Biomedical 02

Cytoplasmic organelles A- Membranous organelles (:The plasma (cell) membrane (plasmalemma- 1 It is very difficult to seen by light microscope (80-100 Angstrom). By using electron microscope, it shows three layers model Dark layer Light layer Dark layer

Three layers (trilaminar) model;

Cytoplasmic organelles A- Membranous organelles (:The plasma (cell) membrane (plasmalemma- 1 It is very difficult to seen by light microscope (80-100 Angstrom).

By using electron microscope, it shows three layers model Dark layer

Minute pores are present in the cell membrane which are electrically charged

Light layer Dark layer

Three layers (trilaminar) model;

Minute pores are present in the cell membrane which are electrically charged

Molecular structure of cell membrane: It is made of 1) Lipid component:

i- Phosopholipid molecules: a- Heads: (phosphate groups) (hydrophilic) (polar) (charged). b- Tails: (fatty acids) (hydrophobic) (non-polar) (non-charged). Phosphate polar heads

Dark layer

Cytoplasm

Light layer

Fatty acids nonpolar tails

Dark layer Exracellular (intercellular) fluid

Phospholipid bilayer →(Trilamellar membrane) Extracellular fluid

Hydrophillic heads (phosphate groups) (polar)

Bilipid layer

Hydrophobic tails

(fatty acid tails) (non-polar)

Phospholipid Cytoplasm

So, phospholipids are arranged into two layers i.e. form a bilipid layer. Bilipid layer is arranged in trilamellar structure (dark, light and dark layers).

Molecular structure of cell membrane (continue): ii- Cholesterol molecules: a- Hydroxyl radicals: (hydrophilic). b- Steroid nuclei: (hydrophobic). Note: Cholesterol is found in the hydrophobic tails of phospholipid especially to the inner cytoplasmic ones. 2) Protein component: i- : Integral (intrinsic) protein: a- Small molecules: embedded in the lipid bi-layer. b- Large molecules: in the center & extended from both surfaces. ii- Peripheral (extrinsic) protein: loosely attached to both outer and inner surfaces of the cell membrane.

Protein component

Small molecule Small

large molecule Large

molecule

molecul e

Molecular structure of cell membrane (continue): 3) Carbohydrate component: It is polysaccharides. It may be attached to: i- : Protein forming glycoproteins. ii- Phospholipid forming glycolipids. Both glycoproteins & glycolipids are called glycocalyx (cell coat). The following structure of plasma membrane form what is known as:

fluid-mosaic model

which states that membrane is phospholipid bilayer with protein molecules partially or wholly embedded. The following diagrams represent this model.

Plasma (cell) membrane

Extracellular fluid

)fluid mosaic model( glycoprotein glycolipid

carbohydrate

lipid s

protein

cholesterol phospholipid

filaments of cytoskeleton

cytoplasm

Functions of the protein in the plasma membrane: 1) Acts as channels and carriers for selective transport. 2) Acts as enzymes. 3) Acts as receptors 4) Acts as markers (cell identification markers): It allows body cells to distinguish its cells from the foreign ones. 5) Acts for cell adhesion: Protein molecules at the surfaces of the cell serve to bind them together or may be used for attachment with the cytoskeleton inside cells themselves.

Functions of plasma membrane proteins

(1(

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(2(

(5(

(3(

(5(

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