Summarize how DNA directs the making of a protein.
The production of a new protein actually begins outside of the cell when a signaling molecule binds to a specific receptor on the cell membrane. Common signaling molecules include hormones, neurotransmitters, and growth factors. The binding of a receptor by a signaling molecule triggers a series of biochemical events that result in the activation of transcription factors within the nucleus of the cell. Transcription factors are cell proteins involved in converting specific DNA sequences into RNA.
Transcription is the process of turning a particular DNA sequence into its corresponding RNA sequence. The process of transcription is activated when transcription factors bind to specific sequences on the DNA. The binding of transcription factors to DNA leads to the activation of a protein called RNA polymerase. RNA polymerase copies a sequence of DNA into RNA. The new RNA sequence is called pre-messenger RNA.
The pre-messenger RNA sequence often contains sections of RNA that are not needed for protein production. These sequences are edited out by cellular enzymes. The resulting RNA sequence is called messenger RNA (mRNA). The messenger RNA strand is then transported out of nucleus into the cytoplasm of the cell.
Translation is the process of creating a protein from the mRNA strand. Once in the cytoplasm, the messenger RNA strand is bound by a particle called a ribosome. Ribosomes are small proteins that are able to bind both messenger RNA and another type of RNA call transfer RNA. Transfer RNA (tRNA) molecules have specific amino acids attached to them. Amino acids are the building blocks of proteins. Each tRNA is able to recognize and bind to a particular three base sequence of mRNA called a codon. Each codon sequence is associated with a particular amino acid. As the ribosome moves along the mRNA strand, tRNA molecules bring in new amino acids corresponding to each codon sequence. A chain of amino acids is created based on the codon sequences in the mRNA.
The strand of amino acids is then released from the ribosome. The chain of amino acids often undergoes further folding before it becomes a functional protein. The new protein is then packaged and secreted from the cell or used within the cell itself.