34. Ahern's BB 350 at Oregon State University - Photosynthesis

1. Contact - [email protected] 2. Kevin's lectures with The Great Courses - https://www.thegreatcoursesplus.com/b... 3. Kevin's Lecturio videos for medical students - https://www.lecturio.com/medical-cour... 4. Course materials at https://kevingahern.com/biochemistry-... 5. Course video channel at    • 1. Ahern's BB 350 at Oregon State Universi...   6. Metabolic Melodies at https://teeheetime.com/category/lyric... 7. Kevin's Free Biochemistry books - https://kevingahern.com/biochemistry-... 8. Kevin's Pre-med Audio course on Listenable - https://listenable.io/web/courses/143... 1. LDLs are also called "bad cholesterol" because increased levels of them are correlated with increased risk of atherosclerosis (plugged arteries) and heart attack. HDLs, by contrast, are called "good cholesterol" because they help in scavenging cholesterol and LDLs from the bloodstream. Highlights Photosynthesis 1. Photosynthesis is a process in plants and some bacteria that use energy from the light of the sun to synthesize glucose using carbon dioxide and water as starting reagents. It accomplishes this in a multistep process that is divided into two phases, called the light reactions (require light) and the dark reactions (don't require light). 2. Photosynthesis occurs in plants in organelles called chloroplasts. The thylakoid disks of the chloroplast are the sites where the light reactions of photosynthesis occur. 2. Molecules involved in the capture of light energy are known as the chlorophylls. These molecules contain a porphyrin ring (like hemoglobin) with a magnesium ion at the center (instead of the iron molecule found in hemoglobin). 3. In the light reactions of photosynthesis, 1) electrons are removed from water (producing oxygen); 2) ATP is produced by the process of photophosphorylation as electrons pass through the membrane of the thylakoids; and 3) NADPH is produced from NADP+ in the final reduction reaction. NADP+ is therefore the terminal electron carrier in photosynthesis, whereas water is the electron source for the process. 4. There are two photosystems (I and II) that act together to produce the reactions of photosynthesis. Photosystem II is involved in the first set of reactions. Here electrons from the first porphyrin ring complex are excited by light. As these electrons are passed to the electron transport chain of the membrane, the ring extracts electrons from water, creating oxygen. 5. Movement of electrons through the electron transport chain in the thylakoid membrane causes protons to be pumped INTO the thylakoid. This creates a proton gradient (higher proton concentration in the thylakoid than the stroma). Protons in the thylakoid move outside through a proton translocating ATP synthase (PTAS) complex (same general structure as the mushroom-like complex with the same function in mitochondrial membranes). As protons move through the PTAS, ATP is generated from ADP (photophosphorylation). 6. Electrons released from photosystem II eventually reach photosystem I where they are excited by sunlight of a different wavelength. These newly excited electrons are passed to ferredoxin and ultimately to NADP+, creating NADPH, the final product of the light reactions. 7. Quinones are molecules that help carry electrons in the thylakoid membrane (and mitochondrial membrane too). 8. The dark reactions of photosynthesis are where the glucose is synthesized. Thus, we can think of the light reactions as the ones where the energy necessary for making glucose is stored up (charging a battery) and the dark reactions as the ones that use energy from the light reactions to store that energy in another form - glucose. 9. The dark reactions of photosynthesis are also known as the Calvin cycle in honor of their discoverer, Melvin Calvin.