Question

Calculate the number of week hydrogen bonds in a DNA strand `204Å` long with 15% thymine bases.

Answer 1

One turn of DNA double helix is 3.4 nm long and has 10 bp; therefore, a 204 nm long DNA strand will have 3.4/10 * 204= 600 bp. According to the question, this DNA strand has 40% adenine. According to Chargaff’s rule in all cellular DNAs, regardless of the species, number of adenosine residues is equal to number of thymidine residues which means that A=T; and the number of guanosine residues is equal to the number of cytidine residues; G= C. Therefore, the DNA strand has 40 % adenine and 40% thymine. Out of total 600 bp, number of adenine residues = 40/100 *600= 240. And the number of thymine will also be 240. Out of total 600 bp, rest base pairs (600-240+240= 120) are C+G. Hence the number of cytosines = 120/2= 60 and the number of guanine base is also 60. As defined forms double hydrogen bonds with thymine, hence, a total number of double hydrogen bonds= 240. And guanine forms triple hydrogen bonds with cytosine; a number of triple hydrogen bonds= 60. Hence the ratio of double and triple hydrogen bonds is 240: 60= 4:1. Thus, the correct answer is option C.

Answer 2

Question

Answers

Related Questions

In 68 nm

long DNA segment, 30%

adenines is present, and then calculate how many hydrogen bonds are present in this segment?

Answer

VerifiedVerified

46.5k+ views

Hint: DNA is composed of nucleotides and is a nucleotide consisting of three basic components-the nitrogenous bases, a pentose sugar and a phosphate group. There are four types of nitrogenous bases which are found in DNA namely, adenine, thymine, guanine and cytosine. Adenine forms two hydrogen bonds with thymine and guanine forms three hydrogen bonds with cytosine.

Complete answer:

Concept to be applied:

To solve this question, we need to apply the basic rules given by Sir Erwin Chargaff which helps in understanding the total content of various nitrogenous bases in DNA segments.

According to Chargaff’s rules:

Purines (double ringed nitrogenous bases) and Pyrimidines (single ringed nitrogenous bases) occur in equal amounts in DNA.

Purines found in DNA are Adenine and Guanine while pyrimidines are Thymine and Cytosine.

Since the average length of nucleotides is 3.4

angstroms, there are 200

nucleotides in a DNA with a length of 68nm

.

2

nucleotides form a base pair, so there are 100

base pairs. Thymine forms a double bond base paired with hydrogen and guanine-Cytosine forms a base pair with a triple bond.

Now, according to our question, 30%

of the DNA molecule is composed of adenine, which means that thymine exists in equal parts and forms 60%

of DNA in the form of adenine-thymine base pairs (60

base pairs).

The remaining 40%

of DNA is composed of guanine-cytosine (40

base pairs).

According to this number of existing hydrogen bonds, they are -

2 × 60 + 3 ×40 = 240

Hence, 240

hydrogen bonds is the answer.