In this article we will discuss about the X-ray crystallographic studies of DNA. In 1920, the basic chemical composition of nucleic acid was elucidated through the efforts of P.A. Levene. In 1940, for the first time W.T. Astbury gave first three dimensional structure of DNA model studied through X-ray crystallography. He concluded that its flat nucleotides get stacked to form [...]
In this article we will discuss about:- 1. Meaning of Chemo-taxis 2. Demonstration of Chemo-taxis 3. Chemotactic Behaviour of Bacteria. Meaning of Chemo-Taxis: Chemo-taxis is the movement of bacteria towards chemical attraction and away from chemical repellants. Bacteria are attracted towards the nutrients such as sugars and amino acids, and are repelled by harmful substances and bacterial wastes. They also [...]
Like bacteria, the cell of cyanobacteria also consists of a mucilaginous layer called sheath, the cell wall, plasma membrane and cytoplasm. These are shown in Fig. 4.32 and described below: 1. Sheath: Usually the cell of cyanobacteria are covered by a hygroscopic mucilaginous sheath which provides protection to cell from unfavourable conditions and keeps the cells moist (Fig. 4.32). Thickness, [...]