The ability of organisms to produce more of their own kind is the one characteristic that best distinguishes living things from nonliving matter. This unique capacity to procreate, like all biological functions, has a cellular basis. The continuity of life is based on the reproduction of cells, or cell division. Cell division plays several important roles which are giving rise to a new organism, enabling development, renewing and repairing and also replacing damaged tissue is multicellular organisms.
توانایی موجودات زنده در تولید بیشتر از نوع خود یکی از ویژگی‌هایی است که موجودات زنده را از مواد غیر زنده به بهترین وجه متمایز می کند. این ظرفیت منحصر به فرد برای تولید مثل، مانند همه عملکردهای بیولوژیک، دارای پایه سلولی است. تداوم زندگی براساس تولید مثل سلول‌ها یا تقسیم سلولی است. تقسیم سلولی چندین نقش مهم را ایفا می‌کند که نه تنها باعث ایجاد یک ارگانیسم جدید می‌شود، همچنین امکان رشد، تجدید و ترمیم و همچنین جایگزینی بافت آسیب دیده موجودات چند سلولی را نیز فراهم می کند.
2. Cell division
“Where a cell arises, there must be a previous cell, just as animals can only arise
from animals and plants from plants.”
◦ Rudolf Virchow in 1858
reproduction of cells is carried out as the sequence of reactions in which the cell
duplicates its contents and divides into two cells - cell cycle
3. Cell division
Unicellular organism
• production of a complete new organism
Multicellular organism
• reproduction of individuals
• embryonic development of the individuals
• repair processes
4. Cell cycle
basic function: duplicate accurately the amount of DNA in the
chromosomes and distribute the copies into genetically
identical daughter cells
• duration of the cell cycle varies greatly from one cell type to
another
5. Cell division in bacteria
• one circular chromosome is
attached to the plasma membrane
Binary Fission
• DNA replication
• cell growth after doubling
the size - simple division
http://techhydra.com/science/biology/cel
lular-biology/cell-division/binary-fission
6. Cell division – eucaryotic cell
more complicated then cell division in bacteria
• genetic information in nucleus
• cytoskeleton
• organelles
7. Chromosomes
• a threadlike linear strand of DNA and associated proteins
in the nucleus of eukaryotic cells that carries the genes
and functions in the transmission of hereditary
information
components:
• DNA
• acidic and basic protein
Human - 46 chromosomes
• 2 sets of 23 chromosomes
• 22 pairs of autosomes (homologous chromosomes) and 2
sex chromosomes (X and Y)
8. Chromosomes
the structure varies according to the phase of cycle - metaphase
chromosome
http://www.elu.sgul.ac.uk/rehash/guest/scorm/53/package/content/metaphase.htm
9. Cell cycle
4 phases
G1 phase
S phase
G2 phase
M phase
• Mitosis
• Cytokinesis
period between one M phase and the next one
• interphase
10. Cell cycle
G1 phase
• from the english word gap – G phase
• the first preparing phase
• 30-40% of the cell cycle time
11. Cell cycle
G1 phase
• cell grows in size and synthesizes:
RNA, proteins
nucleotides
enzymes for replication
organelles
mitochondia, chloroplasts, centriols
ER, GA – fragmentation : distribution of organelles fragments
forming organelles in the daughter cells
GO phase
12. Cell cycle
S phase
• synthetic phase
• nuclear DNA replication
• 30-50% of the cell cycle time
14. Cell cycle
DNA replication (duplication of DNA)
DNA synthesis begins at replication origin
• binding of initiator protein
• unwinding of DNA
• binding other components of the replication complex
DNA polymerase
16. Cell cycle
S phase
synthesis of histones
• simultaneously with the DNA synthesis
• formation of nucleosomes and chromatin
• in replicated DNA – histones
• Centriols - Procentriols
17. Cell cycle
G2 phase
• the second preparing phase
• 10-20% of the cell cycle time
• cell continue in growing
• synthesis of RNA, protein
preparing for mitotic cell division
18. Cell cycle
M phase
• the last phase of the cell cycle
• 5-10% of cell cycle time
• chromosomes are replicated - sister
chromatids
• cell organelles are multiplicated
cell is prepared for mitotic cell division
25. Mitosis
Metaphase
• alignment of chromosomes in the equator of the
spindle (halfway between two spindle poles) -
metaphase plate
movement of chromosomes
• continual growth and shrinkage of the microtubules
– dynamic instability
• microtubule motor proteins
https://slideplayer.cz/slide/2588156/
27. Mitosis
Anaphase
• segregation of chromosomes - two identical sets of chromosomes
Anaphase A – shortening of kinetochore tubules
