Dictionary > Nucleoporin

Nucleoporin

Definition

noun
plural: nucleoporins
Any of the family of porins that make up the nuclear pore complex

Details

Overview

The cell nucleus is the organelle of the eukaryotes responsible for maintaining the integrity of DNA and for controlling cellular activities such as metabolism, growth, and reproduction by regulating gene expression. It is a double-membraned organelle and this double membrane is referred to as nuclear envelope (also called nuclear membrane, plasmalemma, sor karyotheca). The nuclear envelope surrounds most of the eukaryotic cell’s genetic material as opposed to the genetic material of the prokaryotes that is not membrane bound. The nuclear envelope is a lipid bilayer and has many perforations. These perforations are called nuclear pores. Each nuclear pore is formed by the nuclear pore complex, the assembly of nucleoporins.

Features

The nucleoporins are the protein units of the nuclear pore complex. They form the nuclear pore where biomolecules may pass through it. Thus, nucleoporins forming a pore when they aggregate into a complex aid in the transport of biomolecules into and out of the nucleus. There are at least 456 nucleoproteins that make up the nuclear pore complex. The resulting nuclear pore is octagonal in shape, measures about 9 nm in diameter and with a depth of about 200 nm, and spans the nuclear envelope.

Types

The nucleoporin family is comprised of proteins involved in the formation of the nuclear pore complex. The nucleoporin 62 is the most abundant type of nucleoporins. Other examples of nucleoporins are nucleoporin 35, nucleoporin 37, nucleoporin 43, nucleoporin 50, nucleoporin 54, nucleoporin 85, nucleoporin 88, nucleoporin 93, nucleoporin 98, nucleoporin 107, nucleoporin 133, nucleoporin 153, nucleoporin 155, nucleoporin 205, nucleoporin 210, etc. They are named according to their molecular weight in kilo Daltons. Many of them contain solenoid protein domains.

Common biological reactions

Common biological reactions

The presence of the nuclear envelope prevents the easy passage of large molecules (e.g. proteins and RNA) into and out of the nucleus. Although the nuclear envelope is perforated with nuclear pores, large molecules would still need a nuclear transport mechanism in order to enter and exit the nucleus. Small particles (< ~30-60 kDa), such as ions, can pass through the nucleus by passive transport. However, cargo proteins and RNAs that need to be transported require importins and exportins to enter and exit the nucleus, respectively. On one hand, the cargo binds with the importin in the cytoplasm, and then moved into the nucleus through the nuclear pore. On the other hand, the cargo binds with the exportin inside the nucleus, and then moved outside the nucleus via the nuclear pore. Nuclear transport needs energy to proceed. Thus, GTPases (e.g. Ran enzyme) help by hydrolyzing GTP (guanosine triphosphate) so that energy would be released in the process. The energy released would be used to dissociate the cargo from the importins and to bind the cargo to the exportins.

Biological functions

Nucleoporins serve as the structural unit of the nuclear pore complex that is involved in the entry and exit of biomolecules across the nuclear envelope. A nuclear pore complex can translocate about 60,000 protein molecules per minute.

Supplementary

Etymology

Abbreviation

  • NUP
  • Further reading

    See also


    © Biology Online. Content provided and moderated by Biology Online Editors



    You will also like...

    Lights' Effect on Growth
    Lights’ Effect on Growth

    This tutorial elaborates on the effect of light on plant growth. It describes how different plants require different amo..

    takahē
    Takahē (Porphyrio hochstetteri)

    Meet the colorful takahē, an extremely rare flightless bird. Find out more about its unique features and why they matte..

    Growth Patterns
    Growth Patterns

    This tutorial describes the sigmoid curve, annual plant growth, tree growth, human growth, and insect growth as the grow..

    Gibberellins and Gibberellic Acid
    Gibberellins and Gibberellic Acid

    This tutorial describes the role of gibberellin family in plants. Find out the effects of gibberellin on plant growth an..

    human respiratory system
    Respiration

    The human respiratory system is an efficient system of inspiring and expiring respiratory gases. This tutorial provides ..

    Freshwater lake ecosystem
    Freshwater Producers and Consumers

    Freshwater ecosystem is comprised of four major constituents, namely elements and compounds, plants, consumers, and deco..