Metabolism – Enzymes

Introduction to Metabolism

Metabolism encompasses all chemical reactions occurring within living organisms to maintain life. These reactions are organized into metabolic pathways, which are sequences of enzymatically catalyzed steps.

• Anabolic Pathways: Pathways that build complex molecules from simpler ones, requiring energy input (e.g., protein synthesis).

• Catabolic Pathways: Pathways that break down complex molecules into simpler ones, releasing energy (e.g., cellular respiration).

• Laws of Thermodynamics: Govern energy transformations in biological systems.

  • First Law: Energy cannot be created or destroyed, only transformed.

  • Second Law: Every energy transfer increases the entropy of the universe.

Enzymes and Their Function

• Enzymes: Biological catalysts, usually proteins, that speed up chemical reactions by lowering activation energy.

• Active Site: The region on the enzyme where substrate molecules bind and undergo a chemical reaction.

• Substrates: The reactants upon which enzymes act.

• Products: The molecules produced from the enzymatic reaction.

• Enzyme Anatomy: Includes the active site, allosteric sites, and sometimes cofactors or coenzymes.

Enzyme Regulation and Inhibition

• Conditions Affecting Enzymes: Temperature, pH, and substrate concentration can affect enzyme activity.

• Inhibitors:

  • Competitive Inhibitors: Bind to the active site, blocking substrate binding.

  • Non-Competitive Inhibitors: Bind elsewhere, changing enzyme shape and reducing activity.

• Cofactors: Non-protein molecules (often metal ions) required for enzyme activity.

• Coenzymes: Organic cofactors (often derived from vitamins) that assist enzymes.

Respiration

Cellular Respiration Overview

Cellular respiration is the process by which cells extract energy from organic molecules, primarily glucose, to produce ATP. It involves glycolysis, the Krebs cycle, and the electron transport chain.

• Glycolysis: Occurs in the cytoplasm; breaks glucose into two pyruvate molecules, producing ATP and NADH.

• Krebs Cycle (Citric Acid Cycle): Occurs in the mitochondrial matrix; oxidizes acetyl-CoA to CO2, generating NADH, FADH2, and ATP.

• Electron Transport Chain (ETC): Located in the inner mitochondrial membrane; uses electrons from NADH and FADH2 to create a proton gradient, driving ATP synthesis via ATP synthase.

• Key Molecules: CoA, pyruvate, NADH, FADH2, ATP.

Aerobic vs. Anaerobic Respiration

• Aerobic Respiration: Requires oxygen; produces more ATP per glucose molecule.

• Anaerobic Respiration: Occurs without oxygen; less efficient, producing lactic acid or ethanol as byproducts.

Fermentation Pathways

• Alcoholic Fermentation: Converts pyruvate to ethanol and CO2 (e.g., in yeast).

• Lactic Acid Fermentation: Converts pyruvate to lactic acid (e.g., in muscle cells under low oxygen).

Photosynthesis

Overview of Photosynthesis

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy, producing glucose and oxygen from CO2 and water.

• Light Reactions: Occur in the thylakoid membranes; convert light energy to chemical energy (ATP, NADPH).

• Calvin Cycle (Dark Reactions): Occurs in the stroma; uses ATP and NADPH to fix CO2 into glucose.

• Key Molecules: ATP, NADPH, RuBP, CO2, G3P.

Chloroplast Structure

• Thylakoids: Membranous sacs where light reactions occur.

• Stroma: Fluid surrounding thylakoids; site of the Calvin cycle.

• Grana: Stacks of thylakoids.

Adaptations and Pigments

• Chlorophyll: Main pigment for capturing light energy.

• Accessory Pigments: Expand the range of light absorption.

• Adaptations: C3, C4, and CAM photosynthesis allow plants to thrive in different climates.

The Cell Cycle

Phases of the Cell Cycle

The cell cycle is the series of events that cells go through as they grow and divide. It consists of interphase (G1, S, G2) and mitosis (M phase), followed by cytokinesis.

• G1 Phase: Cell growth and preparation for DNA replication.

• S Phase: DNA synthesis (replication).

• G2 Phase: Preparation for mitosis.

• Mitosis: Division of the nucleus into two genetically identical daughter nuclei.

• Cytokinesis: Division of the cytoplasm, resulting in two daughter cells.

Key Terms

• Centrosomes: Organelles that organize microtubules during cell division.

• Chromatin: DNA-protein complex that condenses to form chromosomes.

• Nuclear Envelope: Membrane enclosing the nucleus.

Regulation and Cancer

• Cyclins and CdKs: Proteins that regulate cell cycle progression.

• Density-Dependent Inhibition: Cells stop dividing when they become too crowded.

• Cancer: Uncontrolled cell division due to loss of cell cycle regulation.

Meiosis

Overview of Meiosis

Meiosis is a type of cell division that reduces the chromosome number by half, producing four genetically unique gametes (sperm or egg).

• Stages: Interphase, Meiosis I (homologous chromosomes separate), Meiosis II (sister chromatids separate).

• Tetrads: Paired homologous chromosomes during prophase I.

• Genetic Variation Mechanisms:

  • Independent Assortment: Random distribution of maternal and paternal chromosomes.

  • Crossing Over: Exchange of genetic material between homologous chromosomes.

  • Random Fertilization: Any sperm can fertilize any egg.

Genetics and Chromosomes

• Genes: Units of heredity located on chromosomes.

• Gametes: Haploid reproductive cells (sperm or egg).

• Diploid (2n): Two sets of chromosomes (in somatic cells).

• Haploid (n): One set of chromosomes (in gametes).

• Karyotype: Display of an individual's complete set of chromosomes.

• Human Chromosomes: 46 total (23 pairs: 22 autosomes, 1 pair sex chromosomes).

• Sex Chromosomes: XX (female), XY (male).

Evolution

Introduction to Evolution

Evolution is the process by which populations of organisms change over generations through mechanisms such as natural selection. Sexual reproduction increases genetic variation, which is essential for evolution.

• Mechanism: Natural selection acts on heritable variation, leading to adaptation.

• Role of Sexual Reproduction: Increases genetic diversity, providing material for evolution.