Edited by simon
2025-11-30 06:08 · Updated content
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The Central Dogma: DNA → RNA → Protein
The Central Dogma of Molecular Biology describes how genetic information flows inside a cell.
It explains how instructions written in DNA are converted into RNA, and then used to build proteins, the molecules that perform most cellular functions.
This page covers:
- What transcription is
- What translation is
- Types of RNA
- How information flows
- Why this process is essential for life
- What parts (if any) can be seen under a light microscope
1. Overview of the Central Dogma
DNA → RNA → Protein
This happens in two major steps:
-
Transcription (DNA → RNA)
Occurs in the nucleus of eukaryotes (yeast, onion, human).
DNA is read by the enzyme RNA polymerase, producing messenger RNA (mRNA). -
Translation (RNA → Protein)
Occurs in the cytoplasm on ribosomes.
The ribosome reads the mRNA and assembles amino acids into a protein.
This flow of information is universal across life.
2. Step 1: Transcription (DNA → RNA)
Transcription is the process of making an RNA copy of a section of DNA (a gene).
2.1. Key enzyme
- RNA Polymerase — binds to a gene, reads DNA, and synthesizes RNA.
2.2. Steps of transcription
-
Initiation
RNA polymerase binds the promoter, a regulatory DNA region. -
Elongation
The enzyme moves along DNA, forming an RNA strand complementary to the DNA template. -
Termination
RNA polymerase stops and releases the RNA molecule.
2.3. Where it happens
- Eukaryotes (plants, yeasts, humans): inside the nucleus
- Prokaryotes (bacteria): directly in the cytoplasm
3. Step 2: Translation (RNA → Protein)
Translation is the process of converting mRNA information into a chain of amino acids (a protein).
3.1. Where translation occurs
- On ribosomes, found in the cytoplasm or bound to the rough ER.
3.2. Key players
mRNA (Messenger RNA)
Carries the instructions copied from DNA.
tRNA (Transfer RNA)
- Brings amino acids to the ribosome.
- Each tRNA recognizes a specific 3-letter mRNA sequence (a codon).
rRNA (Ribosomal RNA)
- Forms the core of the ribosome.
- Catalyzes peptide bond formation.
3.3. Steps of translation
-
Initiation
Ribosome binds mRNA at the start codon (AUG). -
Elongation
tRNAs bring amino acids in the correct order; the ribosome links them together. -
Termination
When a stop codon is reached, the protein is released.
3.4. Optical visibility
Ribosomes, mRNA, and proteins cannot be seen individually with a light microscope.
4. Types of RNA
Cells use several kinds of RNA, each with a specific purpose:
4.1. mRNA (Messenger RNA)
Carries genetic instructions.
4.2. tRNA (Transfer RNA)
Delivers amino acids to ribosomes.
4.3. rRNA (Ribosomal RNA)
Structural and catalytic component of ribosomes.
4.4. snRNA / snoRNA
Used in RNA processing (splicing, modification).
4.5. miRNA / siRNA
Regulate gene expression (epigenetic control).
4.6. lncRNA
Long non-coding RNAs with regulatory roles.
5. The Genetic Code
The genetic code uses codons — groups of three nucleotides on mRNA.
Examples:
- AUG → Methionine (start)
- UGA → Stop
- GGU → Glycine
Features:
- Universal (same in yeast, plants, humans)
- Redundant (multiple codons for the same amino acid)
- Non-overlapping
6. Why the Central Dogma Matters
It explains how cells:
- build proteins
- respond to signals
- repair themselves
- differentiate into specialized types
- age
- reprogram (OSK, CRISPR)
Most biotechnology — vaccines, gene editing, RNA therapies — directly manipulates this flow.
For example:
- mRNA vaccines provide mRNA so your cells make a protein.
- CRISPR modifies DNA so transcription produces different RNA/proteins.
- OSK reprogramming changes gene expression to reverse epigenetic age.
8. Quick Summary
- Transcription: DNA → RNA
- Translation: RNA → Protein
- Ribosomes read mRNA and assemble amino acids.
- Proteins perform almost every function in the cell.
- This process is universal to life and essential for understanding biology, aging, disease, and biotechnology.