Biochemistry and physiology p.2 test 3

Carbohydrate Digestion

• Monosaccharides are the simplest carbs that cannot be further hydrolyzed
• Examples of monosaccharides: Glucose, Fructose, and Galactose
• Disaccharides consist of two monosaccharide units
• Examples of disaccharides: Maltose (Glucose + Glucose), Lactose (Glucose + Galactose), and Sucrose (Glucose + Fructose)
• Oligosaccharides contain a small number (2-10) of monosaccharide units
• Polysaccharides are large polymers of monosaccharides
• Examples of Polysaccharides: Starch, Glycogen, and Cellulose

Lipid Digestion

• Monosaccharides exist in linear (Fischer projection) and cyclic (Haworth projection) forms
• Cyclic structures form due to hemiacetal or hemiketal formation
• Glucose forms a six-membered pyranose ring
• Fructose forms a five-membered furanose ring

Protein Digestion

• Proteins are colorless, crystalline solids that are soluble in water but insoluble in nonpolar solvents
• Protein chemical properties: can be oxidized to form carboxylic acids, reduced to form sugar alcohols (e.g., glucose → sorbitol) and form glycosidic bonds to create disaccharides and polysaccharides

Enzymes and Locations

• In the stomach, pepsin (activated by HCl) hydrolyzes proteins into polypeptides
• In the small intestine, pancreatic proteases such as trypsin & chymotrypsin cleave peptide bonds, while carboxypeptidase removes terminal amino acids, and aminopeptidase & dipeptidase cleave peptides into free amino acids
• Free amino acids are absorbed via Na⁺-dependent active transport

Protein Digestion in Ruminants vs. Non-Ruminants

• In ruminants, rumen microbes digest dietary protein, producing microbial protein
• Microbial proteases degrade proteins into peptides & ammonia
• Microbes synthesize new proteins from ammonia and volatile fatty acids
• Rumen Undegradable Protein (RUP) passes to the small intestine for absorption
• Non-ruminants utilize gastric and pancreatic enzymes for protein digestion

Chemical Composition of Membranes

• Membranes are composed of lipids, proteins, and carbohydrates
• Lipids include phospholipids, sphingolipids, and cholesterol
• Proteins can be integral or peripheral
• Carbohydrates are present as glycolipids and glycoproteins for cell recognition

Structural Elements of Membranes

• Phospholipid bilayers have hydrophilic heads facing outward and hydrophobic tails facing inward
• Integral proteins are embedded and help in transport
• Peripheral proteins are attached to surfaces and involved in signaling
• Carbohydrates are attached to proteins (glycoproteins) or lipids (glycolipids, and are crucial for cell recognition

Types of Membrane Transport

• Passive transport requires no energy
• Diffusion involves movement from high to low concentration
• Facilitated diffusion uses carrier or channel proteins
• Osmosis is water movement through the membrane via aquaporins.
• Active transport needs energy (ATP)
• Primary active transport uses ATP directly (e.g., Sodium-Potassium pump: 3 Na+ out, 2 K+ in)
• Secondary active transport uses energy from another molecule's concentration gradient (e.g., glucose transport)
• Bulk transport: Endocytosis engulfs substances, while exocytosis releases them

Carbohydrates

• Amylose is unbranched with α-1,4 glycosidic bonds
• Amylopectin is branched, with α-1,4 and α-1,6 glycosidic bonds

Glycogen

• Glycogen is similar to amylopectin but more highly branched (every 8–12 glucose units)

Cellulose

• Cellulose has β-1,4 glycosidic bonds, indigestible by humans

Glycolysis Stages

• Fehling’s/Benedict’s Test gives a brick-red precipitate (Cu₂O) if positive
• Iodine test gives a blue-black color with starch, reddish-brown with glycogen
• Stage 1 (Energy Investment Phase, Reactions 1-5)
• Glucose is converted to Glucose-6-Phosphate (G6P) using Hexokinase/Glucokinase (in liver) and consumes 1 ATP
• G6P becomes Fructose-6-Phosphate (F6P) via Phosphoglucose Isomerase
• F6P turns into Fructose-1,6-Bisphosphate (F1,6BP) with Phosphofructokinase-1 (PFK-1) and consumes 1 ATP
• F1,6BP results in Glyceraldehyde-3-Phosphate (G3P) + Dihydroxyacetone Phosphate (DHAP) using Aldolase
• DHAP makes G3P via Triose Phosphate Isomerase
• Net ATP used: -2
• Stage 2 (Energy Payoff Phase, Reactions 6-10)
• G3P leads to 1,3-Bisphosphoglycerate (1,3-BPG) using Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH), producing NADH
• 1,3-BPG converts to 3-Phosphoglycerate (3PG) using Phosphoglycerate Kinase, generating 2 ATP (substrate-level phosphorylation)
• 3PG becomes 2-Phosphoglycerate (2PG) with Phosphoglycerate Mutase
• 2PG becomes Phosphoenolpyruvate (PEP) via Enolase
• PEP leads to Pyruvate, using Pyruvate Kinase generating 2 ATP (substrate-level phosphorylation)
• Net ATP produced: +4 ATP, +2 NADH, +2 Pyruvate.
• Overall ATP Yield: +2 ATP per glucose.

