Largest organelle   (a montage)*       
                                                                                                         
        -  average dia = 6um [max10 um],  volume up to 40 um³ is about 8% of cell volume.

        -  found in all eukaryote cells   (except mature erythrocytes & sieve tubes cells of phloem)
        -  evolutionary origin... a membrane "surrounded" an early prokaryotes nucleoid (genophore).
                  Origin of nucleus is not well established;  possibly via an invagination-like process, i.e.,?
                 a  Mesosome*   is a folded invagination in the cell membrane of bacteria that are
                                             produced by the chemical fixation techniques used to prepare
                                             samples for electron microscopy. 
                     
         

 

 

 

 

 

 
Components*  of the nucleus  -   fig 6.8 (11e-overview of cell)  
    
    a. nuclear envelope* -  nucleus is a double membrane bound organelle - SEM image
  
    b. nuclear pore complexes* =   pore structure* &  computer models Human np's
        human pore complex has about 2000/nucleus & some 450+ nucleoproteins (30 diff kinds)
                inquiry based experimentation helped establish the role of and
                functional diameter of pores = 10 nm                  NUCLEAR TRANSPORT*
 
     c. chromatin* - the genetic stuff 'inside of' the nucleus is...
                DNA (5x10^-12gm)  complexed with  histone proteins  &  acidic nuclear proteins
                          heterochromatin    (condensed & inactive - dark in EM's)
                          euchromatin          (less dense & active - greyish in EM's)  structural image*
          

    d. nucleolus* - a dense spherical structure... the site of rDNA genes which make rRNA.
                             in the Human genome there are 5 chromosomes with nucleolar rDNA genes.
    
    e. nucleoplasm* - interior complex-phase of the nucleus that contains...
                                  enzymes, RNA's, solutes, chromatin, etc... akin to cytoplasm.
    

Role of Nucleus     - site of genetic information, control of cell divisions & heredity

                                  Chromosome locations*   and   functional locations within nucleus*                   

      
 

 

 

          

 

   
 Nuclear Transport Experiments to Determine functional   Pore Sizes  &  Transport Mechanisms
  
    1960's - Carl Feldherr injects gold particles in unicellular amoeba's
                          TEM's showed particles congregating at nuclear pores within a minute;
                           within 10 min, gold particles were in nucleoplasm        see a micrograph* 
    1970's - fluorescent tagged proteins - showed proteins of less than 60,000 MW as passable
    1990's - How do proteins get in/out?     (including ribosomal proteins & rRNA of ribosome)
                  Ron Laskey - studied a nuclear transport protein... nucleoplasmin (a thermostable
                                        acidic protein helps assemble nucleosomes & in ribosome biogenesis) 
                  He radioactively tagged nucleoplasmin & used autoradiography* to follow its movement   

    Laskey experiment*    panel a - shows nucleoplasmin (head & tail regions) enters nucleus
                                                        and suggests protein has an aa sequence that helps mobility
                                         panel b - where is signal in head or tail? - they split & tagged
                                                        tail entered nucleus, thus it holds aa sequence
                                         panel c - where in the tail? cut tail into pieces & spliced to a
                                                        non-nuclear cytoplasmic protein.
 
  ►►► result:  nucleoplasmin holds a 17 amino acid sequence that targets transport into nucleus
                          it is known as the  NUCLEAR LOCALIZATION SEQUENCE (SIGNAL) (NLS).
                        suggests a likely mechanism* for nuclear protein transport.
                                                                                                                  skip

 
Mitochondria...

     site of :   Cellular Respiration   -  aerobic [redox rx's] oxidation of C₆H₁₂O₆  -->   CO₂ +  H₂O

                    Gas exchange in cell   -  CO₂ is released   &   O₂ is taken up & reduced to H₂O
    

                    KREBS cycle   -  an aerobic pathway that oxidizes pyruvate  --->  CO₂  +  H₂O
   

                    ETC chain,   ATP synthase  &  Oxidative Phosphorylation which makes ATP  

     its role :  conversion of covalent bond energy in food molecules --> into bond energy in ATP
                              for cellular activities of all kinds by coupling
                              redox transfers of e- & H⁺ protons...   via   ATP-synthase -->  to make ATP

