An isolate of  Erythropsidinium . The arrow indicates the piston; the double arrowhead indicates the  ocelloid . Scale bar 20 μm. [ 1 ]


Plastid types


Leucoplasts  in plant cells.


An illustration of the stages of inter-conversion in plastids


Cartoon representation of a proteasome. Its active sites are sheltered inside the tube (blue). The caps (red; in this case, 11S regulatory particles) on the ends regulate entry into the destruction chamber, where the protein is degraded.


Top view of the proteasome above.


Schematic diagram of the proteasome 20S core particle viewed from one side. The α subunits that make up the outer two rings are shown in green, and the β subunits that make up the inner two rings are shown in blue.


Cartoon representation of the 26S proteasome. [ 30 ]


Three distinct conformational states of the 26S proteasome. [ 37 ]  The conformations are hypothesized to be responsible for recruitment of the substrate, its irreversible commitment, and finally processing and translocation into the core particle, where degradation occurs.


Ribbon diagram  of  ubiquitin , the highly conserved  protein  that serves as a molecular tag targeting proteins for degradation by the proteasome


The  ubiquitination  pathway


A cutaway view of the proteasome 20S core particle illustrating the locations of the  active sites . The α subunits are represented as green spheres and the β subunits as protein backbones colored by individual  polypeptide chain . The small pink spheres represent the location of the active-site  threonine  residue in each subunit. Light blue chemical structures are the inhibitor  bortezomib  bound to the active sites.


The assembled complex of  hslV  (blue) and  hslU  (red) from  E. coli . This complex of  heat shock proteins  is thought to resemble the ancestor of the modern proteasome.


Chemical structure of  bortezomib  (Boronated form of MG132), a proteasome inhibitor used in  chemotherapy  that is particularly effective against  multiple myeloma


Bortezomib  bound to the core particle in a  yeast  proteasome. The bortezomib molecule is in the center colored by atom type ( carbon  = pink,  nitrogen  = blue,  oxygen  = red,  boron  = yellow), surrounded by the local protein surface. The blue patch is the catalytic  threonine  residue whose activity is blocked by the presence of bortezomib.


Tachyzoites  of  Toxoplasma gondii , transmission electron microscopy. [ 1 ]   Rhoptries: ro  (click to enlarge)


A cartoon section of  skeletal muscle , showing  T-tubules  running deep into the centre of the cell between two terminal cisternae/junctional SR. The thinner projections, running horizontally between two terminal cisternae are the longitudinal sections of the SR.


Septins in  Saccharomyces cerevisiae   (fluorescent micrograph)  • Green: septins ( AgSEP7- GFP )  • Red: cell outline ( phase contrast )  • Scale bar: 10 μm


Figure 2 . Calcium uptake and calcium release by the spine apparatus [ 11 ]


Spliceosomal splicing cycle


Figure 1. Above are  electron microscopy [ 8 ]  fields of negatively stained yeast ( Saccharomyces cerevisiae ) tri-snRNPs. Below left is a schematic illustration of the interaction of tri-snRNP proteins with the U4/U6 snRNA duplex. Below right is a cartoon model of the yeast tri-snRNP with shaded areas corresponding to U5 (gray), U4/U6 (orange) and the linker region (yellow).


A section of a root nodule cell showing symbiosomes enclosing bacteroids.


Paramecium tetraurelia,  a ciliate, with discharged trichocysts (artificially colored in blue).


A  transmission electron microscope  image of isolated T3SS needle complexes from  Salmonella  Typhimurium


Diagram of individual substructures of the needle complex from  Salmonella typhimurium


The topology and organization of the  Salmonella  needle complex. [ 21 ]


Flagellum of Gram-negative bacteria. The rings of the base are very similar to needle-complex rings, although the existence of a C-ring in the needle complex has not been proven. The flagellar hook is homologous to the T3SS needle


Scheme of a liposome formed by  phospholipids  in an  aqueous  solution


Sarfus  image of lipid vesicles


Electron micrograph of a cell containing a food vacuole (fv) and transport vacuole (tv) in a  malaria parasite


Large (red) and small (blue) subunits of a ribosome


Ribosomes assemble  polymeric  protein molecules, the order of which is controlled by the  messenger RNA 's molecule sequence.


Ribosomal RNA  composition for  prokaryotes  and  eukaryotes


Molecular structure of the 30S subunit from  Thermus thermophilus . [ 16 ]  Proteins are shown in blue and the single RNA chain in brown.


Figure 4:  Atomic structure of the 50S subunit from  Haloarcula marismortui . Proteins are shown in blue and the two RNA chains in brown and yellow. [ 39 ]  The small patch of green in the center of the subunit is the active site.


Figure 5:  Translation of mRNA (1) by a ribosome (2)(shown as  small  and  large  subunits) into a  polypeptide chain  (3). The ribosome begins at the start codon of RNA ( AUG ) and ends at the stop codon ( UAG ).


Figure 6:  A ribosome translating a protein that is secreted into the  endoplasmic reticulum .


Ribophorin is a subunit of oligosaccharide transferase in the RER


rRNA biogenesis and assembly in prokaryote and eukaryotes. Notably in Eukaryotes 5S rRNA is synthesised by  RNA polymerase III  whereas other eukaryote rRNA molecules are transcribed by  RNA polymerase I .


Nucleus with a dark nucleolus. The cell usually measures between 20 and 30 micrometers.


Nuclear bodies in human embryonic lung cells


Diagram of the formation of nuclear bodies.


Immunofluorescence staining pattern of sp100 antibodies. Nuclear dots can be seen in the nucleus of the cells. Produced using serum from a patient with primary biliary cirrhosis on HEp-20-10 cells with a FITC conjugate.


Examples of different levels of nuclear architecture.


The hierarchical structure through which DNA is packaged into chromosomes.


A cartoon representing an enhancer interacting with genes through DNA looping.


The 23 human  chromosome territories  during  prometaphase  in  fibroblast  cells


The Ran-GTP cycle, which drives the import and export of RNA and proteins through the nuclear protein complex.


Scanning and illumination microscopy of nuclear pores,  lamina , and  chromatin .


Cell nucleus containing nuclear pores.


Diagram of nuclear uptake of proteins