Lecture 2   General medicine_2nd semester <ul><li>Hyaloplasm and c ytoskeleton </li></ul><ul><li>Cell organelles - their b...
<ul><li>HYALOPLASM AND CYTOSKELETON </li></ul><ul><li>h yalopla s m   (cytosol,  cytoplasmic ground substance )   -  a por...
Components of the cytoskeleton: intermediate filaments    microtubules   microfilaments     (actin filaments) Microtubules...
<ul><li>Function of microtubules:  </li></ul><ul><ul><li>they are responsible for organization of the cytoplasm  and intra...
<ul><li>Mi c rotubul es provide the structural basis for   </li></ul><ul><li>cilia  a nd flagella – 9 sets of microtubules...
Chief distribution of microtubules:    interphase   cell in mitosis   cilia + kinetosomes
Mi c rofilament s (actin filaments) have diameter   only  5-7 nm are composed  of  actin, a protein involved in muscle con...
<ul><li>distribution of m icrofilaments : </li></ul><ul><li>may be  attached to the plasma membrane  -  are involved in de...
in muscle cells – rhabomyocytes and cardiomyocytes,  microfilaments are associated with myosin filaments and form stable s...
<ul><li>Intermediate filaments </li></ul><ul><li>have average diameter 10-12 nm  </li></ul><ul><li>are  of proteinaceous c...
<ul><li>INTERMEDIATE FILAMENTS </li></ul><ul><li>type     thickness   protein   cell type     detection </li></ul><ul><li>...
<ul><li>CELL ORGANELLES   </li></ul><ul><li>are the &quot;little organs&quot; of the cell that posses a distinctive struct...
<ul><li>m itochondria  are  spherical corpuscles or filament ou s  corpuscles  varying from 0.5 to 2   m in diameter and ...
<ul><li>Main differences between mitochondrial membranes: </li></ul><ul><li>outer mitochondrial membrane  - contains integ...
mitochondria are autonomic organelles  –  contain own DNA and ribosomes that differ from cytoplasmic ones and produce seve...
<ul><li>Golgi apparatus </li></ul><ul><li>organelle is known similar as mitochondria since the end of the 19-century </li>...
 
Function of G.a.:   is engaged in segregation of newly formed or synthesized cellular constituents and their directing to ...
<ul><li>Ribosomes </li></ul><ul><li>are very small particles, observable only by the electron microscope </li></ul><ul><li...
Function: free ribosomes / polysomes /  are site s  of protein synthesis  for the use of  the  cell bound ribosomes
Endoplasmic reticulum   was discovered with introduction of electron microscope  in to  cytology t he organelle is identic...
RER is abundant especially in glandular cells and corresponds to basophilic regions of the cytoplasm glucose-6-phosphatase...
Smooth endoplasmic reticulum is made up  convoluted tubules or small vesicles  that intercommunicate each other contains  ...
Function:  the site of lipid synthesis , the site of synthesis and break-down of glycogen,   is angaged in formation of me...
steroidogenic cells  abundant SER mitochondria with tubules
<ul><li>Lysosomes </li></ul><ul><li>are involved in digesting processes in cells   </li></ul><ul><li>firstly  have been  i...
Secondary  lysosomes   are larger than primary ones; the diameter of them ranges between 1 to 2 mm originate  as a result ...
Residual bodies  ( telolysosomes )   = are  final form s  of secondary  lysosomes  that  are enzymic inactive c ontain   m...
 
Peroxisomes  (microbodies ) are spherical, membrane-limited  organelle s, about  0,5 -  1.0   m in diameter in several  c...
Centriol e paired organelle ovoid body   ( cca 0,2 µm  wide   x  0,2-0,5 µm  long) in all cells that divide mitotically (e...
<ul><li>triplets are turned counterclockwise to each other at a constant angle </li></ul><ul><li>Function of centrioles: <...
<ul><li>CELL INCLUSIONS </li></ul><ul><li>cytoplasmic deposits </li></ul><ul><li>are lifeless  structures in ther cytoplas...
Lipid droplets variable diameter 100 nm - 10 µm they  serve as a local store of energy and also as a source of short carbo...
Carbohydrates  are  most ly stored in the form of glycogen is not apparent in routine histological sections but may be sel...
 -  granul es /  cca  20 nm    - granul es /   cca  450 - 600 nm   g ly c ogen  in TEM
<ul><li>Pigments  </li></ul><ul><li>are  inclusions  that possess color and they do not have to be stained by histological...
