Photosynthesis

cell membranes of the host organism. Glycerol and fatty acids come from triglycerides and get further degraded into two-carbon groups through beta-oxidation. When the two carbon molecules come off the triglyceride chain, FADH2 and NADH are made that go into the electron transport chain. The acetyl groups also made go into the Krebs cycle. Ultimately, CO2 is made from them and more ATP is made via the Krebs cycle.

There are protease enzymes that help to break down proteins. Smaller peptides are taken up by the cell for further metabolism. Certain pathogens can be identified by their ability to break down extracellular proteins in differing ways. Peptides are further broken down into amino acids that get deaminated to remove the amino group. The carbon atoms can be metabolized and will break down into compounds that will enter the transition reaction or the Krebs cycle.

PHOTOSYNTHESIS

Phototrophic organisms participate in photosynthesis, which takes sun energy and makes chemical energy. This process happens in plants but also happens in a number of microbial organisms. There are two phases to this process: the first is the lightdependent reactions, where energy from sunlight gets absorbed and turned into chemical energy. The second phase is light-independent phase does not depend on light but is responsible for making sugar from CO2. Light-dependent reactions make ATP, NADH, or NADPH in order to temporarily have a means for energy storage.

In eukaryotic organisms, photosynthesis takes place in the chloroplast, which contains thylakoids that have pigments that capture light. One stack of thylakoids is called a granum, which is surrounded by stroma. Prokaryotes do not have chloroplasts but have infoldings of their cell membrane that contain photosynthetic pigments.

The photosynthetic process involves light-harvesting complexes that get excited when light is absorbed by them. Light energy gets transported to a reaction center, which involves a pigment giving up an electron. Each microorganism has different pigments associated with it. This means that they can be red, purple, green, blue, orange, or yellow, depending on the pigment. The electron given up by the pigment in the reaction

center goes to an electron transport chain that makes NADH or NADPH. ATP is also made through chemiosmosis, just as is done in oxidative phosphorylation.

As we have talked about, there is oxygenic and anoxygenic photosynthesis, depending on the organism. When there is oxygenic photosynthesis, water is split to create the electron in the reaction center. Oxygen is released as a byproduct. In anoxygenic photosynthesis, hydrogen gas, hydrogen sulfide or thiosulfate are electron donors, making elemental sulfur or sulfate as byproducts.

Light-independent reactions take the energy made in the light-dependent reactions to make carbohydrates. It mainly involves the Calvin-Benson cycle, which fixes CO2. Figure 42 shows the Calvin-Benson cycle:

Figure 42.