Biochemistry · MU Pleven

7. Nucleotide Structure and Function. Nucleotides as Nucleic Acid Components. Nucleotides with Important Biological Functions: Energy-Rich Compounds. Redox Systems and Coenzymes.

Covers the three parts of a nucleotide: the purine and pyrimidine bases, the ribose or deoxyribose sugar, and the phosphate group, then how nucleotides link into DNA and RNA. It goes on to energy-rich nucleotides such as ATP, GTP, UTP and CTP, and to nucleotide-based redox coenzymes including NAD, NADP, FAD, FMN and coenzyme A. It finishes with cAMP and cGMP as signalling molecules and the adenine-based coenzymes.

Inside: 5 sections · 16 labelled pictures · 35 flashcards · 7 min

Topic 7 of 76 in the MU Pleven syllabus for Biochemistry (Medicine, Year 2). The free AceMed note covers it in 5 sections, about 1,007 words (7 min of reading), with 35 flashcards.

In this note

  1. Nucleotide Structure and Function.
  2. Nucleotide Structure and Function
  3. Nucleotides in Redox Systems and Coenzymes
  4. Nucleotides in Signal Transduction
  5. Nucleotides as Components of Coenzymes in Metabolic Pathways

Nucleotide Structure and Function

I. Structure of Nucleotides

A nucleotide is the basic structural and functional unit of nucleic acids (DNA and RNA). Each nucleotide consists of three components:

  • Nitrogenous base
  • Pentose sugar
  • Phosphate group

1. Nitrogenous Base

The nitrogen-containing base provides the identity of the nucleotide and can be of two types:

  • Purines: Adenine (A) and Guanine (G)
  • Double-ring structures.
  • Found in both DNA and RNA.
  • Pyrimidines: Cytosine (C), Thymine (T), and Uracil (U)
  • Single-ring structures.
  • Cytosine occurs in both DNA and RNA.
  • Thymine is found only in DNA, while uracil is found only in RNA.

The bases are planar, aromatic molecules that can form hydrogen bonds — allowing specific base pairing (A with T or U, and G with C).

2. Pentose Sugar

The sugar is a five-carbon (pentose) molecule linked to the base by an N-glycosidic bond.

  • In RNA, the sugar is ribose, with a hydroxyl (-OH) group on the 2' carbon.
  • In DNA, the sugar is deoxyribose, lacking the hydroxyl group on the 2' carbon (only a hydrogen atom is present instead).

This small difference is crucial: the extra hydroxyl group in RNA makes it more reactive and less stable than DNA.

3. Phosphate Group

  • The phosphate group is attached to the 5' carbon of the sugar by a phosphoester bond.
  • A nucleotide may have one, two, or three phosphate groups — giving rise to nucleoside monophosphates (NMPs), diphosphates (NDPs), or triphosphates (NTPs) respectively.
  • The phosphates carry negative charges, making nucleotides highly polar and soluble in water.

When the phosphate is absent, the compound is called a nucleoside (base + sugar only).

II. Nucleotides as Components of Nucleic Acids

Nucleotides are the monomeric units of nucleic acids (DNA and RNA).

  • In nucleic acids, nucleotides are joined together by phosphodiester bonds between the 3' hydroxyl group of one sugar and the 5' phosphate group of the next.
  • This linkage forms a sugar–phosphate backbone with nitrogenous bases projecting outward.
  • The sequence of bases along this backbone stores genetic information.

In DNA:

  • The structure is a double helix of two complementary strands running in opposite directions (antiparallel).
  • Hydrogen bonding between bases stabilizes the structure (A–T has two bonds, G–C has three).

In RNA:

  • Usually single-stranded, though secondary structures like hairpins may form.
  • It serves as a messenger, adaptor, or catalytic molecule (mRNA, tRNA, rRNA).

Thus, nucleotides form the structural foundation of the genetic material and the basis for heredity and information transfer.

Continue reading free

The whole note, all 5 sections, is free with an AceMed account, with its 35 flashcards. Premium adds flashcard recall, highlights and Ask AI.

Start freeAlready a member? Open the note