Cellular Metabolism AHEA 116

Introduction To carry on its functions, the cell must metabolize its fuel: the carbohydrates, proteins, and fats.

Metabolism 1. Definition – all the chemical reactions that occur within the cells a. anabolism – reactions that build more complex substances from simpler substances and require energy (ATP) b. catabolism – the breakdown of complex substances into simpler ones and release energy

2. ATP http://www.biologyinmotion.com

Carbohydrates: Structure and Function 1. Composed of monosaccharides, disaccharides, and polysaccharides. 2. Glucose (monosaccharide) is the primary source of energy. 3. Glucose can be stored as glycogen (in muscles and the liver) and converted to and stored as fat. 4. Helps to regulate blood sugar.

How does glycogen participate in the regulation of blood glucose? Answer. When blood glucose levels decrease, the liver can break down glycogen into glucose and release the glucose into the blood. When blood glucose levels increase, the liver can convert and store glucose as glycogen.

Cont’ 5. Glucose can be catabolized anaerobically and aerobically. a. Anaerobically (without oxygen), glucose is incompletely broken down (glycolysis) into lactic acid and small amounts of ATP.

Cont’ b. Aerobically, (with oxygen) glucose is broken down completely (citric acid cycle) into carbon dioxide (CO2) and water (H2O) and large amounts of energy (ATP).

Clinical Correlates Shock causing hypoxemia and a shift from aerobic to anaerobic metabolism  lactic acidosis Cyanide poisoning… makes O2 unavailable for mitochondrial use Use of the drug nitroprusside (can make cyanide in the presence of light)

Lipids (fats) 1. The most common lipids are triglycerides, phospholipids, and steroids. 2. Lipids are used primarily in the synthesis of membranes. 3. The long chains of fatty acids are broken down into two-carbon units and metabolized by the enzymes of the citric acid (Krebs) cycle into CO2 and H2O, releasing large amounts of energy.

Clinical Correlates Rapid and incomplete catabolism of fatty acids causes ketone body formation and ketoacidosis Effect of poor diet on fat metabolism  obesity

Protein 1. Proteins are used primarily in the synthesis of hormones, enzymes, antibodies, plasma proteins, muscle proteins, hemoglobin, and cell membranes. 2. Proteins are also used as fuel and as raw material for making glucose (gluconeogenesis).

Clinical Correlates Protein deficiency disorders: kwashiorkor – protein and kilocalorie deficiency Anorexia and starvation… use of body protein for fuel – muscle wasting Effects of oral diabetic drugs on glucose transport - suppress gluconeogenesis

Protein 3. Protein is composed of a series of amino acids linked together by peptide bonds in a specific sequence. 4. There is special handling of protein nitrogen by the urea cycle. a. Liver breaks down protein and converts the nitrogen to urea b.Urea is excreted by the kidneys in the urine

Clinical Correlates Ammonia build-up causes hepatic encephalopathy Diagnostic test: BUN, blood ammonia

DNA and the genetic code 1. DNA is a series of nucleotides arranged in a twisted ladder formation 2.The genetic code is stored here in an exact sequence of amino acids for protein synthesis Clinical Correlates ● Misreading the genetic code can be caused by mutations/drugs ● There may be a defect in the genetic code (e.g., PKU, sickle cell anemia)