DNA

• DNA (Deoxyribonucleic Acid) is a fundamental molecule that carries the genetic instructions necessary for the growth, development, reproduction, and survival of all living organisms.

• It serves as the hereditary material, and understanding its structure, function, replication, and role in gene expression and the genetic code is essential for insights into genetics, molecular biology, and biotechnology.

DNA

Structure of DNA

1.Basic Composition:

• DNA consists of two complementary strands forming a double helix.

• Each strand is made up of nucleotides, which are the building blocks of DNA.

  • A nucleotide is composed of three parts:

  • A sugar molecule (deoxyribose).

  • A phosphate group.

  • One of four nitrogenous bases: adenine (A), cytosine (C), guanine (G), or thymine (T).

2.Sugar-Phosphate Backbone:

• The nucleotides are linked by covalent bonds between the sugar of one nucleotide and the phosphate group of the next, forming a sugar-phosphate backbone.

3.Base Pairing:

• The two DNA strands are held together by hydrogen bonds between paired nitrogenous bases:

  • Adenine (A) pairs with Thymine (T).

  • Cytosine (C) pairs with Guanine (G).

5.Double Helix Structure:

• The specific pairing of bases and the arrangement of nucleotides cause the DNA to twist into its characteristic double helix shape.

Function of DNA

1.Genetic Information Storage:

• DNA holds the genetic blueprint for protein synthesis and the regulatory sequences needed for gene expression.

• This information determines the inherited traits of an organism.

2.Transmission of Genetic Information:

• During cell division, DNA is replicated and passed down to offspring, ensuring the continuity of genetic information across generations.

3.Template for Protein Synthesis:

• The nucleotide sequence in genes dictates the amino acid sequence of proteins, influencing their structure and function.

Replication of DNA

1.Semi-conservative Mechanism:

• DNA replication is semi-conservative, meaning that each new DNA molecule consists of one original strand and one newly synthesized strand.

2.Process:

• Replication begins with the unwinding of the double helix.

• DNA polymerase enzymes add complementary nucleotides to each original strand, following the base-pairing rules.

Genetic Code

1.Codons:

• The genetic code is read in three-nucleotide units called codons. Each codon specifies a particular amino acid.

2.Universality:

• The genetic code is nearly universal across all organisms, with 61 codons encoding amino acids and 3 codons serving as stop signals for protein synthesis.

Role in Gene Expression

1.Transcription and Translation:

• DNA acts as a template for synthesizing messenger RNA (mRNA) during transcription.

• The mRNA is then used during translation to guide the synthesis of proteins on ribosomes.

2.Regulation of Gene Expression:

• The expression of genes is regulated by DNA sequences (regulatory elements) and proteins that bind to these sequences to control when and how much protein is produced.

DNA's Role in Inheritance

• DNA serves as the hereditary material, passed from one generation to the next.

• During cell division (mitosis or meiosis), DNA is replicated and transmitted, ensuring that offspring inherit genetic information from their parents.