Question

Each of the following statements about the structure of DNA may be either true or false. Choose the appropriate answer for each of these statements. Bonding between adenine and thymine on opposite strands involves two hydrogen bonds. Nitrogenous bases are located on the outside of the double helix: phosphates are located towards the middle of the double helix. Bonding between guanine and cytosine on opposite strands involves three hydrogen bonds. DNA and RNA are structurally different due to the difference in the number of phosphates in the backbone unit. DNA has a single phosphate between each sugar, while RNA has two phosphates between each sugar. a. True DNA and RNA differ in the composition of the sugar group and some of the nitrogenous b. bases that are found in their nucleotide building blocks. The two strands of the DNA double helix are organized in an antiparallel manner. The complementary pairing of the nucleotides between the two strands is a structural feature of DNA that suggests a possible method of its replication. The model of DNA replication that hypothesizes the separation of the two strands of the original DNA (the template) and the use of each of those strands as templates to synthesize two new DNA strands is called semiconservative replication.

Answer 1

1. TRUE

Explanation: The adenine and Thymine has two hydrogen bond in between

1st hydrogen bond is formed between hydrogen atom at C-6 of Adenine and Oxygen atom (keto group) at C-4 of thymine.

the 2nd bond is formed between Nitrogen atom at position 1 of Adenine and Hydrogen atom at N-3 of Thymine.

Here is a pictorial depiction -

N" NH--- Q N- 14-- C "C ó 5 6 H-N 3 Pa 2_EN 103N ---- H N3 4 &_N 5 Ne GO Adenine - Thymine Borse fair

2.FALSE

Explanation: the phosphate groups form the backbone and are present on the outside and the nitrogenous bases are present in the middle of the double helix in bonded condition.

3.TRUE

Explanation: There are three hydrogen bonds between Guanine and Cytosine.

The 1st hydrogen bond is formed between Oxygen atom (keto group) at C-2 of Cytosine and hydrogen atom at C-2 of Guanine.

2nd bond is formed between N-3 of cytosine and Hydrogen at the N-1 atom of Guanine.

3rd Hydrogen bond is formed between the Hydrogen at C-4 of Cytosine and Oxygen at C-6 of Guanine.

Here is a pictorial depiction-

4.FALSE

Explanation: DNA and RNA are structurally different due to their difference in the ribose sugar and their nitrogen base composition.

DNA has deoxy-ribose sugar and RNA has ribose sugar.

DNA has A, T, G, C while RNA has A, U, G, C.

There is no difference in the phosphate backbone of DNA and RNA.

5.TRUE

Explanation: Same as the previous explanation.

6.TRUE

Explanation: The two strands of the double helix are in an antiparallel manner.

One of the strands runs in 5" to 3" direction and the other one runs in 3" to 5" direction.

7.TRUE

Explanation: The bases in the DNA strands are complementary in nature. It is a structural feature of the DNA molecule. This complementarity helps the replication process to be semiconservative.

8.TRUE

Explanation: The DNA molecule is replicated in a semiconservative manner. In which two parental strands are separated and new strands are synthesized using the two mother strands in a complementary manner.

So, the newly synthesized double helices have one newly synthesized strand and the other one from the parental DNA.