                    Mitochondria animation*

 

      

   
    1st described 1857 by Albert von Kolliker & labeled as 'mitochondria' by Carl Brenda in 1898.
            today:   often visualized via  dyes*,   B&W-TEM*,  &   false color scanning SEM's*

    double membrane bound organelle*
             outer membrane - contains transport protein porin (passage of molecules up to 5K)

             inner membrane - very selectively permeable (i.e., impermeant to most molecules)
            peri-mitochondrial space* - (in between)  area where H⁺ accumulate (low pH)           
            cristae* - inner membranes that hold the respiratory assemblies of ETC (tomography*)
            mitoplasm - "matrix"  interior compartment = DNA, ribosomes, KC enzymes, etc
  
            structure :    elongate cylinders to prolate spheroids*  
                                 3-5 um long by 0.5-1.0 um dia,

                                "shape-shifters", mobile

            number :       20 to 1,000 per cell ;     the more active a cell  = the greater their #'s 
                                 can make-up as much as 20% of cell's volume
            contents:      has its own circular DNA - 16,569 nucleotide pairs: about 37 genes
                                 has its own ribosomes (prokaryotic size) & protein synthesizing ability
                                 holds enzymes for cellular respiration  

   

   
  CHLOROPLAST...   develops in the light from proplastids,
                                                     

        site* of autotrophic metabolism = PHTS,  O₂ evolution,  CO₂ reduction to glucose

        shape* - oblate spheroid in higher plants, but shape is variable (stellate, reticulate)      

        size:   2-3 um diameter   by   5-10 um long   &   numbering   15/20 - 100's/cell

        Chloroplasm (stroma) contents = interior compartment that holds within itself...
                1)  internal membrane system made of thylakoid membranes:
                                      Granal Stacks & Intergranal Membranes*
                2)  70s ribosomes (bacterial size)  -  Eukarya have different size ribosomes [80s]

                3)  lipid droplets
                4)  'naked' DNA pieces (circular, highly super-coiled & repetitive)

                5)  pyrenoids (protein centers for CO₂ reduction) & starch granules
                6)  enzymes of CO₂ reduction to CH₂O
                                                                  

  

    What is the origin of organelles as mitochondria and chloroplasts?

               are mitochondria & chloroplasts endosymbionts*
                                                 by Lynn Margulis - 1967

          "Mitochondria  &  Chloroplasts  are derived from archaean prokaryotes,
           which were once free living, but joined into a symbiotic relationship
           with a primitive eukaryotic during cellular evolution"

                             
                                        

 

Some striking similarities of Prokaryotes with Mitochondria and Chloroplasts         that support the endosymbiont hypothesis:

›  both organelles have double membrane bound....                        possibly the result of  a phagocytotic engulfment?                            of mitochondria?           of chloroplasts?    via  eukaryotic evolution*                       thus a double membrane arose from endosymbiosis

› both are semiautonomous :                        derived from themselves, by divisional fission...                            i.e., replicate independently from their eukaryotic cell hosts

› both have their own DNA (a circular molecule,  like the DNA of prokaryotes)                       & their protein biosynthetic systems can make some of own proteins

› DNA sequence homology...  each has similar DNA sequences                       mitochondria DNA related   to   aerobic bacterial DNA                       chloroplast DNA related      to   cyanobacterial DNA

› ribosomes are same size as bacterial ribosomes* 70s vs. eukaryotes with 80s sizes                      [ S = Svedberg unitsG ]    Animation of Endosymbiont Hypothesis(long version)

