BIOLOGY UNIT 1: THE MOLECULAR BASIS OF
LIFE
> Sub-topic: DNA Structure & Watson-Crick
Double Helix Model
Comprehensive Study Guide, Detailed Diagrams & Calculation Examples
Detailed Nucleotide Components
Step-by-step Watson-Crick Model
Chargaff’s Rule with Solved Problems
High-Quality labelled Diagrams
Exam oriented Short Notes for biology students
MCQs, SAQs, FRQ
Prepared by: Sania Tasnim
Target Level: AP Biology / High School / College
, Introduction to DNA
Deoxyribonucleic Acid (DNA) is the hereditary material present in almost all living organisms.
It stores genetic information that determines the structure, function, and reproduction of
cells. In 1953, James Watson and Francis Crick proposed the double-helix structure, aided by
Rosalind Franklin’s X-ray diffraction data.
DNA is composed of two long strands twisted around each other, forming a double helix
structure.
Structure Of Nucleotide
DNA is a polymer made of repeating units called Nucleotides. Each nucleotide consists of
three essential components:
1. A Phosphate Group: Attached to the 5' carbon of the sugar; it gives DNA its acidic
property and negative charge.
2. Deoxyribose Sugar: A 5-carbon pentose sugar. It lacks an oxygen atom at the 2' carbon
position (hence "deoxy").
3. Nitrogenous Base: Attached to the 1' carbon of the sugar. There are two types:
3.1. Purines (Double-ring): Adenine (A) and Guanine (G).
3.2. Pyrimidines (Single-ring): Thymine (T) and Cytosine (C).
DNA Nucleotide Structure
LIFE
> Sub-topic: DNA Structure & Watson-Crick
Double Helix Model
Comprehensive Study Guide, Detailed Diagrams & Calculation Examples
Detailed Nucleotide Components
Step-by-step Watson-Crick Model
Chargaff’s Rule with Solved Problems
High-Quality labelled Diagrams
Exam oriented Short Notes for biology students
MCQs, SAQs, FRQ
Prepared by: Sania Tasnim
Target Level: AP Biology / High School / College
, Introduction to DNA
Deoxyribonucleic Acid (DNA) is the hereditary material present in almost all living organisms.
It stores genetic information that determines the structure, function, and reproduction of
cells. In 1953, James Watson and Francis Crick proposed the double-helix structure, aided by
Rosalind Franklin’s X-ray diffraction data.
DNA is composed of two long strands twisted around each other, forming a double helix
structure.
Structure Of Nucleotide
DNA is a polymer made of repeating units called Nucleotides. Each nucleotide consists of
three essential components:
1. A Phosphate Group: Attached to the 5' carbon of the sugar; it gives DNA its acidic
property and negative charge.
2. Deoxyribose Sugar: A 5-carbon pentose sugar. It lacks an oxygen atom at the 2' carbon
position (hence "deoxy").
3. Nitrogenous Base: Attached to the 1' carbon of the sugar. There are two types:
3.1. Purines (Double-ring): Adenine (A) and Guanine (G).
3.2. Pyrimidines (Single-ring): Thymine (T) and Cytosine (C).
DNA Nucleotide Structure
