S

o-o items o-o are in brief format :
o-o second messengers
o-o serine/threonine kinases
o-o signal join
o-o signaling enzymes, signaling proteins, signaling receptors, signaling transduction
o-o spindle
o-o spliceosomes
o-o splice-sites
o-o structure - cellular
o-o sulfur bacteria
o-o symbiont, symbiosis (commensal)
o-o sympatry

Links to more detailed items on Companion Sites:
§ scaffold proteins ~ second messengers ǒ Secondary endosymbiosis ~ selectins ~ self-splicing ǒ Serial Endosymbiosis Theory (SET) ǒ SET chloroplast origins ǒ SET endosymbiotic transfers ǒ SET evidence ǒ SET gene transfer ǒ SET history of ideas ǒ SET mitochondrial origins ǒ SET plastid origin ǒ SET proposed mechanisms - diagrams ◊ serine/threonine kinases ~ serine/threonine kinases סּ signal transduction ₪ signaling סּ signaling cascades ~ signaling items ф signaling סּ signaling cascades סּ signaling gradients ¤ signaling molecules ♦ signaling enzymes § signaling proteins ◊◊ signaling receptors ◊◊ signaling transduction ~ silencers »» single nucleotide polymorphism ~ snoRNAs »» SNP »» Speciation סּ spindle ~ splicing items ~ splice-site ~ spliceosome סּ spindle ¤ SRC genes ~ SSOs סּ structure ф surface receptors »» synthesis »» The modern synthesis

| 0 Guide-Glossary

second messengers

Second messengers are small, readily diffusible molecules that operate in signal transduction. Second messengers relay and amplify signals received by cell-surface receptors, and are typically generated by ligand-receptor bonding. Џ animation 2nd messenger Џ

calcium ions : cAMP : ceramide : cGMP : ceramide : diacylglycerol (DAG): inositol-1,4,5-trisphosphate (IP3)

diacylglycerol kinases, DGKs, eicosanoids,GPCRs, GPCR family, guanyl cyclase, inositol, inositol phospholipids, InsP3, InsP3 (PKC), kinase, PIPs, phosphatase ♦ phosphatases ♦ phospholipases ♦ phosphodiesterases ♦ phosphorylases ♦ PIKK ♦ PI3K ♦ PKA ♦ PKB ♦ PKCs ♦ protein kinases ♦ phosphatidylinositols, phosphatidylinositol phosphates, phospholipase A2, phospholipase C family, phospolipase C-γ, PI3K, PI3K ARF, PI3K cancer, PI3K Kit, PI3K signaling, PLC-γ, polyphosphoinositides, prostaglandins, phospholipase C (PLC), signaling molecule .

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serine/threonine kinases

Serine/threonine kinases phosporylate serine and threonine residues in target proteins. Specific protein kinases transfer a phosphate group from a donor such as ATP to amino acid acceptors in proteins, while protein phosphatases remove the phosphate groups that have been attached by protein kinases.

Several serine/threonine kinases function in signal transduction pathways, associated with receptors of the TGF-β superfamily that employ intrinsic serine/threonine kinase (phosporylating) activity to signal through the Smad family of proteins.

The signaling pathways utilized by the TGF-β, activin, and BMP receptors are different than those for receptor tyrosine kinases (RTKs) or receptor proteins associated with intracellular protein tyrosine kinases (PTKs).

♦ cAMP-dependent protein kinase ♦ cyclin-dependent kinases ♦ Akt ~ ERKs ♦ MAPKs ♦ MEKs ♦ mitogen activated protein kinases ♦ MPF ♦ M-phase promoting factor ♦ mTOR ♦ PDK1 ♦ PTEN ♦ PIKK ♦ PI3K ♦ PKA ♦ PKB ♦ PKCs ♦ protein kinases ♦ Raf .

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spindle

The spindle apparatus choreographs chromosome segregation during mitosis. The spindle begins to assemble from microtubules during mitotic prophase at the centrosome, and the apparatus persists until telophase.

סּ cell cycle סּ cell-cycle control סּ centrioles סּ cytoskeleton סּ meiosis סּ microfilaments סּ microtubules ¤ mitogens סּ mitosis סּ signal transduction סּ

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spliceosomes

Spliceosomes are complex ribonuclear machines in eukaryotes that remove (splice out) the non-coding introns from primary transcript, precursor mRNA (pre-mRNA or hnRNA). Almost all eukaryotic protein coding genomes contain non-coding intervening sequences called introns.

