Cell Structure

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  • CELL STRUCTUREProf. Redem C. Deligero, MATMRS;MSES

  • RIBOSOMES1. Small SubunitSedimentation Value (40S & 33 Proteins)P-site - for binding peptidyl transfer ribonucleic acid (tRNA)A-site - for binding aminoacyl tRNA

    2. Large SubunitSedimentation Value (60S & 49 Proteins)

  • PolyribosomesResponsible for protien synthesis.Proteins for package is made in the RER surface.Proteins for cytosol are made within the cytosol.Components of Polyribsome:1. DNA2. mRNA3. tRNA4. rRNA


  • Synthesis of Cytosolic Proteins 1. P-site of of the ribosomal subunit recognize the iniator tRNA with AUG codon.2. Large ribosomal subunit binds to small subunit & moves mRNA in 5'-3' direction.3. tRNA binds to A site.4. Amino acids in A site and P site form peptide bond catalyze by Peptidyl Transferase.5. Deaminted tRNA leaves P-site and tRNA with two amino acids moves to the A-site.6. When A-site of small ribosomal subunit reach the stop codon (UAG, UAA, & UGA) release factor binds the A site.7. tRNA release from P-site, release factor dettached from A-site, small & large ribosomal unit leaves MRNA

  • ENDOPLASMIC RETICULUMSystem of interconnected tubules & vesiclesCistern - the vesicles lumen.Metabolic process:Protein synthesis & modificationLipid & Steroid synthesisDetoxification of toxic compoundsMembrane manufacture.

  • Synthesis of Protein in RERIdentification of proteins for delivery outside the cell by signal peptide. Signal Recognition Particles (protein complex) recogize signal peptide.Small subunit ribsome halts translation as SRP-signal peptide complex occupy the P-site.Polysome migrateto RER.SRP receptor protein (docking protein) in RER membrane contacts SRP& ribosome receptor protein contacts large subunit ribosome.Polysome attach to the cytosolic surface of the RER.

  • GOLGI APPARATUSSynthesis of carbohydrates.Modification and sorting of proteins from RER.Made up of series of flattened, slightly curved membrane bound cisternae.Each cisterna is dilated peripherally and rimmed with vesicle that either fuse or bud-off from that particular compartment.

  • Golgi Additional Compartment1. Endoplasmic Reticulum/Golgi Intermediate Compartment (ERGIC).Between RER & cis-face.Derived from fusion of transfer vesicle.2. trans Golgi Network (TGN) Located at the distal side of G.A.

  • Golgi & RER - Associated VesiclesVesicle carrying protein bud-off facilitated by proteinaceous coat on the cytosolic aspect of the organelle.1. COP I2. COP II3. Clathrin

  • LYSOSOMESHave an acid pH & hydrolytic enzymes.A specialized organelle for digestion of substance from the late endosomes.Diameter is 0.3 - 0.8 m.Acid hydrolyses present:SulfatasesProteasesNucleasesLipasesGlycosideses


  • ENDOSOMESAlso involved in ingestion, sequestering & degradation of substance internalized from extracellular space.Has two compartments:Early endosomes - at the cell peripheryLate endosomes - deeper into cytoplasm.

  • PEROXISOMESelf replicative with oxidative enzymes.Maintainance of protein population.Responsible for proteolysis.Aided by the following enzymes:Ubiquitine-activating enzymesUbiquitine-conjugation enzymesUbiquitine ligases


  • MITOCHONDRIAPerform oxidative phosphorylation.Involved in lipid synthesis.Component Structure:Outer MembraneInner Membrane - Folds within is called cristae.Intermembrane Space - Between the inner & outer membrane.Matrix Space - Large space within the inner membrane.

  • CYTOSKELETONProtein filaments responsible for maintenance of cellular morphology.Responsible for intracellular movement.Types of Cytoskeleton:Thin Filaments (Actin)Intermediate FilamentsMicrotubules

  • Actin FilamentsResponsible for intracellular movement.15 % in non-muscle cells.It has G-actin - 2 chains of globular subunits coiled around each other forming filaments.It has a + end - fast growing end & - end; a slower growing end.

  • Intermediate FilamentsMaintain the 3-D framework of the cell.Anchor the nucleus in place.Provide connection between cell membrane and cytoskeleton.Help nuclear envelope reorganization subsequent to mitosis.

  • MicrotubuleLong, straight, hollow cylindrical structure.Provide cell rigidity.Establish intracellular compartments.Provide ciliary and flagellated movement.