Highlights Lipid Metabolism III
1. Cholesterol gives rise to the bile acids – detergent-like molecules such as cholate or glycocholate that help to emulsify fat in the digestive system. They also are precursors of the steroid hormones.
2. Pregnenolone is derived from cholesterol and is the precursor of all of the steroid hormones. These include the glucocorticoids, such as cortisone, the mineralocorticoids, such as aldosterone, the androgens, such as testosterone, and the estrogens, such as estragen/estradiol. Among the sex hormones, the male hormones (androgens) are precursors of the female hormones (estrogens). The enzyme that catalyzes this conversion is known as an aromatase. Since some tumors are stimulated by estrogen, strategies for treating them involve the use of aromatase inhibitors to cease the production of estrogens.
3. Movement of lipids in the body occurs via lipoprotein complexes (contain lipids and protein) in the bloodstream. These start beingcarried out of the digestive system in large molecules called chylomicrons. Chylomicrons enter the blood stream from the lymph system. In the blood stream, chylomicrons move to the capillaries, where they are digested by cellular lipase enzymes. The result of this action is to reduce the chylomicron size, creating chylomicron remnants. These exit the capllaries and move to the liver.
4. The liver serves as the major organ regulating the formation and release of lipoprotein complexes (VLDLs, IDLs, LDLs). The liver accomplishes this by monitoring the concentration of complexes. As the concentration increases (indicating reduced uptake by target cells), the liver slows the release of complexes. As the concentration decreases (indicating increased uptake), the liver releases more VLDLs. People with deficiencies in the LDL receptor protein on the liver cells tend to have high concentrations of LDLs. They have a genetic disease known as familial hypercholsterolemia.
5. 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.
6. 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.
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 and the stroma is the location of the dark reactions.