A gene is a segment of DNA that contains a set of instructions to make molecules that organisms need to survive. In a process called gene expression, these instructions are converted into some sort of product. And the product usually is either a protein or functional RNA.
So what is gene expression? And, how do genes express themselves? To understand them, it’s crucial that you know the process called protein synthesis because gene expression and protein synthesis are basically the same molecular process. And being familiar with these processes will help you better understand the underlying causes of cancer, and eventually help you find better diagnosis and treatment for the same.
Proteins make up the enzymes and other essentials elements cells need to survive and to keep the body healthy. All proteins are made of chains of amino acids. Cells make their proteins using the information stored in their genes in a process called protein synthesis. In their DNA each gene carries the information in the sequence of bases that make up the gene. Now, let’s explore the relationship between DNA, chromosomes and genes.
Human cells have 23 pairs of chromosomes – one set inherited from the mother and one set from the father. Each chromosome is one long filament of DNA and each of those DNA filaments, each of the 46 chromosomes is encoded with genetic information.
Each long molecule of DNA, each chromosome is divided into genes. And each gene contains the instruction the cell requires to make a protein. The instruction tells which amino acids are needed to make that protein and in what order to put them. This information is spelled out in the sequence of cross pieces that make up the DNA in that gene.
The cross pieces are made up of pairs of chemical units called bases, which are abbreviated A, C, G and T. The bases pair up only one way – A pairs with T and C pairs with G, this is called complementary base pairing. The information in DNA (the message encoded in that gene) is spelled out in the sequence of those A’s, C’s, G’s and T’s along the length of the gene.
For more about how the bases pair up in DNA and what this means read: “How Does DNA Store Genetic Information?”
During protein synthesis, the sequence of bases in a gene’s DNA is copied, then the copy is used to make a protein. The process happens in four steps: gene activation, gene transcription (copying the DNA message in the gene), gene editing (editing the message), and translation (translating the message into a protein).
- Gene Activation – it happens when a protein called a transcription factor binds with the gene at a certain place on the gene.
- Gene Transcription – the DNA for the activated gene unwinds and opens up during this stage. This exposes the sequence of A’s C’s GS and T’s and the genes DNA. The sequence of bases is copied in the form of RNA. Like DNA, RNA is made up of bases but RNA has only one strand rather than two as in DNA . Also RNA does not use the base abbreviated “T” (thymine) – instead it has a base call to uracil abbreviated “U”. So as the RNA copy is made, every A in the DNA is copied as U in the RNA. This RNA is called messenger RNA (or, mRNA)
- Editing – the mRNA is edited. Unneeded bits of it are cut out and removed. The remaining mature messenger RNA molecule then leaves the nucleus and enters the cell cytoplasm.
- Translation – As mRNA enters the cytoplasm, the information encoded in it is read by small structures called ribosomes. The ribosomes move along the strand of messenger RNA reading the sequence of bases and as they do, they ate amino acids one by one to a growing, chain rule that will become the final protein.
But, what does protein synthesis have to do with cancer?
The protein produced by a gene and the RNA copy of the gene are called the products of the gene. In fact, the term gene products is a general name for the RNA and protein made by activated genes during the process.
Gene expression is one more important term that relates protein synthesis to cancer. Like I mentioned above, it’s basically the same molecular process as protein synthesis, and it refers to how busy or how active a gene is in making its products. In healthy cells, which genes express themselves, how much they express themselves and when they express themselves are carefully balanced and highly controlled.
Cancer happens because cells grow out of control and that happens because some genes express themselves too much, others express themselves too little or not at all, or they express themselves at the wrong time.
Further Readings and References:
- What Is Gene Expression? (YourGenome.org)
- An Introduction to Molecular Biology/Protein synthesis (WikiBooks)
- Protein Synthesis (SparkNotes)
- Change In Genes (American Cancer Society)