Nucleotide Metabolism

The following are roles played by nucleic acids in metabolism except:

• nucleotide triphosphate hydrolysis fuels many metabolic reactions

• nucleotides serve as regulatory molecules

• nucleotide triphosphates are the substrates for RNA and DNA synthesis

• nucleotides are components of many coenzymes

• All

Answer explanation

All the above mentioned are roles played by nucleic acids in metabolism.

Which of the following molecules is not a component of a nucleotide?

• nitrogenous base

• sugar

• phosphate group

• fatty acid

• all

Answer explanation

A nucleotide consists of a phosphate group, a nitrogenous base, and a sugar (either deoxyribose in DNA or ribose in RNA). Fatty acids are not part of the nucleotide structure; they are involved in lipid metabolism.

Which of the following is true about the de novo pyrimidine synthesis pathway in microorganisms?

• The pathway begins with the direct formation of uracil from aspartate.

• Carbamoyl phosphate is synthesized as the first step in the pathway, requiring glutamine as a nitrogen source.

• The synthesis of pyrimidines does not involve any cofactors or energy input.

• In microorganisms, the pathway starts with the formation of a ribose sugar, followed by the addition of nitrogenous bases.

Answer explanation

In microorganisms, the de novo pyrimidine synthesis pathway begins with the formation of carbamoyl phosphate, which requires glutamine for nitrogen. This molecule is then used to build pyrimidine rings, ultimately leading to the synthesis of uracil, cytosine, and thymine.

Which of the following is true about the salvage pathway of pyrimidine synthesis in microorganisms?

• The salvage pathway requires de novo synthesis of pyrimidine rings from amino acids and ribose.

• In the salvage pathway, uracil and thymine are directly converted into their corresponding nucleosides and nucleotides.

• The salvage pathway is only used under conditions of pyrimidine deficiency, not during normal growth.

• The salvage pathway involves the synthesis of new pyrimidine bases from scratch using acetyl-CoA.

Answer explanation

The salvage pathway of pyrimidine synthesis allows microorganisms to recycle free pyrimidine bases (such as uracil and thymine) by converting them into their corresponding nucleosides and nucleotides, which can then be used for RNA and DNA synthesis. This pathway helps conserve energy and resources by reusing existing pyrimidine bases.

Which of the following is true about the salvage pathway of purine synthesis in microorganisms?

• The salvage pathway involves the de novo synthesis of purine rings from scratch using ribose and amino acids.

• In the salvage pathway, free purine bases like adenine and guanine are recycled to form nucleotides with the help of specific enzymes like hypoxanthine-guanine phosphoribosyltransferase (HGPRT).

• The salvage pathway is only active during periods of high cellular stress and not during normal growth.

• The salvage pathway does not require any energy input, as it is a purely passive recycling process.

Answer explanation

In the salvage pathway of purine synthesis, microorganisms recycle free purine bases such as adenine, guanine, and hypoxanthine by using enzymes like HGPRT to convert them into purine nucleotides. This pathway is energetically efficient, as it conserves purine bases for nucleotide synthesis without requiring the complete de novo synthesis of purine rings.

Which of the following is true about the de novo purine synthesis pathway in microorganisms?

• The de novo purine synthesis pathway starts with the direct formation of guanine and adenine from ribose.

• The de novo purine synthesis pathway does not require any energy input, as it is a simple process of base assembly.

• The pathway involves the stepwise assembly of a purine ring on a ribose-5-phosphate molecule using various amino acids, carbon donors, and ATP.

• The pathway exclusively synthesizes adenine and guanine, without producing any intermediates.

Answer explanation

In the de novo purine synthesis pathway, a purine ring is synthesized from ribose-5-phosphate and a series of precursors, including amino acids (such as glutamine), carbon donors (like formyl-THF), and ATP. This pathway requires significant energy input and leads to the production of purine nucleotides, including adenine and guanine.