Cell Structuremitosisandmeiosisfor Upload Sept 2006
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Transcript of Cell Structuremitosisandmeiosisfor Upload Sept 2006
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Cell Structure/Mitosis & Meiosis
SE Shir ley
Dept of Patho logy
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Lecture Objectives
At the end of the lecture, the student should
be able to:Describe the stru ctu ral features o f
eukaryo t ic cells
Outline the special ized stru ctu raladaptat ionsof epithelial cells
Define mitos is and meiosis, and discuss
the roles of each in relation to the cell cycle
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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 1665German pathologist, Rudolf Virchow
(18211905) credited with initiating the
study of disease at the cellular level
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The Cell
Eukaryotes: e.g. mammals and other
higher organisms - characterized by the
presence of membrane-bound nucleus
Prokaryotes: e.g. bacteria are non-
nucleatedApproximately 100 billion cells in humans
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Cell Structure
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Cell Membrane
Acts as boundary to contain cellcontents
Lipid bilayer; phopholipids andcholesterol
Proteins are embedded throughoutthe bilayer
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Cell Membrane
Selective barrier
Transport
Communication
Recognition
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Nucleus
Initiates and regulates
most cellular activities
Bound by inner and
outer nuclearenvelopes
Contains:
DNA (genetic codes)
RNA (essential
molecules for protein
synthesis)
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Nucleus
DNA = deoxyribonucleic acid; double helix of
4 deoxyribonucleotidesComplementary 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
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Nucleus
RNA = ribonucleic acidGenetic information in DNA is transcribed
to mRNA (messenger RNA)and translated
in the cytoplasm (protein synthesis), with
help of tRNA (transfer RNA)
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Nucleolus
Sites of ribosome synthesis
Ribosomal DNA is transcribed into rRNA
(r ibosomal RNA)precursor; further
processed into ribosomal subunits which
function in protein synthesis in thecytoplasm
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Normal cell Cancer cells
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The Nucleus in Disease
Hyperchromasia:increased staining of the
nucleus usually due to chromatin (e.g.genetic abnormalities DNA)Active protein synthesis = prominent
nucleol i
Nucleoli assembled from specificchromosomal regions (nucleolar organizer
regions) which may be disturbed in cancer
cells mult ip le/odd shaped nuc leol i
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Cytoplasm
Composed largely of water
Approx. 8% of proteinHigh concentrations of potassium,
magnesium, phosphate (osmotic pressurewithin cells is similar to that of the
extracellular fluid)Membrane-bound structues = organel les
Filaments and granules
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Organelles
Mitochondria
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
Golgi apparatusLysosomes
Cytoskeletal system
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Mitochondria
Organelles of energy production
Products of carbohydrate, fat and
protein metabolism are oxidized to
produce energy
Final product = ATP/adenosine
triphosphate
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Endoplasmic reticulum and
Golgi apparatus
Biosynthesis and transport ofproteins and lipids
Flattened sheets or elongated tubules
Content depending on cellularmetabolic activity
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Rough endoplasmic reticulum
Series of membranes studded withribosomes that are the site of protein
production.
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Smooth endoplasmic reticulum
Series of membranes without
attached ribosomes that function insynthesis of lipids and processing of
proteins (including steroid,
carbohydrate and drug metabolism)
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Golgi apparatus
Series of flattened sacs and vesicles
that functions in the modification andpackaging of material synthesized in
the endoplasmic reticulum
Examples: addition of sugars,proteolysis of proteins , sorting of
macromoleciles
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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
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Cytoskeletal system
Internal scaffolding: system of filaments
and microtubules provides rigidity, aswell as allows for movement within the
cell (e.g. excretion of material) and
locomotion
Microf i laments 5 nm actin
Intermediate f i laments 10 nm - 6 main
proteins which vary between cel ls
Microtubules25 nm
tubul in
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Intermediate filaments
Cytokerat in- epith elial cel ls
Desmin sm oo th/skeletal musc les
Glial f ibr i l lary acidic protein astrocytes
Neuro f i lament pro tein neurone
Nuclear lam in - nuc leus
Viment in mesenchymal cel ls
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Epithelial cells
Cover body surfaces (skin) and linebody cavities and tracts (e.g.
respiratory, gastrointestinal)
Functional units of secretory glands
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Epithelial Cell Specialization
Cell surface projections
Cilia: facilitate transport along cell surfaceMicrovilli: increase surface area for
absorption
Secretory adaptationsWell developed ER and Golgi apparatus
Cell junctions
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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)
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Mitosis & Meiosis
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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 onesex chromosome; X in ova and either X or
Y in spermatozoa)
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Cell cycle
Begins at the completion of one celldivision (mitosis) and ends at the
completion of the next division
Divid ing phase = Mitosis
Resting phase = Interphase
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Interphase
Phases:G1 (resting; variable length)
(G0 for quiescent cells)
S (DNA replication tetraploid DNA
content)
G2 (second gap; approx 4-5 hrs)
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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)
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Mitosis
Prophase:condensation and shorteningof chromosomes/formation of mitoticspindle cell apparatus: centrosomes with
intervening microtubules
Metaphase:centromeres attach to centre
of apparatus
Anaphase:centromeres split and eachhalf of chromosome (chromatid) move to
opposite pole
Telophase:nuclear membrane reforms.
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Mitosis
Mitosis facilitates:
Increased number of cells increase
in size (growth) of organ/organism
Replacement of dead cells
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Meiosis
Crossover eventsare possible between
maternally and paternally derived
chromosomal material
Chiasmata = points of junction of the
exchanged segments Each gamete contains a haplo id num ber of
chromosomes(pairing at fertilization will
result in restoration of diploid number)
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Info on the Web
The Biology Project at University ofArizona: Cell Biology
http://www.biology.arizona.edu/cell_bi
o/cell_bio.html