Anabolic and Catabolic Pathways

Metabolic Pathways

• Metabolic pathways are either catabolic or anabolic.
• Catabolism involves the breakdown of molecules to release energy in the form of ATP.
• Anabolism involves the synthesis of complex molecules and consumes energy.
• Anabolic and catabolic pathways are metabolic processes that do opposite things.

Anabolic Pathways

• Anabolic pathways build complex molecules from simpler ones.
• These pathways require energy, usually in the form of ATP.
• Examples include protein synthesis, fat synthesis, and DNA synthesis.
• Anabolic pathways are important for growth, repair, and storing energy.

Catabolic Pathways

• Catabolic pathways break down complex molecules into simpler ones.
• These pathways release energy, usually in the form of ATP.
• Examples include glycolysis, cellular respiration, and fat breakdown.
• Catabolic pathways help provide energy for the body to perform its functions.

Key Differences

• Anabolic pathways build molecules and require energy.
• Catabolic pathways break down molecules and release energy.

Catalysts

• Catalysts help reactions happen faster, help lower the amount of energy needed for a reactions to start
• A catalyst is not used up or changed in the reaction, so it can keep working over and over.
• Catalysts lower activation energy.
• Catalysts help molecules collide correctly.
• Enzymes (biological catalysts) are special proteins in living things that speed up processes like digestion and metabolism.
• For example amylase in saliva breaks down starch into sugar.
• Cofactors and coenzymes assist enzymes in catalyzing biochemical reactions.
• Cofactors are non-protein molecules or ions.
• Coenzymes are organic, non-protein molecules derived from vitamins.

Molecular Collision

• A molecular collision happens when two molecules bump into each other.
• For a reaction to happen, there must be enough energy and correct position.
• Enzymes have an optimal temperature and pH range.
• Inhibitors are molecules that decrease enzyme activity.
• Competitive inhibitors compete with the substrate for the active site.
• Non-competitive inhibitors bind to a different part of the enzyme, changing its shape.

Biochemical Catabolic Pathways

• Energy production in cells involves biochemical pathways that convert nutrients into usable energy
• This is primarily in the form of ATP (adenosine triphosphate).

ATP

• ATP (adenosine triphosphate) is the primary energy carrier in cells.
• ATP consists of adenine (a nitrogenous base), ribose (a sugar), and three phosphate groups.
• High-energy bonds between the phosphate groups store energy.
• Hydrolysis breaks one of these bonds (usually the bond between the second and third phosphate groups) and converts ATP into ADP (adenosine diphosphate), releasing energy.
• ADP can be "recharged" back into ATP through processes like cellular respiration, replenishing the energy supply.
• Redox reactions involve two key processes: oxidation and reduction.
• Oxidation: occurs when a substance loses electrons
• Substance often gains oxygen or loses hydrogen.
• Reduction: occurs when a substance gains electrons.
• Substance typically loses oxygen or gains hydrogen.
• Electron carriers help transfer electrons during redox reactions in cells.

Carbohydrate catabolism

• Carbohydrate catabolism refers to the breakdown of carbohydrates (like glucose) to produce energy.
• There are two main pathways:
• respiration
• fermentation.

Respiration

• Respiration is a more efficient way of breaking down carbohydrates to produce energy (in the form of ATP).
• It occurs in the presence of oxygen (aerobic respiration) and involves several stages:
• Glycolysis
• breakdown of glucose (a 6-carbon sugar) into two molecules of pyruvate (3 carbons each)
• Occurs in the cytoplasm
• Produces 2 ATPs and 2 NADH molecules
• Glycolysis is a series of enzyme catalyzed chemical reactions
• Citric Acid Cycle (Krebs Cycle)
• Pyruvate molecules fuel the Krebs cycles
• Acetyl-CoA is processed through a series of reactions
• Generates 2 ATPs, 6 NADH, 2 FADH2, and 4 CO2 molecules
• Krebs cycle is a series of enzyme catalyzed chemical reactions
• Electron Transport Chain (ETC)
• NADH and FADH2 carry electrons to the ETC
• Electrons are passed through protein complexes in the mitochondria, creating a proton gradient.
• Gradient drives the production of ATP (about 34 ATPs)
• Oxygen is the final electron acceptor, forming water.
• The total energy yield from one glucose molecule through aerobic respiration is around 36–38 ATPs.

