Metabolic Pathways and Bioenergetics

Metabolic Pathways

• Metabolism is a complex network of interconnected pathways
• Pathways include metabolism of complex carbohydrates, complex lipids, lipids, energy, carbohydrates, nucleotides, amino acids, other amino acids, cofactors and vitamins, and biosynthesis of secondary metabolites
• Biodegradation of xenobiotics is also a part of metabolic pathways
• All these pathways are interconnected

Bioenergetics and Metabolism

• Metabolism is a very complicated network where all pathways are connected

Cellular Respiration

• Describes how organisms acquire and transform energy to perform biological work
• Studies different biological processes that lead to energy production and utilization (e.g., ATP, GTP)
• Metabolism is the sum of chemical reactions to maintain the organism's living state
• Divided into catabolism (breaking down molecules for energy) and anabolism (building compounds needed by the cells). These two processes are coupled
• Metabolism is linked to nutrition and nutrient availability

Cell Macromolecules

• Cell macromolecules include proteins, polysaccharides, lipids, and nucleic acids
• NAD and FAD are hydrogen carriers. NADP is not used for energy metabolism
• Chemical energy produced is stored in ATP, NADH, NADPH, and FADH2

Types of Cell Respiration

• Aerobic respiration utilizes oxygen to produce 30 ATP molecules per glucose molecule
• Anaerobic respiration does not use oxygen; produces only 2 ATP molecules per glucose molecule, using inorganic molecules as oxidants
• Glycolysis, TCA cycle, and electron transport chain are phases of aerobic cell respiration

Entropy

• Measure of a system's thermal energy unavailable for useful work per unit temperature
• Heat production is associated with entropy

Enthalpy

• State function determined by internal energy, pressure, and volume
• Simplifies energy transfer descriptions
• Under standard conditions, enthalpy changes equal energy transferred from the environment through heating or work, excluding expansion work
• Measured as enthalpy change (ΔH)
• ΔH is positive in endothermic reactions and negative in exothermic processes

Redox Reactions

• Chemical reactions where oxidation numbers change due to electron gain or loss
• Coupled oxidation reactions with reduction in many biological processes
• Oxidation is loss of electrons; reduction is gain of electrons
• Electrons, protons, and hydrogen ions are associated with redox reactions

High Energy Phosphate

• ATP formed by adding phosphate to ADP (phosphorylation)
• ATP releases phosphate ions to provide energy for cellular metabolism; ADP reappears
• ADP can further release phosphate to generate AMP or non-phosphorylated adenosine in response to urgent oxygen need (e.g., myocardial infarction)
• This process increases vasodilation

Oxidative Phosphorylation

• ATP formed as a result of electron transfer
• Electrons transfer from NADH or FADH2 to O2 through a series of electron carriers in the electron transport chain
• The energy from these redox reactions is captured as a proton gradient
• Chemiosmosis, a proton-dependent process for ATP synthesis
• Mitochondria are the major site of ATP production in aerobic organisms

Electron Transport Chain

• Series of complexes transferring electrons from electron donors to acceptors via redox reactions
• Electron transfer couples with proton transfer (H+ ions) across membrane
• Creates an electrochemical proton gradient driving ATP synthesis
• ETC components include peptides, enzymes, and other molecules
• The final electron acceptor in aerobic respiration is O2 (oxygen)

Substrate Level Phosphorylation

• Direct phosphorylation of ADP with phosphate from a coupled reaction
• ATP generated from the oxidation of NADH and FADH2, and the subsequent electron transfer and proton pumping
• ATP is directly generated, unlike oxidative phosphorylation

Carbohydrates Metabolism

• Stage 1: Digestion and hydrolysis break down large carbohydrates into smaller molecules that enter the bloodstream
• Stage 2: Degradation breaks down the smaller molecules into two- and three-carbon compounds
• Stage 3: Oxidation of small molecules in the citric acid cycle and electron transport, generating ATP energy

Glycolysis

• Metabolic pathway degrading glucose to pyruvate (six-carbon to three-carbon molecule)
• Anaerobic process occurring in the cytoplasm
• Divided into 2 stages:
  • Stage A: Reaction steps that consume energy
  • Stage B: Reaction steps that produce energy

TCA Cycle (Krebs Cycle)

• Requires oxygen, occurring within aerobic organisms
• Oxidation of Acetyl-CoA to CO2 and Chemical energy, producing energy in the form of ATP. This process happens in the mitochondria
• Key process in extracting energy from carbohydrates, fats, and amino acids.

Glycogenesis

• Process for storing glucose by converting it into glycogen in the liver and muscles
• Occurs when high levels of glucose-6-phosphate are produced during glycolysis
• Doesn't happen when glycogen stores are full or when energy stores are sufficient. Additional glucose is converted to fat

Glycogenolysis

• Process of breaking down glycogen to glucose in the liver and muscles
• Occurs when blood glucose levels drop below 70mg%
• Glucose-1-phosphate is a product

Gluconeogenesis

• Generation of glucose from non-carbohydrate substrates (e.g., amino acids, lipids)
• Occurs when glycogen stores are depleted.
• Occurs in starvation or diabetes, when the body cannot use glucose

Pentose Phosphate Pathway (PPP)

• Parallel metabolic pathway to glycolysis
• Generates NADPH and pentoses (e.g., ribose-5-phosphate)
• Important for nucleotide synthesis
• Also involved in fatty acid biosynthesis

Lipid Metabolism

• Synthesis and degradation of lipids, including fat breakdown or storage for energy
• Lipids obtained from consuming food or produced by the liver
• Minimal amount of essential fat needed in the diet. Essential fatty acids are critical for synthesis.
• Fat soluble vitamins are also absorbed
• Fatty acids can generate 9.1 calories per gram
• End products include carbon dioxide (CO2), water (H2O), and ATP
• Complete combustion requires glucose for conversion and avoids ketone production

Lipolysis

• Breakdown of triglycerides into fatty acids and glycerol
• Released fatty acids in blood, used by other tissues for beta-oxidation and ATP production, and may be re-esterified back into intracellular triglycerides
• Process regulated by autonomic nervous system and hormones (e.g., catecholamines)

Beta Oxidation of Fatty Acids

• Degrading saturated fatty acyl-CoA
• Repeated four-step reaction cycle
• Shortens the fatty acyl chain by two carbons
• Produces FADH2, NADH, and acetyl-CoA

Ketogenesis

• Process producing ketone bodies from fatty acids and ketogenic amino acids when the body cannot use glucose
• Ketone bodies include acetoacetate and β-hydroxybutyrate, also acetone. These are energy sources
• These are produced when the body needs energy and glucose isn't available

Protein Metabolism

• Proteins too large for absorption, are broken down into amino acids through proteolytic enzymes
• Enzymes produced by stomach, pancreas, and small intestine
• Amino acids are absorbed and utilized or converted to other molecules (e.g. , glucose, glycogen, fatty acids)

Amino Acid Catabolism

• First phase involves removing the α-amino groups, producing ammonia
• The carbon skeletons are then further metabolized via central pathways.
• Occurs in two phases, with transamination in the initial phase, followed by oxidative deamination in a further reaction, to produce urea or other catabolic products.

Explore the intricate network of metabolic pathways and their connection to bioenergetics. This quiz covers the metabolism of carbohydrates, lipids, amino acids, and more, delving into cellular respiration and energy transformation in biological systems. Understand how catabolism and anabolism interplay to maintain life.