Always in motion is the future.

Week 9: Movement

Metabolism in a Nutshell

Due to the week lost for Thanksgiving break, we will not cover metabolism this term.

Chemical processes allowing cells to continue living.

ATP, composed of adenine, ribose and 3 phosphate radicals which release energy when removed, helps extract energy from food and supplies energy for cell functions such as muscular activity, gland secretions, maintenance of action potentials, synthesis of cell substances.

Glucose, lipids and protein can all be hydrolyzed down into ATP in different processes.

Glucose

Glucose is transported through cell membranes via facilitated diffusion with a protein carrier. As discussed in the endocrinolgy section, this process is enhanced by insulin. Once in the cell, it is converted into glucose 6-phosphate and is either used immediately or undergoes glycogenesis for storage. Stored glycogen goes through glycogenolysis, which is activated by epinephrine or glucagon release, to be reconverted to glucose 6-phosphate.

Energy release is initiated by a process called glycolysis, in which the glucose is split to form pyruvic acid and 2 ATP molecules. The pyruvic acid is converted to acetyl coennzyme A (acetyl Co-A), which then enters the citric acid (or Krebs) cycle to form 2 more molecules of ATP. The final breakdown, known as oxidative phosphorylation, yields 34 more ATP molecules.

Glucose can be formed from amino acids and glycerol portion of fat via gluconeogenesis when the body's stores are strained.

Lipids

Lipids are converted to triglycerides in the adipose cells for storage, and travel through the circulation as free fatty acids to the tissues. Some lipids circulate in the form of lipoproteins, composed of triglycerides, phospholipids, cholesterol and protein. Triglycerides formed in the liver are trasported in Very Low Density Lipoproteins to the tissues. The residue after the the triglycerides have been delivered are the Low Density Lipoproteins that have been known to clog arteries. High Density Lipoproteins transport cholesterol from the tissues to the liver.

As an energy substrate, lipids enter the mitochondria where they are oxidized into Acetyl Coenzyme A, when then enters the citric acid cycle in much the same way as Acetyl Co-a from glucose. The metabolism of one lipid molecule ultimately yields 146 molecules of ATP.

Proteins

Before protein can be used for energy, it is deaminated -- the amino groups are removed from the amino acids and filtered through the renal system for excretion. Once deaminated, the resulting acid is oxidized and converted to a substance suitable to enter the citric acid cycle.