Lipofuscin  a tan or light brown pigment  that  fluoresces a golden-brown in ultraviolet light an  amount of lipofuscin is...
THE CELL CYCLE cell cycle  or  generation time   (individual history of the cell) =   time from one  mitosis  to the  begi...
<ul><li>2 checking (restriction) points included: </li></ul><ul><li>to the end of  G 1 </li></ul><ul><li>in the middle  G ...
Mitosis cca  1 h  (40-120 min)
Metaphase
Late anaphase constriction ring from  microfilaments is organized in the equatorial plane of the parent cell further narro...
 
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Lecture2

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Lecture2

  1. 1. Lecture 2 General medicine_2nd semester <ul><li>Hyaloplasm and c ytoskeleton </li></ul><ul><li>Cell organelles - their basic structural </li></ul><ul><li>characteristics and function </li></ul><ul><li>Cell inclusions and pigments </li></ul><ul><li>Cell cycle, cell division, and cel l differentiation </li></ul>
  2. 2. <ul><li>HYALOPLASM AND CYTOSKELETON </li></ul><ul><li>h yalopla s m (cytosol, cytoplasmic ground substance ) - a portion of the cytoplasm surround ing organelles a nd inclusions that forms millieau for their functioning; seems to be structureless </li></ul><ul><li>consists of : </li></ul><ul><li>H 2 0 </li></ul><ul><li>Ma cromolecules </li></ul><ul><li>L ow molecular substances (aminoacids, mono- and oligo-saccharides) </li></ul><ul><li>I ons (K + , Na + , Mg 2+ , Ca 2+ ), </li></ul><ul><li>pho s phate + chloride anions etc. </li></ul><ul><li>Cytoskeleton </li></ul><ul><li>a part of cytoplasmic matrix that is responsible for its dynamic properties formed by very fine network extending between nuclear envelope and cell mebrane and that is closely associated to the cell organelles </li></ul><ul><li>shape of cells, movement of organelles, movement of entire cells </li></ul>
  3. 3. Components of the cytoskeleton: intermediate filaments microtubules microfilaments (actin filaments) Microtubules: diameter 25 nm are hollow tubes composed of 13 strands of protofilaments that are formed from proteinaceous tubulin subunits (alpha and beta-tubulin ) m icrotubules are bound to other cytoskeletal elements and cytoplasmic organelles
  4. 4. <ul><li>Function of microtubules: </li></ul><ul><ul><li>they are responsible for organization of the cytoplasm and intracellular transport of organelles and vesicles </li></ul></ul><ul><ul><li>they help to determine cell shape and polarity </li></ul></ul><ul><ul><li>they participate in a variety of motile activities (the movement chromosomes during mitosis, the beating of cilia) </li></ul></ul><ul><li>dis ru ption or depolymerisation of microtubules or inhibition of their synthesis stop mitotic division, phagocytosis, processes of releasing of secretory granules, result also in the loss of cell symmetry etc. </li></ul>
  5. 5. <ul><li>Mi c rotubul es provide the structural basis for </li></ul><ul><li>cilia a nd flagella – 9 sets of microtubules arranged in doublets that surround two central microtubules = axoneme </li></ul><ul><li>centriol es and kinetosomes - 9 sets of microtubules arranged in triplets </li></ul><ul><li>with m i c rotubul es are associated special proteins called motor proteins (take participation in transporting processes in cells with utilization of ATP) </li></ul>
  6. 6. Chief distribution of microtubules: interphase cell in mitosis cilia + kinetosomes
  7. 7. Mi c rofilament s (actin filaments) have diameter only 5-7 nm are composed of actin, a protein involved in muscle contraction each microfilament is formed with hundreds of globular subunits - G-actin - organized into a double-stranded helix with a 36 nm repeat - F- actin microfilaments are very dynamic structures that are continually dissociated and reassembled
  8. 8. <ul><li>distribution of m icrofilaments : </li></ul><ul><li>may be attached to the plasma membrane - are involved in defining the surface morphology of the cell - C </li></ul><ul><li>may penetrate the cytoplasm and be intimately associated with several cell organelles, vesicles or granules - B </li></ul><ul><li>cytoplamic streaming </li></ul><ul><li>may support microvilli as terminal web and maintain their shape - A </li></ul><ul><li>may be organized in constriction ring - D </li></ul>
  9. 9. in muscle cells – rhabomyocytes and cardiomyocytes, microfilaments are associated with myosin filaments and form stable structures called as myofibrils
