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

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 are the functional divisions of the nervous system, What are the funct...

What are the functional divisions of the nervous system? Functionally the nervous system can be separated into the somatic nervous system and visceral nervous system. The so

Acute mitral regurgitation-mitral regurgitation, Acute Mitral Regurgitation...

Acute Mitral Regurgitation :  This may be caused by chordal rupture, infective endocarditis or acute myocardial infarction. In acute myocardial infarction, one of the papilla

What is the function of the iris and of the pupil, What is the function of ...

What is the function of the iris and of the pupil? The iris works like the diaphragm of a photographic camera as it has muscles that contract or relax varying the pupil diamete

Illustrating how neuropsychologists evaluate young children, Illustrating h...

Illustrating how neuropsychologists evaluate young preschool children, older children, youngster adults, and elderly adults. The brain is an evolving organ and functions very

Agro industrial-proteins, Proteins Protease inhibitors: Protease inh...

Proteins Protease inhibitors: Protease inhibitors are protein-based substances widely distributed within the plant kingdom, including the seeds of most cultivated legumes wh

Determine factors affecting zn absorption - micro minerals, Determine Facto...

Determine Factors affecting Zn Absorption - Micro Minerals? In the last unit you have studied that absorption of various minerals (bioavailability) is influenced by number of f

Zoonotic diseases-yellow fever, Yellow fever Yellow fever also known a...

Yellow fever Yellow fever also known as Black Vomit and American plaque is a viral disease primarily of monkeys and transmitted to man by female Aedes mosquitoes. It is caused

Heroin (diacetylmorphine or diamorphine), HEROI N (DIACETYLMORPHINE OR DIA...

HEROI N (DIACETYLMORPHINE OR DIAMORPHINE) - Heroin is a white, crystalline semi synthetic compound prepared from morphine by acetylation. Most dangerous opiate. It i

Dietary management of oesophagitis, Q. Dietary Management fo oesophagitis? ...

Q. Dietary Management fo oesophagitis? Providing adequate nutrition support may require emphasis of different aspects during acute and chronic oesophagitis. In acute phase,

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