CYTOLOGY : CYTOLOGY Prepared by
3sam Mo7amed CELL MEMBRANE Cell Membrane : Cell membrane is one of the most important components of the cell; it founds in all cells, it also called Plasma membrane, Plasmalamella or Phospholipids bilayer.
Membrane that enclose cell organelles, and
separate them from the external environment.
Thin membrane (Its size ranging between 7.5: 10 nm) seen by electron microscope as two thick layers and there is a pale layer between them. Cell Membrane Cell membrane Structure : Structure Cell membrane consists of three main components:-
- 42% Lipids.
- 55% Proteins.
- 3% Carbohydrates. 1. LIPIDS:- : 1. LIPIDS:- Lipids consist of:-
Phospholipids are a major component of
cell membrane; it is appear as two distinct
Hydrophilic head on the outside (Associated
with water or charged molecule, because of
the presence of phosphate radical).
Hydrophobic tails on the inside (Not associated
with water nor charged molecule, because of the presence of fatty acids radical).
Cholesterol insoluble in water because of the presence of hydroxyl radical. 2. PROTEINS:- : 2. PROTEINS:- Proteins are globular masses floating in the lipid bilayer of cell membrane. It is classified into:-
Integral protein:- In which the protein span the width of the membrane entirely one or more times.
Peripheral protein:-In which the protein is partially embedded in the membrane phospholipids. 3. CARBOHYDRATES:- : 3. CARBOHYDRATES:- Carbohydrates form complex molecules with proteins and lipids (Glycoproteins and Glycolipids) on the outer surface of the membrane.
- Functions of carbohydrates:-
1-Many of carbohydrates are negative charged that give the cell surface its negative charge which repels other negative charge objects.
2-Work as receptors for extra cellular compounds.
3-Some of carbohydrates enter into immune reactions. THE GENERAL FUNCTIONS OF THE CELL MEMBRANE : THE GENERAL FUNCTIONS OF THE CELL MEMBRANE 1.Separate the inside organelles from the external environment.
2.Regulate the entrance and exit of substances.
3.Transfer of information.
4.Establishment of electric potential difference.
5.Site of biological activities.
6.Attachment between cells.
7.Removal of wastes. The transporting of materials through the cell membrane : The transporting of materials through the cell membrane Cell membrane work as a gate keeper for the entrance and exit substances, As some substances pass from cell membrane easily, others pass more difficult, and others can't pass through cell membrane, this selective passage (selective permeability) because of the conditions outside the cell are different from inside. outside cell inside cell sugar H2O salt NH3 lipid The transporting of materials through the cell membrane : The transporting of materials through the cell membrane If substances move from high concentration to low concentration that's called passive transport, but if the substances move from low concentration to high concentration required energy for transporting this process called active transport, also substances can enter and exit the cell by endocyosis and exocytosis.
From the previous we can know that; there are three ways for transporting of substances through the cell membrane:-
3.Exocytosis and endocyosis. 1. PASSIVE TRANSPORT:- : 1. PASSIVE TRANSPORT:- I-Diffusion:- 1. PASSIVE TRANSPORT:- : 1. PASSIVE TRANSPORT:- II-Osmosis:- 2. ACTIVE TRANSPORT:- : 2. ACTIVE TRANSPORT:- The most active transport mechanism in the body is the transport of sodium ions out of the cell and at the same time pump the potassium ions to the inside, this mechanism is called sodium-potassium pump, this pump is responsible for maintain the sodium and potassium concentrations inside cell.
-Functions of the sodium-potassium pump:-
1.It has three receptor sites for binding sodium ions on the portion of the protein that move to the interior of the cell.
2.It has two receptor sites for potassium ions on the outside.
3.The inside portion of this protein adjacent to or near to the sodium binding sites has ATP activity. Summary the cell membrane transport mechanism : Summary the cell membrane transport mechanism High concentration Low concentration High concentration High concentration Low concentration Low concentration lipid bilayer opining Protein carrier sodium-potassium pump Simple diffusion Facilitated diffusion Active transport ATP 3. EXOCYTOSIS AND ENDOCYTOSIS:- : 3. EXOCYTOSIS AND ENDOCYTOSIS:- Thank you for your attention : Thank you for your attention References
Essentials of anatomy & physiology
Pro:-Martini / Bartholomew
P: 61, 62
Integral principles of zoology
P: 46:50 Working team
Mohsen Tolba Best wishes
3sam Mo7amed Websites