Pyruvate Fates

• Aerobic conditions:
• Pyruvate is converted to Acetyl-CoA by Pyruvate Dehydrogenase Complex (PDC)
• Acetyl-CoA enters the Krebs Cycle for further oxidation, yielding CO₂, NADH, and Acetyl-CoA.
• Anaerobic conditions:
• Pyruvate is converted to Lactate by Lactate Dehydrogenase
• This regenerates NAD⁺, allowing glycolysis to continue
• Lactate production regenerates NAD⁺ for glycolysis in the absence of oxygen
• Lactic Acid Fermentation:
• Pyruvate → Lactate (via Lactate Dehydrogenase)
• NADH is oxidized to NAD⁺, allowing glycolysis to continue
• Alcoholic Fermentation (Yeast):
• Pyruvate → Acetaldehyde + CO₂ (via Pyruvate Decarboxylase)
• Acetaldehyde → Ethanol (via Alcohol Dehydrogenase)
• Regenerates NAD⁺ for glycolysis.

Oxidative Decarboxylation

• Enzyme Complex: Pyruvate Dehydrogenase Complex (PDC)
• Coenzymes involved:
• Thiamine Pyrophosphate (TPP) – (Bound to E1)
• Lipoamide – (Bound to E2)
• Coenzyme A (CoA) – (Substrate for E2)
• FAD (Flavin Adenine Dinucleotide) – (Bound to E3)
• NAD⁺ (Nicotinamide Adenine Dinucleotide) – (Substrate for E3)
• E1: Pyruvate Decarboxylation
• Pyruvate reacts with TPP, forming Hydroxyethyl-TPP
• CO₂ is released
• E2: Acetyl Transfer to CoA
• The hydroxyethyl group is oxidized and transferred to lipoamide
• The acetyl group is transferred to Coenzyme A (CoA) forming Acetyl-CoA
• E3: Regeneration of Lipoamide
• FAD oxidizes lipoamide, regenerating its disulfide form
• NAD⁺ oxidizes FADH₂, producing NADH + H⁺
• Products: Acetyl-CoA (enters the Krebs Cycle), NADH (goes to the electron transport chain), and CO₂ (exhaled)
• Regenerated coenzymes: Lipoamide and FAD
• Non-regenerated coenzymes: NADH and Acetyl-CoA.

Krebs Cycle

• Reactions and Enzymes:
• Acetyl-CoA + Oxaloacetate → Citrate (Citrate Synthase)
• Citrate → Isocitrate (Aconitase)
• Isocitrate → α-Ketoglutarate (Isocitrate Dehydrogenase). Oxidative Decarboxylation and Produces NADH
• α-Ketoglutarate → Succinyl-CoA (α-Ketoglutarate Dehydrogenase). Oxidative Decarboxylation and Produces NADH
• Succinyl-CoA → Succinate (Succinyl-CoA Synthetase). Generates GTP/ATP, and is Substrate-Level Phosphorylation
• Succinate → Fumarate (Succinate Dehydrogenase). Produces FADH₂
• Fumarate → Malate (Fumarase)
• Malate → Oxaloacetate (Malate Dehydrogenase). Produces NADH
• Energy-producing reactions include Isocitrate → α-Ketoglutarate, α-Ketoglutarate → Succinyl-CoA, and Malate → Oxaloacetate produce NADH
• Succinate → Fumarate produces FADH₂
• Succinyl-CoA → Succinate generates ATP/GTP.

