Video Transcript
Which of the following is formed at the end of transcription? (A) Amino acid chain, (B) mDNA, (C) eRNA, (D) mRNA, (E) DNA.
Transcription is the first of two steps in protein synthesis. So, let’s review how cells produce protein as we complete this diagram, an organizer. Humans produce more than 30,000 different kinds of proteins, and their functions range from forming the basis of muscle tissue to roles as hormones and neurotransmitters, cell transport and signaling proteins, and more. So, protein synthesis is a large part of a cell’s activity.
Proteins are polymers built from smaller repeating units or monomers called amino acids. And there are 20 different types of amino acids such as methionine or tryptophan used to build proteins. The sequence of amino acids determines the shape of a protein, and the shape of a protein determines its functional ability, in the same way that the functional ability of a chair is determined by its shape. The information required to assemble amino acids into sequences that fold into specific shapes is stored in the more than 21,000 protein-coding DNA genes in the nucleus.
Although the definition of a gene is evolving as scientists learn more about DNA, a protein-coding gene is a section of DNA containing the genetic code or sequence of DNA basis that determines the order of amino acids in a protein. So, we can fill in the top oval of our organizer with DNA.
While the information for building proteins is located inside the nucleus, ribosomes, which assemble proteins, are located outside the nucleus, either floating in the cytoplasm or embedded in the rough endoplasmic reticulum. A messenger molecule is needed to transfer the information from the gene to the ribosome. And that molecule is called messenger or mRNA. Although there is a difference in one base, mRNA is produced in the nucleus according to the same base-pairing rules used with DNA, using the sequence of bases in the gene as a template. So, we can fill in our second oval in the organizer now with the term mRNA because it’s the intermediary between DNA and protein.
After a bit of processing, the mRNA moves into the cytoplasm through exit holes called nuclear pores. Now, the genetic code in the mRNA can be read and translated by the ribosome into the sequence of amino acids that will form the protein. The process of reading and translating genetic code into a sequence of amino acids is called translation, since the language of DNA and mRNA is converted into the language of proteins. But what about step one, where the information from DNA is used to produce a strand of mRNA? This step is called transcription, since it can be compared to a scribe rewriting a message in the language of genetic code.
So now, we have the information needed to select the correct option. The question asks, what is formed at the end of transcription? And we can see that the answer is mRNA.
