Nutrition Basics Quiz

Chapter 24: Nutrition, Metabolism, and Energy Balance

• Video: Why This Matters (Career Connection)
  • Understanding body's nutrient conversion to energy helps advise patients on diets for peak performance.

Part 1 - Nutrients

• Nutrient: substance in food needed for growth, maintenance, and repair.

• Five categories.

• Three macronutrients form most of our diet: carbohydrates, lipids, and proteins.

• Two micronutrients (vitamins and minerals) are important but needed in smaller amounts.

• Most nutrients act as metabolic fuel, some build molecules and cells.

• Water accounts for ~60% of food volume.

• ~40 molecules are essential nutrients.

• Cells (especially liver cells) have the ability to convert one type of molecule to another, adapting to varied food intakes.

• Energy value: measured in kilocalories (kcal).

  • One kcal raises 1 kg of water by 1°C.
  • 1 kcal = one Calorie (C).
  • Carbohydrates and proteins have 4 kcal/g, lipids have almost 9 kcal/g.

• USDA's MyPlate: guidelines represented as portions on a dinner plate.

  • Includes fruits, vegetables, grains, protein, and dairy.

• Basic dietary principles:

  • Eat only what is needed.
  • Eat plenty of fruits, vegetables, and whole grains.
  • Avoid junk food,

Part 2 - Metabolism

• Metabolism: sum of all biochemical reactions in the body involving nutrients.
  • Substances are constantly built (anabolism) and broken down (catabolism).
  • Even at rest, the body uses energy for essential activities like breathing and nutrient absorption.

24.3 Metabolism as the Sum of Biochemical Reactions in the Body

• Anabolism: reactions that build larger molecules/structures from smaller ones.
  • Example: protein synthesis from amino acids.
• Catabolism: reactions that break down complex structures into simpler ones.
  • Example: protein hydrolysis to amino acids.
• Three major stages in processing energy-containing nutrients:
  • Stage 1: digestion and absorption in the gastrointestinal tract.
  • Stage 2: in cytoplasm, nutrients are built into macromolecules (anabolism) or partially broken down (catabolism) with glycolysis as the main path.
  • Stage 3: in mitochondria, complete breakdown of stage 2 products (mostly converted to acetyl CoA). This uses oxygen and produces ATP, carbon dioxide, and water.

Cellular Respiration

• Catabolic reactions involving glycolysis, citric acid cycle, and oxidative phosphorylation.
  • Convert chemical energy of nutrients (e.g., glucose) into usable energy (ATP).

Phosphorylation

• Transfer of high-energy phosphate groups from ATP to another molecule.
• Primes molecules for activity, motion, or work.

Oxidation-Reduction Reactions and the Role of Coenzymes

• Many reactions in cells are oxidation reactions.
  • Oxidation involves either gaining oxygen or losing hydrogen atoms (with their electrons).
  • Oxidized substances lose electrons.
  • O2 is the final electron acceptor; it joins with removed H atoms to form H2O.
• Dehydrogenases: catalyze removal of hydrogen atoms
• Oxidases: catalyze the transfer of oxygen
• NAD+ and FAD: important coenzymes in oxidative pathways.

ATP Synthesis

• Two mechanisms capture energy to produce ATP:
  • Substrate-level phosphorylation: direct transfer of high-energy phosphate groups from a substrate to ADP, producing ATP.
  • Oxidative phosphorylation: more complex process; mostly produces ATP via an electron transport chain and chemiosmosis.

24.4 Carbohydrate Metabolism

• Body converts carbohydrates to glucose, which enters cells via glucose transporters.
• The process is enhanced by insulin.
• Glucose is phosphorylated within the cell to prevent it from leaving.
• Only in cells of the intestine, kidney, and liver is glucose released back in.
• This keeps intracellular concentrations low, which facilitates continued glucose entry via facilitated diffusion.

Oxidation of Glucose

• Glucose is catabolized through glycolysis, citric acid cycle, and oxidative phosphorylation.
  • Glycolysis: occurs in the cytosol, requires ten chemical steps, produces pyruvate molecules anaerobically, yields 2 ATP molecules, and 2 NADH+H+.
  • Citric acid cycle: occurs in the mitochondrial matrix, generates 2 molecules of CO2, 3 NADH + H+, 1 FADH2, and 1 ATP (as GTP).
  • Oxidative phosphorylation: process mostly occurs in mitochondria through electron transport chain and chemiosmosis. This generates 28 ATP per glucose.

Glycogenesis, Glycogenolysis, and Gluconeogenesis

• Glycogenesis: The synthesis of glycogen, a large polysaccharide used to store carbohydrate in animals. Most active in liver and skeletal muscle.
• Glycogenolysis: The breakdown of glycogen to release glucose. Active in liver and some kidney and intestinal cells, releasing glucose into the bloodstream.
• Gluconeogenesis: The formation of new glucose molecules from noncarbohydrate sources like glycerol and amino acids. It is triggered by low blood glucose, and occurs primarily in the liver and some kidney and intestinal cells.

