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
Which term is used to describe organisms that live on or in the bottom of an ocean or lake. Such organisms can be found anywhere from the shoreline to greatest ocean depths? a)


Q. Common symptoms linked to lactose intolerance? Common symptoms linked to lactose intolerance include: 1. Anorexia and nausea. 2. Intestinal distension 3. Abdominal

Define Sex as a determinants of nutrient requirements? There are some differences in requirements between the two sexes. However, except for iron, these are apparent rather tha

What is the constitutional unit of proteins? The constitutional units of proteins are the amino acids. Protein Structure Review - a) Image Diversity b) amino acid stru

It is the most common (occurring in 75 per cent cases of ARF) manifestation of ARF. It involves large joints, it is typically fleeting in character shifting from one large joint t

Define How to Prevent the Cancer? A continuing and urgent need is there to take all steps to prevent cancer. Cancer rates are set to increase another 50 percent by the year 202

MIDDLE LAMELLA It is thin, amorphous, intercellular matrix between 2 adjacent plant cell. The cells of plant tissue generally cemented together by an intercellular matrix

You observe the following numbers of individuals of each genotype in a population: AA 700 Aa 200 aa 100 a.) what are the observed genotype frequencies in this populaiton?

Q. What is the fundamental difference between algae and protozoans? The basic difference between algae and protozoans is the fact that algae are photosynthetic autotrophs while