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

Pathophysiology of endocrine system, What is the relation between posterior...

What is the relation between posterior pituitary gland and diabetes insipidus?

Explain the requirements of special stains, Explain the requirements of Spe...

Explain the requirements of Special Stains? Special stains are required to make spores clearly visible. Different techniques like negative staining, dorner staining method, sch

Pangenesis theory - pre-mendelian theory, Pangenesis Theory (i)        ...

Pangenesis Theory (i)         Charles Darwin propounded pangenesis theory. (ii)         According to this theory every cell, of animal body produces many minute particles kn

Social determinants of health - transport, Social Determinants of Health - ...

Social Determinants of Health - Transport Rising worldwide incomes have led to a massive use of automobiles and in particular cars. Cars are seen as a threat to health because

Explain brotherhood and sisterhood using abo blood typing, Is it possible t...

Is it possible to perform investigation of natural paternity, maternity or brotherhood and sisterhood using the ABO blood typing? By using an ABO blood typing it is possible on

How different is the gametogenesis in men and in women, Q. Concerning event...

Q. Concerning events during the periods of life how different is the gametogenesis in men and in women? The formation of spermatogonia in men takes place during the embryonic p

Which are the specialized conductive tissues of the plants, Which are the s...

Which are the specialized conductive tissues of the plants? The vascular tissues of the plants are the xylem and the phloem. Xylem is the plant tissue that forms the vessels t

Internal ear, INTERNA L EAR - It is called membranous labyrinth p...

INTERNA L EAR - It is called membranous labyrinth protected by bonny labyrinth of periotic bone (Frontal, Temporal and  Parietal). Between internal ear and bonny la

Integumentary system - nails, NAILS - Cover terminal segment of fing...

NAILS - Cover terminal segment of fingers & toes. Highly vascular dermis under lying the nail is called nail bed . It gives pinkish colour to nail. The small part

Define the nutritional assessment tools, Define the Nutritional Assessment ...

Define the Nutritional Assessment Tools? Malnutrition/protein energy malnutrition amongst elderly persons has been observed in various studies -be it hospitalized patients, nur

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