What is Gene Expression?

Gene expression refers to the process of synthesizing genetic information from genes into functional gene products. Gene expression products are usually proteins, but non-protein encoding genes such as transfer RNA (tRNA) or small nuclear RNA (snRNA) genes are functional RNA.

Gene expression refers to the process of synthesizing genetic information from genes into functional gene products. Gene expression products are usually proteins, but non-protein encoding genes such as transfer RNA (tRNA) or small nuclear RNA (snRNA) genes are functional RNA.

All known life, whether eukaryotes (including multicellular organisms), prokaryotes (bacteria and archaea) or viruses, use gene expression to synthesize macromolecules of life.

Gene expression can be regulated through several steps, including transcription, RNA splicing, translation, and post-translational modification. Gene regulation gives cells control over structure and function. Gene regulation is the basis for cell differentiation, morphogenesis, and the versatility and adaptability of any organism. Gene regulation can also be used as a substrate for evolutionary changes, because controlling the time, location, and amount of gene expression can have a profound effect on the function (function) of a gene in a cell or multicellular organism.

In genetics, gene expression is the most basic level at which a genotype produces a phenotype. The genetic code stored in DNA is "translated" by gene expression, and the characteristics of gene expression produce the phenotype of the organism. Therefore, the regulation of gene expression is essential for the development of organisms.

Gene expression and transcription regulation

It can be divided into three main ways: 1) genetic regulation (direct interaction of transcription factors and target genes); 2) regulation of transcription factors interacting with transcription mechanisms, and 3) epigenetic regulation (non-sequences that affect the structure of transcribed DNA Variety).

Direct regulation of target DNA expression by transcription factors is the simplest and most direct method of transcriptional regulation to change the level of transcription. Gene coding regions usually have several protein-binding sites around them, with specific functions that regulate transcription. Common regulatory sites for protein-DNA binding are enhancers, insulators, and silencers. The mechanisms for regulating transcription are very diverse. They can block key sites on DNA that bind to RNA polymerase, and can also act as an activator to help RNA polymerase bind to promote transcription.

The activity of transcription factors is further regulated by intracellular signals, causing post-translational modifications of proteins, including phosphorylation, acetylation, or glycosylation. These changes affect the binding of transcription factors directly or indirectly to promoter DNA, the recruitment of RNA polymerase, and the extension of newly synthesized RNA molecules.

The nuclear membrane in eukaryotes further regulates the transcriptional environment by allowing the duration of these transcription factors to exist in the nucleus. Stimuli or endocrine signals may lead to the modification of regulatory proteins, triggering a cascade of intracellular signals, leading to regulation of gene expression.

Epigenetics has a significant effect on transcription. In general, epigenetics alters the binding of DNA to proteins and affects transcription.

DNA methylation is a broad mechanism of epigenetic effects on gene expression, and is found in bacteria and eukaryotes, and plays a role in heritable transcriptional silencing and transcriptional regulation. In eukaryotes, the structure of chromatin, which is controlled by the histone code, affects the acquisition of DNA and has a significant effect on gene expression in the chromatin and heterochromatin regions.

Post-transcriptional regulation of gene expression

Eukaryotic RNA needs to be exported through the nuclear pore before translation, so nuclear export has a significant effect on gene expression. All mRNAs entering and leaving the nucleus are transported through the nuclear pores and are controlled by various input and output proteins.

The mRNA carrying the genetic code needs to survive long enough to be translated, because the mRNA must be transported over a long distance before translation. In typical cells, RNA molecules are stable only under conditions of specific protection and are not degraded by RNases. RNA degradation is particularly important for the regulation of gene expression in eukaryotic cells. In eukaryotes, RNA is stabilized by certain post-transcriptional modifications, particularly 5-terminal capping and 3-terminal polyadenylation.

Gene expression translation regulation

Translation regulation is less effective than transcription regulation or regulation of mRNA stability, but it is also occasionally used. Inhibition of protein translation is the main target of toxins and antibiotics, so they can kill cells by going beyond their normal control of gene expression. Protein synthesis inhibitors include the antibiotic neomycin and the toxin ricin.

Post-translational regulation of gene expression

Post-translational modification (PTM) is a covalent modification of a protein. Like RNA splicing, they help enrich the proteome. These modifications are usually catalyzed by enzymes. In addition, modification processes such as the covalent addition of amino acid side chain residues can often be reversed by other enzymes. However, proteolytic enzymes' cleavage of the protein backbone is irreversible ^[7] . PTM plays many important roles in cells. For example, phosphorylation is mainly involved in activating and inactivating proteins and signaling pathways ^[8] . PTM is involved in transcriptional regulation, because an important function of acetylation and methylation is the modification of histone tails, which changes the transcriptability of DNA ^[7] .