Chapter 24: Nutrition, and Metabolism. Flashcards
Nutrition:
o Nutrient: a substance in food that promotes normal growth, maintenance, and repair.
o Major nutrients: Carbohydrates, lipids (fats), and proteins.
o Other nutrients: Vitamins and minerals (and even water).
Carbohydrates:
o Dietary sources:
o Starch (complex carbohydrates produced by plants) in potatoes, grains and vegetables.
o Sugars (simple = crystalline carbohyrate = sucrose, lactose, fructose) in fruits, sugarcane, sugar beets, honey and milk.
o Insoluble fiber: whole grains, wheat bran, cellulose in vegetables provide roughage.
o Soluble fiber: oats, barley, pectin in apples and citrus fruits; reduces blood cholesterol levels.
o Uses:
o Glucose is (a monosaccharide = simple carbohydrate) is the fuel used by cells to make ATP.
o Glucose is only energy source for Neurons and RBCs.
o Carbs are stored as glycogen primarily in the liver and muscle cells (all cells can store a limited amount of glycogen).
o Excess carbs can be converted to TG (Fat).
o Dietary requirements:
o Minimum 100 g/day to maintain adequate blood glucose levels…but not known for sure.
o Recommended minimum 130 g/day.
o Recommended intake: 45–65% of total calorie intake; mostly complex carbohydrates.
Lipids:
o Dietary sources
o Triglycerides (fats):
o Saturated fatty acids in meat, dairy foods (cheese, cream, butter and tropical oils = contributes to cardio disease.
o Unsaturated fatty acids in seeds, nuts, canola oil, olive oil, most vegetable oils, avocados, rapeseed.
o Cholesterol fat that is from animal foods (egg yolk, meats, organ meats, shellfish, and milk products)
o Essential fatty acids (essential because the body can’t manufacture this stuff).
o Linoleic and linolenic acid, found in most vegetable oils.
o Must be ingested.
o Essential uses of lipids in the body:
o Help absorb fat-soluble vitamins.
o Major fuel of hepatocytes and skeletal muscle.
o Phospholipids = diglyceride + phosphate are essential in myelin sheaths and all cell membranes.
o Glycoproteins and glycolipids are part of cell membranes.
o Functions of fatty deposits (adipose tissue):
o Protective cushions around body organs.
o Temperature regulation = Insulating layer.
o Concentrated source of energy, oxidized (catabolized) to make ATP.
o Helps body absorb fat-soluble vitamins.
o Slows gastric emptying = satiety.
o Regulatory molecules (hormone like) that are derived from fatty acids are called prostaglandins and involved in:
o Smooth muscle contraction (thromboxanes, prostacyclins).
o Control of blood pressure.
o Inflammation.
o Functions of cholesterol: (not used as an energy source), made in the liver, cells of the small intestine.
o Stabilizes (or makes up) plasma membranes.
o Precursor of bile salts and steroid hormones.
o Precursor to Vitamin D.
o Nerve mylenation.
o Dietary requirements suggested by the American Heart Association:
o Fats should represent 30% or less of total caloric intake.
o Saturated fats should be limited to 10% or less of total fat intake.
o Daily cholesterol intake should be no more than 300 mg.
Proteins:
o Dietary sources:
o Eggs, milk, fish, and most meats contain complete proteins (all amino acids present to sustain human life).
o Legumes, nuts, and cereals contain incomplete proteins (lack some essential amino acids).
o Legumes and cereals together contain all essential amino acids (nine altogether).
o Essential Amino Acids are amino acids that the body cannot manufacture on its own, so they must be obtained through the diet = nine essential amino acids altogether.
o Uses:
o Structural materials: to make keratin, collagen, elastin, muscle proteins.
o Functional molecules = to make enzymes and some hormones.
o The use of amino acids in the body entails:
o All-or-none rule: All amino acids needed must be present for protein synthesis to occur.
o Adequacy of caloric intake: Protein will be used as fuel if there is insufficient carbohydrate or fat available.
o Need enough protein to keep us in nitrogen balance.
o Need nitrogen of amino acids to make nucleic acids, creatine, hemoglobin, myoglobin + other proteins.
o Nitrogen balance: = nitrogen input minus nitrogen output. In healthy persons the rate of protein synthesis equals the rate of breakdown and loss.
o Positive if protein synthesis (input) exceeds breakdown (normal in children and tissue repair).