24.5 Lipid Metabolism

• Fats are the most concentrated source of energy, yielding twice the energy as carbohydrate or protein.
• Products of fat digestion are transported in lymph via chylomicrons and enter capillaries for various uses.
• Glycerol: converted into glyceraldehyde-3-phosphate (a glycolysis intermediate), and eventually to acetyl CoA. Yields about 15 ATP.
• Fatty acids: undergo beta oxidation in the mitochondria to break down into two-carbon fragments which are reduced, producing FADH2, and NADH+H+, which are used to produce ATP. Each fragment binds with coenzyme A to form acetyl CoA to enter the citric acid cycle.

Lipogenesis and Lipolysis

• Lipogenesis: Synthesis of triglycerides; stimulated by high glucose levels.
• Lipolysis: Breakdown of stored fat into glycerol and fatty acids; utilized when carbohydrate intake is insufficient.
• The breakdown of fatty acids produces acetyl CoA that can be used in the citric acid cycle or in ketogenesis.

24.6 Amino Acids

• Proteins have a limited life span and must be broken down and replaced.
  • Amino acids are recycled into new proteins or different N-containing compounds (like nucleotides).
  • Cells constantly take up dietary amino acids for tissue protein replacement at rates of ~100g per day.
• If dietary amino acids are in excess, they are oxidized for energy or converted to fat or glycogen storage.
• Deamination: removal of the amino group (-NH2). The resulting molecule is converted into pyruvate or a keto acid. Important molecule in these conversions is amino acid glutamate.
• Three Degradation Events
• Transamination: transfer of amine groups between molecules.
• Oxidative deamination: removal of the amine group and its conversion to urea.
• Keto acid modification: altering of keto acids so they can enter the citric acid cycle.

24.7 Energy Storage

• Energy is stored in the fed state as glycogen and fat.
• In the fasting state, energy is released through glycogenolysis and gluconeogenesis from the liver, and lipolysis and ketogenesis from adipose tissues.

24.8 The Liver

• The liver carries out over 500 metabolic processes. – Carbohydrate metabolism (blood glucose homeostasis). – Fat metabolism (beta oxidation, fatty acid synthesis, lipoproteins, cholesterol). – Protein metabolism (urea synthesis, amino acid metabolism, protein synthesis).

24.9 Neural and Hormonal Control of Food Intake

• For body weight to remain stable, energy intake must equal energy output.
• Neural and hormonal factors regulate food intake to maintain energy balance.
• Short-term regulation: (neural signals from digestive tract, nutrient signals in blood, gut hormones, and other hormones).
• Long-term regulation: (hormone leptin, and/or other hormones).

Obesity

• Body mass index (BMI) is a measure used to determine obesity.
  • The clinically defined BMI range for obesity is >30.
• Obesity is associated with chronic diseases (e.g., inflammation, insulin resistance, type 2 diabetes mellitus, cardiovascular disease, and some types of cancers, etc.).

24.10 Thyroxine and Basal Metabolic Rate

• Basal metabolic rate (BMR): rate of energy output for essential activities in a fasting, relaxed state at a normal temperature
• Metabolic rate is affected by several things: – Age and gender – Body temperature – Stress   – Thyroxine hormone levels.

24.11 The Hypothalamus and Thermoregulation

• The hypothalamus is the primary regulatory center for thermoregulation.
• Receives afferent sensory input from peripheral and central thermoreceptors and initiates appropriate heat-promoting or heat-loss mechanisms.

Mechanisms of Heat Exchange

• Body uses four mechanisms of heat transfer:
  • Radiation: loss of heat in the form of infrared waves.
  • Conduction: transfer of heat through direct contact.
  • Convection: transfer of heat via movement of fluids (air).
  • Evaporation: heat loss as water turns to vapor from skin. This is sensible (noticeable) or insensible (unnoticeable) depending on whether the rate of evaporative heat loss matches body's heat production.

Clinical-Homeostatic Imbalances

• Hyperthermia: occurs when the body's heat loss mechanisms fail. This is a serious medical condition which can lead to heat stroke, which can cause multiple organ failure, including brain damage. Often happens after prolonged or extreme heat exposure.
• Hypothermia: occurs when body temperature falls below normal and can lead to decreased cellular activities. This condition can lead to a decline in vital signs like blood pressure, respiration rate, and heart rate; and is a medical emergency. Can be caused by prolonged cold exposure.
• Fever: a regulated increase in body temperature triggered by chemicals called pyrogens as a response to infection that promotes healing, inhibits bacterial growth, and enhances immune response.

Developmental Aspects of Nutrition

• Good nutrition is essential for all phases of life, particularly during fetal development where sufficient calories, proteins, and vitamins are needed for brain growth.
• In older adults, medication use can influence nutrient absorption and utilization.