2.1.3 Nucleotides and nucleic acids (a-c) SYI

What are the three components of a nucleotide?

• Pentose Sugar, Nitrogenous base, Phosphate Group

• Deoxyribose, Uracil, Guanine

• Ribose Sugar, Adenine, Cytosine

• Thymine, Purines, Phosphodiester Bond

Answer explanation

A nucleotide consists of three components: a pentose sugar, a nitrogenous base, and a phosphate group. The correct choice is 'Pentose Sugar, Nitrogenous base, Phosphate Group'. This choice includes all three components required for a nucleotide.

Which component of a nucleotide can be either ribose or deoxyribose?

• Nitrogenous base

• Phosphate group

• Purines

• Pentose sugar

Answer explanation

The pentose sugar is a component of a nucleotide that can be either ribose or deoxyribose. It is responsible for providing the backbone structure to the nucleotide. The other options, such as the nitrogenous base, phosphate group, and purines, are also important components of a nucleotide, but they do not determine the type of sugar present. Therefore, the correct choice is the pentose sugar.

Where are nitrogenous bases attached in a nucleotide?

• Second carbon of sugar

• Third carbon of sugar

• First carbon of sugar

• Fourth carbon of sugar

Answer explanation

In a nucleotide, nitrogenous bases are attached to the first carbon of the sugar. This attachment is important for the structure and function of nucleic acids. The first carbon provides a stable connection for the nitrogenous base, allowing for the formation of the nucleotide sequence. The other options, such as the second, third, and fourth carbon of the sugar, are not involved in the attachment of nitrogenous bases. Therefore, the correct choice is the first carbon of the sugar.

How many types of nitrogenous bases are there in nucleotides?

• 1

• 2

• 3

• 4

Answer explanation

There are four types of nitrogenous bases in nucleotides: adenine, cytosine, guanine, and thymine. However, only two of these bases are present in DNA, which are adenine and thymine. Therefore, the correct answer is 2.

Which of the following is a purine nitrogenous base?

• Cytosine

• Thymine

• Adenine

• Uracil

Answer explanation

Adenine is a purine nitrogenous base. It is one of the four bases found in DNA and RNA. Adenine pairs with thymine in DNA and with uracil in RNA. Cytosine and thymine are pyrimidine bases, not purine bases. Uracil is also a pyrimidine base. Therefore, the correct answer is Adenine.

Which nitrogenous base pairs with thymine (or uracil) with two hydrogen bonds?

• Cytosine

• Guanine

• Adenine

• Purines

Answer explanation

Adenine is the nitrogenous base that pairs with thymine (or uracil) with two hydrogen bonds. This is because adenine forms two hydrogen bonds with thymine (or uracil) in DNA or RNA. Cytosine pairs with guanine with three hydrogen bonds, while guanine pairs with cytosine with three hydrogen bonds. Purines are a type of nitrogenous base that includes adenine and guanine. Therefore, the correct choice is Adenine.

How many hydrogen bonds are formed between cytosine and guanine?

• 1

• 2

• 3

• 4

Answer explanation

Three hydrogen bonds are formed between cytosine and guanine. These hydrogen bonds occur between the nitrogenous bases of the two nucleotides. The hydrogen bonds play a crucial role in stabilizing DNA. The correct choice is 3.

What is the combination of a nitrogenous base and a pentose sugar called?

• Nucleotide

• Phosphodiester Bond

• Nucleoside

• Purine

Answer explanation

A nucleoside is the combination of a nitrogenous base and a pentose sugar. In this question, the correct choice is 'Nucleoside'. The nitrogenous base and pentose sugar together form a nucleoside, which is an essential component of nucleotides and nucleic acids. It is important to understand the concept of nucleosides in biochemistry and genetics.

How many phosphate groups can a nucleotide have?

• One

• Two

• Three

• Four

Answer explanation

A nucleotide can have up to three phosphate groups. An example being ATP, a phosphorylated nucleotide.

How are two or more nucleotides attached to each other?

• Disulphide Bond

• Hydrogen Bond

• Ionic Bond

• Phosphodiester Bond

Answer explanation

Two or more nucleotides are attached to each other by a Phosphodiester Bond. This bond forms between the phosphate group of one nucleotide and the sugar molecule of another nucleotide. The Phosphodiester Bond plays a crucial role in the formation of the DNA and RNA strands. It provides stability and allows for the sequential arrangement of nucleotides, which is essential for the genetic code. The other options, Dispulphide Bond, Hydrogen Bond, and Ionic Bond, are not involved in the attachment of nucleotides in DNA or RNA.