Chapter 24 - Nutrition and Metabolism
What is glycogenesis?
-glucose molecules are combined in long chains to form glycogen -begins as glucose entering cells is phosphorylated into glucose-6-phosphate and then converted to its isomer glucose-1-phosphate
Know the steps of the electron transport chain
-hydrogens removed during the oxidation of food fuels are combined with O2 to form water and the energy released during those reactions is harnessed to attach Pi groups to ADP, forming ATP (oxidative phosphorylation) -
Know the steps of the citric acid cycle
-1: Decarboxylation: one of pyruvic acid's carbons is removed and released as carbon dioxide gas (decarboxylation); CO2 diffuses out of the cells into the blood to be expelled by the lungs -2: Oxidation: the remaining 2C fragment is oxidized to acetic acid by removing hydrogen atoms, which are picked up by NAD+ -3: Formation of acetyl CoA: acetic acid is combined with coenzyme A to produce the reactive final product, acetyl coenzyme A (Acetyl CoA)
Know the efficiency of ATP production of all the steps of glucose metabolism
-When O2 is present, cellular respiration is remarkably efficient -substrate-level phosphorylation: gives us a net gain of 4 ATP (2 during glycolysis and 2 during the citric acid cycle -oxidative phosphorylation: NADH + H+ and FADH2 feeding into oxidative phosphorylation give us about 28 ATP -the oxidation of FADH2 is less efficient because it doesn't donate electrons to the "top" of the electron transport chain as does NADH + H+, but to a lower energy level (at complex II).
What is transamination?
-a number of amino acids can transfer their amine group to a-ketoglutaric acid (a citric acid cycle keto acid), thereby transforming a-ketoglutaric acid to glutamic acid -in the process, the original amino acid becomes a keto acid -this reaction is fully reversible
What are nutrients?
-a substance in food the body uses to promote normal growth, maintenance, and repair -nutrients needed for health divide into five categories: carbohydrates, lipids, and proteins are macronutrients; vitamins and minerals are micronutrients
What is metabolism?
-a variety of biochemical reactions -sum of all biochemical reactions in the body -during metabolism, substances are constantly built up and torn down -cells use energy to extract more energy from foods, and then use some of this extracted energy to drive their activites -is either anabolic or catabolic
What is the citric acid cycle?
-aka Krebs cycle -next stage of glucose oxidation and is named for its first substrate -occurs in the mitochondrial matrix and is fueled largely by pyruvic acid produced during glycolysis and by fatty acids resulting from fat breakdown
What is the post-absorptive state?
-aka fasting state -the period when the GI tract is empty and body reserves are broken down to supply energy -net synthesis of fat, glycogen, and proteins ends, and catabolism of these substances beginds -the primary goal during the post-absorptive state is to maintain blood glucose levels within the homeostatic rnage -most events of the post-absorptive state either make glucose available to the blood or make certain organs (ex: skeletal muscle) switch over to using fats instead of glucose to spare glucose for organs that can't use fats
What is the absorptive state?
-aka fed state -lasts about five hours after eating beings, when nutrients are flushing into the blood from the GI tract -anabolism exceeds catabolism and nutrients are stored -glucose is the major energy fuel -dietary amino acids and fats are used to remake degraded body protein or fat, and small amounts are oxidized to provide ATP -excess metabolites, regardless of source, are transformed to fat if not used for anabolism
What is glycolysis?
-also called glycotic pathway -occurs in the cytosol of cells -series of ten chemical steps to convert glucose to two pyruvic acid molecules -an anaerobic proces -does not use oxygen and occurs whether or not oxygen is present
How are proteins synthesized?
-amino acids are most important anabolic nutrients (form all protein structures and bulk of body's functional molecules) -protein synthesis occurs on ribosomes where ribosomal enzymes oversee the formation of peptide bonds linking the amino acids together into protein polymers -hormones precisely control the amount and type of protein synthesized -the rate of protein anabolism changes as we age and our balance of hormones changes -during your lifetime, your cells will synthesize 225-450kg proteins, depending on your size
What is the difference between a LDL and HDL?
-as a rule, high levels of HDLs are considered good because the transported cholesterol is destined for degradation (think H for healthy) -high LDL levels are considered bad (think L for lousy) because when LDLs are excessive, potentially lethal cholesterol deposits are laid down in the artery walls -a good rule of thumb is that HDL levels can't be too high and LDL levels can't be too low
What are essential nutrients?
