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1. Transcription: DNA to RNA

Published in Protein Synthesis 3 mins read

How is Protein Made Step by Step?

Protein synthesis is a fundamental biological process crucial for life. It's a two-step procedure common to all organisms: transcription and translation.

This initial step occurs within the cell's nucleus. Here's a breakdown:

  1. Initiation: The DNA double helix unwinds at a specific gene location. RNA polymerase, an enzyme, binds to the promoter region of the gene.
  2. Elongation: RNA polymerase moves along the DNA template strand, synthesizing a complementary messenger RNA (mRNA) molecule. This mRNA molecule carries the genetic code from the DNA. The DNA bases (adenine, guanine, cytosine, thymine) are transcribed into RNA bases (adenine, guanine, cytosine, uracil), following the base pairing rules (A-U, G-C).
  3. Termination: RNA polymerase reaches a termination sequence on the DNA, signaling the end of transcription. The newly formed mRNA molecule is released. The mRNA then undergoes processing (splicing, capping, and polyadenylation) before leaving the nucleus.

2. Translation: RNA to Protein

This second step takes place in the cytoplasm, specifically at the ribosomes.

  1. Initiation: The mRNA molecule binds to a ribosome. A transfer RNA (tRNA) molecule carrying the amino acid methionine (the start codon) attaches to the mRNA's start codon (AUG).
  2. Elongation: The ribosome moves along the mRNA molecule, reading each three-base codon (a sequence of three nucleotides). Each codon specifies a particular amino acid. tRNA molecules with anticodons complementary to the mRNA codons bring in their corresponding amino acids. Peptide bonds form between the amino acids, creating a growing polypeptide chain.
  3. Termination: The ribosome encounters a stop codon on the mRNA (UAA, UAG, or UGA). This signals the end of translation. The completed polypeptide chain is released from the ribosome. The polypeptide chain then folds into a functional protein, sometimes requiring further processing.

Key Players:

  • DNA: The genetic blueprint containing the instructions for protein synthesis.
  • RNA Polymerase: Enzyme responsible for synthesizing mRNA during transcription.
  • mRNA: Carries the genetic code from DNA to the ribosome.
  • Ribosomes: Cellular machinery where protein synthesis occurs.
  • tRNA: Carries amino acids to the ribosome during translation.
  • Amino Acids: The building blocks of proteins.

This two-step process – transcription and translation – ensures that the genetic information stored in DNA is accurately used to produce functional proteins, the workhorses of the cell. As noted in several sources (Nature Scitable, Science Learn, Biology LibreTexts, BCcampus, MedlinePlus, Azo Life Sciences), this process is essential to all living organisms.

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