SALADIN C. 26 Nutrition & Metabolism,
Body Weight & Energy Balance • 30 – 50% of variation in human body weight is heredity, rest is environmental factors – eating & exercise habits.
Appetite • Many peptide hormones & regulatory pathways are involved in short & long term appetite control • Short term regulators • Ghrelin – from stomach – sensation of hunger + stimulates hypothalamus to release • GHRH
Appetite • Peptide YY [PYY] – from ileum & colon – secreted with feeding – proportional to calories consumed – stop eating signal. • CCK – from SI – stimulates secretion of bile & pancreatic enzymes. – Also causes appetite suppressing effect on vagus – a stop eating signal
Appetite • Long term regulators • Leptin – from adipocytes – proportional to levels of body fat – most human obesity related to leptin is due to receptor defect, not hormone defect • Insulin – from pancreas – receptors in brain – functions like leptin - weaker
Appetite • Brain center = arcuate nucleus of hypothalamus – 2 groups of neurons 1 – secretes neuropeptide Y – stimulates appetite 2 – secretes melanocortin – inhibits eating Gastric peristalsis also stimulates hunger
Control of Feeding & Satiety Figure 24.23
Appetite • Neurotransmitters influence types of food consumed • Norepinephrine – CBH • Galanin – fat • Endorphins - protein
Appetite • Obesity – more than 20% above norm for demographic. In US 30% are obese and an additional • 35% are overweight. • Predisposition to obesity is increased by over-feeding in infancy and early childhood.
Heat – kinetic energy • Heat = kinetic energy • calorie-amount of heat required to raise one gram of H2O 1oC
Energy Yields • Carbohydrates - 4Kcal/g • Lipid- 9 Kcal/g • Protein – 4 Kcal/g
Nutrients • Nutrient – a substance that promotes normal growth, maintenance, and repair. • Major nutrients – carbohydrates, lipids, and proteins. • Other nutrients – vitamins and minerals (and technically speaking, water).
Nutrition – [see www.mypyramid.gov for details] Figure 24.1
CBH Fates of CBH’s • ATP production – aerobic respiration, anaerobic fermentation • Glycogen & adipose storage • Amino Acid synthesis • Structural component of nucleotides, glycoproteins, glycolipids
CBH • Excretion – spill over onto urine • Neurons & erythrocytes depend almost entirely on CBH • Review Insulin/glucagon homeostasis – Ch 17; CBH in API notes
Requirements – higher than other nutrients • Sources – plants • Fiber – resist digestion – plant & animal
CBH • Promotes intestinal function. Water soluble forms reduce blood cholesterol & LDL’s. • Blood sugar levels – 70 -110 mg/dL = normal
Lipids • Fatty acids, glycerol, cholesterol • Meet 80 – 90% of resting energy needs • Required for absorption of fat soluble vitamins • Membrane & hormone structural components.
Lipids • Needs – no more than 30% of diet – most should be unsaturated; • Must get linoleic acid from diet – rest appear to be able to be made.
Lipids Cholesterol Metabolism • Structural unit of bile salts, steroids, Vitamin D and cell membranes. • 15% of blood cholesterol is from diet • 85% is made by the body
Lipids • Cholesterol & Lipoproteins - transported as spheres • The spheres are lipoproteins – hydrophobic triglycerides & cholesterol esters are in interior, hydrophilic phospholipid heads, cholesterol & proteins are on exterior
Lipids Classes • Chylomicrons – 2% protein, 90% triglyceride, 3% phospholipid, 5% cholesterol • VLDL – 8% protein, 55% triglycerides, 17% phospholipid, 20% cholesterol
Lipids • LDL (bad cholesterol – gets deposited in blood vessels) 20% protein, 6% triglyceride, 21% phospholipid, 53% cholesterol – gets deposited in vessel walls [from adipose]. • HDL – 50% protein, 5% triglyceride, 25% phospholipid, 20% cholesterol (good cholesterol) cleared by liver – no vascular buildup. [transport TO liver]
Lipids Desirable levels • Total cholesterol - < 200mg/dL • LDL < 130mg/dL • HDL > 40mg/dL [60 or higher gives some protection against heart disease] • Total <200mg/dL • Ratio of total/HDL <4 desired
Lipids • Bad • LDL > 159 mg/dL • Total > 239 mg/dL
Lipids Factors regulating plasma cholesterol • Increased dietary cholesterol decreases liver production, BUT doesn’t stop it. • Saturated fatty acids increase liver synthesis and decrease excretion • Unsaturated fatty acids increase excretion • Hydrogenated fats increase LDL’s and decrease HDL [worst effect of all]
Proteins Proteins amino acids • 8 essential amino acids - we don't or can't make enough • 12 non-essential - synthesized by the body by transamination. • Not stored – must be present from ingestion. • Nitrogen balance –in = out – positive with growth, negative with insufficiency.
