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

Value of biodiversity, Q. Value of biodiversity? Today, there is widesp...

Q. Value of biodiversity? Today, there is widespread concern for conservation of wild animals and plants. One might wonder why there is so much concern about protecting other s

Reduction in the birth rate, State three conditions in a society which coul...

State three conditions in a society which could contribute to a reduction in the birth rate. Birth rate might be decreased by (i) later marriages (as smaller families), (

What is the procedure of gas exchange in human body, What is the procedure ...

What is the procedure of Gas Exchange in human body? Exchange of oxygen with the blood is a specialized process. If oxygen were carried in solution in blood plasma (the liquid

Define diabetic ketoacidosis, Q. Define Diabetic Ketoacidosis? Diabetic...

Q. Define Diabetic Ketoacidosis? Diabetic Ketoacidosis (DKA) is one of the acute complications of diabetes mellitus. The name itself implies that there is acidosis (decrease in

Explain seed gums, Seed gums Polysaccharides derived from plants and se...

Seed gums Polysaccharides derived from plants and seeds have been in use for thousand of years. Seed gums are a group of polysaccharides with the following properties: S

Explain the blood plasma levels of calcium, Which of the following serves a...

Which of the following serves as a controlled variable in a negative feedback system? A. Levels of hydrogen ions in the interstitial spaces of the brainstem. B. Blood plasma

Explain ribosomes in eukaryotic and in prokaryotic cells, How different are...

How different are the location of ribosomes in eukaryotic and in prokaryotic cells? In prokaryotes ribosomes are create free in cytoplasm. In eukaryotic cells they can also be

Botony, is a wheat plant a eustele or a siphonostele or a protostele?

is a wheat plant a eustele or a siphonostele or a protostele?

Explain the stages in taxonomic procedures - gamma taxonomy, Explain the st...

Explain the stages in taxonomic procedures - Gamma Taxonomy This phase of taxonomy is also called biological taxonomy and is concerned with the study of speciation. It is inclu

Determine environmental factors of viscosity and plasticity, Environmental ...

Environmental factors of viscosity and plasticity a) Temperature affects the viscosity of a colloid. Generally, its viscosity decreases as the temperature increases. For e.g.

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