Cell membrane, Biology

Assignment Help:

CELL MEMBRANE

As discrete units of life  all living cells are separated from each other and from their external environment by an  extremely delicate (75 A to 100 a= 0.00075 to 0.001 thick ) covering  membrane invisible under  light  microscope. The covering is called cell membrane,  plasma membrane,  cytoplasmic  membrane or plasmalemma . Its  presence was presumably  visualized by Naegeli and Cramer(1855)  and confirmed by  E. Overton(1899) who believed   that it was a double layer of lipid molecules .Since  then, scientists have been making efforts to properly  elucidate the molecular structure of this  membrane. Gorter  and gremdel (1925) postulated  that it was a bimolecular lipid layer formed mainly  of  polar lipids  with  the double hydrophobic  tails of their  molecules in both  layers directed towards  the interior of the  membrane, and their  polar , hydrophilic heads, at the two surfaces of the membrane.

Danielli and  Davson (1935) ascertained that the plasma membrane contains a good amount  of globular proteins in addition  to the  lipids. They postulated  a lipid  protein bilaye r moderl  of  membrane  structure  with hydrated  globular protein molecules  adsorbed upon both exposed  surfaces of the original  biomolecular  lipid       layer, forming a protein lipid  sandwich  Later (1954)  Danielli  further proposed that there were places where lipid bilayer  is perforated  by pores lined by protein molecules, only polar solute molecules and  ions can  pass through  these  pores.

Using electron  microscopy  Robertson (1959) observed that the plasma membrane has a characteristic  trilaminar  appearance in  a dark light dark or  railway track  pattern . Each  dark line consists of a pleated sheet of protein on surface and sheet of polar heads of lipid molecules,  while the light  central line  consists of a bilayer  of nonpolar  fatty  acid of lipid molecules Robertson .called  the trilaminar  structure a unit  membrane which is continuous  with certain membranous  structures  present inside a cell.


Related Discussions:- Cell membrane

Pre-requisites of counselling, In diabetes mellitus counsellor help the dia...

In diabetes mellitus counsellor help the diabetic patient to cope up with the stress and take own decision for their treatment and life style changes. Decision making  capacity of

What fraction of the total number of possible, Assuming that all human prot...

Assuming that all human proteins are 300 amino acids long, what fraction of the total number of possible different proteins is found in the human body?

Illustrate artificial active immunization, Q. What are artificial active im...

Q. What are artificial active immunization and natural active immunization? Natural active immunization is that in which a previous natural infection induces the primary immune

Theory of germplasm - pre-mendelian theory, Theory of Germplasm (i)    ...

Theory of Germplasm (i)         'August Weismann' (1889) suggested the theory of continuity of germplasm. (ii)         He referred to the reproductive cells as germplasm and

What is meant by unsaturation or saturation of oils and fats, Q. What is me...

Q. What is meant by unsaturation or saturation of oils and fats? When it is said that a triglyceride is saturated it means that in its molecule the carbon chain is bound in its

What do you mean by pericardial effusion, Q. What do you mean by Pericardia...

Q. What do you mean by Pericardial effusion? Collection of fluid in the pericardial sac is known as Pericardial effusion. All cases of pericarditis can lead to pericardial effu

Explain skin changes during kwashiorkor, Explain Skin changes During Kwashi...

Explain Skin changes During Kwashiorkor? In many cases, dermatosis (changes in skin) is seen. Such changes are common in areas of friction. Dark pigmented patches, akin to sun-

Class of crustacea - malacostraca, Class of Crustacea - Malacostraca M...

Class of Crustacea - Malacostraca Malacostraca involves most of the larger forms such as crabs, lobsters, shrimps etc. and constitute the majority of crustacean species. The c

Define some detrimental effects of fungi, Define some Detrimental Effects o...

Define some Detrimental Effects of Fungi? These cause diseases of animals and humans. These either cause superficial mycoses (infection of skin, hair and nails) or systemic

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd