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Chapter 1

Chapter 1. The Cell: A Microcosm of Life. Cells--the essence of life. Basic units of the body Eukaryotic cells Have a defined nucleus Evolved from prokaryotic cells (which don’t) Specialization. Components of Typical Cells. Plasma membrane Cytoplasmic matrix Mitochondrion Nucleus

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Chapter 1

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  1. Chapter 1 The Cell: A Microcosm of Life 2009 Cengage-Wadsworth

  2. Cells--the essence of life • Basic units of the body • Eukaryotic cells • Have a defined nucleus • Evolved from prokaryotic cells (which don’t) • Specialization 2009 Cengage-Wadsworth

  3. Components of Typical Cells • Plasma membrane • Cytoplasmic matrix • Mitochondrion • Nucleus • Endoplasmic reticulum • Golgi apparatus • Lysosomes • Peroxisomes 2009 Cengage-Wadsworth

  4. Plasma Membrane • Sheetlike structures made of phospholipids & proteins • Have hydrophobic & hydrophylic moiety • Phospholipids = phosphoglycerides & phosphingolipids • Proteins give them their functions 2009 Cengage-Wadsworth

  5. Plasma Membrane • Asymmetrical • Fluid structures • Distinct from other membranes: • Greater CHO content • Greater cholesterol content 2009 Cengage-Wadsworth

  6. Plasma Membrane • Lipid bilayer concept • Glycocalyx • Glycoproteins • Membrane proteins • Integral • Peripheral 2009 Cengage-Wadsworth

  7. Cytoplasmic Matrix • Microtrabecular lattice or cytoskeleton • Microtubules • Microfilaments • Fluid 2009 Cengage-Wadsworth

  8. Cytoplasmic Matrix • Structural arrangement influences metabolic pathways: • Glycolysis • Hexose monophosphate shunt • Glycogenesis & glycogenolysis • Fatty acid synthesis • Communication 2009 Cengage-Wadsworth

  9. Mitochondrion • Energy production & oxygen use site • Matrix surrounded by double membrane • Mitochondrial membrane • Outer membrane - porous • Inner membrane - selectively permeable; site of electron transport chain 2009 Cengage-Wadsworth

  10. Mitochondrion • Mitochondrial matrix • Site of TCA cycle & fatty acid oxidation • Contains DNA so organelle can divide • In all cells except erythrocytes 2009 Cengage-Wadsworth

  11. Nucleus • Contains DNA (genome) • Surrounded by nuclear envelope • Nucleoli - condensed chromatin • DNA replication • Protein synthesis = transcription, translation & elongation 2009 Cengage-Wadsworth

  12. Nucleus • Nucleic acids • DNA & RNA • Consist of nucleotides or bases • Adenine, guanine, cytosine in both • Uracil in RNA only • Thymine in DNA only • Complementary base pairing 2009 Cengage-Wadsworth

  13. Nucleus • Cell replication • DNA unravels and nucleotides are added to each strand to make 2 sets • Cell transcription • mRNA created from sequence of 1 DNA strand (sense strand) • Genes • Introns - intervening sequences • Exons - no posttranslational processing 2009 Cengage-Wadsworth

  14. Nucleus • Translation • mRNA codes for amino acid sequence to form protein • mRNA is synthesized in nucleus, then moves to RER in cytoplasmic matrix • Codons - 3-base sequences that code for amino acids • tRNA bring AAs to mRNA on ribosomes 2009 Cengage-Wadsworth

  15. Nucleus • After AAs are positioned, peptide bonds form between them = elongation • “Nonsense” codon signals end of protein 2009 Cengage-Wadsworth

  16. Endoplasmic Reticulum & Golgi Apparatus • ER = network of membranous channels • Types: • Rough ER (studded with ribosomes) - protein synthesis • Smooth ER - lipid synthesis • Sarcoplasmic reticulum (SER in muscle) - calcium ion pump 2009 Cengage-Wadsworth

  17. Endoplasmic Reticulum & Golgi Apparatus • Golgi apparatus • Protein trafficking & sorting • 4-8 cisternae • Tubular networks at either end: • Cis-Golgi network - entrance • Trans-Golgi network - exit • Connected to ER by transport vesicles 2009 Cengage-Wadsworth

  18. Lysosomes & Peroxisomes • Enzyme-filled organelles • Lysosomes - cell’s “digestive system” • Peroxisomes - site of oxidative catabolic reactions 2009 Cengage-Wadsworth

  19. Lysosomes & Peroxisomes • Lysosome functions: • Phagocytosis • Autolysis • Bone resorption • Hormone secretion & regulation • Peroxisome functions: • Oxidize fatty acids to acetyl CoA • Amino acid catabolism • Detoxifying reactions 2009 Cengage-Wadsworth

