1_ultra structure of cell

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ULTRA STRUCTURE OF CELLRef: 1. Cell & Molecular BiologyCh.1, Cell Theory & The Cell

HISTORY

Aristotle (384-322 BC)All animals & plants consists of certain structural units

Robert Hooke (1665)term Cell derived from Greek words

Kytos = Cell, Cella = Hollow space

Observed cells first time in a piece of cork under

a very primitive microscope.

Grew & MalphigiObserved cells in the form of cavities with cellulose wallsin different plants.

Leeuwenhoek (1674)Discovered free cells & observed some organization

within these cells.

CellStructural unit, unit of life.

Cell theoryCell is the basic unit of life.

Dutrochetgave the idea of cell theory.Schleiden M.I.German botanist (1839)- outlined the basic features of cell theory

Schwann T.German zoologist

R. Virchow (1858)Extended cell theory

All living cells arise from pre-existing living cells.

Earlier belief was spontaneous generation of life.


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Louis Pasteurgave experimental evidence to Virchows theory

Two components of cell theory :

i) Living things are composed of cells

ii) All cells arise from pre-existing cells

Large no.of sub-cellular structures have been discovered & studied.

Cell is no longer a basic units of life, because life may exist without cells also

VirusesInfectious, sub-cellular & ultramicroscopic particle representing potentially

Pathogenic agents which replicate in host cells.

Animal & plant viruses, bacteriophageslack internal organization of a cell.Outside the cell they are just like non-living inert particle.

Viruses, Mycoplasma, Viroids, Prions, VirusoidsThey dont fit in definition of a cell

and described as living chemicals or cellular forms that have not reached a cellular state.

Protozoa & AlgaeDont fit in the definition of cell theory.

Paramecium, a protozoan; Rhizopus, a fungus & in Vaucheria, an algaLiving substance

is enclosed in a wall &^ there is hardly any organization.

Great amount of variability

Amoeba & Leukocyteschange their shapes frequently

BacteriaRods, Spirals, comma

AlgaeDiatoms, DesmidsTake varied shape

AcetabulariaSingle celled algastalk & cap

Cell shape:

Exceptions to cell theory:


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Multicellular organismspartly controlled by pressure of the cells exert against

each other

Cell shape may be based on function eg. Glandular hairs, guard cells, root hair cells.

Stability to cell shapeby cytoskeleton associated with inner surface ofplasma membranemembrane skeleton

Cell size:Varies greatly in various plants and animals

Smaller cellsbacteria, 0.2-5 (light microscope)

Larger cellsEgg of an ostrich 6 outside 3 when shell removed

Cell size also depends on size & no.of chromosomes

Volume increases as a cube of a radius, while surface area increases

as a square of a radius

Cell volume is constant for a cell type called Law of constant volume

Cell Number:

Single (unicellular) to 60,000 billion (human, 80 kg)

No. of cells in most multicellular organisms is indefinite

No. of cells is fixed in organisms like Pandorina (8, 16, 32 or 64 cells) &

Eudorina (16, 32 or 64 cells)


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Prokaryotic vs Eukaryotic cells

Prokaryoteswith no organized nucleus eg. Bacteria, BGA

Eukaryoteswith organized nucleus & having nuclear envelope eg. Higher organisms

Thermophile / Archaeon

Bacteria Archaea Eukarya

ArchaeaDiscovered in 1977, descibed as Archaebacteria

Prokaryotesdivided into Eubacteria & Archaebacteria

Archaea is distinct from bacteria & eukaryotes

Living cells are divided intoBacteria, Archaea and Eukarya

Conclusively proved in 1996, when genome of an archaeon Methanococcus jannaschii

was fully sequenced & compared with sequence of genomes of bactria and eukaryotes


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Feature Prokaryote Eukaryote

1 Cell size & organization 1-10 , unicellular 5-100 , multicellular

2 Organelles Few or none Nucleus, Mitochondria, Chloroplast,

Endoplasmic reticulum, Golgi

apparatus

3 DNA Circular/linear DNA

in a nucleiod

Linear organized in chromosomes

bounded in a nucleus

4 Synthesis of RNA &protein

In samecompartment

RNA synthesized & processed innucleus and protein synthesized in

cytoplasm

5 Cytoskeleton Absent Present

6 Spindle apparatus in

cell division

Absent, replicated

DNA pulled byattachment to

plasma membrane

Present, chromosome pulled by

spindle apparatus

7 Metabolism Anaerobic / Aerobic Aerobic


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i) 56% genes are new to science

ii) Lives at temperature 48-94 C, pressure >200 atmosphere, autotroph utilizing CO2,

N2 and H and produces methane. Oxygen kills it.

iii) Some arhaeon genes resemble bacteria and others resemble eukaryotes and others

completely new to science.

Archael system is more like eukaryotic system

Belief that common ancestor of all modern living creatures was a thermophile,

which branched off >3.6 billion years ago into 3 life forms, prokaryotes, arhaea &eukarya

Novel features of archaeon:


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Eukaryotic cellsare organized into compartments, cell organelles

Nucleuscontrols all activities of cell

Plastidsinvolved in formation & storage of carbohydrates

MitochondriaPower house of cell & supply energy

Endoplasmic reticulumactive role in protein synthesis & transport

Ribosomessite of protein synthesis

Endosomes

Lysosomesrich in enzymes & lytic in nature

Golgi bodiessecretory in nature

Peroxysome & Hydrogenosomes

Centrosomeorganization & function of spindle apparatus

Cytosolarea of cell excluding all membrane bound cell organelles

Organellesclosed compartments

Mitochondria & choloroplasthave their own replicating machinery like nucleus

and are independent

DNA is found in them & their function is similar to nuclear DNA.

Eukaryotic cells


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http://en.wikipedia.org/w/index.php?title=File:Chloroplast_diagram.svg&page=1

1_ultra structure of cell

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