  10. 10. <ul><li>Intermediate filaments </li></ul><ul><li>have average diameter 10-12 nm </li></ul><ul><li>are of proteinaceous character and of tissue specific </li></ul><ul><li>are non-contractile and provide cells with mechanical strength - resistance in the traction and pressure </li></ul><ul><li>can be visualized with the use of immunocytochemical methods and </li></ul><ul><li>TEM </li></ul><ul><li>recently, the microscopic visualization of filaments (their proteins) is used in human pathology for diagnosis of tumours </li></ul><ul><li>filaments are classified into 5 groups: </li></ul>
  11. 11. <ul><li>INTERMEDIATE FILAMENTS </li></ul><ul><li>type   thickness protein cell type detection </li></ul><ul><li>--------------------------------------------------------------------------------------------------- </li></ul><ul><li>k eratin </li></ul><ul><li>filaments 8-11nm cytokeratin epithelial cells TEM </li></ul><ul><li>t onofilaments (about 20 kinds) immun </li></ul><ul><li>------------------------------------------------------------------------------------------------------------------------------------ </li></ul><ul><li>vimentin </li></ul><ul><li>filament s 8-11nm vimetin mesenchymal cells TEM , immun </li></ul><ul><li>(fibroblasts, chondroblasts, endothelial cells, vascular smooth muscle, macrophages) </li></ul><ul><li>------------------------------------------------------------------------------------------------------------------------------------ </li></ul><ul><li>desmin </li></ul><ul><li>filament s 8-11nm desmin striated + smooth TEM , immun </li></ul><ul><li> muscle cells </li></ul><ul><li> (except vascular smooth muscle) </li></ul><ul><li>----------------------------------------------------------------------------------------------------------------- </li></ul><ul><li>glial </li></ul><ul><li>filaments 8-11nm glial fibrillary astrocytes TEM , immun </li></ul><ul><li> acidic protein (GFAP) </li></ul><ul><li>----------------------------------------------------------------------------------------------------------------- </li></ul><ul><li>n euro - </li></ul><ul><li>filaments 8-11 nm neurofilament triplet neurons TEM , impreg </li></ul><ul><li> (NT) protein </li></ul>
  12. 12. <ul><li>CELL ORGANELLES </li></ul><ul><li>are the &quot;little organs&quot; of the cell that posses a distinctive structure and well </li></ul><ul><li>established function </li></ul><ul><li>al l organelles act in concert and to allow the cell to exist </li></ul><ul><li>they standardly occur in most cells , in several highly specialized cells organelles may be missing </li></ul><ul><li>List of organelles: </li></ul><ul><li>- mitochondria </li></ul><ul><li>- endoplasmic reticulum </li></ul><ul><li>- ribosomes </li></ul><ul><li>- Golgi apparatus </li></ul><ul><li>- lysosomes </li></ul><ul><li>- peroxisosomes </li></ul><ul><li>- centrioles </li></ul><ul><li>Mitochondria </li></ul><ul><li>are largest and generally most abundant of all cytoplasmic organelles </li></ul><ul><li>d iscovered by Altmann in 1890 year </li></ul><ul><li>t heir volume can reach to 25 % of the entire one of the cytoplasm </li></ul><ul><li>e xcept red blood cells and terminal keratinocytes mitochondria occur practically in all cells </li></ul><ul><li>of the human body </li></ul>
  13. 13. <ul><li>m itochondria are spherical corpuscles or filament ou s corpuscles varying from 0.5 to 2  m in diameter and from 5 to 10  m in length </li></ul><ul><li>function: transform the energy of metabolites obtained by their oxidation into energy bound to ATP molecules </li></ul><ul><li>the transformation process is known as oxidative (aerobic) fosforylation </li></ul><ul><li>the m itochondrion consists of a wall and matrix </li></ul><ul><li>the wall : </li></ul><ul><li>an outer mitochondrial membrane smooth, 6 -7 nm </li></ul><ul><li>an inner mitochondrial membrane thinner, it projects folds called as cristae </li></ul><ul><li>(i n steroid-producing cells, the inner mitochondrial membrane forms invaginations of tubular or vesicular shape - termed as mitochondria with tubules or mitochondria with tubular cristae ) </li></ul><ul><li>intermembrane space </li></ul><ul><li>the matrix – contains enzymes of the tricarboxylic acid cycle , ADP, ATP, DNA, RNA, ribosomes </li></ul>
  14. 14. <ul><li>Main differences between mitochondrial membranes: </li></ul><ul><li>outer mitochondrial membrane - contains integral protein porin that functions as channels </li></ul><ul><li>they serve for transportation of ions and metabolites from cytosol into the interior of the mitochondrion </li></ul><ul><li>inner mitochondrial membrane - two kinds of proteins are associated with it </li></ul><ul><li>electron transport system (cytochromes, coenzyme Q, cytochrome oxidase), </li></ul><ul><li>globular units with ATPase activity </li></ul>
