DNA

DNA

This Wikipedia article for **DNA (Deoxyribonucleic acid)** describes it as the molecule that carries the genetic instructions for the development, functioning, growth, and reproduction of all known organisms and many viruses.

Here is a summary of the key sections:

### 1. Structure

* **Double Helix:** DNA consists of two long strands coiled around each other like a twisted ladder.
* **Nucleotides:** Each strand is a chain of "nucleotides," which consist of three parts: a phosphate group, a sugar (deoxyribose), and a nitrogenous base.
* **The Four Bases:** There are four types of bases: **Adenine (A)**, **Thymine (T)**, **Guanine (G)**, and **Cytosine (C)**.
* **Base Pairing:** The two strands are held together by hydrogen bonds between the bases. Crucially, **A always pairs with T**, and **G always pairs with C**. This complementarity allows the molecule to be copied accurately.
* **Antiparallel Strands:** The two strands run in opposite directions to each other.

### 2. Function

* **Storage of Information:** The "genetic code" is determined by the specific sequence of the four bases (A, T, G, and C) along the DNA strand.
* **Protein Synthesis:** DNA provides the instructions for making proteins. This happens in two main steps:
1. **Transcription:** DNA is copied into a related molecule called RNA.
2. **Translation:** The RNA is used as a template by ribosomes to build proteins.


* **Replication:** Before a cell divides, it makes an exact copy of its DNA so that each new "daughter cell" has a complete set of instructions.

### 3. Organization in Cells

* **Chromosomes:** In complex cells (eukaryotes), DNA is very long and must be tightly coiled around proteins called **histones** to form structures called chromosomes.
* **Location:** Most DNA is located in the cell nucleus, though some is found in organelles like mitochondria.

### 4. History of Discovery

* DNA was first isolated by **Friedrich Miescher** in 1869.
* Its double-helix structure was famously identified in 1953 by **James Watson** and **Francis Crick**, a discovery heavily reliant on X-ray diffraction data produced by **Rosalind Franklin** and **Raymond Gosling**.

### 5. Modern Applications

* **Genetic Engineering:** Scientists can manipulate DNA to alter organisms or produce medicines (like insulin).
* **Forensics:** Because DNA sequences are unique to individuals (except identical twins), it is used in "DNA profiling" to identify suspects or determine paternity.
* **Anthropology:** By comparing DNA sequences, researchers can track human evolution and migration patterns over thousands of years.