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

Dietary fibre requirement during diabetes, Q. Dietary Fibre requirement dur...

Q. Dietary Fibre requirement during diabetes? Dietary fibre is that part of food which is not digested by the intestines. High fibre meals have shown to give the best glycemic

Muscle, names and locatio

names and locatio

Show imbalances of basal nuclei, Q. Show Imbalances of basal nuclei? BA...

Q. Show Imbalances of basal nuclei? BASAL NUCLEI - Gray matter "islands" located deep within cerebral white matter. These nuclei process a variety of descending motor informat

What is the estimated percentage of water in the human body, Q. What is the...

Q. What is the estimated percentage (in mass) of water in the human body? Is this percentage expected to be larger in the adult or in the old individual? Ans. Approximatel

Calculate the minimum dissolved oxygen tension, Given our knowledge so far ...

Given our knowledge so far we now need to evaluate if it is feasible to run the process in the designed vessel. We therefore need to compare the oxygen uptake rate and the oxygen t

What is leaf morphology, What is Leaf Morphology? Leaf Arrangemen...

What is Leaf Morphology? Leaf Arrangement : These show the different types of leaf arrangement on a twig. The point on the twig at which the leaves are attached is refer

Determine the long lasting vaccine against common cold, Why doesn't a long ...

Why doesn't a long lasting vaccine against common cold exist yet? Viruses that show a high mutation rate like the virus that causes the common cold escape simply from the actio

The eye refract the light, Which parts of the eye refract ('bend') the ligh...

Which parts of the eye refract ('bend') the light in such a way as to form an image on the retina?   The curved surface of the cornea, and the aqueous humour enclosed by it,

Polymorphism in lysosomes, Polymorphism in Lysosomes Polymorphism, i.e. e...

Polymorphism in Lysosomes Polymorphism, i.e. existence of a structure in more than one form, is an important feature of lysosomes. Several different forms of lysosomes have been

Explain about left cerebral hemisphere, How is it structurally explained th...

How is it structurally explained that the motor activity of the left side of the body is controlled by the right cerebral hemisphere and the motor activity of the right side of the

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