Biochemistry: Key Concepts

• Biochemistry merges biology and chemistry to study chemical processes within living organisms
• Biochemistry is fundamental to understanding all life processes

Core Areas

• Biomolecule structures include carbohydrates, lipids, proteins, and nucleic acids
• Biomolecule functions are a core area of study
• Metabolism's chemical processes are key
• Biochemical signaling and genetic information flow are crucial

Metabolism

• Metabolism encompasses all chemical processes in living organisms for sustaining life
• Processes include growth, reproduction, structure maintenance, and environmental response
• Metabolism is divided into catabolism and anabolism

Catabolism

• Catabolism breaks down complex molecules into simpler ones, often releasing energy
• Energy is captured as ATP or other energy-rich molecules
• Catabolic pathways oxidize molecules.
• Examples include glycolysis (glucose breakdown), beta-oxidation (fatty acid breakdown), and proteolysis (protein breakdown)

Anabolism

• Anabolism synthesizes complex molecules from simpler ones, requiring energy input
• ATP typically supplies energy from catabolism
• Anabolic pathways reduce molecules
• Examples: protein synthesis (amino acids to proteins), DNA replication (nucleotide precursors to DNA), and photosynthesis (CO2 and H2O to glucose using light)

Metabolic Pathways

• A metabolic pathway is a series of linked chemical reactions in a cell
• Metabolites include reactants, products, and intermediates
• Pathways are regulated to maintain homeostasis and respond to environmental changes
• Pathways may be linear, cyclic, or branched

Key Biomolecules in Metabolism

• Carbohydrates: primary energy source, with glucose as a central metabolite
  • Glucose is broken down via glycolysis or stored as glycogen
• Lipids: energy storage, cell membrane structure, and signaling molecules
  • Fatty acids are broken down via beta-oxidation to produce energy
  • Phospholipids form the lipid bilayer of cell membranes
• Proteins: catalysts, transporters, and structural components
  • Amino acids are the building blocks of proteins
  • Broken-down proteins yield amino acids that enter metabolic pathways
• Nucleic Acids: store and transmit genetic information
  • DNA and RNA are nucleotide polymers
  • Nucleotides participate in energy transfer (ATP) and signaling (cAMP)

Enzymes in Metabolism

• Enzymes are biological catalysts that accelerate chemical reactions
• Most enzymes are proteins
• Enzymes lower activation energy, facilitating reactions
• Enzymes are substrate-specific
• Enzyme activity is regulated by substrate concentration, product concentration, allosteric regulators, and covalent modification

Regulation of Metabolism

• Regulation maintains homeostasis and responds to changing conditions
• Regulation occurs at enzyme activity (allosteric regulation, covalent modification, synthesis/degradation), compartmentalization, hormonal control, and genetic regulation
• Compartmentalization separates pathways into different cellular compartments
• Hormones influence pathways by altering enzyme activity or gene expression
• Genetic regulation controls the expression of genes encoding metabolic enzymes

Energy Currency: ATP

• ATP (adenosine triphosphate) is the cell's primary energy currency
• Energy is stored in phosphoanhydride bonds
• ATP hydrolysis releases energy for unfavorable reactions or work
• ATP is continuously synthesized and consumed

Redox Reactions

• Oxidation-reduction (redox) reactions are fundamental
• Oxidation is electron loss, while reduction is electron gain
• Electrons are transferred from one molecule to another in metabolic pathways
• NADH, NADPH, and FADH2 are important electron carriers

Key Metabolic Pathways

• Glycolysis: glucose breakdown to pyruvate in the cytoplasm, producing ATP and NADH
• Citric Acid Cycle (Krebs Cycle): acetyl-CoA oxidation to carbon dioxide in the mitochondrial matrix, producing ATP, NADH, and FADH2
• Oxidative Phosphorylation: electron transport chain and ATP synthase in the inner mitochondrial membrane
  • Energy from NADH and FADH2 generates a proton gradient, driving ATP synthesis
• Gluconeogenesis: glucose synthesis from non-carbohydrate precursors, mainly in the liver and kidneys
  • Important for maintaining blood glucose during fasting
• Pentose Phosphate Pathway: produces NADPH and pentose sugars in the cytoplasm
  • NADPH provides reducing power for anabolic reactions
  • Pentose sugars are precursors for nucleotide synthesis
• Fatty Acid Metabolism: synthesis and breakdown of fatty acids
  • Fatty acid synthesis occurs in the cytoplasm
  • Fatty acid breakdown (beta-oxidation) occurs in the mitochondrial matrix
• Amino Acid Metabolism: synthesis and breakdown of amino acids
  • Amino acids are building blocks for proteins and other biomolecules
  • Amino acid catabolism produces intermediates for other metabolic pathways

Compartmentalization of Metabolism

• Eukaryotic cells separate pathways in different organelles
• Compartmentalization improves regulation and prevents pathway interference
• Glycolysis occurs in the cytoplasm
• The citric acid cycle and oxidative phosphorylation occur in the mitochondria
• Fatty acid synthesis occurs in the cytoplasm, while fatty acid oxidation occurs in the mitochondria
• The endoplasmic reticulum is involved in lipid and protein synthesis
• The Golgi apparatus is involved in protein modification and sorting

Metabolic Disorders

• Diseases arise from defects in metabolic pathways due to genetic mutations in genes encoding metabolic enzymes, deficiencies in essential nutrients or exposure to toxins
• Diabetes is a disorder of glucose metabolism
• Phenylketonuria (PKU) is a genetic disorder affecting phenylalanine metabolism
• Lysosomal storage diseases are genetic disorders causing substance accumulation in lysosomes

Importance of Biochemistry

• Biochemistry provides the molecular basis of life
• Applications span medicine, agriculture, and biotechnology
• Biochemical research develops new drugs, diagnostic tests, and therapies
• It enhances understanding of nutrition, health, and disease at a molecular level