Glycolysis Energy

• To Pyruvate: Net ATP Gain: 2 ATP, NADH Produced: 2 NADH
• To Lactate: 2 ATP (same as pyruvate stage, NADH is used to convert pyruvate to lactate)
• To CO₂ and H₂O (Complete Oxidation): Glycolysis: 2 ATP, 2 NADH (5 ATP), Krebs Cycle (Per Glucose): 2 GTP, 6 NADH (15 ATP), 2 FADH₂ (3 ATP), Total ATP Yield: ~30-32 ATP per glucose
• Glycolysis to Pyruvate: 2 ATP (net), 2 NADH (5 ATP if fully oxidized in mitochondria)
• Glycolysis to Lactate (Anaerobic): 2 ATP (since NADH is used in lactate formation)
• Complete Oxidation to CO₂ & H₂O: Glycolysis: 2 ATP + 2 NADH (5 ATP), Pyruvate → Acetyl-CoA: 2 NADH (5 ATP), Krebs Cycle (2 rounds): 6 NADH (15 ATP), 2 FADH₂ (3 ATP), 2 GTP (2 ATP), Total: ~30-32 ATP per glucose molecule.
• Final Energy Yield:
• Glycolysis → Pyruvate: 8 ATP
• Pyruvate → Acetyl-CoA: 6 ATP
• Acetyl-CoA → CO₂ + H₂O (Krebs Cycle): 24 ATP
• Total ATP (Complete Oxidation of Glucose): 38 ATP

Glycogenolysis

• Stages & Enzymes:
• Glycogen Phosphorylase removes glucose from non-reducing ends, converts glycogen Glucose-1-Phosphate, and stops 4 residues before a branch point.
• Debranching Enzyme α(1,4) Transglycosylase shifts 3 glucose residues and α(1,6) Glucosidase hydrolyzes branch point glucose → Free Glucose.
• Phosphoglucomutase converts Glucose-1-Phosphate → Glucose-6-Phosphate.
• Products: Glucose-6-Phosphate (for glycolysis or blood glucose regulation) and Free Glucose (from branch points).

Glycogen Synthesis

• Steps:
• Glucose → Glucose-1-P, using Phosphoglucomutase
• Glucose-1-P + UTP → UDP-Glucose, using UDP-Glucose Pyrophosphorylase
• Glycogen Synthase forms α(1→4) glycosidic bonds
• Branching Enzyme introduces α(1→6) branches

Pentose Phosphate Pathway

• Stages:
• Oxidative Stage (Irreversible): Glucose-6-Phosphate → Ribulose-5-Phosphate, using Glucose-6-Phosphate Dehydrogenase (G6PD). Products: NADPH & CO₂.
• Non-Oxidative Stage (Reversible): Converts 3-7 carbon sugars for biosynthetic use, provides Ribose-5-Phosphate for nucleotide synthesis.
• Uses: NADPH production for fatty acid synthesis (liver, adipose tissue) and maintains glutathione in its reduced form (antioxidant in RBCs)
• Glucose-6-Phosphate Dehydrogenase Deficiency can cause hemolysis in RBCs due to oxidative stress.

Gluconeogenesis

• Not a simple reversal of glycolysis and bypasses 3 irreversible steps.
• Pyruvate → Phosphoenolpyruvate (PEP): Pyruvate Carboxylase converts Pyruvate Oxaloacetate, then PEP Carboxykinase (PEPCK) converts Oxaloacetate → PEP.
• Fructose-1,6-Bisphosphate → Fructose-6-Phosphate: Fructose-1,6-Bisphosphatase.
• Glucose-6-Phosphate → Glucose: Glucose-6-Phosphatase (in ER of liver/kidney).
• Precursors for Glucose Synthesis: Lactate (from anaerobic glycolysis), Amino Acids (mainly Alanine), Glycerol (from triglyceride breakdown).

Metabolism

• Metabolism: Energy and substance transformations along with anabolic and catabolic processes
• ATP Structure: Adenine + Ribose + Three Phosphate groups
• Role: Anabolic Reactions provide energy for biosynthesis.
• Catabolic Reactions: ATP is regenerated via glycolysis, Krebs cycle, and oxidative phosphorylation.

