Cell Structuremitosisandmeiosisfor Upload Sept 2006

8/13/2019 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

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