Spliceosomes are variably composed of as many as 300 distinct proteins and five RNAs, making them among the most complex macromolecular machines known. Small RNA-protein complexes called small nuclear ribonucleoproteins (snRNPs, pronounced 'snurps') are essential components of the spliceosome.

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splice-sites

Splice-sites are the intron-exon junctions in the precursor mRNA of eukaryotes, and are recognized by trans-acting factors (prokaryotic RNAs are mostly polycistronic).

In constitutive nuclear pre-mRNA splicing the intronic sequences are excised and the exons are ligated to generate the mature, spliced mRNA.

Pre-mRNA splicing is a form of RNA processing, which yields a mature mRNA comprising the coding exons that direct sequencing of amino acids inserted into elongating polypeptides during cytoplasmic translation at ribosomes. However, a cell typically splices a single mRNA transcript in multiple ways to generate an assortment of proteins. Alternatively spliced introns tend to lie between those exonal segments of a gene that encode the functional units, or domains, of a protein (ORF).

The length and sequence of nucleotides in nuclear pre-mRNA introns is highly variable, except for the short conserved sequences at the 5´ and 3´ splice sites and the branch points. These splice sites immediately surrounding the intron-exon junction can be regarded as consensus sequences.

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structure - cellular

Cellular structure items on Cell Biology
סּסּ cells סּ extracellular matrix סּ eukaryotic סּ cytoplasm סּ ribosomes סּ plant cell סּ prokaryotic
סּסּ adhesion סּ adhesion ~ adhesion molecules ~ cadherins סּ catenins סּ cytoskeleton סּ desmosomes ~ immunoglobulins ~ integrins סּ microtubules ~ selectins
סּסּ membranes סּ cell membranes סּ ion channels סּ plasma membrane
סּסּ nucleus סּ lamins סּ nuclear membrane סּ nuclear pore סּ nucleolus סּ nucleus
סּסּ organelles סּ centrioles סּ chloroplasts סּ cilia סּ endoplasmic reticulum סּ Golgi apparatus סּ mitochondrion סּ plastids סּ ribosomes
סּסּ skeleton סּ actin סּ cadherins סּ catenins סּ cytoskeleton סּ desmin סּ desmoplakin סּ ECM סּ intermediate filaments סּ intermediate-filament associated proteins סּ keratins סּ keratin diversity סּ lamins סּ lattice סּ microfilaments סּ microtubules סּ mitotic spindle סּ receptor control סּ spindle סּ tensegrity סּ tubulin
סּסּ vesicles סּ endosomes סּ exosome סּ lysosome סּ peroxisome סּ proteasome סּ vacuole סּ vesicle סּ

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sulfur bacteria

The rather confusing term 'sulfur bacteria' encompasses green sulfur bacteria plus purple sulfur bacteria (distinguised from green nonsulfur and purple nonsulfur bacteria) .

The green sulfur bacteria (Chlorobiaceae) are photosynthetic bacteria that form a coherent group phylogenetically isolated from all other microbes, such that they are the sole occupants of their phylum (Phylum Chlorobi).

The purple sulfur bacteria are photosynthetic anaerobic or microaerophilic Proteobacteria found in meromictic lakes and sulfur (hot) springs.

Chlorobiaceae (green sulfur) are anaerobic obligate photoautolithotrophs that use sulfide, elemental sulfur or hydrogen as their source of electrons, employing bacteriochlorophylls c, d, and e in vesicles called chlorosomes that are attached to the membrane. As anaerobes, their environment must be oxygen-free, and, as phototrophs, they require light as an energy source.

In conducting nonoxygenic photosynthesis, green and purple sulfur bacteria employ sulfide ions (H2S) as an electron donor:

CO2 + 2H2S → CH2O + H2O + 2S

Members of the purple Chromatiaceae family produce internal sulfur granules, while members of the Ectothiorhodospiraceae family produce external sulfur granules on oxidation of H2S.

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sympatry

Sympatry involves no geographical separation of sub-populations of individuals. Sympatric speciation events occur most often in plants by the mechanism of polyploidy in which the number of chromosomes is doubled or tripled. John Maynard Smith proposed a model called disruptive speciation, in which homozygotes might have greater fitness than heterozygotes under some environmental conditions.

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