Anatomy and Physiology I Unit 24 ReviewMetabolism and Nutrition

Key Concepts and Definitions

• Metabolism encompasses all chemical reactions involved in maintaining the living state of cells and organisms
• Anabolism constructs molecules from smaller units (requires energy input)
• Catabolism breaks down molecules into smaller units (releases energy)
• Metabolic pathways are series of enzymatic reactions that convert an initial molecule into a final product
  • Pathways can be linear, cyclic, or branched
• Enzymes are biological catalysts that speed up chemical reactions without being consumed in the process
  • Enzymes lower the activation energy required for reactions to occur
• Coenzymes are non-protein molecules that assist enzymes in catalyzing reactions (vitamins, minerals)
• Adenosine triphosphate (ATP) is the primary energy currency of the cell
  • ATP consists of adenosine and three phosphate groups

Metabolic Pathways Overview

• Glycolysis breaks down glucose into pyruvate (occurs in the cytoplasm)
  • Glycolysis is an anaerobic process that does not require oxygen
  • Glycolysis yields a net gain of 2 ATP and 2 NADH molecules per glucose molecule
• Citric acid cycle (Krebs cycle) oxidizes acetyl-CoA to generate NADH, FADH2, and ATP (occurs in the mitochondrial matrix)
• Oxidative phosphorylation is the process of creating ATP using the electron transport chain and chemiosmosis (occurs in the inner mitochondrial membrane)
• Gluconeogenesis synthesizes glucose from non-carbohydrate precursors (amino acids, lactate, glycerol)
• Beta-oxidation breaks down fatty acids to generate acetyl-CoA (occurs in the mitochondrial matrix)
• Amino acid metabolism involves the synthesis and degradation of amino acids
  • Transamination transfers amino groups between amino acids and alpha-ketoacids
• Urea cycle removes toxic ammonia by converting it to urea (occurs in the liver)

Carbohydrate Metabolism

• Carbohydrates are the primary source of energy for most organisms
• Monosaccharides are simple sugars (glucose, fructose, galactose)
• Disaccharides are formed by joining two monosaccharides (sucrose, lactose, maltose)
• Polysaccharides are long chains of monosaccharides (starch, glycogen, cellulose)
• Glycogenesis is the synthesis of glycogen from glucose (occurs in the liver and muscles)
  • Glycogen is the storage form of glucose in animals
• Glycogenolysis is the breakdown of glycogen into glucose (occurs in the liver and muscles)
• Pentose phosphate pathway generates NADPH and pentose sugars for biosynthetic reactions (occurs in the cytoplasm)
• Gluconeogenesis produces glucose from non-carbohydrate precursors (amino acids, lactate, glycerol)

Lipid Metabolism

• Lipids are a diverse group of hydrophobic molecules (triglycerides, phospholipids, steroids)
• Triglycerides are the primary form of energy storage in animals
  • Triglycerides consist of three fatty acids attached to a glycerol backbone
• Fatty acids are long hydrocarbon chains with a carboxyl group at one end
  • Fatty acids can be saturated (no double bonds) or unsaturated (one or more double bonds)
• Beta-oxidation breaks down fatty acids to generate acetyl-CoA (occurs in the mitochondrial matrix)
• Ketogenesis produces ketone bodies from acetyl-CoA when glucose is limited (occurs in the liver)
  • Ketone bodies can be used as an alternative fuel source by the brain and heart
• Lipogenesis is the synthesis of fatty acids from acetyl-CoA (occurs in the cytoplasm)
• Cholesterol is a steroid molecule that is a component of cell membranes and a precursor for steroid hormones

Protein Metabolism

• Proteins are polymers of amino acids joined by peptide bonds
• Essential amino acids cannot be synthesized by the body and must be obtained from the diet
• Non-essential amino acids can be synthesized by the body from other amino acids or precursors
• Protein digestion begins in the stomach with pepsin and continues in the small intestine with pancreatic enzymes
• Amino acids are absorbed by the small intestine and transported to the liver via the portal vein
• Transamination transfers amino groups between amino acids and alpha-ketoacids
  • Transamination is catalyzed by aminotransferases (alanine transaminase, aspartate transaminase)
• Deamination removes the amino group from amino acids, generating ammonia and an alpha-ketoacid
• Urea cycle removes toxic ammonia by converting it to urea (occurs in the liver)
  • Urea is excreted in urine by the kidneys
• Glucogenic amino acids can be converted to glucose via gluconeogenesis
• Ketogenic amino acids can be converted to ketone bodies or fatty acids

