Question

Where would the following structures be found in a cell?
(a) Microtubules (b) Thylakoids (c) $F_0-F_1$ complex (d) Ribosomes (e) Nucleolus

Answer 1

• Microtubules: Microtubules are unbranched hollow submicroscopic tubules of protein tubulin which develop on specific nucleating regions and can undergo quick growth or dissolution at their ends by assembly or disassembly of monomers. With the exception of Slime Moulds and Amoebae, microtubules occur widely in eukaryotic cells. They are present in the cytoplasm as well as in specialized structures like centrioles, basal bodies, cilia or flagella, sensory hair, equatorial ring of thrombocytes, spindle apparatus, chromosome fibres, etc.
  
• Thylakoids: Thylakoids are membrane lined flattened sacs which run through-out the stroma or matrix of the chloroplast. Since they take part in photosynthesis; they are also called photosynthetic thylakoids. Thylakoids are thus the structural elements of the chloroplast. They generally run parallel but may show interconnections. Thylakoids may also be attached to the inner membrane of chloroplast envelope.
  
• $F_0-F_1$ complex: These are small tennis-racket like particles, present in inner membrane mitochondria. These are also called elementary particles or oxysomes. Each elementary particle or $F_0-F_1$ particle has a head, a stalk and a base. Elementary particles function as ATP-ase. They are, therefore, the centres of ATP synthesis during oxidative phosphorylation.
  
• Ribosomes: Ribosomes occur in all living cells with the exception of mammalian erythrocytes or red blood corpuscles. Depending upon the place of their occurrence, ribosomes are of two types, cytoplasmic and organelle. The organelle ribosomes are found in plastids and mitochondria. The cytoplasmic ribosomes may remain free in the cytoplasmic matrix or attached to the cytosolic surface of endoplasmic reticulum with the help of a special ribophorin or SRP protein.
  
• Nucleolus: It is the principal site for the development of ribosomal RNAs. Nucleolus is a naked, round or slightly irregular structure which is attached to the chromatin at a specific region called nucleolar organiser region. Commonly 1-4 nucleoli are found in a nucleus. A covering membrane is absent around nucleolus. It is the centre for the formation of ribosome components. Nucleolus is an essential and integral part of the eukaryotic cell. It stores genetic information in its DNA molecules which can be passed on to daughter cells. It also controls cellular activities.