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Summary

Lysosomes

• Spherical membranous organelles
• contain more than 40 of hydrolytic enzymes for intracellular digestion.
• if involved in digestion, it is called secondary lysosomes.
• if not involved in digestion, it is called primary lysosomes.

Peroxisomes (Microbodies)

• small spherical membranous bodies
• contain enzymes involved in lipid metabolism and catabolism and detoxification of free radicals.
• Deficiency of peroxisomal enzymes results in “Zellweger syndrome”

Microtubule Organizing Centers “MTOC” include:

1. Centrioles.
2. Basal bodies.
3. Centromeres of chromosomes.

Centrioles:

• paired cylindrical structures, perpendicular to each other
• each centriole is composed of 9 triplets (9+0 array) of microtubules

Flagella & Cilia

• Microtubular motile processes
• Cilia are multiple processes
• The flagellum is a single longer process
• Their core consists of 9 pairs of microtubules and 2 central tubules.

The basal body is similar to the centriole in structure.

Cytoskeleton Consists of:

1. Microtubules: consist of and a & b tubulin
2. Thin filaments (microfilaments): Mainly contractile thin (actin) and thick (myosin) filaments
3. Intermediate filaments: include keratins, vimentin, desmin glial filaments, and neurofilaments.

Cellular junctions

• are specialized junctional structures
• help in: contact, communication, signaling, exchange, union, and creating barriers.

Types of Cellular junctions

1. Occluding “impermeable” junctions e.g.tight junctions
2. Anchoring “adhering” junctions: e.g adhering junction, desmosomes & hemidesmosomes
3. Communicating Junctions e.g. gap junction “nexus”

 - Inclusions are non-living components of the cell e.g. glycogen, pigments and lipids

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