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

Horse diseases-horse-pox, Horse-pox Horse pox is a benign disease chara...

Horse-pox Horse pox is a benign disease characterized by the typical pox lesions on the lower limbs or around the muzzle and buccal mucosa. This is a rare disease, caused by a

INVERTEBRATES - STRUCTURE & FUNCTION, 1. Write general characters of phylum...

1. Write general characters of phylum mollusca and classify it upto classes, giving at least two examples of each class.

Determine about the diseases sleep attacks, Determine about the diseases Sl...

Determine about the diseases Sleep attacks These are brief, often irresistible, episodes of sleep, probably slow wave, NREM, naplike sleep that last about 15 minutes and can oc

Define the term hot water blanching, Define the term Hot water blanching? ...

Define the term Hot water blanching? A appropriate water-blanching process in traditional processing is as follows: The sliced material is placed on a square piece of cl

Absolute time, Absolute time is one of the two types of geologic time (rel...

Absolute time is one of the two types of geologic time (relative time being the other), with the distinct age date established generally by the decay of the radioactive elements,

What is the difference between an acid and a base, What is the difference b...

What is the difference between an acid and a base? Base is anything, which has a capability to abstract a proton. Using the easiest definition, an acid is something when add

Causes of deforestation, Other Causes - Deforestation Natural enemies ...

Other Causes - Deforestation Natural enemies like termites, pests and several kinds of diseases affect the forests adversely. There is also massive destruction of forests beca

Protein percentage in lowry method, How to calculate protein percentage in ...

How to calculate protein percentage in Lowry method? Ans) By verification of optical density by coloimetric method

Can you explain secondary metabolites, Q. Can you explain Secondary Metabol...

Q. Can you explain Secondary Metabolites? Secondary metabolites or secondary plant products are those macromolecules that lack nitrogen and arc of restricted occurrence and 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