Fermentation

• Fermentation is an anaerobic process (does not require oxygen)
• Begins with glycolysis, breaking glucose into pyruvate
• Does not proceed to the citric acid cycle or electron transport chain.
• Lactic Acid Fermentation: In muscle cells or some bacteria, pyruvate is converted into lactic acid. This regenerates NAD+ so that glycolysis can continue, but it produces only 2 ATPs per glucose molecule.
• Alcoholic Fermentation: In yeast and some bacteria, pyruvate is converted into ethanol and carbon dioxide. This process also regenerates NAD+ but produces only 2 ATPs per glucose molecule.
• Fermentation is less efficient than respiration because it produces fewer ATPs per glucose molecule
• It allows cells to generate energy in the absence of oxygen.
• Bacteria can use respiration or fermentation or both

Electron transport chain

• Electron Carriers Deliver Electrons: Molecules like NADH and FADH2, made earlier in cellular respiration, bring high-energy electrons to the ETC.
• Electrons Move Through Proteins: The electrons move through protein complexes in the inner mitochondrial membrane. As they move, they release energy.
• Protons are Pumped: The energy from the electrons is used to pump protons (H+) across the membrane, from the inside of the mitochondria to the outside.
• ATP is Made: Protons want to move back to the inside, so they flow through a protein called ATP synthase. This flow of protons helps make ATP, which is the cell's energy.
• Oxygen Takes the Electrons: At the end of the chain, the electrons are passed to oxygen, which combines with the electrons and protons to form water.

Chemiosmosis

• Chemiosmosis is the process that uses the proton gradient created by the electron transport chain (ETC) to produce ATP.
• Proton Gradient: Protons (H+) are pumped across the mitochondrial membrane, creating a high concentration of protons outside the inner membrane and a low concentration inside the membrane.
• ATP Synthase: The protons flow back into the matrix by passing through a protein called ATP synthase.
• ATP Production: As protons flow through ATP synthase, the enzyme combines ADP and inorganic phosphate (Pi) to form ATP.
• In short, chemiosmosis uses the flow of protons through ATP synthase to create ATP
• The last electron on the electron transport chain binds up to oxygen as the final electron acceptor at the end of the electron transport chain

Lactic Acid Fermentation

• Requires no oxygen and still allows cells to generate energy by breaking down glucose
• Process starts with Glycolysis: The process starts with glycolysis, where one molecule of glucose (6 carbon atoms) is broken down into two molecules of pyruvate (3 carbon atoms each).
• Regenerates NAD+: In the absence of oxygen, the cell can't use the electron transport chain to recycle NADH back to NAD+.
• There are two types of fermentation:
• Lactic Acid Fermentation: in which In muscle cells or some bacteria, the pyruvate produced from glycolysis is converted into lactic acid.
• This regenerates NAD+ so glycolysis can keep happening, but it produces only 2 ATP per glucose molecule.
• Alcoholic Fermentation: In which in yeast and some bacteria, pyruvate is converted into ethanol and carbon dioxide. This process also regenerates NAD+ and produces 2 ATP per glucose molecule.
• Streptococcus and Lactobacillus are both bacteria that carry out lactic acid fermentation.

Lipid Catabolism

• Lipid Catabolism is the process by which lipids (fats) are broken down to release energy.
• Lipolysis:
• Triglycerides (fat molecules) are broken down into glycerol and fatty acids by lipase.
• Glycerol can be converted into glyceraldehyde-3-phosphate (G3P) and enter glycolysis
• Fatty acids undergo further breakdown through a process called beta-oxidation.
• Beta-Oxidation (for Fatty Acids):
• Fatty acids are transported into the mitochondria, where they undergo beta-oxidation.
• This process breaks the fatty acid chain into 2-carbon units, forming acetyl-CoA. Each round of beta-oxidation produces NADH and FADH2, which are electron carriers used in the electron transport chain (ETC) to produce ATP.
• The acetyl-CoA formed in beta-oxidation enters the Krebs cycle (Citric Acid Cycle), where it is further broken down to generate additional ATP.
• Krebs Cycle: The acetyl-CoA from beta-oxidation enters the Krebs cycle, where it combines with oxaloacetate to form citric acid. Through a series of reactions, ATP, NADH, and FADH2 are produced.
• Electron Transport Chain (ETC): NADH and FADH2 deliver electrons to the ETC, driving the production of ATP via chemiosmosis and the ATP synthase enzyme.
• Lipid catabolism is a highly efficient way for the body to produce energy, especially during periods of fasting or prolonged exercise.

Anabolic Pathways

• Anabolic pathways build complex molecules from simpler ones.
• Anabolic pathways help the body grow, repair itself, and store energy.
• Protein synthesis builds proteins from amino acids.
• Fat synthesis creates fats from smaller molecules. Glycogen synthesis stores glucose as glycogen in muscles and the liver.