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Cell Structure/ Mitosis & Meiosis. SE Shirley Dept of Pathology. Lecture Objectives. At the end of the lecture, the student should be able to: Describe the structural features of eukaryotic cells Outline the specialized structural adaptations of epithelial cells

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cell structure mitosis meiosis

Cell Structure/Mitosis & Meiosis

SE Shirley

Dept of Pathology

lecture objectives
Lecture Objectives
  • At the end of the lecture, the student should be able to:
    • Describe the structural features of eukaryotic cells
    • Outline the specialized structural adaptations of epithelial cells
    • Define mitosis and meiosis, and discuss the roles of each in relation to the cell cycle
the cell
The Cell
  • Basic unit of structure and function in living organisms
  • Derived from Latin cella –little room
  • First used in a biologic sense by Robert Hooke in 1665
  • German pathologist, Rudolf Virchow (1821–1905) credited with initiating the study of disease at the cellular level
the cell4
The Cell
  • Eukaryotes: e.g. mammals and other higher organisms - characterized by the presence of membrane-bound nucleus
  • Prokaryotes: e.g. bacteria are non-nucleated
  • Approximately 100 billion cells in humans
cell membrane
Cell Membrane
  • Acts as boundary to contain cell contents
  • Lipid bilayer; phopholipids and cholesterol
  • Proteins are embedded throughout the bilayer
cell membrane7
Cell Membrane
  • Selective barrier
  • Transport
  • Communication
  • Recognition
nucleus
Nucleus
  • Initiates and regulates most cellular activities
  • Bound by inner and outer nuclear envelopes
  • Contains:
    • DNA (genetic codes)
    • RNA (essential molecules for protein synthesis)
nucleus9
Nucleus
  • DNA = deoxyribonucleic acid; double helix of 4 deoxyribonucleotides
    • Complementary base pairing of adenine(A) with thymine (T) and cytosine (C) with guanine (G)
    • Held together by hydrogen bonds
    • Attached to sugar phosphate backbone
  • Chromatin = chromosomal material = DNA, histones, non-histone proteins, RNA
nucleus10
Nucleus
  • RNA = ribonucleic acid
    • Genetic information in DNA is transcribed to mRNA (messenger RNA) and translated in the cytoplasm (protein synthesis), with help of tRNA (transfer RNA)
nucleolus
Nucleolus
  • Sites of ribosome synthesis
    • Ribosomal DNA is transcribed into rRNA (ribosomal RNA) precursor; further processed into ribosomal subunits which function in protein synthesis in the cytoplasm
normal cell
Normal cell

