Definition of metabolism
The sum of all chemical and physical processes by which the body breaks down and builds up molecules. Chemical reactions require or release energy.
Metabolic pathway
Biochemical reactions that occur in progression from beginning to end
Intermediates
Compounds formed in a pathway
Anabolic
pathways that build compounds
Catabolic
Pathways that break down compounds
Anabolism
The process of making new molecules from smaller ones. "building up". Requires energy.
Catabolism
The breakdown or degradation of larger, more complex molecules to smaller, more basic molecules. During digestion, chemical reactions break down proteins, lipids, and carbs. "breaking down". Releases energy.
Energy for the cell: Adenosine Triphosphate (ATP)
Body's source of immediate energy. When phosphate bonds are broken energy is released.
Energy for the cell: Adenosine Diphosphate
Cells break high phosphate bond from ATP
Energy for the cell: Adenosine Monophosphate (AMP)
Hydrolysis of ADP
Metabolic pathways
Chemical reactions that occur sequentially to achieve a particular goal. Occur in specific types or parts of the cell. May be limited to specific organs or tissues. Mitochondria is the major site of energy production in the cell.
Energy from carbs (glucose--> liver)
When glucose is transported to the liver, it is: metabolized for energy or stored as glycogen (in the liver), released into circulation for other cells to use as fuel or stored as glycogen (muscle tissue), converted to fatty acids, if glucose exceeds calo
Energy from carbs (fructose and galactose)
Fructose and galactose are converted to glucose in the liver and follow the same fate.
Aerobic cellular respiration of glucose: glycolysis
Glycolysis, glucose is oxidized to pyruvate.
Aerobic cellular respiration of glucose: synthesis of acetyl CoA
Pyruvate is oxidized and joined with CoA
Aerobic cellular respiration of glucose: citric acid cycle (CAC)
Acetyl CoA enters cycle producing NADH + H, FADH2 and ATP. Occurs in the mitochondria.
Aerobic cellular respiration of glucose: electron transport chain
NADH + H, FADH2 are oxidized to NAD+ and FAD
Summary of glucose oxidation
Aerobic respiration of one glucose molecule: net gain 32 ATP. Anaerobic respiration of one glucose molecule: net gain 2 ATP.
ATP production from fats: lipolysis
Lipolysis: dietary and adipose triglycerides are broken down by lipase to yield one glycerol and 3 fatty acids: glycerol is converted to pyruvate, then to acetyl CoA for entry into the CAC. Free fatty acid are used for energy or stored.
ATP production from fats: Fatty acid oxidation (beta oxidation)
Takes place in mitochondria. Yields acetyl CoA.
B-oxidation of fatty acids
Fatty acids are transported to working cells needing energy (such as liver or muscle cells). Long chain fatty acids are sequentially broken down into two-carbon segments that lead to forming acetyl CoA.
Fatty acids and glucose
Fatty acids cannot form glucose. There is no pathway to convert acetyl CoA to pyruvate. Since acetyl CoA cannot be converted to glucose fatty acids cannot be converted to glucose. (Note: triglycerides can make carbs, its the FA component which cannot)
Energy from protein
the body prefers using carbs and fat for energy. Protein is reserved for metabolic functions that cannot be performed by others. Building and repairing body tissues. Protein are used for fuel primarily during low total energy or carb intake.
Energy from protein (con't)
Dietary proteins are digested into amino acids or small peptides. Amino acids are transported to the liver: made into proteins, released into the blood for uptake by other cells for building and repair functions. Excess dietary protein: used for energy or
Gluconeogenesis
Forming glucose from glucogenic amino acids and other compounds. Typical fatty acids cannot be converted to glucose, although glycerol can. 4 substrates that can be used for gluconeogenesis: amino acids, glycerol, pyruvate, and lactate.
Fasting encourages
glycogen breakdown, fat breakdown, gluconeogenesis, synthesis of ketone bodies.
Feasting encourages
glycogen synthesis, fat synthesis, protein synthesis, and urea synthesis.
Stored energy
Stored energy can be used during times of sleep, fasting, or exercise. Extra energy is stored as carb in limited amounts as liver and muscle glycogen and Fat (triglycerides) in unlimited amounts. The body has no mechanism for storing amino acids or nitrog
Synthesizing macronutrients: gluconeogensis
making glucose from non-glucose substrates. Primarily from amino acids. Small amount from glycerol (triglyceride). Maintains blood glucose during sleep, fasting, illness, and exercise.
Synthesizing macronutrients: protein catabolism
For glucose production can draw on vital tissue proteins (skeletal and heart muscles and organ proteins)
Synthesizing macronutrients: lipogenesis
Making fat from nonfat substances such as carbs, amino acids, and alcohol. Occurs when consuming excess calories. Acetyl CoA units assemble into fatty acid chains. Fatty acids combine with glycerol to form triglycerides. Mostly occurs in liver cells.
Synthesizing macronutrients: amino acid synthesis
The body make the carbon skeleton of nonessential amino acids (NEAA). Amino group comes from transamination (taking amine group, transferring to another AA). synthesis of NEAA occurs only when the body has enough energy and nitrogen. Since essential amino
Hormones regulate metabolism
Insulin is the primary anabolic hormone: increases in the blood after eating, activates storage enzymes, signals cellular uptake of glucose, fatty acids, and amino acids. Glucagon, epinephrine, and cortisol are catabolic hormones: trigger the breakdown of