Lect 5 Nucl Chromatin Cell Cycle New PDF

 Lecture content Structure of the nucleus Human chromosomes The Cell Cycle Mitosis & Meiosis Cell Renewal Stem cell Cell Death  Learning objectives Define Describe Describe Compare Define De...

 Lecture content Structure of the nucleus Human chromosomes The Cell Cycle Mitosis & Meiosis Cell Renewal Stem cell Cell Death  Learning objectives Define Describe Describe Compare Define Describe Define Describe the Compare the different structure and structure between Define components correlated and the different function of extended & stages of of interphase correlated nuclear condensed cell cycle nucleus. function of envelop chromatin chromatin Define Compare Define Describe Underline Define mitosis Describe Define Compare and meiosis the role of apoptosis between Define stem and Describe stem cells and clarify mitosis and cells in tissue its phases of meiosis renewal importance mitosis  Nucleus The number varies; mostly one nucleus RBCs devoid of nucleus binucleated (hepatocytes) multinucleated e.g. skeletal muscle cells, osteoclasts shapes; spherical, oval, kidney-shaped, lobulated or flattened.  Nucleus location: centrally peripherally (eccentric) basally (close to basal surface of the cell) The size of the nucleus varies; it may be small or large (5-10μm in diameter). There is a constant ratio (nucleo – cytoplasmic ratio) between the size of the nucleus and the size of the cytoplasm.  Nucleus L.M Basophilic structure due to nucleic acids (DNA & RNA) Vesicular nucleus Condensed nucleus Pale [In nerve cells] Dark [In lymphocytes]  Nuclear Envelope E.M: Double membrane separated by perinuclear space [30-50 nm] Outer membrane & perinuclear space are continuous with rER Outer & Inner membranes fuse at intervals forming Nuclear pores [3000-4000 pores in one growing cell] Nuclear pores are closed by diaphragms Nuclear pores regulate passage of substances between nucleus & cytoplasm in both directions  Nucleoplasm [Nuclear sap] -The clear homogenous ground substance of the nucleus -Contains nucleotides for DNA formation & enzymes Acts as transport medium ….Carry ribosomes from nucleus to cytoplasm Nuclear pore  Cytoplasm Thick filaments Ribosomes Outer nuclear Cytoplasmic ring membrane Middle ring Perinuclear space Inner nuclear Nuclear ring membrane Nuclear basket Central granule Nucleus Cytoplasm 4 7 1 3 9 2 8 5 6 Nucleus  Chromatin The genetic material Formed of Nucleoprotein (DNA + Histone) Forms chromosomes during cell division  Peripheral heterochromatin Chromatin Nucleolus associated islets heterochromatin  Nucleolus L.M. Dark basophilic due to concentrated rRNA [The site of formation of rRNA] One, two or no nucleoli according to cell’s activity E.M. Nucleolar Organizer or Fibrillar centers [FC]: Contain DNA filaments carrying rRNA genes Pars fibrosa[F]: Contain newly formed rRNA Pars granulosa[G]: Contain granules of mature rRNA  Functions of the Nucleus 1.Controls all cell functions [mainly protein synthesis] 2.Storage of genetic information 3.Formation of the three types of RNA 4.Controls cell division  Nuclear changes indicating cell death It is a shrinkage of nuclear material which appears darkly- Pyknosis stained. Pyknosis Karyorrhexis the nucleus disintegrates into tiny fragments Karyorrhexis the nucleus dissolves and disappears Karyolysis (nuclear fading). Karyolysis  Apoptosis ▪ It is a programmed single cell death ▪ It occurs in living tissues to regulate cell renewal and growth ▪ The nucleus undergoes pyknosis, karyorrhexis then karyolysis. ▪ The cytoplasm is fragmented into apoptotic bodies which are rapidly engulfed by adjacent cell or macrophages. ▪ Apoptosis occurs in embryos (for shaping of developing organs) and in the thymus (to destroy T lymphocytes which can react against self-antigens). Medical application Apoptosis is a protective mechanism against cancer as most cells undergo apoptosis when major changes occur in their DNA.  Human Chromosomes Chromosomes are chromatin fibers that become condensed & tightly packed during mitosis and meiosis → Become visible with light microscope Each chromosome is formed of 2 chromatids connected at centromere Kinetochores are 2 discs of protein located on centromere for attachment of spindle fibers during cell division DNA molecules coiled around histone and non-histone proteins 2 nm 10 nm 30 nm 300 nm 700nm  Human Chromosomes Each chromatid is formed of DNA molecules coiled around histone and non-histone proteins Genes are segments of DNA that code for formation of specific proteins Telomeres are regions of repeated sequence at the end of chromosomes which protects it from destruction  karyotyping Telocentric Straight or Submetacentric acrocentric chromosomes Metacentric chromosomes chromosomes club – like chromosomes the centromere at unequal arms and have (L) having one. a very short arm arms almost equal in length and the ends shape in the anaphase stage. and a much longer are thus V- shaped in anaphase  To identify chromosome abnormalities as the cause of karyotyping malformation or disease Karyotyping is very helpful method for studying chromosomes.. In this method a number of dividing cells in a tissue culture treated with colchicine which arrests the division at metaphase At this stage, chromosomes are short and clear They are photographed and each chromosome is cut Homologous chromosomes are put together and the