 
RIBOSOME...
                     ... is a a non-membrane bound organelle
                     ... is a subcell ribonucleo-protein particle (RNP) made of RNA & proteins
                     ... discribed by  George Palade in the 1940' via TEM
                          ... is universal to all known cells - prokaryote & eukaryote
                     ... is the cellular site of protein synthesis (mRNA + ribosomes -  artistic concept) 

spheroid shape  - 17 to 23 nm dia       (Noller model & 2009 Nobel Prize)
composed of 2 subunits	each contains rRNA & proteins
small subunit and a large subunit, which binds tRNA's  (Structure*)                     prokaryotic & eukaryotic composition  =   35% protein   and   65% rRNA
found in 3 different places* in cells...                1.  free in cytoplasm, as individual subunits or dimers,                 2.  membrane bound to the outer surface of Endoplasmic Reticulum membranes,                3.  attached to mRNA molecule  in a   POLYSOME   [or  polyribosome*]

  
                   
  

           

  
ENDOPLASMIC RETICULUM... a set of membraneous tubules contiguous with
           nuclear membrane and found in ALL EUKARYOTIC CELLS with a nucleus,
           (fig 6.11*) making up 50% of all internal membranes in eukaryotic cells.
           The ER is involved in protein and lipid synthesis in eukaryotic cells.

  

           Consists* of flattened sheets, sacs  &  tubes of membranes making a

                 convoluted 3-D membrane network enclosing internal spaces

                Lumen - is internal compartment of cisternae  [makes up to 10% of cell's volume]

                                             

           2 Types:              Smooth E.R.   (SER - tubular membranes without ribsosomes) &
                                    Rough E.R.*   (RER - surface of cisternae with ribosomes)     
           Functions:
              SER:   lipid & steroid synthesis and drug detoxification (adds -OH's solubilizing them)
              RER:   synthesizes, transports, & packages proteins into membrane vesicles  
  
                 SIGNAL SEQUENCE* -   aa's @ N-term, bind, release into lumen...    Gunter Blobel
    
                 GLYCOSYLATION*  - adding carbohydrate groups to ER proteins ---> glycoproteins
                                                        which will help transport the proteins to specific cell sites

                                          

 
 
Golgi Apparatus*...   is part of the Endomembrane system...
          a eukaryotic cell's internal membrane system responsible for                             
              1.   endocytosis - packaging of extracellular molecules for internal distribution
              2.   exocytosis (secretion) - packaging & delivery of newly synthesized
                                                          proteins/carbo's for extra-cellular secretion

Number & image* of the Golgi - up to 100 per cell    Size - 1 to 3 µm diameter  by  4 to 7 membranes stacks high    Structure & function* -  three parts   (or sides)...
CIS side [entry side]... faces R.E.R              proteins made on R.E.R.               pass from E.R. lumen --> vesicles --> cis Golgi
MEDIAL cisternae elements...              proteins are modified with sulfates, carbohydrates & lipids              modifications --> "address" vesicles to a destination
TRANS side [exit]... Golgi side          modified vesicles leave as...              export vesicles,   lysosomes,  other membrane bound vesicles

  
 Organelles of Cellular Digestion... 

        
  LYSOSOME...  a  cytoplasmic single membrane bound vesicle,
                            derived via the ER and Golgi body by glycosylation changes, & 
                       containing hydrolytic enzymes with acid pH optima (pH 5.0);
           Lysosome animation*... 
 
                      function: intracellular digestion via phagocyotosis*  and   autophagy.
                                     Yoshinori Ohsumi (2016 Nobel Prize for mechanisms of autophagy)
                       may have diverse shapes, but mostly spherical*, with acidic interior due to  
                       lysosomal membrane having ATP driven membrane H⁺pump^g (faces inward*)

                          
  PROTEASOMES... large barrel shaped protein complex, found in all eukaryotes and archaea,
                 and in some bacteria, that are responsible for intracellular Protein Digestion... (structure)
                 ubiquitin binds to proteins & transports them into a proteasome  figure*

 
 Endomembrane System visualization*...  migration path via vesicular transport.
        Was first proposed by George Palade in 1940's and is part of a cell's compartmentation                   

        with the outer nuclear envelope connecting to the rough ER & smooth ER.

