DNA Question

[strwberry]

1. The problem statement, all variables and given/known data

Which of the following are true statements ?

a) DNA is composed of a series of necleotides, each of which is made up of a phosphoric acid unit, a sugar unit and a cyclic nitrogen base.

b) In DNA the base must be either alanine, threonine, glutamine, or cysteine.

c) In the three-dimensional Watson-Crick structure of DNA, two polynucleotide DNA strands wind around each other to form a double helix.

d) The DNA sequence of base pairs in the nucleus of a cell represents the genetic code that controls inherited characteristics.

e) Genes are the sequence of bases in DNA that are the code for the synthesis of a single protein within the body.

2. The attempt at a solution

NOT SURE BUT :
a) [FALSE]It can not be a because it should be phosphate group instead of cyclic nitrogen base
b) [TRUE?] I thought it should be correct, since DNA bases are adenine (A), guanine (G), thymine (T), and cytosine (C)
c) [TRUE] It's true that the two polynucleotide chains in DNA molecule.
d) [TRUE] the bases are unique, that tells the characteristics
e) [FALSE?] I'm not sure, but I thought that it should be since genes are code for synthesis of proteins.

I tried bcde and bcd but it's incorrect. Please help, thank you!

[canalon]

A) What is the first group listed?
B) Read what you wrote (you are correct), and what is written are they the same thing after the first letter?
C) I would agree too
D) I do not really like your definition, but you are correct
E) It is weirldy put in my opinion, but I am with you. More than one protein from the DNA.

[kolean]

I love the (b) question! I will have to use that on a quiz one of these days. I will see if the students know what A, T, C, and G, actually stand for: either amino acids or nitrogenous bases.

[JackBean]

I love the (b) question! I will have to use that on a quiz one of these days. I will see if the students know what A, T, C, and G, actually stand for: either amino acids or nitrogenous bases.

Yeah, that one is good

[gehaan]

i have a question and want one replay it for me,
why in DNA A binds to T by 2 hydrogenous bonds, but G binds to C by 3

[JackBean]

beacause of their structure
http://images.google.com/images?q=hydro ... CCgQsAQwAw

[gehaan]

i know that is its structure..
i mean why ??
it is my supervisor question to me!!!!

[kolean]

DNA is two strands, that wrap around each other, into a double helix. Now the phosphate backbone keeps the strands together, but it is the Hydrogen Bonding between the nitrogenous bases that keeps the double helix together.
Hydrogen bonding is not a very strong one, so you need to have optimal bonding to keep the strands together. Thus, the nitrogenouse bases need to pair up optimally. This is figured out by the bases depending on the placement of hydrogen from a NH source, or the strong pull of Oxygen's unpaired electrons toward the hydrogen, to have maximal pairing.
This turns out to be Cytosine with Guanine, with the max 3 hydrogen bonds, and Thymidine with Adenine for 2 hydrogen bonds. You also have to remember that these nitrogenous bases are stacked upon each other, and for the structure of the double helix, they should be as flat as possible. Flat means hydrogen bonding that is condusive to this aspect, and not hydrogen bonding that causes a buckle (non flatness) in the DNA structure.