4..Non-Membranous cell organelles

Non-Membranous cell organelles – structure and function:

1. Free Floating Ribosomes:
   • Ribosomes are essential cellular structures responsible for protein synthesis.

1. • They consist of small and large subunits, composed of proteins and ribosomal RNA (rRNA).
   • The basophilia of ribosomes is due to the densely concentrated rRNA.
   • Ribosomes producing proteins are gathered by mRNA into polyribosomes.
   • Synthesized proteins are used by the cell itself (e.g., hemoglobin, actin, myosin, and mitochondrial enzymes).
   • Translation occurs on ribosomes, where mRNA codons are decoded into amino acids.
2. Cytoskeleton:
   • The cytoskeleton is a dynamic network of filaments and tubules extending throughout the cytoplasm.
   • It provides mechanical support, shape, and resistance to deformation.
   • Functions of the cytoskeleton include:
     • Active contraction (allowing cell movement).
     • Involvement in cell signaling pathways.
     • Uptake of extracellular material (endocytosis).
     • Segregation of chromosomes during cell division.
     • Cytokinesis (division of a mother cell into two daughter cells).
     • Organization of intracellular contents and transport.
   • Three types of cytoskeletal elements: Microfilaments, Microtubules, and Intermediate filaments.

3.     Centrosome:

1. • The centrosome serves as the main microtubule organizing center (MTOC) in animal cells.
   • Composed of two centrioles, each with nine triplets of microtubules.
   • During mitosis, centrosomes migrate to opposite poles of the cell.
   • They interact with chromosomes to build the mitotic spindle.
   • Centrosomes replicate during the S phase of the cell cycle.
   • Basal bodies, derived from centrioles, anchor microtubules and facilitate vesicle and organelle movement.