-at least 45 and possibly 50 molecules -cannot be made fast enough to meet the body's needs so our diet must provide them -as long as we ingest all the essential nutrients, the body can synthesize the hundreds of additional molecules required for life and good health
How are cholesterol and triglycerides transported in blood?
-because triglycerides and cholesterol are insoluble in water, they don't circulate free in the blood -instead they are transported to and from tissue cells bound to small lipid-protein complexes called lipoproteins -these complexes solubilize the hydrophobic lipids, and contain signals that regulate lipid entry and exit at specific target cells
Minerals
-body requires moderate amounts of seven minerals (calcium, phosphorus, potassium, sulfur, sodium, chlorine, magnesium) and trace amounts of about a dozen others -make up about 4% of body weight -not used for fuel but work with other nutrients to ensure a smoothly functioning body -most are ionized in body fluids or bound to organic compounds to form phospholipids, hormones, and various proteins
What is the electron transport chain?
-carries out the final catabolic reactions that occur on the inner mitochondrial membrane -requires oxygen
What aids redox reactions?
-catalyzed by enzymes -those that catalyze redox reactions in which hydrogen atoms are removed are called dehydrogenases while enzymes catalyzing the transfer of oxygen are oxidases
What is anabolism?
-general term for all reactions that build larger molecules or structures from smaller ones -example: bonding together of amino acids to build proteins
What is carbohydrate metabolism?
-glucose enters tissue cells by facilitated diffusion, a process that is greatly enhanced by insulin -immediately after entering a cell, glucose is phosphorylated to glucose-6-phosphate by transfer of a phosphate group to its sixth carbon during a couple reaction with ATP -most body cells lack the enzymes needed to reverse this reaction, so it effectively traps glucose inside the cells -the reaction also keeps intracellular glucose levels low, maintaining a concentration gradient for glucose entry -only intestinal epithelial cells, kidney tubule cells, and liver cells have the enzymes needed to revers this phosphorylation reaction
Carbohydrates
-glucose is THE carbohydrate molecule ultimately used as fuel for the body cells to produce ATP -can be received from sugars (monosaccharides and disaccharides), starch (polysaccharide), cellulose (polysaccharide)
What is oxidative deamination?
-in the liver, the amine group of glutamic acid is removed as ammonia, and a-ketoglutaric acid is regenerated -the NH3 molecules are combined with CO2, yielding urea and water -the urea is released to the blood and excreted from the body in urine -because ammonia is toxic to body cells, the ease with which glutamic acid funnels amine groups into the urea cycle is extremely important -this cycle rids the body not only of NH3 produced during oxidative deamination, but also of bloodborne NH3 produced by intestinal bacteria
What is keto acid modification?
-keto acids resulting from transamination are altered as necessary to produce metabolites that can enter the citric acid cycle -the most important of these metabolites are pyruvic acid, acetyl CoA, a-ketoglutaric acid, and oxaloacetic acid -because the reactions of glycolysis are reversible, deaminated amino acids that are converted to pyruvic acid can be reconverted to glucose and contribute to gluconeogenesis
Compare and contrast micronutrients and macronutrients
-macronutrients make up the bulk of what we eat; these include carbohydrates, lipids, and proteins -micronutrients are equally crucial for health but are only required in minute amounts; these include vitamins and minerals
Lipids
-most abundant dietary lipids are triglycerides -necessary in the body -fatty deposits in adipose tissue provide a protective cushioning around body organs, and insulating layer beneath the skin, and an easy to store concentrated source of energy -phospholipids are an integral component of myelin sheaths and cellular membranes -cholesterol is a stabilizing component of plasma membranes and is a precursor from which bile salts, steroid hormones, and other essential molecules are formed -prostaglandins (regulatory molecules formed from linoleic acid via arachidonic acid) play a role in smooth muscle contraction, control of blood pressure, and inflammation -triglycerides are the major energy fuel of skeletal muscle and hepatocytes -fat helps the body absorb fat-soluble vitamins
Vitamins
-organic compounds needed in minute amounts for growth and good health -unlike other organic nutrients, vitamins do not serve as an energy source nor as building blocks, but they are crucial in helping the body use those nutrients that do -without vitamins, all the carbohydrates, proteins, and fats we eat would be useless -either water soluble or fat soluble -water soluble (B, C) are absorbed along with water from the gastrointestinal tract -fat soluble (A, D, E, and K) bind to ingested lipids and are absorbed along with their digestion products
Proteins (all or none rule)
-proteins in eggs, milk, fish, and most meats are complete proteins that meet all the body's amino acid requirements for tissue maintenance and growth -all or none rule: all amino acids needed to make a particular protein must be present in a cell at the same time and in sufficient amounts. If one is missing, the protein cannot be made. Because essential amino acids cannot be stored, those not used immediately to build proteins are oxidized for energy or converted to carbohydrates or fats
What is reduction?
