The model was proposed by Singer & Nicolson in 1972
Structure of membrane –
7-10 nm (70 to 100 A) in thickness.
Tri layered structure- two electrons dense and one electron lucent layer
Lipids --- 40%.
Phospholipids (Phosphatidyl choline, Phosphatidyl ethanolamine, Sphyngomyeli etc.)
Functions : major barrier to water soluble sub. like urea, glucose & ions. but alcohol, oxygen & carbon dioxide can easily pass
Proteins -- 50%
A. Integral proteins: run throughout the mem. & act as channel, carriers etc.
B. Peripheral proteins: mostly present inside of the mem. & act as enzymes
Have –ve charge so makes cell surface –ve that repels negative objects
Glycocalyx causes attachment of cells to each other
Some carbohydrates enter into immune reaction
Many act as receptors for binding hormones like insulin
Most accepted model is FLUID MOSAIC model of Singer and Nicolson(1972)
2 Selective permeability
4 Links adjacent cells together
5 Forms glycocalyx
6 Partcipate in immune response
Channels-voltage gated, ligand gated
Contribute to cytoskeleton
Serves as enzymes
Cytoplasm is aqueous substance in which organelles are dispersed.
Organelles are permanent components bounded by limiting membrane. These are:
Mitochondria, endoplasmic reticulum, ribosomes, golgiapparatus peroxisomes, centrosomes, lysosomes and centrioles
Mitochondria (power house) makes ATP available
RER - involved in protein synthesis
SER -Site of lipid synthesis
-Contains enzymes controlling glycolysis
Also contain detoxifying enzymes
Ribosomes attached to RER & composed of RNA
- Protein synthesis
- Concen. of proteins & polysaccharides
- Packaging & formation of vesicles
- Completion of glycoprotein synthesis
Lysosomes: intracellular digestive system, contain about 50 different hydrolytic enzymes
- Make defense system of body
- Bacteria & debris of dead tissues taken up by the cells are destroyed
Peroxisomes: contain oxidases mainly present in kidney & liver cells.
- Detoxify drugs & neutralize free radicals
- Catalase one of the enzymes, breaks toxic hydrogen peroxide into water & oxygen
Centrioles: initates cell division
-Responsible for transmission & expression of genetic information
-Cell reproduction & multiplication
-Synthesis of RNA
Chromatin: network of threads composed of DNA & proteins
Chromosomes: thread like st. formed from chromatin at the time of cell division. Pass genetic information
-There are 23 pairs of chromosomes. 22 are somatic & one pair of sex chromosomes
Cytoplasmic inclusions (temporary components) are also present. They are not living st.
1. Stored foods
Fat as droplets in a section they look like signet ring
Glycogen can only be stained by PAS (periodic acid-Schiff) & gives a brilliant red colour
Proteins rarely stored
2. Secretary granules like digestive enzymes synthesized in cytoplasm
A Endogenous pig.
Hemoglobin & it’s derivatives eg. Hemosiderin,
B Exogenous eg. lipofusin, dust, minerals like lead or silver