Substrate-Level Phosphorylation

• Definition & Mechanism: Substrate-level phosphorylation directly forms ATP by transferring a phosphoryl group from a high-energy intermediate to ADP.
• This process doesn't require oxygen and occurs in Glycolysis and Krebs Cycle (TCA Cycle)
• Examples:
• Glycolysis: 1,3-Bisphosphoglycerate + ADP → 3-Phosphoglycerate + ATP (enzyme: Phosphoglycerate Kinase), Phosphoenolpyruvate (PEP) + ADP → Pyruvate + ATP ( enzyme: Pyruvate Kinase)
• Krebs Cycle: Succinyl-CoA + GDP → Succinate + GTP (enzyme: Succinyl-CoA Synthetase)

Oxidative Phosphorylation

• Definition: Oxidative phosphorylation forms ATP, using energy from electron transfer in the Electron Transport Chain (ETC), and oxygen is the final electron acceptor
• Enzymes & Complexes in the Respiratory Chain:
• Complex I (NADH-CoQ Reductase): Transfers electrons from NADH to Coenzyme Q (Ubiquinone), pumping 4 H⁺ into the intermembrane space.
• Complex II (Succinate-CoQ Reductase): Transfers electrons from FADH₂ to Coenzyme Q, but does not pump protons
• Complex III (CoQ-Cytochrome c Reductase): Transfers electrons from CoQ to Cytochrome c, pumping 4 H⁺.
• Complex IV (Cytochrome c Oxidase): Transfers electrons from Cytochrome c to O₂, reducing O₂ to H₂O and pumping 2 H⁺
• Proton Transport & ATP Synthesis: Electron movement creates a proton gradient across the inner mitochondrial membrane called the proton motive force (PMF). ATP Synthase (Complex V) uses this gradient to produce ATP.

ATP Synthase

• Mechanism of ATP:
• Location: Inner mitochondrial membrane
• Structure: F₀ Subunit: Proton channel that allows H⁺ back into the matrix and F₁ Subunit: Catalyzes ATP synthesis from ADP + Pi
• Mechanism (Chemiosmotic Theory): Protons flow through F₀ due to the proton gradient, and the F₁ subunit rotates, inducing conformational changes to synthesize ATP from ADP and Pi.
• Energy Yield of Oxidative Phosphorylation:
• NADH oxidation → 3 ATP
• FADH₂ oxidation → 2 ATP
• Total ATP yield per glucose molecule (glycolysis, Krebs cycle, and oxidative phosphorylation) = 38 ATP

Utilization of Organic Nutrients

• Metabolism: All chemical reactions in the body
• Catabolism breaks down complex molecules to release energy.
• Anabolism uses energy to synthesize large molecules.
• Energy Source: During digestion, energy is transferred to the body as glucose, fatty acids, and amino acids. Some are used for synthesis, and others are oxidized, producing CO₂, H₂O, and heat.
• Absorptive and postabsorptive states:
• Absorptive State (Anabolic): Body gets energy by oxidizing nutrients absorbed from the intestine. Carbohydrates, fats, and proteins are used for growth and energy storage.
• Postabsorptive State (Catabolic): Energy is mobilized from stores, and the liver produces glucose via Glycogenolysis (breakdown of glycogen) and Gluconeogenesis (conversion of lactate, pyruvate, amino acids, glycerol into glucose).
• Carbohydrate metabolism:
• Non-Ruminants: Starch and glycogen are broken down into monosaccharides (glucose, galactose, fructose), and glucose is the main monosaccharide absorbed.
• Herbivores: Cellulose is the main carbohydrate
• Ruminants: Cellulose is converted to volatile fatty acids (VFAs) by microbes
• Simple-Stomached Herbivores: Cellulose metabolism occurs in the large intestine.
• Liver’s Role: Stores glucose as glycogen or converts it to lipids, maintaining blood glucose levels through Glycogenolysis, Gluconeogenesis, and Glucose sparing (lipids as energy)
• Protein metabolism:
• Liver functions: Converts amino acids to glucose or fatty acids, producing albumin, enzymes, and clotting factors.
• Deamination converts amino acids to keto acids, used for energy or stored as fat
• Transamination converts amino acids into non-essential amino acids.
• Urea Cycle converts toxic ammonia (NH₃) into urea for excretion.
• In Ruminants: Microbial proteins are synthesized in the forestomach, making dietary amino acid composition less important.
• Lipids metabolism: Triglycerides are the major form of energy storage
• Lipids are transported in the blood via Chylomicrons (dietary lipids) and VLDL (liver-produced lipids).
• Lipid Breakdown: Lipolysis releases fatty acids for energy.
• Glucose Sparing: During fasting, tissues switch to fat metabolism.
• Regulation of the metabolism of organic nutrients -Hormonal Control:
• Insulin lowers glucose and fatty acids in plasma.
• Glucagon stimulates glycogenolysis and gluconeogenesis.
• Cortisol and Epinephrine stimulate gluconeogenesis and glycogenolysis, respectively. Growth Hormone mobilizes fatty acids.
• Nervous System Control:
• Sympathetic increase glucose release
• Parasympathetic stimulates insulin secretion.

