The chloroplast
-double membrane, own circular DNA and ribosomes, also thought to have once been a free-living photosynthetic bacterium
Three compartments include the intermembrane space, the stroma, and the thylakoid compartment.
Thylakoids form a membranous system within the stroma. Thylakoids resemble disks or coins; grana are stacks of thylakoids.
Chloroplasts contain chlorophyll embedded in thylakoid membranes and enzymes in the matrix that direct photosynthesis
The cytoskeleton
-consists of fibrous proteins: microtubles, intermediate filaments, and
microfilaments.
Functions:
-cell shape, movement, cell division, organelle anchor and movement,
form centrioles, cilia and flagella, muscle contraction (actin and myosin filaments), and tension-bearing.
Cell Wall
-in plants, contains cellulose fibres for strength
-aids in protection, cell shape and water regulation
Glycocalyx
-in animals, a sticky substance that helps to glue cells together and may aid in cell-cell recognition
Intercellular junctions
Plants have one type of intercellular junctions-plasmodesmata. These channels help to link the cytoplasm of one plant cell to that of another.
Allows easy passage through tissues (water uptake in roots, for example)
Animals have 3 types of intercellular junctions.
1. Communicating junctions: These are gap junctions that connect cytoplasm to cytoplasm. Crucial in development and also in cardiac muscle.
2. Tight junctions, aka belt desmosomes, form around cells to prevent substances from travelling through the extracellular space. Common in epithelial tissues separating two compartments (eg. the lining of the small intestine)
3. Adhering junctions, or desmosomes, spot weld cells together to form strong sheets of tissue.