9.1- metabolism overview

Introduction to Metabolism

Overview of Metabolism in Biochemistry

• Importance: Metabolism comprises a series of complex chemical reactions that are crucial for sustaining life. These reactions enable vital processes such as growth, homeostasis, reproduction, and adaptation to environmental changes, alongside playing a crucial role in the maintenance of homeostasis within organisms.

Definition of Metabolism

• Metabolism: Encompasses all biochemical reactions occurring within organisms that allow for growth, reproduction, and survival. It can be divided into two main categories:

  • Anabolism: The synthesis of complex molecules from simpler ones, requiring energy input.

  • Catabolism: The breakdown of complex molecules into simpler ones, releasing energy in the process.

Truth about metabolism

• all organisms share a common pathway

• limited number of molecules are involved

• common classes of chemical reactions

• reactions have simple mechanisms

• process control points are similar.

Key Functions of Metabolism:

• Growth: Involves the increase of cell size and mass through anabolic processes.

• Maintenance of Steady State homeostasis: Homeostatic regulation ensures the internal environment remains stable amidst external changes.

• Reproduction: Metabolic pathways support cellular division and the formation of gametes.

• Adaptation to Environmental Changes: Metabolic flexibility allows organisms to respond swiftly to varying nutritional and environmental contexts.

Types of Metabolic Reactions

1. Anabolic Reactions:

   • These reactions utilize energy (often in the form of ATP) to assemble complex molecules from simpler precursors. Key anabolic pathways include the synthesis of proteins from amino acids and the formation of glycogen from glucose.

2. Catabolic Reactions:

   • Catabolic processes involve the degradation of larger substrates; for instance, carbohydrates are broken down into glucose molecules. This degradation often liberates energy, utilized by the organism for various biological functions.

Course Structure

• Focus Areas:

  • Carbohydrate metabolism with insights from Mark Skidmore.

  • Fat and Protein metabolism, presented by David Watson.

• Start Point: The course will begin with the breakdown of polysaccharides into simple sugars, leading into pathways like glycolysis, which is fundamental for energy production.

Metabolic Pathways

• Glycolysis: The first step in the breakdown of carbohydrates where glucose is converted into pyruvate, producing a net yield of ATP and NADH.

• Transition to Acetyl CoA: This stage is crucial as it connects glycolysis to the Krebs Cycle. Pyruvate is converted into Acetyl CoA, which is then utilized in the TCA cycle.

• Krebs Cycle (TCA Cycle): A series of enzymatic reactions that process Acetyl CoA to generate NADH and FADH2, contributing to the electron transport chain.

• Oxidative Phosphorylation: This final step utilizes the electrons from NADH and FADH2 to produce ATP through chemiosmosis in the mitochondria.

• ATP as Biological Energy Currency: ATP serves as the main energy carrier of the cell, facilitating energy transfer for myriad cellular functions.

Purpose of Metabolism

• Energy is essential for:

  • Synthesis of Essential Molecules: Building blocks for proteins, nucleic acids, lipids, and carbohydrates.

  • Transport of Molecules and Ions: Active transport mechanisms and secondary transport rely on metabolic energy.

  • Mechanical Work: Cellular activities such as muscle contractions stem from metabolic energy inputs.

• Importance of Energy Input: Energy derived from catabolic reactions fuels anabolic pathways and is vital for all cellular processes, underscoring the interconnectedness of metabolic functions.

Thermodynamics in Metabolism

• Metabolic processes conform to the laws of thermodynamics, particularly concerning energy transformation and conservation.

• Most organisms utilize ATP as a common energy currency, reflecting shared evolutionary pathways in metabolism.

• Control Points: Various regulatory mechanisms exist to ensure metabolic homeostasis and prevent futile cycling within pathways.

Catabolism vs. Anabolism

1. Catabolic Reactions:

   • Function to break down complex biomolecules (carbohydrates, proteins, fats) to release energy. These reactions usually have a negative Gibbs free energy change (ΔG < 0). Examples include glycolysis, β-oxidation of fatty acids, and protein degradation.

