Monday, July 9, 2012


Definition of cells : 

They are the structural and functional units of living organisums.

Classes of cells:



*Prokaryotes cellular organisum laking true nucleus 

E.g. bacteria 

*Eukaryotes much larger, more complex , contain nucleus and intra cellular membranes organelles.E.g animals and planet cells.

[b]cell structure


Cell Membrane
• Nucleus
• Cytoplasm
• Mitochondria
• Golgi Complex
• Ribosomes 
• Smooth Endoplasmic Reticulum
• Rough Endoplasmic Reticulum
• Cell Wall
• Chloroplast
• Central Vacuole
• Lysosome

Plant and animal cells
• Both cells have many common components like:
• Nucleus, Mitochondria, ER, Golgi, Ribosome, Plasma
membrane, Cytosol, & Microtubules and microfilaments 
• But Plant Cell has these unique components:
• Cell wall
• Chloroplast
• Central Vacuole
• By contrast, Animal Cell has
• Centrioles (important for cell division)
• Lysosomes (plant cell has peroxisomes and glyoxisomes)

1.Cell membrane: also call as plasma membrane, which is a lipoprotein membrane.

Function: separate cell from environment, allows necessary nutrients and salts to pass into cell and waste products to leave (selective permeable).

2.Cytoplasm: most of the catalyzed reaction of cell metabolism occur. 

3.Ribosomes: protein synthesizing machines.

4. Nucleus :contains the genes.

5.Golgi bodies: it is pack and concentrate products of the cell and secreting waste products .

6. Endoplasmic reticulum (ER):Smooth ER (dose not contain ribosomes)

Rough ER ( contain ribosomes

7.Peroxisomes: contain oxidative enzymes.

8.Lysosome : contain hydrolytic enzymes.

9.Mitochondria: it is power producing plant of all cells. 

cell wall : rigid and strong wall
Protect and maintains the shape of the cell 

VACUOLE (Plant cell):Most plant have one large one
Filled with fluid 
Help maintains pressure and shape of the cell 

CHLOROPLAST (Plant cell): Contains chlorophyll 
Makes plants green 
Uses light energy to make ATP & sugars 
Photosynthesis occur in this organelles 

The difference between prokaryotes and eukaryotes



10-100 micrometers

1 -10 micrometers

Cell size

Contain nucleus and have nuclear membrane

None and dont have nuclear membrane


linear DNA

circular DNA


Have membrane-covered organelles


membrane-covered organelles

Contain mitochondria



Cell membrane

The structure: it composed of lipid bilayer and protein the ratio between them differ according to the type of cell membrane e.g.mitochondria 80%protein and 20%lipid but in myelin membrane of the brain it is 80%lipid and 20%protein.

Membrane lipids

It is composed almost of phospholipids and cholesterol.

The lipid bilayer is arranged as the polar (hydrophilic) head out side and the non polar (hydrophobic) to the in side.

This bilayer is impermeable to the water soluble substances as glucose.

On the other hand fat soluble substances as oxygen can penetrate this layer. 

Membrane proteins

They are two types:

1. Integral proteins: tightly bound to lipid bilayer or as large molecules extend across the bilayer and protrude from both surfaces of the membrane. 

Function: provide the cell membrane with changeable channels through which water soluble substances can pass.

2.Peripheral proteins: attached only to the surface of membrane and don't penetrate it.

There are some CHO present attached to plasma membrane but in small ratio 1-10% in form of glycoprotein and glycolipid

Function of plasma membrane 

Function of plasma membrane 

Øcell recognition and adhesion:

CHO that are attached to cell membrane are responsible of recognition and adhesionØAntigen specificity:

There are glycoprotein located on surface of cell membrane there function are determine the antigen e.g. WBS.s ØEndocytosis &exocytosis:
§Endocytosis: it is up take of materials by a cell from surrounding environment by formation vesicles 

It includes both:A.Phagocytosis ( cell eating )
B.Pinocytosis ( cell drinking) 
§Exocytosis:materails are discharged out of cell by forming vesicles ( opposite of endocytosis ) 
ØOxidative phosphorylation


the cell membrane is selectively permeable material doesnt pass freely across cellular membrane. 

They are transport by different mechanical systems

A- simple diffusion: 

Materials are transported across the membrane along the concentration gradient, so no need for energy (ATP) or carrier.

B-facilitated diffusion:

Materials are transported across the membrane along the conc. Gradient with out use of energy but it require a carrier protein e.g. glucose transport 

C-active transport :

It requires the use of energy to transport material against the concentration gradient e.g. Na/K pump

Best Wishes: Dr.Ehab Aboueladab, Tel:01007834123
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