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 are the male and the female gonads in humans, Q. What are gonads? What...

Q. What are gonads? What are the male and the female gonads in humans? Gonads are the organs that produce gametes they contain the germ cells that undergo division and generate

Explain the concept of selective breeding, Explain the  concept  of  selec...

Explain the  concept  of  selective  breeding a) Understood  the  concept  of  selective  breeding  and/or  were  able  to  use  their Knowledge  of  Mendelian  genetics  to  e

Biogenesis of mitochondria, BIOGENESI S OF MITOCHONDRIA De Novo for...

BIOGENESI S OF MITOCHONDRIA De Novo formation i.e. new formation. It is not confirmed. New mitochondria are formed by division (Amitosis) of pre-existing mitochondria.

Explain about central nervous system, Central Nervous System (CNS) Cove...

Central Nervous System (CNS) Covering of the brain and spinal cord is called Meanings (membranes which cover and protect brain and spinal cord are called meanings) There is flu

Do protozoans have a cellular nucleus, Q. Do protozoans have a cellular nuc...

Q. Do protozoans have a cellular nucleus? All protozoans, as eukaryotes have nucleus, some species like the paramecium have two nuclei the micronucleus and the macronucleus.

The mitochondria contain their own dna, Why do you think the mitochondria c...

Why do you think the mitochondria contain their own DNA (circular) and have a double membrane?

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