2. Anabolic Reactions:

   • These are synthetic processes that build more complex molecules from simpler ones and require energy input (ΔG > 0). Examples include gluconeogenesis (synthesis of glucose from non-carbohydrate sources) and fatty acid synthesis from Acetyl CoA. Gibbs free energy is positive

ATP: The Energy Currency

• ATP Formation: Produced from ADP and inorganic phosphate (Pi) through substrate-level phosphorylation or oxidative phosphorylation. extra phosphate-covalently bonds

• ATP Breakdown: Hydrolysis of ATP to ADP is an exergonic reaction that releases energy, driving various endergonic processes such as biosynthesis and active transport.- power anabolic reactions

Redox Reactions in Metabolism

• Oxidation: Loss of electrons or hydrogen atoms, often linked to energy release; coenzymes assist in these reactions.

• Reduction: Gaining electrons or hydrogen, which increases potential energy within the metabolic compound.

• Important coenzymes include:

  • NAD (Nicotinamide adenine dinucleotide)- reduced to NADH

  • NADP (Nicotinamide adenine dinucleotide phosphate)- reduced to NADPH

  • FAD (Flavin adenine dinucleotide), each playing crucial roles in oxidation-reduction reactions. reduced to-FADH2

Overview of Carbohydrates

• Composition: Carbohydrates are organic molecules made of carbon, hydrogen, and oxygen, following the general molecular formula (CH2O)n.

• Not all carbohydrates are sugars but all sugars are carbohydrates

• Basic Units:

  • Monosaccharides: The simplest form of carbohydrates (e.g., glucose, fructose).

  • Polysaccharides: Complex carbohydrates formed from many monosaccharide units linked together by glycosidic bonds.

  • oligosaccharide -3-10 molecules in chain

• Carbohydrates serve critical roles in energy storage (as glycogen or starch) and as metabolic intermediates in various biochemical pathways.

Classification of Carbohydrates

• Monosaccharides: Defined by the number of carbon atoms; include:

  • Triose (3 Carbon)

  • Tetrose (4 Carbon)

  • Pentose (5 Carbon)

  • Hexose (6 Carbon)

• Polysaccharides: Composed of multiple monosaccharide units.

  • Oligosaccharides: Contains 3-10 units.

  • Polysaccharides: Composed of more than 10 units.

• It's essential to note that not all carbohydrates taste sweet; for example, cellulose is a polysaccharide and does not possess a sweet taste.

• aldose sugar- O =C R H

• ketose sugar- O =C R R

Representations of Carbohydrates

• Fischer Projection: A method for depicting 3D molecular structures in a 2D plane; useful for visualizing the arrangement of different functional groups around the carbon backbone, illustrated with D-glyceraldehyde.

• In Fischer Projections, carbon chains are drawn vertically, while the attached functional groups project to the side.

• carbon chain is vertical

• horizontal bonds project towards the viewer

• vertical bonds project away from the viewer

Stereochemistry of Carbohydrates

• Stereoisomerism: Important for carbohydrates, differentiated by their D or L configuration based on their relationship to D-glyceraldehyde as a reference.

• Anomeric Center: The C1 carbon in cyclic forms determines whether the sugar is in the alpha or beta configuration, depending on the orientation of the hydroxyl (-OH) group. ALPHA- OH point down on Carbon 1(opposite configuration) . BETA- OH point up on Carbon 1 (points in same orientation)

• Cyclic Forms: Carbohydrates may exist in cyclic forms such as pyranose (six-membered ring) and furanose (five-membered ring), influenced by the specific carbon atoms involved in ring closure.

• Highest number of asymmetrical carbon - same conformation as OH group. if it point to right it is D. Left is L

Glycosidic Linkage in Carbohydrates

• Glycosidic bonds are formed via a dehydration synthesis reaction (condensation), resulting in the loss of a water molecule.

• Example: When galactose and glucose combine, they form lactose via a gal beta 1-4 glucose link.

• The specific configuration and type of glycosidic linkage in polysaccharides are crucial for determining their properties and biological functions.

Conclusion on Metabolism

• In conclusion, metabolism encompasses both catabolic and anabolic processes vital to life. Catabolic pathways lead to the generation of energy-storing molecules like ATP, which are then utilized in anabolic pathways to synthesize complex biomolecules.

• For those looking to gain deeper insights, additional resources and detailed studies can be found in the prescribed Biochemistry Textbook, which provides a comprehensive discussion of metabolic processes and their regulation.