o Negative if protein breakdown exceeds synthesis (e.g., stress, burns, infection, or injury, starvation) = NH3 release in the form of urea in liver.
o Hormonal controls: Anabolic hormones (pituitary growth hormone, sex hormones) causes protein synthesis to accelerate.
o Dietary requirements: Rule of thumb: daily intake of 0.8 g per kg body weight
Vitamins:
o Organic compounds.
o Crucial in helping the body use nutrients.
o Most function as coenzymes.
o Vitamins D (skin,liver), some B (intestine), and K (intestine) are synthesized in the body, the rest need to be taken in orally.
o Two types, based on solubility:
o 1) Water-soluble vitamins:
o B complex and C are absorbed with water.
o B12 absorption requires intrinsic factor.
o Not stored in the body.
o 2) Fat-soluble vitamins:
o A, D, E, and K are absorbed with lipid digestion products (fatty chyme).
o Stored in the body, except for vitamin K.
o Vitamins A, C, and E act as antioxidants.
o Free radicals = unpaired electrons are produced as a result of oxidation caused by oxygen and can lead to cell damage or cell death).
Minerals:
o Seven required in moderate amounts: Calcium, phosphorus, potassium, sulfur, sodium, chloride, and magnesium (helps in Ca++ absorption).
o Others required in trace amounts.
o Work with nutrients to ensure proper body functioning = bone and teeth, neuron conductivity, heart rythym, acid-base, enzyme formation).
o Uptake and excretion must be balanced to prevent toxic overload.
Metabolism:
o Metabolism: the sum of all the biochemical reactions that take place in the body.
o Two types of reactions:
o Anabolism: synthesis of large or complex molecules from small ones.
o Catabolism: breakdown of complex molecules to simpler ones.
Stages of Metabolism:
o Processing of nutrients:
o 1) Digestion, absorption and transport to tissues.
o 2) Cellular processing (in cytoplasm). Anabolism or synthesis of lipids, proteins, and glycogen, or Catabolism (glycolysis) into intermediates pyruvic acid and acetyl CoA.
o 3) Oxidative (mitochondrial) breakdown of glucose into CO2, water, and ATP = catabolism.
ATP Synthesis:
o Two mechanisms for ATP Synthesis:
o Substrate-level phosphorylation (glycolysis and Kreb’s cycle).
o Oxidative phosphorylation (yields the most ATP).
Glycolysis:
o Phosphorylation is where high-energy phosphate groups directly transferred to ADP to make ATP = substrate-level phosphorylation (quick energy and occurs in the cytoplasm of the cell). o Glycolysis (catabolism of glucose): o Breakdown of glucose when it enters the cell = an anaerobic process that occurs in the cytoplasm. o Yields 2 ATP plus 2 pyruvic acid molecules.
Kreb’s Cycle:
o Occurs in the mitochondria of the cell.
o Pyruvic Acid produced by glycolysis and also fat breakdown is converted through oxidation (decarboxylation) to form acetyl CoA.
o Acetyl CoA enters the Krebs Cycle (series of many chemical reactions = oxidation / reductions where CO2 and 2 ATP are made.
Oxidative Phosphorylation:
o Makes most of the ATP (= 28) during cellular respiration by pushing H+ (protons) across membranes within the mitochondria through the electron transport chain.
o H+ (protons) then come back across the mitochondrial membranes due to a “proton gradient” which creates electrical current or much energy which is used to attach many PO4 groups to ADP to make many ATP.
o H20 is produced as well.
Glycogenesis and Glycogenolysis:
o Glycogenesis:
o Glycogen formation when glucose supplies exceed need for ATP synthesis.
o Occurs mostly in liver and skeletal muscle.
o Glycogenolysis:
o Glycogen breakdown in response to low blood glucose (ATP = body’s fuel).
Gluconeogenesis:
o Glucose formation from noncarbohydrate (glycerol and amino acid) molecules.
o Occurs mainly in the liver.
o Protects against the damaging effects of hypoglycemia.
Lipid Metabolism:
o Fat catabolism yields 9 kcal per gram (vs 4 kcal per gram of carbohydrate or protein).
o Most TG from digestion are transported as chylomicrons in blood (chylomicrons are produced by intestinal cells).
o Lipolysis in liver: Triglycerides (TG) turn into Fatty acids + glycerol.
o Beta oxidation: breaks down fatty acids into 2-carbon fragments to form acetyl CoA that can enter the Kreb’s cycle.