Biological World

  Flip flop movement : The flip-flop movement in cell membranes refers to the translocation of phospholipids between the inner and outer leaflets of the lipid bilayer. This process is essential for maintaining the structure and functionality of the cell membrane. Factors Affecting Flip-Flop Movement (a) Lipid Structure and Geometry : 1. The rate of flip-flop movement is influenced by the structure and geometry of the lipid molecules. 2. Cylindrical lipids (e.g., phosphatidylcholine) can undergo faster flip-flop compared to cone-shaped lipids (e.g., phosphatidylethanolamine). (b) Membrane Proteins : 1. The presence of membrane proteins can facilitate or inhibit the flip-flop movement of lipids. 2. Certain proteins, called flippases and scramblases, can actively transport lipids from one leaflet to the other. (c) Lipid Saturation : 1. Unsaturated lipids with cis double bonds tend to undergo slower flip-flop compared to saturated lipids due to their rigid structur...

 

M.J. Schleiden, a German botanist in 1838 stated that "All plants are formed of one or more cells" . Theodre Schwann, a German Zoologist in 1839 stated that "All animals are fomed of cells, have nuclei and were enclosed by thin cell membrane instead of thick cell wall as found in plant cells " . Schwann described the cell as membrane bound, nucleus containing structure.  They have published some basic properties of cells, which collectively appreciated as Cell Theory.  Basic Postulates of Cell Theory: The various points of cell theory are : 1.Each cell is made of a small mass of protoplasm having a nucleus and bounded by a cell membrane with or without cell wall.  2. All cells are basically alike in structure & metabolism. 3.Organisms are composed of cells and their products.  4. The functions of an organisms are due to activities and interactions of its cells . Drawbacks of Cell Theory: Important drawbacks to cell theory are given below : 1. Viruses are also ci...