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 the other name given to sex chromosomes, What is the other name giv...

What is the other name given to sex chromosomes? What is the function of sex chromosomes? Sex chromosomes are also known as allosomes (the other chromosomes that are not sex ch

Why do leaves change color, Why do leaves change color? Leave is the fo...

Why do leaves change color? Leave is the food factories of plants. During the spring and summer, leaves are actively making food and they are filled with chlorophyll, which giv

Excretory organs, classification of excretory organs in helminthes, nermato...

classification of excretory organs in helminthes, nermatodes, annelids, molluscs, arthropods and echinodems

Define endocytosis of glut4 transporters, Define endocytosis of GLUT4 Trans...

Define endocytosis of GLUT4 Transporters Person X is a healthy human who has volunteered to take experimental drug Y.  Person X has a normal dinner at 6 PM on April 1 and then

What are the three major types of rna, Q. What are the three major types of...

Q. What are the three major types of RNA? What is meant by heterogeneous RNA? Messenger RNA, or mRNA, transfer RNA, or tRNA, and ribosomal RNA, or rRNA, are the three main type

Describe schizocoelus and its role., Describe Schizocoelus and its role. ...

Describe Schizocoelus and its role. One of two ways that a body cavity forms within mesoderm. (The other is enterocoelic pouching.) Block of mesoderm splits apart to create the

Which terrestrial vertebrate group is extremely rare deserts, Which terrest...

Which terrestrial vertebrate group is extremely rare in deserts? The Amphibians are terrestrial vertebrates very rare in desert environments (although there are a few species a

How can the formation of sperm cells from germ cells, Indicating the name a...

Indicating the name and respective ploidy of each involved cell how can the formation of sperm cells from germ cells be described? The formation of sperm cells, or spermatogene

Explain submarginal scalloped rectangular, Explain Submarginal Scalloped Re...

Explain Submarginal Scalloped Rectangular - Limited Mucoperiosteal Flaps - Modification of Rectangular flap in that the Horizontal incision placed in the buccal and labial atta

Define sugar as a type of carbohydrates, Define Sugar as a type of Carbohyd...

Define Sugar as a type of Carbohydrates? This group includes monosaccharide and disaccharides. List down the names of sugars under both these groups and check it out with those

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