  15. 15. mitochondria are autonomic organelles – contain own DNA and ribosomes that differ from cytoplasmic ones and produce several own proteins new mitochondria originate from preexisting mitochondria by division
  16. 16. <ul><li>Golgi apparatus </li></ul><ul><li>organelle is known similar as mitochondria since the end of the 19-century </li></ul><ul><li>G. a. is ubiquitous cell compartment found usually in close proximity to elements of ER and lysosomes in most cells </li></ul><ul><li>3 components - the all are limited by a single and smooth membrane </li></ul><ul><ul><li>3 –8 flattened sacs termed as cisternae with dilated rims, cisternae are usually curved and parallel </li></ul></ul><ul><ul><li>vesicles (200 nm) – mostly numerous </li></ul></ul><ul><ul><li>vacuoles - ( 1 or more  m) </li></ul></ul>on thin sections, G. a. may occupy even several separate areas that are termed as Golgi fields
  17. 18. Function of G.a.: is engaged in segregation of newly formed or synthesized cellular constituents and their directing to their final destination in cell s the cis-fa c e is closest to the ER and represents the site at which the material enters the organelle ( forming face ) the trans-face is adjacent to secretion vesicles and storage granules and represents the exit site for most constituents ( maturing face )
  18. 19. <ul><li>Ribosomes </li></ul><ul><li>are very small particles, observable only by the electron microscope </li></ul><ul><li>15 to 20 nm in diameter </li></ul><ul><li>c hemically, they are defined as complexes of ribonucleic acid (RNA) and protein s </li></ul><ul><li>in cells they occur ubiquitous and form the catalytic sites for translation of messenger ribonucleic acid into a peptide chain </li></ul><ul><li>ribosomes are composed of a large and a small subunit, each of which contain specific RNA and protein molecule </li></ul><ul><li>in cells ribosomes occur in two forms: </li></ul><ul><ul><li>free in the cytoplasmic matrix (cytoplasmic ground substance or cytosol ) </li></ul></ul><ul><ul><li>attached to outer surfaces of membranes of ER ( bound ribosomes ) </li></ul></ul>f ree ribosomes are scattered throughout the hyaloplasm either singly as monosomes or are grouped in spiral or rosette pattern s termed as polysomes p olysomes originate by joining of individual monosomes along the molecule (strand) of mRNA
  19. 20. Function: free ribosomes / polysomes / are site s of protein synthesis for the use of the cell bound ribosomes
  20. 21. Endoplasmic reticulum was discovered with introduction of electron microscope in to cytology t he organelle is identical with the cytoplasmic compartment that stains with basic dyes and is known as the ergastoplasm in the light microscope 2 forms: the rough ER , with ribosomes bound to the outer membrane surface (RER), and smooth ER that is ribosome-free (SER) Rough endoplasmic reticulum consists of anastomosing flattened sacs - cisternae with polysomes on external surface of limiting membrane
  21. 22. RER is abundant especially in glandular cells and corresponds to basophilic regions of the cytoplasm glucose-6-phosphatase is used as marker for this compartment Function of t he RER : is a major site of synthesis of proteins that are produced for the use of other cells
  22. 23. Smooth endoplasmic reticulum is made up convoluted tubules or small vesicles that intercommunicate each other contains no attached ribosomes is usually found more peripherally in the cell it corresponds with cytoplasmic areas that are neutrophilic or sligthly acidophilic t he relationship between both forms of ER is very flexible Golgiho aparát
  23. 24. Function: the site of lipid synthesis , the site of synthesis and break-down of glycogen, is angaged in formation of membran in the cell, converts toxic molecules to nontoxic derivatives that can be excreted in muscle cells – functions as pool of Ca ions
  24. 25. steroidogenic cells abundant SER mitochondria with tubules
