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Rabu, 22 Mei 2013

CELL



A cell is the basic unit of life. The modern cells theory states that :
All living organism are made up of one or more cells.
New cells are formed by the division  of pre existing cells.
Cells contain genetic material of an organism which is passed from parent to daughter cells.
All metabolic reaction take place with in cell.

A cell consists of protoplasm surrounded by plasma membrane. Some organism have a non living cell wall on outer most layer. Some organism are unicellular, they are made up of just one cell. Other organism are multicellular and consists of many cells. Cells is divided into 2 categories :
a.       Prokaryotic cells, (pro, before; karyon, nucleus) which include bacteria and archae have DNA enclosed by nucleus membrane and lack organelles bounded by a double membrane.
b.      Eukaryotic cells (eu, true) which include the protoctists, fungi animals and plants have chromosomes surrounded by well defined nuclear membranes.



Table the different of prokaryoict and eukaryotic


Prokaryotic
Eukaryotic
Examples are bacteria
Examples are plants

Average diameter of cell 0,5-5 µm
Average diameter of cell 10- 100 µm

Genetic materials is circular double strand of DNA not surrounded by double membrane nuclear envelope.
Most DNA are associated with histone protein to form chromosomes. Chromoshomes are surrounded by double membrane nuclear envelope . Circular DNA are present in mithocondrion and choloroplast.

Some bacteria have small circular DNA called plasmid
Plasmid are absent.


Few organelles. No double membrane bound organelle such as mitochondrion and chloroplast.
Many organelle . Presence of double membrane organelle such as nucleus, mitochondrion and choolroplast in plant and algae

 No mitosis or meiosis
No spindle formation, just binary division
Mitosis, meiosis or both can occur. There is spindle formation.

Ribosomes are smaller, 70 Svedberg. ribosomes occur as free particles in cytoplasma
Ribosomes are larger, 80 Svedberg. Ribosomes occur as free particle or are bounded to endoplasmic reticulum

Rigid cell walls containing murein (peptidoglycan)
Cell walls of plants and algae contain cellulose, fungi contain chitin and animal cells have no cell walls.

Mesosomes in bacteria and plasma membrane of cyanobacteria contain respiratory enzym. No mithocondrion
There are no mesosomes . Mitochondria function as sites for cellular respiration  to produce ATP

Some prokaryotic are photoautrotophs. Photosinthetic membranes not staked into grana. No chloroplast

Chloroplast containing  grana
Flagella, if present, contain flagellin and lack of microtubules.
Flagella, if present have a “9 + 2” formula arrangement of microtubules

Some prokaryotic cells have enzym that can fix atmospheric nitrogen for use in amino acid synthesis
Eukaryotic cells do not contain enzym that can fix atmospheric nitrogen


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