Vitamins & Mnerals • Vitamins – review table 26.3 • Fat soluble - A, D, E, K • Water soluble - B1, B2, niacin, B6, B12, Folic acid, C • Minerals – review table 26.2 - Ca, P, Fe, I, Cu, Na, K, Cl, Mg, S, Zn, F, Mn
Metabolism • Metabolism – all chemical reactions necessary to maintain life. • Anabolic reactions – synthesis of larger molecules from smaller ones. • Catabolic reactions – hydrolysis of complex structures into simpler ones.
CBH Metabolism • All oxidative CBH consumption is essentially glucose catabolism C6H12O6 + 6O2 6H2O +6CO2 + ATP [+heat] • Glucose catabolism – glycolysis, anaerobic fermentation, aerobic respiration
Oxidation-Reduction (Redox) Reactions • Oxidation removes electrons. • Reduction adds electrons. • Coenzymes act as hydrogen (or electron pair) acceptors. • Two important coenzymes are nicotinamide adenine dinucleotide (NAD+)and flavin adenine dinucleotide (FAD).
Carbohydrate Metabolism • Glucose is catabolized in three pathways: • Glycolysis & anaerobic fermentation • Krebs cycle • The electron transport chain & oxidative phosphorylation
Carbohydrate Catabolism Figure 24.5
Glycolysis • A three-phase pathway in which: • Glucose is oxidized into pyruvic acid. • NAD+ is reduced to NADH + H+. • ATP is synthesized by substrate-level phosphorylation.
Glycolysis • Glycolysis – occurs in cytoplasm – converts glucose to pyruvate • Immediately upon entry into the cell, glucose is converted to glucose-6-phosphate • 10 steps –SEE HANDOUT and Figure 26.3 • Ends [for 1 glucose] 2 pyruvates, 2 net ATP and 2NADH + 2H+
Glycolysis Anaerobic fermentation • Glucose Metabolism in the Absence of O2 • Lactic acid fermentation – in muscle cells • Starts with pyruvate and NADH • Produces lactic acid and NAD+. Lactic acid can be used in liver for glucose synthesis. • Renews NAD+ in cytoplasm for continued ATP production.
Matrix Reactions • Starts with pyruvate, NAD+ and Coenzyme A [CoA] --> AcetylCoA + CO2 + NADH + H+ • Runs twice per original glucose 2 Acetyl CoA’s
Matrix Reactions • Kreb’s Cycle – in matrix of mitochondrion • 8 steps – SEE Handout • Starts with Acetyl CoA, oxaloacetic acid, NAD+, FAD+ • Runs twice per original glucose molecule • Ends - [with 2 pyruvates] 6CO2 + 2 ATP + 8 NADH + 8H+ + 2FADH2
Membrane Reactions • Membrane reactions - oxidize NADH & FADH2 to move electrons, & regenerate NAD+ & FAD+ • Electron Transport System – on inner mitochondrial membrane – cristae - pumps H+ ions for Chemiosmosis.
Membrane Reactions • Need electron carriers – pass electrons from one carrier to another by paired redox reactions. • Carriers = Flavin Mononucleotide [FMN], cytochromes, Fe-S centers, Cu, Coenzyme Q.
Electronic Energy Gradient Figure 24.9
Membrane Reactions 3 pumps present • 1 – NADH dehydrogenase complex – FMN & 5 Fe-S centers – start – NADH + H+ is oxidized to NAD+ and FMN is reduced to FMNH2. Ends with Coenzyme Q – a mobile carrier that transports the electrons it receives to the next pump.
Membrane Reactions • 2 – Cytochrome b-c1 complex – electrons passed from Q to cyt b --- to cyt c –> passes electrons to next pump • 3 – cytochrome oxidase complex – receives electrons from cyt c & passes them o Cu then to cyt a, cyt a3 & then to O. The negative O picks up 2 H+ H2O [only place in respiration where O is consumed!!!]
Chemiosmosis • Energy from step-wise release powers pumping H+ into intermembrane space by chemiosmosis • The concentration of H+ outside > than that inside – this produces an electrostatic gradient and a net voltage. • Since it is positive charges – it is called proton motive force instead of electromotive force (from electron distribution).
Chemiosmosis • Facilitated diffusion channels containing enzymes for ATP formation [ATP synthase] allow the H+ to move back across the membrane driven by this force. • The energy from the force is used for the ATP production.