MCAT Content / Genetic Code / Central Dogma Dna Rna Protein

Central Dogma: DNA → RNA → protein

Topic: Genetic Code

The central dogma in biology describes the flow of genetic information from DNA to RNA to proteins.

Genes are composed of DNA and are linearly arranged on chromosomes. Protein-encoding genes specify the sequences of amino acids, which are the building blocks of proteins. In turn, proteins are responsible for orchestrating nearly every function of the cell. Both protein-encoding genes and the proteins that are their gene products are absolutely essential to life as we know it. Some genes alternatively encode structural and regulatory RNAs. Replication, transcription, and translation are the three main processes used by all cells to maintain their genetic information and to convert the genetic information encoded in DNA into gene products. In eukaryotic cells, replication and transcription take place within the nucleus while translation takes place outside of the nucleus in cytoplasm. In prokaryotic cells, all three processes occur in the cytoplasm.

Because the information stored in DNA is so central to cellular function, the cell keeps the DNA protected and copies it in the form of RNA. An enzyme adds one nucleotide to an RNA strand for every nucleotide it reads in a DNA strand. This is known as transcription. This RNA then acts as a messenger for DNA and is used to create proteins.

The translation of this information to a protein is more complex because three RNA nucleotides (one codon) correspond to one amino acid in a polypeptide sequence. Each codon instructs the addition of a specific amino acid to a polypeptide chain. There are 64 possible codon combinations. Three of them are stop codons and don’t encode for any amino acid. Sixty-one of the codons encode twenty different amino acids.

The image below shows the central dogma in action: DNA is transcribed into RNA and RNA is translated into a polypeptide chain (protein).


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Key Points

• DNA is copied into RNA and RNA is then translated into protein.

• Out of 64 codons, three are stop codons. The remaining 61 codons encode twenty different amino acids.

Key Terms

Central dogma: DNA encodes RNA and RNA encodes protein.

DNA: Deoxyribonucleic acid (DNA) is a nucleic acid molecule composed of two polynucleotide chains that base pair with one another through individual nucleotides and form a double helix; genes are encoded by DNA.

RNA: Ribonucleic acid (RNA) is a polymeric nucleic acid molecule that is copied from DNA during transcription.

Protein: Macromolecules composed of amino acids linked together into polypeptide chains that carry out the functions of cells.

Transcription: The process of converting a specific sequence of DNA into a new RNA molecule.

Translation: The process where RNA is used to create a new polypeptide chain (protein).

Codon: A sequence of three adjacent nucleotides in mRNA that encode a specific amino acid during protein synthesis (translation).

Amino acid: Organic molecules that make up proteins; they contain an amino group (−NH2), a carboxyl group (−COOH), and a side chain specific to each amino acid.

Polypeptide: A chain of amino acids that are connected by peptide bonds.

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