3 Cell Structure and Function •
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3 Cell Structure and Function Studying Cells Cell Theory: Four Basic Concepts • Basic building blocks of all animals and plants • Smallest functional units of life • Products of cell division • Basic homeostatic units Studying Cells The Diversity of Cells in the Human Body Studying Cells Cytology Study of structure and function of cells Cytology depends on seeing cells • Light microscopy (LM) • Electron Microscopy (EM) • Scanning EM (SEM) • Transmission EM (TEM) Studying Cells Overview of Cell Anatomy • Extracellular fluid • Also called interstitial fluid • Cell Membrane • Lipid barrier between outside and inside • Cytoplasm (intracellular fluid) • Around nucleus • Cytosol + organelles Studying Cells Anatomy of a Representative Cell The Cell Membrane Functions of the plasma membrane • Physical isolation • Regulation of exchange with the environment • Sensitivity • Structural support The Cell Membrane Membrane Structure • Phospholipid bilayer • Molecular components • Lipids • Proteins • Carbohydrates The Cell Membrane The Cell Membrane The Cell Membrane Functions of Membrane Proteins • Receptors • Channels • Carriers • Enzymes • Anchors • Identifiers The Cell Membrane The Cell Membrane Membrane Transport • Selective permeability • Permeability factors • Molecular size • Electrical charge • Molecular shape • Lipid solubility The Cell Membrane Membrane Transport Processes • Passive transport • Diffusion • Filtration • Carrier-Mediated transport • Facilitated transport • Active transport The Cell Membrane Membrane Transport Definitions • Diffusion Random movement down a concentration gradient (from higher to lower concentration) • Osmosis Movement of water across a membrane down a gradient in osmotic pressure (from lower to higher osmotic pressure) The Cell Membrane Diffusion The Cell Membrane Diffusion Across Cell Membranes The Cell Membrane Osmosis The Cell Membrane Key Note Things tend to even out, unless something—like a cell membrane— prevents this from happening. Across a freely permeable or water permeable membrane, diffusion and osmosis will quickly eliminate concentration gradients. The Cell Membrane Osmotic Effects of Solutions on Cells • Isotonic—Cells maintain normal size and shape • Hypertonic—Cells lose water osmotically and shrink and shrivel • Hypotonic—Cells gain water osmotically and swell and may burst. The Cell Membrane Osmotic Flow across a Cell Membrane The Cell Membrane Passive Membrane Transport • Filtration • Hydrostatic pressure pushes on water • Water crosses membrane • Solute follows water • Filtration initiates urine formation The Cell Membrane Carrier-Mediated Transport • Membrane proteins as carriers • Facilitated diffusion (no ATP required) • Co-transport • Counter-transport • Active transport (ATP consumed) • Independent of concentration gradients • Ion pumps (e.g., Na-K exchange) The Cell Membrane Facilitated Diffusion The Cell Membrane The Sodium-Potassium Exchange Pump The Cell Membrane Vesicular Transport • Membranous vesicles • Transport in both directions • Endocytosis • Movement into cell • Receptor-mediated • Pinocytosis • Phagocytosis • Exocytosis • Movement out of cell The Cytoplasm Cytoplasm All the “stuff” inside a cell, not including the cell membrane and nucleus. The “stuff”: • The cytosol • The organelles The Cytoplasm The Cytosol • Intracellular fluid • Dissolved nutrients and metabolites • Ions • Soluble proteins • Structural proteins • Inclusions The Cytoplasm Intracellular-Extracellular Differences The Cytoplasm Organelles • Membranous organelles • Isolated compartments • Nucleus • Mitochondria • Endoplasmic reticulum • Golgi apparatus • Lysosomes • Peroxisomes The Cytoplasm Organelles • Nonmembranous organelles • Cytoskeleton • Microvilli • Centrioles • Cilia • Flagella • Ribosomes • Proteasomes The Cytoplasm Organelles: The Cytoskeleton • Cytoplasmic strength and form • Main components • Microfilaments (actin) • Intermediate filaments (varies) • Microtubules (tubulin) The Cytoplasm The Cytoskeleton The Cytoplasm Nonmembranous Organelles • Centrioles—Direct chromosomes in mitosis • Microvilli—Surface projections increase external area • Cilia—Move fluids across cell surface • Flagella—Moves cell through fluid • Ribosome—Makes new proteins • Proteasome—Digests damaged proteins The Cytoplasm Membranous Organelles • Endoplasmic reticulum—Network of intracellular membranes for molecular synthesis • Rough ER (RER) • Contains ribosomes • Supports protein synthesis • Smooth ER (SER) • Lacks ribosomes • Synthesizes proteins, carbohydrates The Cytoplasm The Endoplasmic Reticulum The Cytoplasm Membranous Organelles • Golgi apparatus • Receives new proteins from RER • Adds carbohydrates and lipids • Packages proteins in vesicles • Secretory vesicles • Membrane renewal vesicle • Lysosomes The Cytoplasm Membranous Organelles • Lysosomes • Packets of digestive enzymes • Defense against bacteria • Cleaner of cell debris • Hazard for autolysis • “Suicide packets” The Cytoplasm Key Note Cells respond directly to their environment and help maintain homeostasis at the cellular level. They can also change their internal structure and physiological functions over time. The Cytoplasm Membranous Organelles • Mitochondria • 95% of cellular ATP supply • Double membrane structure • Outer membrane very permeable • Inner membrane very impermeable Folded into cristae Filled with matrix Studded with ETS complexes The Cytoplasm Mitochondria The Cytoplasm Key Note Mitochondria provide most of the energy needed to keep your cells (and you) alive. They consume oxygen and organic substrates, and they generate carbon dioxide and ATP. The Nucleus Properties of the Nucleus • Exceeds other organelles in size • Controls cellular operations • Determines cellular structure • Directs cellular function • Nuclear envelope separates cytoplasm • Nuclear pores penetrate envelope • Enables nucleus-cytoplasm exchange The Nucleus The Nucleus The Nucleus Chromosome Structure • Location of nuclear DNA • Protein synthesis instructions • 23 pairs of human chromosomes • Histones • Principal chromosomal proteins • DNA-Histone complexes • Chromatin The Nucleus Chromosome Structure The Nucleus Key Note The nucleus contains DNA, the genetic instructions within chromosomes. The instructions tell how to synthesize the proteins that determine cell structure and function. Chromosomes also contain various proteins that control expression of the genetic information. The Nucleus The Genetic Code • Triplet code • Comprises three nitrogenous bases • Specifies a particular amino acid • A Gene • Heredity carried by genes • Sequence of triplets that codes for a specific protein The Nucleus Protein Synthesis • Transcription—the production of RNA from a single strand of DNA • Occurs in nucleus • Produces messenger RNA (mRNA) • Triplets specify codons on mRNA The Nucleus Protein Synthesis • Translation—the assembling of a protein by ribosomes, using the information carried by the mRNA molecule • tRNAs carry amino acids • Anticodons bind to mRNA • Occurs in cytoplasm The Nucleus Key Note Genes are the functional units of DNA that contain the instructions for making one or more proteins. The creation of specific proteins involves multiple enzymes and three types of RNA. The Cell Life Cycle Cell division—The reproduction of cells Apoptosis—Genetically programmed death of cells Mitosis—The nuclear division of somatic cells Meiosis—The nuclear division of sex cells The Cell Life Cycle The Cell Life Cycle DNA Replication The Cell Life Cycle Mitosis—A process that separates and encloses the duplicated chromosomes of the original cell into two identical nuclei • Four phases in mitosis • Prophase • Metaphase • Anaphase • Telophase The Cell Life Cycle Cytokinesis Division of the cytoplasm to form two identical daughter cells The Cell Life Cycle Mitotic Phases • Prophase • Chromosomes condense • Chromatids connect at centromeres • Metaphase • Chromatid pairs align at metaphase plate • Anaphase • Daughter chromosomes separate • Telophase • Nuclear envelopes reform The Cell Life Cycle Key Note Mitosis is the separation of duplicated chromosomes into two identical sets and nuclei in the process of somatic cell division. The Cell Life Cycle Cell Division and Cancer • Abnormal cell growth • Tumors (also called, neoplasm) • Benign • Encapsulated • Malignant • Invasion • Metastasis • Cancer—Disease that results from a malignant tumor The Cell Life Cycle Key Note Cancer results from mutations that disrupt the control mechanism that regulates cell growth and division. Cancers most often begin where cells are dividing rapidly, because the more chromosomes are copied, the greater the chances of error. Cell Diversity and Differentiation Somatic Cells • All have same genes • Some genes inactivate during development • Cells thus become functionally specialized • Specialized cells form distinct tissues • Tissue cells become differentiated