whole set is arranged according to the length of each pair  Gap interphase Gap G1 S G2 Growth Synthesis Growth Preparation for DNA replication Organelles Cytosolic components (proteins Enzymes, and RNAs are synthesized, and, more proteins, especially the centromere and the DNA ATP, other components) replication centrioles  PREPRATORY STAGE BEFOR CELL DIVISION INCREASE CELL SIZE & DNA DUPLICATION Metabolically active cell, duplicate its organelles and cytosolic components G0 2 sisters chromatids held at centromere Resting stage G0 Enzyme & protein synthesis, ATP production, centrioles replicate somatic cells contain 46 chromosomes organized into 23 pairs. gametes are haploid cells that contain 23 chromosomes  Mitosis Prophase Metaphase Anaphase Telophase d-Chromosomes are Chromosomes uncoil & shortened & thickened lengthen → Become invisible Nucleolus & Nuclear Nuclear membrane and membrane disappear nucleoli reappear  Mitosis Prophase Metaphase Anaphase Telophase equator splitting cytokinesis Centrioles move to 1.Chromosomes arrange d-Chromosomes split in cell equator longitudinally by pulling opposite poles of cell of mitotic spindle → Constriction at cell 2.Kinetochore develops Mitotic spindle radiates at centromere for Chromatids [s- equator → divides the out from MTOC attachment of mitotic chromosomes] cytoplasm & organelles spindle separate into 2 identical cells  Mitosis 1. Prophase 1. d-Chromosomes are shortened & thickened 2. Nucleolus & Nuclear membrane disappears 3.Centrioles move to opposite poles of cell 4. Mitotic spindle radiates out from MTOC 2. Metaphase 1.Chromosomes arrange in cell equator 2.Kinetochore develops at centromere for attachment of mitotic spindle 3. Anaphase d-Chromosomes split longitudinally by pulling of mitotic spindle → Chromatids [s-chromosomes] separate 4. Telophase 1. Constriction at cell equator → divides the cytoplasm & organelles into 2 identical cells Cytokinesis 2. Chromosomes uncoil & lengthen → Become invisible 3. Nuclear membrane and nucleoli reappear D (double)-Chromosomes, s (single)- chromosome  Meiosis Reduction Division Def: Special cell division → Formation of gametes (homologous chromosomes) [sperms or ova] with haploid number of chromosomes (23 single chromosomes) Chromosomes arrange as 23 pairs (bivalents) Bivalents chromosome Each bivalent [one from Chiasma Bivalents mother, one from father] chromosome exchange the genetic material in a process called [Crossover] The region of crossover is called Chiasma meiosis II meiosis I 23 pairs of chromosomes (46 chromosomes) 23 chromosomes 23 single chromosomes 23 pairs of chromosomes (46 chromosomes) 23 chromosomes 23 single chromosome 32 pairs of chromosomes (64 chromosomes) In prophase II, two chromatids attached to a common centromere. In metaphase II, chromosomes move to the metaphase plate (equator), and centromeres start to divide. In anaphase II, the divided centromeres Chromosomes (23 pairs (bivalents)) pull sister chromatids to opposite polesthe genetic material in a process called [Crossover] Each bivalent exchange The region of crossover is called Chiasma After telophase II and cytokinesis II, cell division is complete, producing haploid daughter cell 23 chromosomes  Cell renewal STEM cells are undifferentiated cells that have the ability to self- renew and differentiate into various specialized cell types. Self-renewal refers to the ability of stem cells to divide and produce identical copies of themselves, ensuring a continuous supply of stem cells. This process is crucial for maintaining the stem cell population in the body. Microenvironment Stem cells ECM morphogenic self-renewal factors growth differentiation factors small cell lifespan (hours molecules to years) cytokines Cell death  Stem cell classification origin 1-embryonic stem cell 2- induced stem cell 3-adult stem cell renewal capacity (Labile cells (continuos renewal), Stable cells (Low renewal), Permanent cells (no renewal). Potency (types of cells) 1-totipotent, "ability for all” 2-pluripotentia, "ability for many 3-Multipotent differentiate into discrete cell types 4-oligopotent differentiate into a few cell types. 5-unipotent differentiate into a only one cell types.  Types of stem cells 2- Induced 1-embryonic stem cells pluripotent stem 3-Adult stem cells cells (iPSCs) they derived from early-stage iPSCs are artificially generated by reprogramming from a non- They are found in embryos pluripotent cell various tissues totipotentia, "ability for all” pluripotentia, "ability for many Multipotent differentiate into discrete cell types oligopotency differentiate into a few cell types.  Clinical applications Stem cells have shown great potential in regenerative medicine. For example, stem cell therapies have been explored for conditions such as spinal cord injuries, heart disease, diabetes, and neurodegenerative disorders like Parkinson's and Alzheimer's disease.  Apoptosis Def: Programmed single cell death [or small group of cells] Removal of cells with severe DNA damage [By viruses, oxidants, chemicals, radiation,……] Protect against development of cancer Mention the role of mitochondria in Apoptosis?  Necrosis Death of group of cells within living organ due to pathological condition Causes: Hypoxia, bacterial toxins, excess heat,……  Summary Structure of the nucleus Human chromosomes The Cell Cycle Mitosis & Meiosis Cell Renewal Stem cell Cell Death