  25. 26. <ul><li>Lysosomes </li></ul><ul><li>are involved in digesting processes in cells </li></ul><ul><li>firstly have been identified biochemically and then histochemically </li></ul><ul><li>are spherical bodies of diameter varying between 0,05- 2 µm </li></ul><ul><li>is limited by a single membrane, the content of organelle is termed matrix </li></ul><ul><li>it shows very variable electron density and composition </li></ul><ul><li>l ysosomes contain large number of degradative enzymes - more than 6 0, </li></ul><ul><li>most of them are active at an acid pH </li></ul><ul><li>3 subgroups of lysosomes: </li></ul><ul><ul><li>primary </li></ul></ul><ul><ul><li>secondary </li></ul></ul><ul><ul><li>residual bodies </li></ul></ul><ul><li>Primary lysosomes </li></ul><ul><li>are small vesicles with a dense matrix </li></ul><ul><li>0. 05 to 0.2.  m in diameter </li></ul><ul><li>are located near the trans-face of the G.a </li></ul><ul><li>contain newly synthesized hydrolytic enzymes that have not been u tilised in digestion processes </li></ul><ul><li>in the cell </li></ul><ul><li>detection of them needs the use of histochemical methods </li></ul>
  26. 27. Secondary lysosomes are larger than primary ones; the diameter of them ranges between 1 to 2 mm originate as a result of fusion of primary lysosomes with the structure s containing the substance to be digested subdivided on the basis of morphology in to: phagolysosomes – originate by fusion of primary lysosomes with phagocytic Vacuoles autophagic vacuoles – by fusion of primary lysosomes with cellular components such as e.g. mitochondria or RER structural picture of s. l. - variable
  27. 28. Residual bodies ( telolysosomes ) = are final form s of secondary lysosomes that are enzymic inactive c ontain material not digested by lysosomal enzymes Function: degradation not only of intracellular substances and damaged structures but also exogenous provenience
  28. 30. Peroxisomes (microbodies ) are spherical, membrane-limited organelle s, about 0,5 - 1.0  m in diameter in several cells ( in liver and kidney ) , they contain a dense crystalline core termed a nucleoid are usually found close to the ER contain more than 40 enzymes that are responsible for a variety of catabolic and anabolic r eactions very typical enzyme of this organelle is the catalase destroys hydrogen peroxide urate oxidase, oxidase of D- amino acids Function: take participation in synthetic as well as catabolic processes in cells (synthesis of bile acids, synthesis of phospholipids etc)
  29. 31. Centriol e paired organelle ovoid body ( cca 0,2 µm wide x 0,2-0,5 µm long) in all cells that divide mitotically (except blood and nerve cells) located nearly the nucleus and is surrounded by an area of cytoplasm different from the rest by lesser staining = the centrosome ultrastructural appearance 9 sets of microtubule triplets composed of 3 microtubules of 15 to 20 nm in diameter support ing the periphery pericentriolar structures (appendages)
  30. 32. <ul><li>triplets are turned counterclockwise to each other at a constant angle </li></ul><ul><li>Function of centrioles: </li></ul><ul><li>mitosis – induce the organisation of mitotic spindle </li></ul><ul><li>ciliogenesis – centrioles give rise to kinetosomes, from which cilia originate </li></ul><ul><li>(kinetosomes show the same structure as centriole) </li></ul>
  31. 33. <ul><li>CELL INCLUSIONS </li></ul><ul><li>cytoplasmic deposits </li></ul><ul><li>are lifeless structures in ther cytoplasm with temporary occurrence ; in most cases they are of a result of the cell activity </li></ul><ul><li>by accumulation of metabolites or substances with stored function </li></ul><ul><li>by phagocytosis of material from the cell surrounding or even external environment </li></ul><ul><li>stored foods </li></ul><ul><li>crystals </li></ul><ul><li>pigments </li></ul><ul><li>secretion granules </li></ul><ul><li>Stored foods : proteins, lipids and carbohydrates </li></ul><ul><li>p roteins are found in animal cells rarely – they show crystalic organization </li></ul><ul><li> is supposed to be identical with crystals </li></ul><ul><li> occurrence: in intestitial Leydig cells, Sertoli sells (both in the testis) </li></ul><ul><li>l ipids - 2 forms: as </li></ul><ul><li>lipid droplets composed mostly of neutral fats </li></ul><ul><li>masked or bound lipids that are contained mainy in membranes </li></ul>
  32. 34. Lipid droplets variable diameter 100 nm - 10 µm they serve as a local store of energy and also as a source of short carbon chains i n ordinary histological sections these are likely appear as round clear areas in the cytoplasm, because the lipid is extracted by solvents used in the preparation of the specimen , a fter osmium tetroxide fixation, lipid droplets transit into insoluble and extraction resistant form and appear as black spherical structures in the light microscope t he same appearance lipid droplets show also in electron m icrographs th e degree of blackening or electron density depends upon the degree of unsaturation of the lipid and the nature of the fixative used
