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