Anaphase B – spindle poles move apart
29. Mitosis
Telophase
• nuclear envelope reassembles around each group of
chromosomes
two daughter nuclei
decondensation of chromosomes - gene transcription can
start again
https://slideplayer.cz/slide/2588156/
31. Cytokinesis
• the cytoplasm is cleaved in two
• begins in anaphase but is not completed until the two
daughter nuclei have formed in telophase
Plant cell X Animal cell
33. Cytokinesis – animal cell
during anaphase is formed cleavage furrow
• vertical to the axis of the mitotic spindle
• formed between the two groups of daughter
chromosomes
contractile ring
• composed mainly of actin filaments and myosin filaments
• divides cell into two daugther cells
34. Cytokinesis – animal cell
symmetric cytokinesis = symmetric division of cytoplasm together with
organelles
• distribution of organelles – random
36. Cytokinesis – plant cell
plant cell – cell wall
• new cell wall starts to assemble in the cytoplasm between the
two sets of segregated chromosomes at the start of telophase
Phragmoplast - a structure that is formed in the equator of the
old mitotic spindle
• along microtubules are transported vesicles carrying material
for the wall
derived from the Golgi apparatus
carry polysaccharides, glycoproteins
• grows from the center towards the cell surface
37. Meiosis
• type of cell division that reduces the number of chromosomes in the parent cell by
half and produces four gamete cells
• meiosis begins in specialized diploid germ-line cells in the ovaries or testes
these cells contain two copies of each chromosome, one inherited from the father organism (the
paternal homolog) and one from mother (the maternal homolog) – homologous chromosomes
Gamete cell - haploid cell n – single set of chromosomes
Somatic cell - diploid cell 2n – two sets of chromosomes, one from the mother and the
other from the father
38. Meiosis
• one DNA replication is followed by two rounds of cell division to produce four
daughter cells
two successive cell divisions
• first meiotic division – meiosis I
• second meiotic division – meiosis II
39. Meiosis
Meiosis I
Prophase
• takes place in the nucleus with an intact membrane – only
chromosomes undergo changes
5 phases
◦ Leptotene
◦ Zygotene
◦ Pachytene
◦ Diplotene
◦ Diakinesis
40. Meiosis
Leptotene
• chromosomes condense
• sister chromatids - tightly bound and
indistinguishable from one another
Zygotene
• pairing of homologous chromosomes
– bivalent
• contains 4 chromatides
• chromatids are associated by synaptonemal complex
41. Meiosis
Pachytene
• bivalent consists of four sister chromatids
nonsister chromatids of homologous chromosomes may exchange segments -
Crossing-over
• multienzyme systems responsible for chromatid recombination – in
synaptonemal complex
42. Meiosis
Crossing over
nonsister chromatid exchange sections
• chiasma - connection that corresponds to a
crossover between two non-sister chromatids
• many bivalents contain more than one
chiasma - multiple crossovers
43. Meiosis
Diplotene
• degradation of synaptonemal complex and partial
separation of homologous chromosomes
Diakinesis
• nuclear envelope begins to disappear
• centrosomes are moving towards the poles of the cell
44. Meiosis
Meiosis I
Metaphase
• bivalents are moved to the equator
• centromeres of chromosomes are randomly oriented to one or the other pole
of cells
• kinetochore microtubules connect bivalents to centromeres (spindle poles)
45. Meiosis
Meiosis I
Anaphase
• segregation of homologous chromosomes - destrucion of bivalents
• complete set of chromosomes formed by recombination from the original
maternal and paternal chromosomes gets to each pole of the cell
52. Cellular differentiation
genetic basis of differentiation
• all cells have same genetic background – genetic
information for all types of differentiated cells is in
zygote
53. Cellular differentiation
levels of differentiation
molecular - plasma membranes of various differentiated cells
contain different receptor proteins - enabling different
answers
enzyme - production of specific metabolites - specific
metabolic pathways
morphological - changes in the shape and structure of cells
• may lead to the elimination of vital structures - Erythrocytes
• cell loses its ability to divide - terminal differentiation
55. Cellular differentiation
irreversibility of differentiation ??
• dedifferentiation in plants - a plant callus can evolve whole
plant
• partial dedifferentiation - tissue regeneration
the subject of intense research