  33. 35. Carbohydrates are most ly stored in the form of glycogen is not apparent in routine histological sections but may be selectively stained by the P eriodic A cid-Schiff ´s reaction (PAS) (brilliant magenta). i n electron micrographs, the glycogen shows granular appearance (in dependence of fixative used) i t occurs in 2 form s: as dense, roughly izodiametric, 15 to 30 nm particles, referred to as the beta – particles or as rosette-like aggregates of larger size called alpha particles
  34. 36.  - granul es / cca 20 nm  - granul es / cca 450 - 600 nm g ly c ogen in TEM
  35. 37. <ul><li>Pigments </li></ul><ul><li>are inclusions that possess color and they do not have to be stained by histological dyes </li></ul><ul><li>2 groups: </li></ul><ul><li>exogenous - formed outside the cell and later taken into it, or as </li></ul><ul><li>endogenous - formed within the cell cytoplasm </li></ul><ul><li>E xogenous pigments include carotin, lipochromes, dusts (carbon), and minerals such as lead and silver (a n artificial introducing of some dyes into the deeper layers of the skin is called tattooing ) </li></ul><ul><li>Endogenous pigments involve : </li></ul><ul><li>- hemoglobin and its breakdown products (hemosiderin, hematoidin) </li></ul><ul><li>- melanin and lipofuscin </li></ul><ul><li>Hemosiderin is a golden-brown, iron containing pigment that is accumulated in the cytoplasm of the phagocytes (for example in the normal spleen, liver, and bone marrow ) Hemosiderin shows staining reactions for iron. In electron micrographs the masses of pigment include large numbers of 9 nm dense particles of the iron-containing protein, called the ferritin </li></ul><ul><li>Hematoidin is iron-free pigment that is produced after longer time , mostly located extracellulary, near to blood vessels, especially in extravation sites </li></ul><ul><li>Melanin is a brown pigment synthesized by special cells called melanocytes </li></ul><ul><li>in cells it occur in the form of granules – melanosom es </li></ul><ul><li>on the ultrastructural level, melanosomes appear as a homogenous dense granule separated from cytoplasmic matrix by a membrane unit </li></ul>
  36. 38. Lipofuscin a tan or light brown pigment that fluoresces a golden-brown in ultraviolet light an amount of lipofuscin is progressively increased with advancing age (&quot;wear and tear&quot; pigment) – neurons (cells of the autonomic ganglion) r ecently lipofuscin is thought to be end product of lysosomal activity and is regarded as the indigestible residues of phagocytosed material or degenerated organelles
  37. 39. THE CELL CYCLE cell cycle or generation time (individual history of the cell) = time from one mitosis to the beginning of the next , it occurs in all tissues with cell turnover; characterised by many events in both the cell nucleus and the cytoplasm cell cycle : interphase and mitosis Interphase is divided G 1 - postmitotic S- DNA synthesis G 2 - pre mitotic mitosis (pro-, meta-, ana, telophase) G 1 – 8 - 25 h , intense synthesis of RNA and proteins, number of organelles increases, the cell volume of daugter cell is restored to normal size S - 8 h , synthesis of DNA and its duplication, after S phase completion chromosomes composed of 2 identical chromatids, centriol is replicated G 2 - (post DNA duplication) - 3 h , cell continues in growth and cumulates energy, tubulin is synthesized, preparation to mitosis,
  38. 40. <ul><li>2 checking (restriction) points included: </li></ul><ul><li>to the end of G 1 </li></ul><ul><li>in the middle G 2 </li></ul><ul><li>when the cell passes the first restriction point, it continues through the S, G2 and mitosis </li></ul><ul><li>the first restriction point stops the cycle under conditions unfavourable to the cell </li></ul><ul><li>in G 1 the cell can leave the cycle and enter a quiescent phase - G 0 , from this phase it can return to the cycle </li></ul><ul><li>neurons and muscle cells stay in G 0 for their entire lifetime </li></ul><ul><li>cells are highly metabolic active but have no proliferative potential or capacity </li></ul>
  39. 41. Mitosis cca 1 h (40-120 min)
  40. 42. Metaphase
  41. 43. Late anaphase constriction ring from microfilaments is organized in the equatorial plane of the parent cell further narrowing of the ring leads to separation of both daughter cells

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