complex

(noun)

A structure consisting of a central atom, molecule, or protein weakly connected to surrounding atoms, molecules, or proteins.

Related Terms

Examples of complex in the following topics:

  • More complex organic molecules and life

  • Electron Transport Chain

    • To start, two electrons are carried to the first complex aboard NADH.
    • Complex II directly receives FADH2, which does not pass through complex I.
    • Q receives the electrons derived from NADH from complex I and the electrons derived from FADH2 from complex II, including succinate dehydrogenase.
    • This enzyme and FADH2 form a small complex that delivers electrons directly to the electron transport chain, bypassing the first complex.
    • Complex III pumps protons through the membrane and passes its electrons to cytochrome c for transport to the fourth complex of proteins and enzymes.

  • The Initiation Complex and Translation Rate

    • In addition, the cell spends GTP energy to help form the initiation complex.
    • Next, the initiatior tRNA charged with methionine (Met-tRNAi) associates with the GTP-eIF-2/40S ribosome complex, and once all these components are bound to each other, they are collectively called the 43S complex.
    • Once the 43S complex is at the initiation AUG, the tRNAi-Met is positioned over the AUG.
    • Therefore, the 43S complex cannot form properly and translation is impeded.
    • Gene expression can be controlled by factors that bind the translation initiation complex.

  • Signaling in Yeast

    • Yeasts are single-celled eukaryotes; therefore, they have a nucleus and organelles characteristic of more complex life forms.
    • Comparisons of the genomes of yeasts, nematode worms, fruit flies, and humans illustrate the evolution of increasingly-complex signaling systems that allow for the efficient inner workings that keep humans and other complex life forms functioning correctly.
    • More complex organisms such as nematode worms and fruit flies have 454 and 239 kinases, respectively.

  • Complex Tissue Structure

    • The complex bodies and activities of vertebrates demand such supportive tissues.

  • The Mechanism of Protein Synthesis

    • Protein synthesis begins with the formation of a pre-initiation complex.
    • The eukaryotic pre-initiation complex then recognizes the 7-methylguanosine cap at the 5' end of a mRNA.
    • After this, eIF2-GDP is released from the complex, and eIF5-GTP binds.
    • In eukaryotes, a preinitiation complex forms made of the small 40S subunit, the initiator Met-tRNAi, and eIF2-GTP.
    • Once at the cap, the preinitiation complex slides along the mRNA until it encounters the initiator AUG codon.

  • Strategies for Acquiring Energy

    • All living things require energy in one form or another since energy is required by most, complex, metabolic pathways (often in the form of ATP); life itself is an energy-driven process.
    • Living organisms would not be able to assemble macromolecules (proteins, lipids, nucleic acids, and complex carbohydrates) from their monomeric subunits without a constant energy input.
    • The energy stored in ATP is used to synthesize complex organic molecules, such as glucose.
    • This allows chemoautotrophs to synthesize complex organic molecules, such as glucose, for their own energy and in turn supplies energy to the rest of the ecosystem.
    • They break down complex organic compounds produced by autotrophs into simpler compounds, releasing energy by oxidizing carbon and hydrogen atoms into carbon dioxide and water, respectively.

  • The Promoter and the Transcription Machinery

    • RNA polymerase binds to the transcription initiation complex, allowing transcription to occur.
    • Once this transcription initiation complex is assembled, RNA polymerase can bind to its upstream sequence.
    • This releases part of the protein from the DNA to activate the transcription initiation complex and places RNA polymerase in the correct orientation to begin transcription; DNA-bending protein brings the enhancer, which can be quite a distance from the gene, in contact with transcription factors and mediator proteins .
    • They are not general transcription factors that bind to every promoter complex, but are recruited to a specific sequence on the promoter of a specific gene.
    • RNA polymerase II then binds and forms the transcription initiation complex.

  • The Role of the Circulatory System

    • Most animals are complex, multicellular organisms that require a mechanism for transporting nutrients throughout their bodies and for removing waste products.
    • The circulatory system has evolved over time from simple diffusion through cells, in the early evolution of animals, to a complex network of blood vessels that reach all parts of the human body.
    • Just as highway systems transport people and goods through a complex network, the circulatory system transports nutrients, gases, and wastes throughout the animal body.

  • Prokaryotic versus Eukaryotic Gene Expression

    • Prokaryotes regulate gene expression by controlling the amount of transcription, whereas eukaryotic control is much more complex.
    • Eukaryotic cells, in contrast, have intracellular organelles that add to their complexity.