cell structure/ mitosis & meiosis se shirley dept of pathology
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Cell Structure/Mitosis & Meiosis
SE ShirleyDept 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
Define mitosis and meiosis, and discuss the roles of each in relation to the cell cycle
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 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 Structure
Cell Membrane
Acts as boundary to contain cell contents
Lipid bilayer; phopholipids and cholesterol
Proteins are embedded throughout the bilayer
Cell Membrane
Selective barrierTransportCommunicationRecognition
Nucleus Initiates and regulates
most cellular activities Bound by inner and
outer nuclear envelopes
Contains: DNA (genetic codes) RNA (essential
molecules for protein synthesis)
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
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
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 Cancer cells
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
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
MitochondriaRough endoplasmic reticulumSmooth endoplasmic reticulumGolgi apparatusLysosomesCytoskeletal system
Mitochondria
Organelles of energy productionProducts of carbohydrate, fat and
protein metabolism are oxidized to produce energy
Final product = ATP/adenosine triphosphate
Endoplasmic reticulum and Golgi apparatus
Biosynthesis and transport of proteins and lipids
Flattened sheets or elongated tubulesContent depending on cellular
metabolic activity
Rough endoplasmic reticulum
Series of membranes studded with ribosomes that are the site of protein production.
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
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
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
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 – actinIntermediate filaments – 10 nm - 6 main
proteins which vary between cellsMicrotubules – 25 nm – tubulin
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
Cover body surfaces (skin) and line body cavities and tracts (e.g. respiratory, gastrointestinal)
Functional units of secretory glands
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
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 & Meiosis
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
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
Begins at the completion of one cell division (mitosis) and ends at the completion of the next division
Dividing phase = MitosisResting phase = Interphase
Interphase
Phases:G1 (resting; variable length)(G0 for quiescent cells)S (DNA replication tetraploid DNA
content)G2 (second gap; approx 4-5 hrs)
Mitosis
Thought to be initiated by triggering factors in cytoplasm or from other cells including various growth factors
30-60 minutesDivision of nucleus* (karyokinesis)
and cytoplasm (cytokinesis)
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.
Mitosis
Mitosis facilitates: Increased number of cells increase
in size (growth) of organ/organism Replacement of dead cells
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
The Biology Project at University of Arizona: Cell Biologyhttp://www.biology.arizona.edu/
cell_bio/cell_bio.html