Centriole

It is present in all animal cells, located just outside the nucleus. It is cylindrical, 0.5 µm in length and without a membrane. It has 9 sets of peripheral tubules but none in the centre. Each set has three tubules arranged at definite angles. It has its own DNA and RNA and therefore it is self duplicating.

Function

Centrioles are involved in cell division. They give orientation to the ‘mitotic spindle’ which forms during cell division.

Peroxisomes

• They are similar to lysosomes but are smaller and contain several oxidases.

Functions

• They oxidise amino acid and fatty acid.
• They oxidise toxic substances, such as alcohol in liver cells.

Proteasomes

• Tiny barrel shaped structures.
• Found in nucleus and cytoplasm.
• Contains proteases (enzyme that cut the protein into smaller peptides).

Functions

• They degrade uneeded, damaged or faulty proteins in to smaller peptides.

The Cytoskeleton

• It is the network of three types of protein filaments i.e. microfilaments, intermediate filaments and microtubules.
• Microfilaments
  • Thin, composed of protein actin.
  • Help generate movement and provide mechanical support.
  • They are involved in muscle contraction, cell division and the cell locomotion.
  • They anchor the cytoskeleton to integral proteins in the plasma membrane.
• Intermediate Filaments
  • They are thicker than microfilaments.
  • They provide tensile strength for the cell.
• Microtubules
  • These largest cytoskeletal components are long, composed of protein tubulin.
  • They help to determine cell shape.
  • Microtubules also form the spindle fibers for separating chromosomes during mitosis.
  • When arranged in geometric patterns inside flagella and cilia, they are used for locomotion.