Microbial Genetics: Structure and Function of DNA

Microbial Genetics

Introduction to Microbial Genetics

Microbial genetics is the study of the mechanisms of heritable information in microorganisms, focusing on the structure, function, and transmission of genetic material. Understanding microbial genetics is fundamental for exploring how microbes grow, adapt, and evolve.

DNA: Deoxyribonucleic Acid

Definition and Structure

DNA (deoxyribonucleic acid) is the molecule that stores genetic information in all living organisms, including microbes. It is composed of two long chains forming a double helix, with each chain made up of repeating units called nucleotides.

• Nucleotide: The basic building block of DNA, consisting of three components:

  • Deoxyribose sugar

  • Phosphate group

  • Nitrogenous base (Adenine, Thymine, Guanine, Cytosine)

• Base Pairing: DNA bases pair specifically: Adenine (A) with Thymine (T), and Guanine (G) with Cytosine (C).

• Double Helix: The two DNA strands twist around each other, forming a helical structure stabilized by hydrogen bonds between paired bases.

Example: The DNA sequence TGCATCAGA contains a specific order of nucleotides that encodes genetic information.

Discovery of DNA Structure

The structure of DNA was discovered in 1953 by James Watson and Francis Crick, with crucial contributions from Rosalind Franklin, whose X-ray diffraction images revealed the helical nature of DNA.

• Watson and Crick proposed the double helix model.

• Franklin's X-ray diffraction photo provided key evidence for the helical structure.

Extraction and Visualization of DNA

Methods and Applications

DNA can be extracted from cells and visualized in laboratory settings. This allows scientists to study its structure and function.

• Extraction involves breaking open cells and isolating DNA using chemical methods.

• Visualization can be achieved by techniques such as gel electrophoresis or staining.

• Example: DNA extracted from strawberries in a biology lab demonstrates the physical properties of DNA.

Structure of DNA: The Double Helix

Nucleotide Composition and Base Pairing

The DNA molecule consists of chains of nucleotides, each containing a deoxyribose sugar, a phosphate group, and a nitrogenous base. The sequence of these bases encodes genetic information.

• Specific Base Pairing: A pairs with T, and G pairs with C, forming the rungs of the DNA ladder.

• Sugar-Phosphate Backbone: The backbone is formed by alternating sugar and phosphate groups, located on the outside of the helix.

• Hydrogen Bonds: Base pairs are held together by hydrogen bonds, providing stability to the DNA molecule.

Example: The double helix model explains how genetic information is stored and replicated.

Table: DNA Nucleotide Components

Component	Description
Deoxyribose Sugar	Pentose sugar lacking one oxygen atom compared to ribose
Phosphate Group	Links sugars together, forming the backbone
Nitrogenous Base	Adenine (A), Thymine (T), Guanine (G), Cytosine (C)

Additional info:

• The unique sequence of nucleotides in DNA forms the genetic code, which is essential for the synthesis of proteins and the regulation of cellular activities.

• Chargaff's rules state that the amount of A equals T and the amount of G equals C in DNA, supporting the base pairing model.