        Vesicles made in ER flow, as transport vesicles, to the Golgi for modifications,
         & from the Golgi to an intracellular location or extracellular release. c10e fig 6.15*                                                                                                  
 
     Exocytosis:    Golgi modifies the molecular composition and metabolic function

                           of the endomembranes vesicles as they flow from ER through the Golgi,

                           & in turn, pinches off vesicles that give rise to lysosomes & vacuoles,  

                           or the plasma membrane can fuse with vesicles born in the ER and Golgi.

                           the result is the release of proteins via a Secretory protein pathway  &

                           other products to the outside of the cell in exocytosis.
     Endocytosis:  external material is captured into a membrane vesicular endosome,
                           which can fuse with a lysosome for intracellular digestion.
                                                     2013 Nobel prize for vesicular transport
  
      Protein Sorting* - proteins bound for different destinations have diff carbohydrate tags
                                   which can be recognized by unique glycoprotein receptors in the cell.   

                                     so far we've seen 3 ways to tag proteins for transport:
                                       Nuclear Localizing Signal,  Signal  Sequence, &  Carbohydrate Tags
                                              proteins have many sorting signals - table of signals  
 

   .            .

 
 cytoskeleton...

      network of protein fibers running throughout the cytoplasm of all cells (prokaryotes & eukaryotes)
      that provides a cell its shape and a basis for cellular transport (ex: cytoplasmic streaming).

                           stained cytoskeleton*   &   TEM's*   &    fibroblast*, 

     The  Cytoskeletal Proteins* that make up the Cytoskeletal Network include... 

            1.  microfilaments (actin proteins)...   7 to 8nm dia & of indefinite lengths   
                    actin is a universal (from protists to verts) contractile eukaryotic protein
                    makes up 5% of total cell protein,
                    F-actin is a linear filament of polymerized monomeric globular proteins of G-actin*
                    each microfilament is made up of two helical, interlaced strands of subunits
.                          ... G-actin is a "conserved" polypeptide of 375aa with an ATP recognition site
                                3 types of G-actins: - alpha actins of muscle cells [actin + myosin]
                           ... beta & gamma actins make up cytoskeleton and are involved in cell motility
                           ... actin filaments form crosslink patterns* and can change lengths.                        

                    ... example of function -  make up microvilli of epithelia*, cellular membrane
                                protrusions that increase the surface area of cells.
                                                     some other actin filament roles*
                                                                              
    

 

 

 

 

 

 

 

 

 

 
       

           2.  intermediate filaments...  (8-12nm dia -   some ex:  keratin, vimentin & lamin)
                     protein fibers [rope-like] with an intermediate diameter
                     spans cytoplasm providing framework for mechanical strength.
                     made from a heterogeneous family of filamentous proteins  (pic*)
 
     
           3.  microtubules... made of tubulin proteins (also highly conserved evolutionarily).
                    alpha & beta tubulin subunts assemble in um long filaments with a 21-25 nm dia.
                    [ MT's* & pic-Hela cell tubulin ] that form depending upon bound GTP/GDP action.

                    MT's are made of repeating globular units of 2 different proteins
                    alpha & beta tubulin, which assemble & disassemble*  [ +growth-*]
   

                 the major cytoskeletal proteins are universal in all eukaryotic cells.  
              

                               a hypothetical roles of cytoskeleton in cell structure*   

    
                                                           

Additional Cytoskeletal Elements  and/or  Organelles... 
   
 Centrosome*  :  Microtubule Organizing Center found in most eukaryotic cells from which
                             MTs emerge: site of MT nucleation; organizes Cilia & Flagella and the mitotic
                             spindle. Animal cell centrosomes contain centrioles - plant cells DO NOT.
  
