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

Examine why humans not evolve with one central repository, Discuss why huma...

Discuss why humans not evolve with one central repository of DNA rather than having it replicated throughout the body?

Define changes in physical development in infants, Define Changes in Physic...

Define Changes in Physical Development in infants? It seems that all infants do is to sleep and hardly Seed. In spite of this observation, a well-fed and cased infant doubles i

Illustrate about the metabolic waste products in the cornea, Illustrate abo...

Illustrate about the metabolic waste products in the cornea? Metabolic Waste Products During the metabolism various waste products including lactic acid, protein an

Aschelminthes, General characters of aschelminthes

General characters of aschelminthes

Digestive system of animals, Q. Why is the digestive system of these animal...

Q. Why is the digestive system of these animals called incomplete? Incomplete digestive system is in that which the digestive cavity has only one opening.

What are the advantages of the closed circulatory system, What are the adva...

What are the advantages of the closed circulatory system over the open circulatory system? The closed circulatory system is more efficient. As blood circulates only inside bloo

What compound composes most of the cell membrane, What compound composes mo...

What compound composes most of the cell membrane? How is this compound suited to the function of the membrane? Phospholipid composes most of the cell membrane. The hydrophob

Define complete and simple circulation, Q. Why is the fish circulation clas...

Q. Why is the fish circulation classified as a complete and simple circulation? Simple circulation is that in which the blood circulates only in one circuit as opposed to the d

Hematology case study , would i be able to get help on these case study que...

would i be able to get help on these case study questions

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