(i) Nucleus contains nucleoprotein fibres called chromatin, nuclear matrix and one or more spherical bodies called nucleoli. It consists of two parallel membranes with space between them called the perinuclear space which forms the barrier between the materials present inside the nucleus and that of the cytoplasm. The outer membrane is continues with endoplasmic reticulum and bears ribosomes on it. Nuclear pores which are formed by the fusion of its two membranes are the passages through which movement of RNA and protein molecule takes
place in both directions. The content of nucleolus is continuous with rest of the nucleoplasm and it is a site for active ribosomal RNA synthesis. Chromatin contains DNA and some basic proteins called histones, some nonhistone proteins and also RNA.
(ii) Centrosome Centrosome is an organelle usually containing two cylindrical structures called centrioles. They are surrounded by amorphous pericentriolar materials. Both the centrioles in a centrosome lie perpendicular to each other. They areV ma.de up of nine evenly spaced peripheral fibrils of tubular protein. Each of the peripheral fibril is a triplet. The adjacent triplets are also linked. The central part of the proximal region of the centriole is also proteinaceous and called the hub, which is connected with tubules of the peripheral triplets by radial spates made of protein.
