Microbial Genetics: Structure and Function of Nucleic Acids

Microbial Genetics

Overview

Microbial genetics is the study of the mechanisms of heritable information in microorganisms, focusing on the structure, function, and regulation of genetic material. This field is fundamental for understanding how microbes inherit traits, adapt, and evolve.

Nucleic Acids

Function

DNA and RNA are essential molecules for the proper functioning of all living cells, including microbes. DNA stores genetic information, while RNA plays a key role in expressing this information and converting it into functional products.

• DNA contains the genes and the genetic code.

• Information in DNA must be transferred to the rest of the cell to direct cellular functions; this transfer is mediated by RNA.

• RNA molecules are involved in converting the genetic code into proteins and other gene products.

Structure

Nucleic acids are polymers composed of nucleotides. Both DNA and RNA contain the elements carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and phosphorus (P).

• The building blocks of DNA and RNA are called nucleotides.

• Each nucleotide consists of three components:

  • A nitrogenous base (A, T, G, C, or U)

  • A five-carbon sugar (deoxyribose in DNA, ribose in RNA)

  • A phosphate group

• DNA contains deoxyribose as its pentose sugar, while RNA contains ribose.

Nucleotides

Nucleotides are the monomeric units of nucleic acids. Each nucleotide is made up of:

• A nitrogenous base (Adenine, Thymine, Guanine, Cytosine, or Uracil)

• A five-carbon sugar (S)

• A phosphate group (P)

Two nucleotides can be represented as:

• P-S-A (Phosphate-Sugar-Adenine)

• P-S-T (Phosphate-Sugar-Thymine)

Types of RNA and Nitrogenous Bases

There are three main types of RNA, each with a specific function:

• Messenger RNA (mRNA): Carries genetic information from DNA to the ribosome.

• Ribosomal RNA (rRNA): Forms the core of the ribosome's structure and catalyzes protein synthesis.

• Transfer RNA (tRNA): Brings amino acids to the ribosome during translation.

The five nitrogenous bases found in nucleic acids are:

• Adenine (A)

• Guanine (G)

• Thymine (T) (found only in DNA)

• Cytosine (C)

• Uracil (U) (found only in RNA)

These bases are classified as:

• Pyrimidines: Cytosine, Thymine, Uracil

• Purines: Adenine, Guanine

DNA Structure

Double Helix

DNA is typically found as a double-stranded molecule, forming a structure known as the double helix. The two strands are held together by hydrogen bonds between complementary nitrogenous bases.

• Adenine (A) always pairs with Thymine (T) via two hydrogen bonds.

• Guanine (G) always pairs with Cytosine (C) via three hydrogen bonds.

• These pairs are called base pairs (A–T and G–C).

• The double helix resembles a right-handed spiral staircase.

Base Pairing

The specificity of base pairing ensures accurate replication and transcription of genetic information.

• If one DNA strand has the sequence 5'-AGTCGT-3', the complementary strand will be 3'-TCAGCA-5'.

Table: Base Pairing in DNA

Base	Pairs With	Number of Hydrogen Bonds
Adenine (A)	Thymine (T)	2
Guanine (G)	Cytosine (C)	3

Summary

• DNA and RNA are nucleic acids essential for genetic information storage and expression in microbes.

• Nucleotides are the building blocks of nucleic acids, each composed of a nitrogenous base, a five-carbon sugar, and a phosphate group.

• DNA forms a double helix with specific base pairing (A–T, G–C), ensuring fidelity in genetic processes.

• RNA exists in several forms, each with a unique role in gene expression.

Additional info: Later sections (not shown in these images) would likely cover DNA replication, transcription, translation, regulation, mutations, and horizontal gene transfer, as outlined in the initial topic list.