Chapter 2 Cellular Physiology Principles of the Cell Theory • The cell is a smallest structural and functional unit capable of carrying out life processes • Functional activities of each cell depend on specific structural properties of the cell • Cells are living building blocks of all multicellular organisms • An organism’s structure and function ultimately depend on individual and collective structural characteristics and functional capabilities of its cells • All new cells and new life arise only from pre-existing cells • Cells of all organisms are fundamentally similar in structure and function Typical Cell Different parts of the cell • Plasma membrane – Also called the cell membrane – Surrounds every cell – Separates cell contents from its surroundings • Separates ICF and ECF – Controls movement of molecules into and out of cell • Nucleus – – – – Typically largest single organized cell component Enclosed by a double-layered nuclear envelope Contains cell’s genetic material, DNA DNA functions • Directs protein synthesis • Serves as genetic blueprint during cell replication Different parts of the cell • Cytoplasm – Portion of cell interior not occupied by the nucleus – Consists of • Organelles – “little organs” – Distinct, highly organized, membrane-enclosed structures • Cytoskeleton – Found in a Complex, gel-like liquid called the Cytosol • Examples of organelles – – – – – – Endoplasmic reticulum Golgi complex Lysosome Peroxisome Mitochondrion Vault Endoplasmic Reticulum (ER) • Elaborate fluid-filled membranous system distributed throughout the cytosol • Primary function – Protein and lipid manufacture • Two types – Smooth ER (lipid synthesis) • Mesh of tiny interconnected tubules – Rough ER (protein synthesis) • Projects outward from smooth ER as stacks of relatively flattened sacs • Surface has attached ribosomes Endoplasmic Reticulum (ER) Golgi Complex • Closely associated with ER • Consists of a stack of flattened, slightly curved, membrane-enclosed sacs called cisternae • Number of Golgi complexes per cell varies with the cell type • Functions (NB) – Processes raw materials into finished products – Sorts and directs finished products to their final destinations – Packages secretory vesicles to release by exocytosis Golgi Complex Lysosomes and Peroxisomes • Lysosomes – Membranous sacs containing hydrolytic enzymes – Serve as intracellular digestive system – Extracellular material attacked by lysosomes enters cell by endocytosis • Pinocytosis • Receptor-mediated endocytosis • Phagocytosis • Peroxisomes – Membranous sacs that house oxidative enzymes that detoxify various waste products Mitochondria • Energy organelle – Major site of ATP production – Contains enzymes for citric acid cycle and electron transport chain • Enclosed by a double membrane – Inner enfolded membrane is called the cristae ATP Production • Sequence of steps involved in generation of ATP within the cell – Glycolysis (anaerobic) – Citric acid cycle (Krebs Cycle) (aerobic) – Electron transport chain (aerobic) • Glycolysis – Chemical process involving 10 separate sequential reactions that break down glucose into two pyruvic acid molecules – Anaerobic process Glycolysis • A ten step process Citric Acid Cycle • Requires oxygen • Pyruvic acid from glycolysis is converted to acetyl CoA which enters citric acid cycle • Citric acid cycle consists of eight separate biochemical reactions that are directed by enzymes of mitochondrial matrix • Important in preparing hydrogen carrier molecules for entry into electron transport system Citric Acid Cycle Electron Transport Chain and oxidative phosphorylation • Requires oxygen • Series of reactions that occur on the inner mitochondrial membrane • Major source of ATP needed for cellular activities Comparison of Anaerobic and Aerobic Respiration • Cellular Activities that Require ATP – Synthesis of new chemical compounds – Membrane transport – Mechanical work Cytosol • Occupies about 55% of total cell volume • Semi-liquid portion of cytoplasm that surrounds the organelles • Contains cytoskeleton (network of protein filaments that enable contraction, relaxation, and structure) • Activities associated with gelatinous portion of cytoplasm – Enzymatic regulation of intermediary metabolism – Ribosomal protein synthesis – Storage of fat (fatty acids), carbohydrates (glycogen and glucose), and secretory vesicles (may contain enzymes) Cytoskeleton • Complex protein network of cytosol that acts as “bone and muscle” of cell • Three distinct elements – Microtubules – Microfilaments – Keratin (Intermediate filaments) Element Function Microtubules • Transport secretory vesicles * • Movement of specialized cell projections • Form mitotic spindle during cell division • Contain Tubulin protein * Microfilaments • Contractile systems * • Mechanical stiffeners • Contain 2 chains of Actin protein * Intermediate filaments • Help resist mechanical stress • Contain Keratin Mitosis • During mitosis, the DNA-containing chromosomes of the nucleus are replicated, resulting in two identical sets. • These duplicate sets of chromosomes are separated and drawn apart to opposite sides of the cell so that the genetic material is evenly distributed in the two halves of the cell. • The replicated chromosomes are pulled apart by a cellular apparatus called the mitotic spindle, which is transiently assembled from microtubules only during cell division. • The microtubules of the mitotic spindle are formed by the centrioles. • As part of cell division, the centrioles first duplicate themselves; then, the new centriole pairs move to opposite ends of the cell and form the spindle apparatus between them through a precisely organized assemblage of microtubules. • The following pictures are a comparison of mitosis and meiosis. Mitosis and Meiosis Mitosis and Meiosis
