How Protein Synthesis Works

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DNA as the Starting Instructions

Protein synthesis begins with DNA, which contains the genetic instructions for building proteins, stored as sequences of nucleotides organized into genes within the cell's nucleus.

Transcription

The process by which a specific segment of DNA is copied into a molecule of messenger RNA (mRNA), which then carries those genetic instructions out of the nucleus to the rest of the cell.

Messenger RNA (mRNA)

A molecule that carries the copied genetic code from the nucleus to the ribosome, the cellular structure where the actual protein-building process, called translation, takes place.

Translation

The process at the ribosome where the mRNA sequence is read three nucleotides (a codon) at a time, with each codon specifying a particular amino acid to be added to a growing protein chain.

Transfer RNA (tRNA)

A molecule that reads each codon on the mRNA and delivers the corresponding amino acid to the ribosome, acting as the crucial link between the genetic code and the physical building blocks of a protein.

The Ribosome

The cellular structure where translation actually occurs, functioning as a molecular assembly line that links amino acids together in the exact order specified by the mRNA sequence to form a complete protein.

The central dogma of molecular biology

This two-step process — transcription followed by translation — is often summarized as the "central dogma" of molecular biology: genetic information flows from DNA to RNA to protein, and this fundamental process is essentially the same across nearly all known forms of life.

Frequently Asked Questions

Why does the cell copy DNA into mRNA instead of using DNA directly?

DNA stays protected inside the nucleus, while mRNA acts as a disposable working copy that can travel out to the ribosomes without risking damage to the cell's permanent genetic master copy.

How many possible codons are there, and how many amino acids do they represent?

There are 64 possible three-nucleotide codons, which collectively code for the 20 standard amino acids used to build proteins, plus start and stop signals — meaning several different codons can sometimes code for the same amino acid.