Gene expression is the process through which a gene's genetic code (the nucleotide sequence) is utilized to control protein synthesis and the formation of cell structures. "structural genes" are genes that code for amino acid sequences. "Operational genes" are genes that control the rate at which cells divide and grow.
In general, structural genes are those that determine a cell's physical characteristics such as size, shape, color, or other phenotypic traits. Operational genes are those that control the flow of information into a cell's DNA, where it can be used to make more proteins. These proteins control the cell's activity and may include enzymes and structural components that allow cells to function properly or respond quickly to external signals.
Some examples of operational genes include the alpha-globin gene, which controls the production of hemoglobin, the molecule that transports oxygen around the body; the beta-globin gene, which has exactly the same effect on blood cells; and the TCA cycle enzyme IDH, which produces CO2 and NADH during oxidative phosphorylation. Some examples of structural genes include the myelin basic protein gene, which is responsible for producing the basic protein that forms the protective sheath surrounding nerve fibers; and collagen, the main component of bone, skin, muscles, and other connective tissue. There are many more structural genes than operational ones.
Gene expression is the process by which a gene's genetic code—the nucleotide sequence—is utilized to drive protein synthesis and generate cell structures. Four steps are involved in translation.
Expression of Genes The process by which the information contained in a gene is used to drive the assembly of a protein molecule is known as gene expression. The cell reads the gene sequence in three-base groups. Each three-base group (codon) corresponds to one of the 20 amino acids utilized to construct the protein. Thus, each mRNA transcript contains an ordered series of codons that specify the amino acid sequence of the protein it encodes. Amino acids are the basic building blocks of proteins. They are encoded by nucleic acids called genes. Proteins are the main functional elements of living organisms. They contain various sequences of amino acids linked together through peptide bonds. These linkages can be between the carboxyl group of one amino acid and the amino group of another or they can be within the same amino acid. A peptide is a polymer of amino acids that can be cross-linked with other polypeptides to form large molecules. Proteins perform vital functions in all living things from bacteria to humans. They are the work horses that keep our bodies running and our cells communicating. Without proteins, life could not exist. Proteins are responsible for almost every biological function including responding to injuries, fighting off infections, clotting blood, and producing hormones. There are five basic classes of proteins: enzymes, antibodies, structural proteins, signaling proteins, and nutrients. Enzymes are responsible for most cellular activities including digesting food, breaking down toxins, and sending messages around the body.
Gene expression is the process by which the cell produces the chemical it requires by interpreting the genetic information encoded in the DNA. To do this, the cell decodes the genetic code and adds one of the 20 distinct amino acids that serve as the fundamental building blocks for proteins for each set of three letters. The cell then uses these instructions to make the protein required. Gene expression occurs in the nucleus of the cell for proteins and RNA molecules.
RNA transcripts are copied from genes to provide the cells with the information to make proteins. Genes are composed of sequences of nucleotides that contain the information for making proteins. These sequences are called codons. Each gene contains its own sequence of codons and can be read directly into an RNA transcript using this sequence as a guide. Some genes are also read in a direction opposite to the direction of transcription to produce complementary RNAs (cRNAs). These cRNAs are used in some cases as templates for further replication. In other cases, they are destroyed or moved to another part of the cell where they can be lost forever.
Genes are located on chromosomes which are contained within the nucleus of living cells. A chromosome is a thread-like structure inside the nucleus of eukaryotic cells. Humans have 23 pairs of chromosomes, one from each of their parents. Each pair of human chromosomes contains a complete set of genes that are passed on to every daughter cell after division. The location of genes on chromosomes is called a locus.
Gene expression is the mechanism through which DNA controls protein synthesis. The process of transforming the genetic information in DNA into the biochemical machinery that produces proteins is complex, and the details of this process remain unknown. However it is known that gene expression involves several steps including transcription, splicing, editing, translation, and degradation.
Transcription involves the synthesis of mRNA from DNA using enzymes called RNA Polymerase. There are three types of RNA Polymerases: I, II, and III. Types I and II use a nucleotide sequence within the genome to determine which enzyme will synthesize the transcript; these enzymes cannot be used as templates for transcription again. Type III polymerases do not have this restriction. They can transcribe any DNA molecule that contains their recognition signal near the 5' end of the DNA strand.
After transcription, pre-mRNA must be processed before it can be translated into protein. This processing includes removing introns and adding exons to the RNA product. Introns are segments of DNA between genes or within a single gene. They are removed during pre-mRNA processing to generate mature mRNA.