Biological World

  Pleomorphism of Lysosomes Lysosomes show pleomorphism, which means they occur in many different forms according to their functional state. They are not always identical in shape, size, or contents. Their appearance changes depending on whether they are newly formed, involved in digestion, or storing undigested waste materials.  Lysosomes are membrane-bound organelles containing hydrolytic enzymes. These enzymes digest proteins, lipids, carbohydrates, nucleic acids, and other cellular materials. Since lysosomes perform different digestive functions inside the cell, they appear in different structural forms. This property is called pleomorphism.  The main pleomorphic forms of lysosomes are primary lysosomes, secondary lysosomes, autophagic vacuoles, and residual bodies. Primary lysosomes are newly formed lysosomes produced by the Golgi apparatus. They contain inactive hydrolytic enzymes and have not yet taken part in digestion. They are small, spherical vesicles surround...

  S tructure of Lysosome Lysosomes are small, spherical, membrane-bound cell organelles mainly found in animal cells. They are involved in intracellular digestion and removal of waste materials. Lysosomes contain many hydrolytic enzymes, so they are commonly called the digestive bags of the cell. They are also known as suicidal bags because, under certain conditions, their enzymes may digest the cell’s own components. Lysosomes were discovered by Christian de Duve in 1955. They are present in large numbers in cells that show active digestion, such as white blood cells, liver cells, and kidney cells. Lysosomes are generally absent or less prominent in mature plant cells because vacuoles perform similar functions in plants. Lysosomes are usually spherical or oval in shape. Their size varies from about 0.1 to 1.2 micrometers , depending on the type of cell and its physiological activity. They are formed by the Golgi apparatus . The digestive enzymes of lysosomes are first synthesi...

  Aquaporins Aquaporins are integral membrane proteins that form special channels for the rapid movement of water molecules across biological membranes. They are also known as water channel proteins. These proteins are present in plants, animals, bacteria, and many other organisms. Aquaporins help water move across the plasma membrane and tonoplast without allowing ions and most solutes to pass through. Structurally, aquaporins are embedded in the membrane and form narrow pores. Water molecules pass through these pores in a single-file arrangement. The pore is very selective, so charged particles such as protons and ions cannot pass through. This selectivity is important because it maintains the ionic balance and electrochemical gradient of the cell. In plants, aquaporins are very important for water absorption and transport. They help roots absorb water from the soil and assist in the movement of water from cell to cell. They are also involved in maintaining cell turgor pressure, ...

  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...