Central Dogma of Life: DNA Replication, Transcription, Translation, and Protein Synthesis

Central Dogma of Life

Overview

The central dogma of life is a fundamental principle in molecular biology that describes the flow of genetic information within a cell. According to this concept, the genetic material encoded in deoxyribonucleic acid (DNA) is copied into messenger ribonucleic acid (mRNA), which subsequently encodes for a specific amino acid sequence of a polypeptide. This process ultimately leads to the creation of various proteins essential for cellular processes, such as enzymes and structural components.

DNA Replication

Initiation

During DNA replication, a double helix is formed from two complementary strands. Elongation occurs when enzymes called helicases unwind and separate the strands, allowing primers to initiate the replication process.

Elongation

Primers are short single-stranded DNA segments that act as starting points for replication. Primer binding allows for the addition of new nucleotides to the template strand via the action of DNA polymerases, which connect nucleotides in a specific sequence following the complementarity rule of base-pairing.

Termination

Once replication is complete, the two newly synthesized strands remain connected by a segment of double-stranded DNA called the Okazaki fragments. Nuclease enzymes break down the remaining primer and the gaps between the primer and the replicated strand, leaving behind a continuous double-stranded DNA molecule.

Transcription

Initiation

Transcription is the process of converting a specific sequence of DNA into mRNA. One strand of the DNA that makes up a gene, called the non-coding strand, acts as a template for the synthesis of a complementary RNA strand. The complementary RNA strand is known as the primary transcript.

Elongation

An enzyme called RNA polymerase binds to the promoter region of the gene and unwinds the DNA around it, creating a clear passageway for transcription factors to bind and guide the enzyme along the DNA strand. RNA polymerase moves along the DNA template, adding nucleotides to the growing mRNA strand in a 5' to 3' direction, following the complementarity rule of base-pairing between the DNA template and the growing mRNA strand.

Termination

Termination of transcription occurs when the RNA polymerase reaches a specific sequence of bases called the terminator sequence. When this occurs, the enzyme detaches from the DNA template, releasing the fully formed mRNA molecule.

Translation

Initiation

During translation, the nucleotide sequence of an mRNA is translated into the amino acid sequence of a polypeptide. This process involves reading the codons, which consist of three consecutive nucleotides on the mRNA. The first codon encountered by the ribosome is the 'start' codon, which usually specifies the amino acid methionine. The ribosome just starts building a chain of amino acids that exactly mirrors the sequence of codons in the mRNA.

Elongation

Transfer RNAs (tRNAs) bring specific amino acids to the ribosome, ensuring that the correct amino acid is added to the growing polypeptide chain. Each tRNA recognizes a specific codon and delivers the appropriate amino acid to the ribosome. The ribosome continues moving along the mRNA, adding amino acids until it encounters a stop codon.

Termination

When a stop codon is reached, the ribosome releases the completed polypeptide, effectively ending the translation process.

Protein Synthesis

Finally, protein synthesis consists of both transcription and translation. The information contained within DNA is copied into mRNA during transcription, and then this mRNA is translated into a specific polypeptide during translation. Together, these processes ensure the accurate production of proteins according to the genetic information encoded within the DNA.