Body Temperature

• Normal body temperatures: 36.5–39.5°C in mammals, 38–42°C in birds, but can vary by species
• Measurement: Rectally with an electronic or liquid thermometer
• Hyperthermia: Excess heat production or reduced heat loss, occurring during exercise, infections (fever), pregnancy, and lactation.
• Hypothermia: Heat loss exceeds heat production. It is common in newborns, old animals, and small breeds, and risk factors include wet fur, prolonged exposure to cold, and inadequate fat/hair coat.
• Clinical Signs of Hypothermia: Shivering, slow breathing, lethargy, and low blood pressure, but severe cases can cause muscle stiffness, dilated pupils, and coma.
• Balance Between Heat Production and Heat Loss: Heat input must equal heat output
• Heat Production: Basal metabolism (normal energy use) and Shivering (involuntary muscle contractions)
• Non-Shivering Thermogenesis: Brown Adipose Tissue (BAT), present in newborns, hibernating animals, and is stimulated by the Sympathetic Nervous System, resulting in fat oxidation and Thyroid Hormones, thereby increasing metabolism and heat production.
• Heat Loss Mechanisms: Radiation (electromagnetic waves), Conduction (direct contact), Convection (moving air/water), and Evaporation (sweating, panting, wetting body surface).
• Thermoneutral Zone, is the most energy-efficient temperature range
• Too warm results in the body spending energy on cooling
• Too cold results in the body spending energy on warming
• Extreme Conditions: Mammals lower body temperature to 4-8°C during hibernation, while estivation is heat dormancy in hot climates
• Regulation of body temperature is controlled by reflexes:
• Sensory Input: Skin and internal organs detect temperature changes
• Integrating Center: Hypothalamus regulates body temperature
• Motor Output: Heat Stress (sweating or panting) and Cold Stress (shivering or reduced blood flow to skin)

Bioenergetics And Growth

• Energy intake = Energy expenditure to maintain body functions
• Energy Substrates: Carbohydrates (4.1 kcal/gram), Proteins (4.1 kcal/gram),, and Lipids (9.3 kcal/gram)
• Metabolic rate: total energy turnover in the body per unit of time, affected by body size, physical activity, environmental temperature, reproductive status, and hormones
• Starvation lowers metabolic rate.
• Basal Metabolic Rate (BMR): Minimum energy required for basic life functions.
• Fasting Metabolic Rate: Energy expenditure when an animal can move but is fasting.
• Maintenance Metabolic Rate: Energy required to maintain body mass without production (no milk, eggs, or movement). -Field Metabolic Rate: Average daily metabolic rate under natural conditions (hunting, feeding, resting, reproduction).
• Production animals require extra energy for work, growth, and milk/wool/egg production Total Energy Requirement = Maintenance Energy + Production Energy
• Respiratory quotient: the ratio of CO₂ produced / O₂ consumed, indicating which energy substrate is being used
• Carbohydrates have RQ = 1.0 -Proteins have RQ = 0.8 -Lipids have RQ = 0.7
• RQ > 1 suggests anaerobic respiration
• Heat increment of digestion is an increase in heat production after eating, high in ruminants, and lower in simple-stomached animals.
• Aerobic metabolic scope: ratio of maximum metabolic rate / maintenance metabolic rate. Animals can increase metabolic rate 25-35 times with intense activity
• Utilization efficiency of feed: Carnivores digest and utilize meat and fat efficiently, whereas herbivores lose about 50% of feed energy in feces, urine, and methane
• Excess energy is stored as triglycerides. Examples are Deer use fat stores for winter survival, migratory birds store fat before migration, and lactating mammals use fat reserves for milk production
• Growth and regeneration require ATP and nutrients for cell building
• Fetal Growth: Mammals – Nutrients come from the placenta, and Birds – Nutrients come from the egg yolk
• Fetal Stage/Hormonal Control: Insulin and T3 regulate growth
• Postnatal Growth: Growth Hormone (GH) and Insulin-Like Growth Factor (IGF)
• Effects of Aging cause reduced appetite, metabolic rate, muscle mass, and mental ability. Cell number decreases, and Production animals are slaughtered before aging effects occur Companion animals live longer and experience aging diseases, while aging accelerates when teeth wear down in herbivores.