Cell Structure/ Mitosis & Meiosis
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Transcript Cell Structure/ Mitosis & Meiosis
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
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 nonnucleated
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 barrier
Transport
Communication
Recognition
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
Mitochondria
Rough
endoplasmic reticulum
Smooth endoplasmic reticulum
Golgi apparatus
Lysosomes
Cytoskeletal system
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
Biosynthesis
and transport of
proteins and lipids
Flattened sheets or elongated tubules
Content 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
– 5 nm – actin
Intermediate filaments – 10 nm - 6 main
proteins which vary between cells
Microtubules – 25 nm – tubulin
Microfilaments
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 = Mitosis
Resting 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 minutes
Division 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:
number of cells increase
in size (growth) of organ/organism
Replacement of dead cells
Increased
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 Biology
http://www.biology.arizona.edu/cell_bi
o/cell_bio.html