  20. Cellular Proteins • Types: • Receptors - modify cell’s response to environment • Transport proteins - regulate flow of materials into & out of cell • Enzymes - catalysts 2009 Cengage-Wadsworth

  21. Receptors & Intracellular Signaling • Ligands - molecular stimuli that attach to receptors • Types of receptors: • Bind to ligand & convert it to internal signal • Serve as ion channels • Internalize stimulus intact 2009 Cengage-Wadsworth

  22. Receptors & Intracellular Signaling • Internal chemical signal • E.g. 3’, 5’-cyclic adenosine monophosphate (cyclic AMP, cAMP) • Ion channel • E.g. receptor for acetylcholine • Internalization stimulus • E.g. insulin, triiodothyronine 2009 Cengage-Wadsworth

  23. Transport Proteins • May act as pumps • May provide pores through which molecules diffuse • Most studied = sodium (Na+) pump • Na+/K+ -ATPase 2009 Cengage-Wadsworth

  24. Catalytic Proteins (Enzymes) • Functionality depends on protein & prosthetic group or coenzyme • Specificity • Maximum velocity (Vmax) - enzyme velocity at substrate saturation • Km (Michaelis constant) - concentration of substrate when reaction is at 1/2 of maximum velocity 2009 Cengage-Wadsworth

  25. Catalytic Proteins (Enzymes) • Reversibility • Regulation • Covalent modification - usually addition/removal of phosphate groups • Allosteric - enzymes with another site besides catalytic site that can bond with modulator • Induction - changes in concentrations of inducible enzymes 2009 Cengage-Wadsworth

  26. Catalytic Proteins (Enzymes) • Examples of enzyme types • Oxidoreductases - reactions in which 1 compound is oxidized, another reduced • Transferases - functional group transferred from 1 substrate to another • Hydrolases - hydrolysis of carbon-? bonds 2009 Cengage-Wadsworth

  27. Catalytic Proteins (Enzymes) • Lyases - cleavage of C-C, C-S, & C-N bonds (no hydrolysis/O-R) • Isomerases - interconversion of optical or geometric isomers • Ligases - catalyze formation of C-? Bonds (O, S, N, others) 2009 Cengage-Wadsworth

  28. Practical Clinical Application of Cellular Enzymes • Conditions for diagnostic suitability • Enzyme’s degree of organ/tissue specificity • Steep concentration gradient of enzyme activity between cell and surroundings • Enzyme must function in cytoplasm • Enzyme must be stable 2009 Cengage-Wadsworth

  29. Practical Clinical Application of Cellular Enzymes • Increased production factors • Malignant disease • Results in tumor markers 2009 Cengage-Wadsworth

  30. Apoptosis • Programmed cell death • Potential mechanisms • Intracellular stimuli • Create DNA damage • Release of cytochrome c • Extracellular stimuli • Tumor necrosis factor family of hormones or agonists • Oncosis 2009 Cengage-Wadsworth

  31. Biological Energy • ATP - major storage form in cells • Energy needed for: • Exertion • Anabolism • Active transport • Transfer of genetic information 2009 Cengage-Wadsworth

  32. Biological Energy • Energy release and consumption in chemical reactions • Energy comes from macronutrients • Transferred from one form to another • Units of energy • Free energy (G) - potential energy in bonds of nutrients that is released 2009 Cengage-Wadsworth

  33. Biological Energy • Exothermic and endothermic reactions • Activation energy - energy to raise reactants to transition state • Cellular energy • Reversibility of chemical reactions • Standard free energy change • 25°C, 1.0 atm, reactants/products at 1.0 mol/L concentrations 2009 Cengage-Wadsworth

  34. Biological Energy • Equilibrium constant (Keq) and standard free energy change • Standard pH - 7 • Nonstandard physiological conditions • In cells: ~37°C, concentrations often not 1.0 mol/L, etc. 2009 Cengage-Wadsworth

  35. Biological Energy • The role of high-energy phosphate in energy storage • Coupled reactions in the transfer of energy • Phosphorylation - adding phosphate • Reduction potentials • Standard reduction potential (E0) - tendency of compound to donate & receive electrons 2009 Cengage-Wadsworth

  36. Perspective 1 Nutritional Genomics: The Foundation for Personalized Nutrition 2009 Cengage-Wadsworth

  37. Nutritional Genomics • What is nutritional genomics? • Pharmacogenomics as a model • Mechanisms underlying nutritional genomics • Nutritional genomics & lipid metabolism • Opportunities for nutrition professionals 2009 Cengage-Wadsworth

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