Energy Converting Organelles and Membranes

Web Lecture

• Chloroplasts
• Mitochondria
• Cytoskeleton
• Cell junctions

Chloroplasts

Chloroplasts are where photosynthesis occurs--the conversion of light energy to energy stored in the chemical bonds of sugars. We generally associate photosynthesis with plants--but in fact, some single-celled organisms are capable of photosynthesis.

• Check out the Cryptomonas site for some pictures of chloroplasts within protists. You can click on the pictures and select a magnification size to view the chloroplast organelles within the organism.Click on the first image (C. platyuris). At the top of the new page, click on the HERE to look at an enlargement of the picture (it may take some time to load). Can you find a nucleus? vacuole? other structures?
• The Hyperphysics Textbook site discusses chloroplasts because energy is properly the study of physics, wherever it changes form! Where does the energy transformed by chloroplasts come from?

Mitochondria

Mitochondria release energy stored in carbohydrates, fats, and other molecules.

• For a close look at mitochondria structure, review the Mitochondria page at the Rice University's Experimental biosciences site. Note how the mitochondrion looks in an electron microscope picture. We'll come back to look at mitochondria more closely when we study cell respiration.
• One of the distinctive characteristics of mitochondria is that they possess their own DNA, completely separate from the DNA in the cell's nucleus. Read about this DNA at the Scitable. What happens if this DNA mutates so that the mitochondria doesn't function properly? What can mitochondrial DNA tell us about inheritance?

The Cytoskeleton

The cytoskeleton is composed of all the pieces which provide structure to the cell. Don't be confused by the term skeleton--the structure is not nearly as firm as your bone-based skeleton.

Cell Junctions

Some proteins exist only to hold cell walls together, like patches of velcro on your clothes. A demosome is an area on the inside of a cell wall, which has filaments that go through the cell wall and connect with the filaments of a demosome on the inside of another cell, like brass rivets. Tight junctions are made between rows of proteins embedded in the walls of two different cells. The cells connected by tight junctions form a barrier which seals off the area behind the cells, creating a division between body parts composed of the cells involved. Gap junctions let material pass between two cells through a channel, like hamsters passing from one cage to another through the habitat tunnels. Plants do not need demosomes for rigidity or tight junctions (since their cell walls are water-resistant already), and their plasmodemata perform the functions of gap junctons.

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