Molecular biology: follow information from DNA to protein
Molecular biology studies how cells store, use and control biological information. DNA, RNA and proteins are different molecules, but their roles are connected. Follow each process separately before trying to explain a more complicated pathway.
Distinguish storing information from copying it
DNA contains genetic information in its nucleotide base sequences. The purpose of DNA replication is to create copies of genetic material during cell division. The difference between creating a DNA copy and using a portion of that genetic information to synthesize an RNA molecule is clearly illustrated through the initial "starting" materials and products involved. Therefore, the most practical approach to separating these processes would be to consider them separately prior to developing a more complex description of the enzymatic systems involved.
In your revised diagrams, include both ends of your arrows with names. DNA to DNA = duplication of genetic material; DNA to RNA = creation of RNA. Both labels will assist you in avoiding the common confusion associated with this subject area until additional details are incorporated into the description.
Follow the production of an RNA message
Transcription utilizes a DNA sequence as a template for an RNA molecule. Messenger RNA (mRNA) carries genetic information that is ultimately translated into a protein. However, in eukaryotic cells, mRNA is processed before translation occurs. Consequently, transcription should be differentiated from translation, although the two processes contribute to the same wider sequence of events.
There are several types of RNA. Some carry information for protein synthesis; others have structural, regulatory or supporting roles. Transfer RNA helps match the message with the amino acids being added, while ribosomal RNA forms part of the ribosome. A diagram centred on messenger RNA represents only part of the picture. State what it covers before extending the explanation to other genes and RNA molecules.
Explain how a message becomes an amino-acid chain
Translation occurs at ribosomes where the sequence of nucleotides in messenger RNA determines the order in which amino acids are linked together. Transfer RNA assists in associating specific codons (sequences of three nucleotides in mRNA) with their corresponding amino acids. Ultimately, translation results in the formation of polypeptide chains, i.e., long chains composed of amino acids. Thus, a new type of macromolecule is formed.
The primary sequence of amino acids provides structural features of a protein; however, a functioning protein is comprised of more than just the sequence of amino acids. Proper folding, along with possible subsequent modifications, enables the protein to perform its biologic functions (e.g., catalytic activity). A specific function (e.g., acting as an enzyme or forming part of structural components) must be established for the final product before completing the explanation from storage of genetic information to contributing to cellular work.
Ask when, where and how much a gene is used
Gene regulation controls when and where genes are expressed and how much product is made. Every gene is not used equally by every cell throughout development. Regulatory proteins and other mechanisms influence whether information in the genome is used. This helps explain why cells with much of the same genetic information can perform different jobs and have different patterns of activity.
If you read an article describing an experiment regarding changes in DNA sequence versus changes in gene expression, recognize that they represent different measurements. Each requires different forms of evidence to support conclusions. Also, measuring levels of RNA does not necessarily reflect all properties exhibited by the resultant protein. Establish what was actually measured in which cells under what conditions before establishing what conclusions can be logically derived from the data collected.
Check your understanding
A short quiz, with an explanation after each answer.
Which process makes an RNA molecule using a DNA template?
Explain replication, transcription and translation by naming their starting materials and products. Then add a sentence about regulation. Keeping those four concepts distinct provides a foundation for following a more detailed pathway.