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 short acting insulin, Q. What is Short acting insulin? Short ac...

Q. What is Short acting insulin? Short acting: This type of insulin begins working quickly, works hardest 2- 3 hours after injection but is completely gone after 4-6 hrs. So if

How alkaline cleaning compounds works, Q. How Alkaline cleaning compounds w...

Q. How Alkaline cleaning compounds works? Carbonates, bicarbonates, hydroxides of various metals are called alkaline compounds. Alkaline cleaning compounds have a pH between

Determine the end of the meiotic process during oogenesis, What is the rela...

What is the relation among fecundation and the end of the meiotic process during oogenesis? The oocyte II only completes the second meiotic division (interrupted at metaphase) i

MOVE MENT.., difference btn massflow and pressure law

difference btn massflow and pressure law

Anomalies related to oral cavity, Anomalies Related to Oral Cavity: Un...

Anomalies Related to Oral Cavity: Under these anomalies we will briefly discuss the cleft lip and cleft palate.  You must have seen and/or nursed a baby born with a cut on

Describe insulin resistance in non-conventional factors, Describe Insulin r...

Describe Insulin resistance in Non-conventional Factors ? Insulin resistance refers to a generalized metabolic disorder in which various tissues are resistant to normal levels of

Ecological pyramids - ecosystem, Ecological Pyramids - Ecosystem The a...

Ecological Pyramids - Ecosystem The ancient Egyptians constructed elaborate tombs called pyramids. The base of the pyramid is broad and it supports the upper levels of the str

Define metabolic response to food - requirement of energy, Define Metabolic...

Define Metabolic response to food - Requirement of Energy? Eating requires energy for the ingestion and digestion of food, and for the absorption, transport, inter conversion,

Ascariasis, Ascariasis This disease is found in young calves causing di...

Ascariasis This disease is found in young calves causing digestive disturbances and poor growth. E t iology: It is caused by Toxocara vitulorum in cow and buffal

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