Bioenergetics, Regulation of Metabolism, and Lipid and Amino Acid Metabolism

MCAT Prep: Biochemistry Part 7

postprandial/well-fed (absorptive) state

insulin secretion is high and anabolic metabolism prevails

postabsorptive (fasting) state

insulin secretion decreases while glucagon and catecholamine secretion increases

prolonged fasting (starvation)

dramatically increases glucagon and catecholamine secretion. Most tissues rely on fatty acids

Liver

maintains blood glucose through glycogenolysis and gluconeogenesis. Processes lipids, cholesterol, bile, urea, and toxins

Adipose

stores and releases lipids

Resting muscle

conserves carbohydrates as glycogen and uses free fatty acids for fuel

Active muscle

may use anaerobic metabolism, oxidative phosphorylation, direct phosphorylation (creatine phosphate), or fatty acid oxidation

Cardiac muscle

uses fatty acid oxidation

Brain

uses glucose except in prolonged starvation, when it can use ketolysis

chylomicrons, VDL, IDL, LDL, and HDL

Lipids are transported via:

cholesterol

may be obtained through dietary sources or through synthesis in the liver

HMG-CoA reductase

the key enzyme in cholesterol biosynthesis

Palmitic acid

the only fatty acid that humans can synthesize, is produced in the cytoplasm from acetyl-CoA transported out of mitochondria

beta-oxidation

Fatty acid oxidation occurs in the mitochondria, following transport by the carnitine shuttle via __________

Ketogenesis

ketone bodies form during a prolonged starvation state due to excess acetyl-CoA in in the liver

Ketolysis

regenerates acetyl-CoA for use as an energy source in peripheral tissues

small intestine

Protein digestion occurs primarily in the?

carbon skeletons

____________ of amino acids are used for energy, either through gluconeogenesis or ketone body formation

urea cycle

Amino groups are fed into the ___________ for excretion