Energy Production and ATP

• ATP is the primary energy currency of the cell
  • ATP consists of adenosine and three phosphate groups
• ATP is generated through substrate-level phosphorylation and oxidative phosphorylation
  • Substrate-level phosphorylation directly transfers a phosphate group from a high-energy molecule to ADP (occurs in glycolysis and the citric acid cycle)
  • Oxidative phosphorylation uses the electron transport chain and chemiosmosis to generate ATP (occurs in the inner mitochondrial membrane)
• Electron transport chain consists of a series of protein complexes that transfer electrons from NADH and FADH2 to oxygen
  • Electron transfer is coupled with the pumping of protons (H+) from the mitochondrial matrix to the intermembrane space
• Chemiosmosis is the flow of protons down their concentration gradient through ATP synthase, driving ATP production
• ATP hydrolysis releases energy that can be used to power cellular processes (muscle contraction, active transport, biosynthesis)
• Creatine phosphate is a high-energy molecule that can rapidly regenerate ATP in muscle cells

Nutritional Requirements

• Macronutrients are nutrients required in large amounts (carbohydrates, proteins, lipids)
  • Carbohydrates are the primary source of energy for most organisms
  • Proteins are essential for growth, repair, and maintenance of tissues
  • Lipids are important for energy storage, cell membranes, and signaling molecules
• Micronutrients are nutrients required in small amounts (vitamins, minerals)
  • Vitamins are organic compounds that serve as coenzymes or antioxidants (vitamin A, B vitamins, vitamin C, vitamin D)
  • Minerals are inorganic elements that have various functions (iron, calcium, sodium, potassium)
• Water is essential for life and plays a crucial role in many metabolic processes
  • Water is a solvent for biochemical reactions and helps regulate body temperature
• Fiber is a type of carbohydrate that cannot be digested by human enzymes
  • Fiber promotes digestive health, regulates blood sugar, and helps control appetite
• Caloric balance is the relationship between energy intake (food) and energy expenditure (physical activity)
  • Positive caloric balance (intake > expenditure) leads to weight gain
  • Negative caloric balance (intake < expenditure) leads to weight loss

Metabolic Disorders and Diseases

• Diabetes mellitus is a group of metabolic disorders characterized by high blood glucose levels
  • Type 1 diabetes is caused by autoimmune destruction of pancreatic beta cells, leading to insulin deficiency
  • Type 2 diabetes is caused by insulin resistance and/or reduced insulin production
• Obesity is a condition characterized by excessive body fat accumulation
  • Obesity increases the risk of developing type 2 diabetes, cardiovascular disease, and certain cancers
• Metabolic syndrome is a cluster of conditions that increase the risk of heart disease, stroke, and diabetes
  • Conditions include abdominal obesity, high blood pressure, high blood sugar, high triglycerides, and low HDL cholesterol
• Phenylketonuria (PKU) is an inherited disorder characterized by the inability to metabolize the amino acid phenylalanine
  • PKU is caused by a deficiency in the enzyme phenylalanine hydroxylase
  • Untreated PKU can lead to intellectual disability and other neurological problems
• Galactosemia is an inherited disorder characterized by the inability to metabolize the sugar galactose
  • Galactosemia is caused by a deficiency in the enzyme galactose-1-phosphate uridylyltransferase (GALT)
  • Untreated galactosemia can lead to liver damage, cataracts, and intellectual disability
• Inborn errors of metabolism are a group of rare genetic disorders caused by defects in specific enzymes or transport proteins
  • Examples include maple syrup urine disease, homocystinuria, and medium-chain acyl-CoA dehydrogenase (MCAD) deficiency