRNA shaped as they are?

Answer
Hi Christina: Thanks for your questions.  This is a little odd, but I'll try to answer and to give you a link so you can research further.

1.Why is DNA called a "Double Helix"?

DNA is twisted into a coil.  Because it is composed of two strands, it's called a double helix.

2.Why does the structure of DNA twist?
The twists are held together by hydrogen bonding.

3.How many strands make up a Double Helix?
There are two strands in the double helix.  Each chromosome is made up of one strand of DNA with its associated proteins.  Since we have 46 chromosomes (23 from each parent), we have 46 strands of DNA in each cell.  We have billions of cells.

4.How does a nitrogenous base know to connect with its complimentary base?
The nitrogenous bases are of two different sizes.  At each pairing, the large one and small one combine.  This helps to keep the edges straight.  Adenine bonds with thymine, cytosine with guanine.

5.How do sugars hold so much information?
The sugars in DNA (deoxyribose) don't hold the information, the sequence of base pairs do.
6.Do the nitrogenous bases have any particular order?
The order of the bases give information to the genetic code.  The genetic code is read in sets of three bases, each code corresponding to a specific amino acid (building blocks of protein).

7.Why don't all cells have their own unique DNA?
I don't know what you mean by unique, but all cells contain DNA, and it follows the same base pairing rules as above.  All cells do have unique DNA, that's what makes a person different from a tree.

8.How does DNA know its own job if it holds all the information?
The information is read as the genetic code, a sequence of three bases which correspond to a specific amino acid.

9.What percent of our body is made up of DNA?
Don't know, probably not much.

10.Why are tRNA shaped as they are?
Hydrogen bonds hold the tRNA in its specific shape.

Here's a link:http://www.thetech.org/exhibits/online/genome/info1.html

Hope this helps, write back if you have more questions.

FM Rollwagen, PhD