Cell membrane, Biology

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.

Posted Date: 10/4/2012 1:37:00 AM | Location : United States







Related Discussions:- Cell membrane, Assignment Help, Ask Question on Cell membrane, Get Answer, Expert's Help, Cell membrane Discussions

Write discussion on Cell membrane
Your posts are moderated
Related Questions
Q What are the biological troubles that molluscs face due to their soft body? Because molluscs have a soft body they are further fragile. They also have more complexity to supp

How does self infection by tapeworms occur? Taeniasis patients might be develop the most severe form of the worm infection, cysticercosis, because their feces have eggs and pre

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

Pathogenesis of Viruses Viral diseases An indicated before, viruses cause a number of infectious human diseases from minor ailments like common cold, to fatal disease, lik

J-shape d - It shows 2 phases - (i) Lay phase (ii) Exponential phase

FUNCTIONS BASED ON MANAGEMENT PRINCIPLES: Planning: The objectives of nursing unit should be achieved through planning, good coordination and supervision. While planning nur

Point out some Difference between Tumor And Cancer? Tumor is a swelling or growth because of an abnormal growth of tissue. Tumors can either be benign or malignant. The benign

Q. Show the Anatomical Evidence? Anatomy is the study of the structure, organisation and development of cells and tissues of plants and animals. For over a century taxonomists

Define the interaction of vitamin c with lead and mercury? Vitamin C, lead and mercury: Iron alleviates lead toxicity but ascorbic acid is ineffective. Ascorbic acid alleviat

What are the main manifestations of leishmaniasis? There are two major forms of leishmaniasis: cutaneous leishmaniasis and visceral leishmaniasis (also called as kala-azar). Th