-reduced substances gain energy as the energy-rich electrons are transferred from one substance to the next
What is catabolism?
-refers to all processes that break down complex structures to simpler ones -example: the hydrolysis of foods in the digestive tract
What are the three stages for metabolism?
-stage 1: digestion in the gastrointestinal tract. Absorbed nutrients are then transported in blood to tissue cells -stage 2: occurs in tissue cells; newly delivered nutrients are either built into lipids, proteins, and glycogen by anabolic pathways or broken down by catabolic pathway to pyruvic acid and acetylCoA in the cell cytoplasm -stage 3: occurs in the mitochondria; almost entirely catabolic; requires oxygen, and completes the breakdown of foods, producing carbon dioxide and water and harvesting large amounts of ATP
Know the steps of glycolysis
-step 1: sugar activation; glucose is phosphorylated and converted to fructose-6-phosphate, which is then phosphorylated again -step 2: sugar cleavage: fructose-1,6-biphosphate is split into two 3-carbon fragments that exist as one of two isomers (glyceraldehyde 3-phosphate or dihydroxyacetone phosphate) -step 3: sugar oxidation: the two 3-carbon gragments are oxidized by the removal of hydrogen, which NAD+ picks up; inorganic phosphates groups are attached to each oxidized fragment by high-energy bonds; when these terminal phosphates are split off, enough energy is captured to form four ATP molecules
What are the three main modes of ATP synthesis?
-stubstrate-level phosphorylation -oxidative phosphorylation -chemiosmotic processes
What is lipolysis?
-the breakdown of stored fats into glycerol and fatty acids -essentially lipogenesis in reverse -fatty acids and glycerol are released into the blood, helping to ensure that body organs have continuous access to fat fuels for aerobic respiration -when carbohydrate intake is inadequate, lipolysis accelerates as the body attempts to fill the fuel gap with fats'
What is oxidation?
-the combination of oxygen with other elements, seen in the rusting of iron and the burning of wood -also occurs when hydrogen atoms are removed from compounds -the gain of oxygen or the loss of hydrogen
What is lipogenesis?
-triglyceride synthesis -occurs when cellular ATP and glucose levels are high -excess ATP leads to an accumulation of acetyl CoA and glyceraldehyde 3-phosphate -acetyl CoA molecules are joined together, forming fatty acid chains that grow two carbons at a time -glyceraldehyde 3-phosphate is converted to glycerol, which is joined with fatty acids to form triglycerides -when blood sugar is high, lipogenesis is the major activity in adipose tissues and is also an important liver function
What is glycogenolysis?
-when blood glucose levels drop, glycogen splitting occurs -the enzyme glycogen phosphorylase oversees phosphorylation and splitting of glycogen to release glucose-1-phosphate which is then converted to glucose-6-phosphate, a form that can enter the glycolysis pathway to be oxidized for energy
What is gluoneogenesis?
-when too little glucose is available to stoke the "metabolic furnace," glycerol and amino acids are converted to glucose -the process of forming new glucose from noncarbohydrate molecules, occurs in the liver -takes place when dietary sources and glucose reserves have been used up and blood glucose levels are beginning to drop
Know the food pyramid and where certain substances are positioned on the chart
NOTES
What is oxidative phosphorylation?
more complicated, but also releases most of the energy that is eventually captured in ATP bonds during cellular respiration; carried out by electron transport proteins embedded in the inner mitochondrial membranes; is an example of a chemiosmotic process
What is substrate-level phosphorylation?
occurs when high-energy phosphate groups are transferred directly from phosphorylated substrates (metabolic intermediates such as glyceraldehyde 3-phosphate) to ADP