 Cilia and Flagella and Cell movements:             animination of cilia & flagella structure*              

  Flagella   are microtubule (MT) extensions (100-200um singly or in pairs) projecting from
                       cells that can push or pull a cell through an aqueous media (ex: bacterial flagella)
   
  Cilia*       are MT extensions (0.25 um in length with hundreds on individual cells)
                       that move move stiffly like oars, to propel a cell or move fluid over stationary cell.
     
           structure*:   both have same structure -  9 MT doublets surrounding 2 singlet MT's in center,
                                collectively called an axoneme;  covered by plasma membrane,
                                & often held by cross-linking proteins (blue)    
           Basal Body*  is a centriole found at the base of flagella or cilia  (anchor of cilia & flagella)
  
      

 
        In 1965 Ian Gibbons described a new protein studding the length of each MT doublet
     in flagella, naming it dynein (dyne for force and in for protein)... which hydrolyzes ATP.
     The bending Motion is via Dynein arms* - a motor protein attaches & releases to MT doublets,
     and converts chemical energy of ATP into mechanical energy of conformational movement.
   
     Dynein & Kinesin are motor proteins* of intracellular movements - walking along MT's
     ex:  Kinesin*- is a dimeric motor protein powered by ATP hydrolysis that changes conformation
            & converts chemical energy into kinetic energy, moving toward + (positive end) of MTs.
            role of kinesin motor proteins by Ron Vale and their discovery.
                      kinesin & dynein motor differences (retrograde & anterograde transports*   
                                            animations of unseeable biology
  
                                                                                          
Flagella & Cillia movements are due to motor proteins as DYNEINs^view@home
     if cross-links are present (blue in fig), the MT's are held in place, then dynein causes
           MT doublets to "curve (bend past each other)* in restrained movement
     if no cross-linking proteins  - one foot of dynein arm binds as other releases
          allowing MT to "walk along" MT as doublets "slide" past each other unrestrained. 
          one of the MT doublets walks or slides toward the body of the cell on dynein feet,
          pushing in neighbor MT doublet toward the tip of the cilium.  

Roles of Cytoskeletal Protein Elements in Cell Structure and Motility -   Structural support:    actin filaments bear the TENSION forces (wires) of the cytoskeleton    microtubules (in fig) are the COMPRESSION units (rods) [tensegrity]    offer inner structural support for organelles (ex: toy & bridge*).	.
Cell motility:    contractile force of muscles*:   myosin & actin (microfilament) are motor proteins           that via repeated cycles of binding and release  = movement (CONTRACTION)         amoeba's crawl*: is via a psuedopodia due to the assembly/disassembly [animation]           of individual actin subunits on microfilaments shifting between sol/gel phases         cytoplasmic streaming*: in plant cells occurs via actin/myosin interactions and sol/gel    transformations which results in a circular flow of cytoplasm around the cell.         cell's respond to pressure* by building & branching actin filaments

 
    
Intercellular junctions...

                    Cell surface regions specialized for intercellular contact = MULTICELLULARITY
                    especially prominent in Epitheial Cells of animals

   3 Major Functions -  1. impermeabilize areas     2.  adhereing junctions     3.  communication
                                       animation about intracellular junctions*^2.5min

                    

     Tight Junctions* -  they impermeabilize regions.
                    they prevent leakage of materials between epithelial cells (normal vs. celiac disease*)...
     Desmosome - an adhering junction -   (anchors cells together)
                    spot desmosome - spot welds made with keratin & cadherin proteins
     Gap Junctions -   intercellular channels for communication    [dia circa = 0.2nm]
                    allows ions, electric impulses, etc... to pass between   image*
   
  Plants have no intercellular junctions as above due to polysaccharide cell walls, but do have  
     Plasmodesma* - cytoplasmic connections between plant cell walls [dia= 70nm].
                    a consequence: makes these plant cells act like a single cell with channels allows

                                              exchange of semi-large molecules to pass through plasmodesma.     
                                                                             

  
 the plant VACUOLE*    animation*      
  
    is a Vacuolar [tonoplast] membrane-bound sac that plays roles in
             intracellular digestion and the release of cellular waste products
             present in all plant, fungal, animal, & bacterial cells.
  
