RNA grows by using a DNA template, with RNA polymerase adding nucleotides to a growing RNA strand based on base pairing rules, always in the 5' to 3' direction.
The Process of RNA Synthesis
RNA synthesis, also known as transcription, is a crucial process where RNA molecules are produced from a DNA template. Here’s a detailed breakdown:
1. The Role of RNA Polymerase
RNA polymerase is the key enzyme responsible for RNA synthesis. It binds to a specific region of DNA called the promoter.
2. Unwinding the DNA
Once bound, RNA polymerase unwinds the DNA double helix, separating the two strands in a localized region. This creates a template for RNA synthesis.
3. Base Pairing and Nucleotide Addition
- Template Strand: RNA polymerase reads the template strand of the DNA.
- Base Pairing Rules: Based on the sequence of the template strand, RNA polymerase adds complementary RNA nucleotides. The base pairing rules are as follows:
- Adenine (A) in the DNA template pairs with Uracil (U) in the RNA molecule.
- Guanine (G) in the DNA template pairs with Cytosine (C) in the RNA molecule.
- Cytosine (C) in the DNA template pairs with Guanine (G) in the RNA molecule.
- Thymine (T) in the DNA template pairs with Adenine (A) in the RNA molecule.
- 5' to 3' Direction: RNA polymerase adds nucleotides to the 3' end of the growing RNA molecule, so synthesis proceeds in the 5' to 3' direction. This means each new nucleotide is attached to the 3' hydroxyl group of the last nucleotide in the chain.
4. Termination
Transcription continues until RNA polymerase reaches a termination signal in the DNA. At this point, the RNA polymerase detaches from the DNA, and the newly synthesized RNA molecule is released.
Example
Let's say we have a DNA template sequence: 3'-TTCGATT-5'
The resulting RNA sequence synthesized would be: 5'-AAGCUAAG-3'
Here's a breakdown:
| DNA Template | RNA Complement |
|---|---|
| T | A |
| T | A |
| C | G |
| G | C |
| A | U |
| T | A |
| T | A |
Summary
RNA growth is a precisely orchestrated process involving RNA polymerase, a DNA template, and the fundamental rules of base pairing, always occurring in the 5' to 3' direction. This ensures accurate transcription and the production of functional RNA molecules.
