Gene expression includes all the processes that take place to convert genetic information from the DNA sequence into a protein. In prokaryotes, only two processes occur, transcription and translation whereas in eukaryotes, one more step is involved, which is splicing or RNA processing.
Gene expression is the basic level where the genotype produces the phenotype. Gene expression interprets the genetic code and the characteristics of the expression products produce the phenotype.
Gene expression usually comes about in two stages:
Transcription is the synthesis of a single stranded RNA molecule with the help of DNA as a template. Genes are transcribed into RNA and then translated to make proteins. Here the gene is duplicated to result in an RNA molecule also called a primary transcript whose gene sequence is the same as the original gene. A protein coding gene is determined by the level of the primary transcript.
Human genes are classified into exons and introns and among these, the exons are the information carriers for protein synthesis. The intron sequence is spliced from primary transcripts to form a mature transcript of messenger RNA or mRNA that is made purely of exons.
Protein expression is a part of gene expression and it is used in monoclonal antibody sequencing and transient expression. Also referred to as translation, protein synthesis has no relation with the nucleotide sequence in DNA and RNA or the amino acid sequence in the protein. An amino acid needs three nucleotides and the string of amino acids finally generates the protein structure. This is just like a library of books, where some books are preferred more than others and get used more. All genes are not express in the same way. While some are expressed in certain cells at certain times in the developmental timeline, some are always expressed in all the cells. For example, genes encoding muscle proteins are only found in muscles. Some genes can be facilitated or hindered by hormones.
Differential gene expression
When the transcription and translation process are controlled, differential gene expression occurs. DNA sequences surrounding the genes regulate their expression. Certain proteins attach themselves to these sequences and determine whether the gene is on or off. As a result, gene expression is regulated by the availability and movement of a variety of transcription factors, which, naturally are proteins. These are in turn produced by genes that are controlled by other transcription factors. This links genes and proteins in a regulatory sequence beginning with the egg state. In humans, many diseases occur due to the absence or failing of the protein, which disrupts gene expression.
The study of gene expression in living cells plays a major role in research, helping to identify and treat diseases. The focus is on proteins since they manifest in large numbers compared to the gene or its transcript. Transient expression is more popular for its ability to produce faster results and remove redundant portions of the gene so that the desired outcome is obtained.