Nuclear gene
Encyclopedia
A Nuclear gene is a gene
located in the cell nucleus
of a eukaryote
. The term is used to distinguish nuclear gene
s from the gene
s in the mitochondrion
, and in case of plants, also the chloroplast
, which host their own genetic system and can produce proteins from scratch. The term "gene" most often refers to nuclear genes.
The distinct genome
s of eukaryotes are thought to have arisen through symbiotic
relationships. The mitochondrion represents a eubacterium
that integrated into its archaea
l host cell
's physiology to such an extent that it became an integral cell component, or organelle
. The process repeated in plants, with a cyanobacterial symbiont in a eukaryote host becoming the chloroplast. The nuclear genes represent the genome of the original host cell, while both of these organelle
s still retain a small genome
, although many of the genes of the organelles have moved to the nucleus during the course of evolution.
The majority of the protein
s of a cell are the product of messenger RNA
transcribed
from nuclear genes, including most of the proteins of the organelles, which are produced in the cytoplasm
like all nuclear gene products and then transported to the organelle. In addition, there are nuclear genes that encode non-translated regulatory RNAs. Genes in the nucleus are arranged in a linear fashion upon chromosomes, which serve as the scaffold for replication and the regulation of gene expression. As such, they are usually under strict copy-number control, and replicate a single time per cell cycle.
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
located in the cell nucleus
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
of a eukaryote
Eukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...
. The term is used to distinguish nuclear gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s from the gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s in the mitochondrion
Mitochondrion
In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...
, and in case of plants, also the chloroplast
Chloroplast
Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.Chloroplasts are green...
, which host their own genetic system and can produce proteins from scratch. The term "gene" most often refers to nuclear genes.
The distinct genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
s of eukaryotes are thought to have arisen through symbiotic
Symbiosis
Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...
relationships. The mitochondrion represents a eubacterium
Eubacterium
Eubacterium is a Gram positive bacteria genus in the family Eubacteriaceae....
that integrated into its archaea
Archaea
The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon...
l host cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
's physiology to such an extent that it became an integral cell component, or organelle
Organelle
In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid bilayer....
. The process repeated in plants, with a cyanobacterial symbiont in a eukaryote host becoming the chloroplast. The nuclear genes represent the genome of the original host cell, while both of these organelle
Organelle
In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid bilayer....
s still retain a small genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
, although many of the genes of the organelles have moved to the nucleus during the course of evolution.
The majority of the protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s of a cell are the product of messenger RNA
Messenger RNA
Messenger RNA is a molecule of RNA encoding a chemical "blueprint" for a protein product. mRNA is transcribed from a DNA template, and carries coding information to the sites of protein synthesis: the ribosomes. Here, the nucleic acid polymer is translated into a polymer of amino acids: a protein...
transcribed
Transcription (genetics)
Transcription is the process of creating a complementary RNA copy of a sequence of DNA. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that can be converted back and forth from DNA to RNA by the action of the correct enzymes...
from nuclear genes, including most of the proteins of the organelles, which are produced in the cytoplasm
Cytoplasm
The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...
like all nuclear gene products and then transported to the organelle. In addition, there are nuclear genes that encode non-translated regulatory RNAs. Genes in the nucleus are arranged in a linear fashion upon chromosomes, which serve as the scaffold for replication and the regulation of gene expression. As such, they are usually under strict copy-number control, and replicate a single time per cell cycle.