    In animal cells, vacuoles are generally small.      Plant cell lack lysosomes.
  
    Plant vacuoles accumulate toxic wastes:  phenolics, acids, and a range of nitrogenous wastes
            & water-soluble pigments, especially anthocyanins - responsible for red-pink-blue-purple
            coloration in many (but not all) flowers and fruits. Its interior is an acid pH environment.
  
    the (tonoplast) vacuolar membrane holds transport proteins, mostly active-transport carriers*
            for one way accumulation of wastes and toxics into the vacuolar spaces.  

    In plant cells, vacuoles tend to be large and play a role in maintaining turgor pressure*.
            When a plant is well-watered, water collects in cell vacuoles producing rigidity.
            With insufficient water, pressure in the vacuole is reduced and the plant wilts.
  
    As plant cells age.. onset of death is usually associated with tonoplast leakage & breakdown.

   

     Key Concepts* 

        -  all the links below may enhance ones learning experience, but are not required.

                    Tour of a Cell^{5 min view at home}         &    Virtual cell animations^recommended
                    E. coli protein molecular model   &    comparison prokaryotes & eukaryotes
                                         Visual Guide to human Cells     &   Inner Life of a Cell   &   Scale of Biological parts

                    Molecular animations to show how small molecules work
 
                       back      next lecture           

                         copyright c2024     Last update - Feb 2024
                         Charles Mallery,    Biology 150, Department of Biology,   U. of Miami,  Coral Gables, FL 33124 
                                                                           

           SKIP ALL THE MATERIAL BLOW THIS POINT

           ignore the material below for Bil 150-pt

          expanded table of differences between Prokaryotes & Eukaryotes

           Chaperones - proteins that help fold other proteins into proper shape
                               (Sumanas protein folding & degradation animation*)

Sumanas animation-vesicle processing*


    protein recycling*      Targeting Signals for semi-autonomous oragnelles (mito, chlp, peroxisome)

experiment & 
(model - eye lashes by P.Satir)

                    belt desmosome (zona adherens) - wide band of desmosomes

  MT's might even play a role on consciousness ???  

    Skip the mateial below on this page only

- Current Model of Nuclear Pore Transport includes as many as 6 different molecules including:

        the molecules                       an analogy to a moving company
        Importins                            the delivery truck proteins
        ATP & ADP                          the gas
        GTP & GDP                          the unloading crew
        and a protein called Ran       the moving supervisor

                               an importin binds to cytoplasmic protein with an NLS (requires ATP)
              figure *      Ran + bound GDP complexes with importin-cyto-protein & diffuses into nucleus
                               in nucleus GDP is phosphorylated & cytoplasmic protein is released,
                               Ran escorts importin back to cytoplasm.

       Exportins - proteins found in nucleus that are counterpoints of importins
                         RAN & GTP are also required, and a Nuclear Export Signal may be involved

    
=  nucleosome & chromatin packaging animation  &   DNA supercoil 

  
PLASTIDS...

        group of double membrane bound plant cell organelles...
            found in all higher plants that produce all the organics
            required by metazoan cells [sucrose, etc...], and
            store polymers of carbon and various pigments.

    cilia:      
                     move via alternating power/recovery stroke cycles  (ex: lining of windpipe & mucus)
                       moving fluids over a stationary cell;  may beat up to 100 times per second.     

                      Hypothesis of assembly of bacterial hair-like pili  bacterial movement via pili.

       Role of Cilia:  1. motion:  as in clearing trachea of foreign substances (fig)
                            2. stereocilia:  mechanosensing cilia of inner ear (fig*)
                          3. ependymal cilia:  keep Cerebral Spinal Fluid flowing in the brain.

   
       , i.e., "SIX-PACK MODEL"

                made of a fibrillar protein network (claudins & occludins) on apical side of epithelial.

               gap junction -  animation
 

                 Proteasomes & Protein Digesting Drugs

           -  transport to + end

next          skip the material above