The Cell The Cell • Basic unit of all multicellular organisms • Smallest structural unit producing all vital functions • Pre-existing cells produce cells Basic Components • Cell Membrane • Cytosol • Organelles • Inclusions 1 Overview Fig.2.1 Cell Membrane • Physical isolation: Extra/intracellular barrier • Regulation of exchange • Sensitivity:Affected by changes in extracellular fluid; receptors for recognition and communication; alterations affect physiology • Structural support Membrane Permeability: Passive processes • Diffusion • Osmosis • Filtration-Hydrostatic pressure forces water across membrane; solutes selected according to size. • Facilitated diffusion 2 Membrane Permeability: Active processes • Active transport • Endocytosis-phagocytosis, pinocytosis Permeability • Selectively permeable: hypertonic isotonic hypotonic Cytoplasm • The cellular material between the plasma membrane and nucleus; site of most cellular activities. • EM has revealed that it consists of cytosol, organelles, and inclusion bodies. 3 Cytoplasm • • • • • • Viscous, semitransparent fluid substance Complex mixture of salts Dissolved proteins (enzymes) Amino acids Lipids Low carbohydrate [ ] Inclusion Bodies • Non functional units/chemical substances • Glycosomes-hepato and myocytes • Lipids-adipocytes 4 Cytoplasmic Organelles • Specialized cellular compartments • Non membranous- cytoskeleton, centrioles, ribosomes, cilia, and flagella. • Membranous- mitochondria, peroxisomes, lysosomes, nucleus,endoplasmic reticulum, and Golgi apparatus. The Cytoskeleton • Intracellular network that supports cell’s structures & providing machinery to generate various cell movements • Four major components:microtubules, microfilaments, intermediate, and thick filaments. Microfilaments • Thinnest elements of the cytoskeleton • Primary protein: actin • Forms dense cross-linked network under cell membrane • Involved in motility or changes in cell’s morphology 5 Microfilaments • Anchors cytoskeleton to integral proteins • Adheres cell membrane to underlying cytoplasm • Responsible for amoebid movements and membrane changes accompanying endo/exocytosis Microtubules • Elements with largest diameter; spherical protein subunits (tubulin);determine cell’s overall morphology and organelle distribution. • Functions as primary component of cytoskeleton/anchor organelles; can adhere to organelles for intracellular movement 6 Microtubules • Form structural component of cilia, flagella, and centrioles. • Motor proteins (kinesins & dyneins) are mainly responsible for repositioning of organelles along microtubules. Motor Molecules Figure 3.25a 7 Microvilli • Microscopic, finger-shaped projections of membrane; increase surface area (absorption) (jejunum/ileum, kidneys) Centrioles • Small, barrel shaped oriented at right angles to each other (nine triplets) • Evident during cell division • Form bases; lacking in osteocytes/mature RBCs Cilia • Contain nine groups of microtubule doublets surrounding central pair (9+2) • Basal body anchor • Exposed aspect of cilia covered by membrane and “beat” rhythmically • Propel substances across cell surface Flagella • Substantially longer projections • Propels cell 8 Cilia Figure 3.27a Cilia Figure 3.27c Ribosomes • Small, dark staining granules composed of ribosomal RNA • Two globular subunits (small, large) • Free ribosomes produce soluble proteins that will function in the cytosol • Membrane-bound (fixed) ribosomes synthesize proteins destined for cellular membranes or cellular export. 9 Mitochondria • • • • • Threadlike, double membraned organelle Inner membrane forms cristae (ATP) Number may vary according to cell type DNA/RNA Cellular respiration Mitochondria Figure 3.17 10 The Nucleus • Gene containing control center • Controls synthesis of proteins • Numbers vary: (osteoclasts, myocytes, RBCs) • Shapes vary: spherical,elongate • Has three distinct regions: nuclear envelope, nucleoli, and chromatin. Nucleus Figure 3.28a 11 Fig. 2.6 Nucleoli • Dark staining spherical bodies located within nucleus responsible for ribosomal production • Non-membrane bound • Typically one or two per cell • Subunits assembled Chromatin • Composed of equal amounts of DNA and globular histone proteins • Chromosome-condensed chromatin coils forming short “barlike” bodies 12 Endoplasmic Reticulum • Network of intracellular membranes and cisternae • Functions: (1) Synthesizes carbohydrates, lipids, and proteins; (2) Transportation Rough ER • Manufactures secreted proteins Smooth ER • Continuum of RER • Lipid metabolism and synthesis/cholesterolsteroid synthesis • Absorption/transport lipids-detoxification Figure 3.18a and c 13 Golgi Apparatus • Principal “traffic director” for cellular proteins • Modifies, concentrates, and packages • “Receiving” side is cis face, “shipping” side is trans face • Secretory vesicles pinch off from trans face and fuse to membrane. Role of the Golgi Apparatus Figure 3.21 Lysosomes • Digests particles taken in by endocytosis • Degrade worn-out or nonfunctional organelles/break down nonuseful tissues • Metabolic functions: glycogenolysis; releasing of ThyH from thyroid cells • Breakdown of bone to release Ca ions 14 Role of the Golgi Apparatus Figure 3.21 Peroxisomes • Membranous sacs containing powerful enzymes(oxidases/catalases) • Oxidases use O2 to detoxify alcohol and formaldehyde • Numerous in hepatocytes and kidney cells • Self replicating/do not arise from Golgi apparatus Life Inside a Cell: Visual analysis http://www.youtube.com/watch?v=B_zD3NxSsD8 15