Cancer cells

the nucleus in disease
The Nucleus in Disease
  • Hyperchromasia: increased staining of the nucleus usually due to chromatin (e.g. genetic abnormalities DNA)
  • Active protein synthesis = prominent nucleoli
  • Nucleoli assembled from specific chromosomal regions (nucleolar organizer regions) which may be disturbed in cancer cells  multiple/odd shaped nucleoli
cytoplasm
Cytoplasm
  • Composed largely of water
  • Approx. 8% of protein
  • High concentrations of potassium, magnesium, phosphate (osmotic pressure within cells is similar to that of the extracellular fluid)
  • Membrane-bound structues = organelles
  • Filaments and granules
organelles
Organelles
  • Mitochondria
  • Rough endoplasmic reticulum
  • Smooth endoplasmic reticulum
  • Golgi apparatus
  • Lysosomes
  • Cytoskeletal system
mitochondria
Mitochondria
  • Organelles of energy production
  • Products of carbohydrate, fat and protein metabolism are oxidized to produce energy
  • Final product = ATP/adenosine triphosphate
endoplasmic reticulum and golgi apparatus
Endoplasmic reticulum and Golgi apparatus
  • Biosynthesis and transport of proteins and lipids
  • Flattened sheets or elongated tubules
  • Content depending on cellular metabolic activity
rough endoplasmic reticulum
Rough endoplasmic reticulum
  • Series of membranes studded with ribosomes that are the site of protein production.
smooth endoplasmic reticulum
Smooth endoplasmic reticulum
  • Series of membranes without attached ribosomes that function in synthesis of lipids and processing of proteins (including steroid, carbohydrate and drug metabolism)
golgi apparatus
Golgi apparatus
  • Series of flattened sacs and vesicles that functions in the modification and packaging of material synthesized in the endoplasmic reticulum
  • Examples: addition of sugars, proteolysis of proteins , sorting of macromoleciles
lysosomes
Lysosomes
  • Organelles containing a range of lytic enzymes that are involved in the digestion of unwanted extrinsic as well intrinsic material
  • Enzymes include nucleases, proteases, lipases, phosphatases
cytoskeletal system
Cytoskeletal system
  • Internal scaffolding: system of filaments and microtubules provides rigidity, as well as allows for movement within the cell (e.g. excretion of material) and locomotion
    • Microfilaments – 5 nm – actin
    • Intermediate filaments – 10 nm - 6 main proteins which vary between cells
    • Microtubules – 25 nm – tubulin
intermediate filaments
Intermediate filaments
  • Cytokeratin- epithelial cells
  • Desmin – smooth/skeletal muscles
  • Glial fibrillary acidic protein – astrocytes
  • Neurofilament protein – neurone
  • Nuclear lamin - nucleus
  • Vimentin – mesenchymal cells
epithelial cells
Epithelial cells
  • Cover body surfaces (skin) and line body cavities and tracts (e.g. respiratory, gastrointestinal)
  • Functional units of secretory glands
epithelial cell specialization
Epithelial Cell Specialization
  • Cell surface projections
    • Cilia: facilitate transport along cell surface
    • Microvilli: increase surface area for absorption
  • Secretory adaptations
    • Well developed ER and Golgi apparatus
  • Cell junctions
cell junctions
Cell junctions
  • Specialized junctional areas between epithelial cells allow for:
    • Adherence to each other
    • Communication channels
  • Three types of junction:
    • Occludens type/tight junction (barrier)
    • Nexus/gap junction (2nm; communication)
    • Adherens type (20nm; adhesion)
mitosis
MITOSIS
  • Mechanism of cell division leading to the production of two daughter cells with exactly the same number of chromosomes and DNA content as parent cell
  • Diploid number of chromosomes = 46; 22 pairs of autosomes and 1 pair of sex chromosomes; XX in females; XY in males)
meiosis
Meiosis
  • Specific type of cell division leading to the production of gametes (ova and spermatazoa)
  • Each gamete contains a haploid number of chromosomes (23; 22 autosomes and one sex chromosome; X in ova and either X or Y in spermatozoa)
cell cycle
Cell cycle
  • Begins at the completion of one cell division (mitosis) and ends at the completion of the next division
    • Dividing phase = Mitosis
    • Resting phase = Interphase
interphase
Interphase
  • Phases:
    • G1 (resting; variable length)
    • (G0 for quiescent cells)
    • S (DNA replication  tetraploid DNA content)
    • G2 (second gap; approx 4-5 hrs)
mitosis32
Mitosis
  • Thought to be initiated by triggering factors in cytoplasm or from other cells including various growth factors
  • 30-60 minutes
  • Division of nucleus* (karyokinesis) and cytoplasm (cytokinesis)
mitosis33
Mitosis
  • Prophase: condensation and shortening of chromosomes/formation of mitotic spindle cell apparatus: centrosomes with intervening microtubules
  • Metaphase: centromeres attach to centre of apparatus
  • Anaphase: centromeres split and each half of chromosome (chromatid) move to opposite pole
  • Telophase: nuclear membrane reforms.
mitosis34
Mitosis
  • Mitosis facilitates:
    • Increased number of cells  increase in size (growth) of organ/organism
    • Replacement of dead cells
meiosis35
Meiosis
  • Crossover events are possible between maternally and paternally derived chromosomal material
  • Chiasmata = points of junction of the exchanged segments
  • Each gamete contains a haploid number of chromosomes (pairing at fertilization will result in restoration of diploid number)
info on the web
Info on the Web
  • The Biology Project at University of Arizona: Cell Biology
    • http://www.biology.arizona.edu/cell_bio/cell_bio.html