Cell Bio 1 PDF

Chapter 3 Cell Structure and Function  An Introduction to Cells Cell Theory – Cells are the building blocks of all plants and animals – All cells come from the division of preexisting cells – Cells are the smallest units that perform all vital physiological functions –...

Chapter 3 Cell Structure and Function  An Introduction to Cells Cell Theory – Cells are the building blocks of all plants and animals – All cells come from the division of preexisting cells – Cells are the smallest units that perform all vital physiological functions – Each cell maintains homeostasis at the cellular level  The Study of 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)  An Overview of Cell Anatomy A cell is surrounded by a watery medium known as the extracellular fluid (interstitial fluid) – Plasma membrane (cell membrane) separates cytoplasm from the extracellular fluid – Cytoplasm: Cytosol = liquid Intracellular structures collectively known as organelles  The Anatomy of a Model Cell Figure 3-2  3-2 The plasma membrane separates the cell from its surrounding environment and performs various functions  Plasma Membrane Functions of the Plasma Membrane – Physical isolation: Barrier – Regulation of exchange with the environment: Ions and nutrients enter Wastes are eliminated and cellular products are released – Sensitivity to the environment: Extracellular fluid composition Chemical signals – Structural support: Anchors cells and tissues  Membrane Lipids Double layer of phospholipid molecules – Hydrophilic heads — toward watery environment, both sides – Hydrophobic fatty-acid tails — inside membrane – Barrier to ions and water — soluble compounds  Membrane Proteins Integral Proteins (Membrane spanning) – Within the membrane Peripheral Proteins – Bound to inner or outer surface of the membrane  Membrane Carbohydrates Glycoproteins and glycolipids – Extend outside cell membrane – Form sticky “sugar coat” (glycocalyx) Functions of the glycocalyx – Lubrication and protection – Anchoring and locomotion – Specificity in binding (receptors) – Recognition (immune response)  The Plasma Membrane Figure 3-3  3-3 Diffusion and filtration are passive transport mechanisms facilitating membrane passage  Membrane Transport The plasma (cell) membrane is a barrier, but – Nutrients must get in – Products and wastes must get out Permeability determines what moves in and out of a cell, and a membrane that – Lets nothing in or out is impermeable – Lets anything pass is freely permeable – Restricts movement is selectively permeable  Membrane Transport Plasma membrane is selectively permeable – Allows some materials to move freely – Restricts other materials Selective permeability restricts materials based on – Size – Electrical charge – Molecular shape – Lipid solubility  Membrane Transport Transport through a plasma membrane can be – Active (requiring energy and ATP) – Passive (no energy required) Diffusion (passive) Carrier-mediated transport (passive or active) Vesicular transport (active)  Diffusion Diffusion – Molecules mix randomly – Solute spreads through solvent – Eliminates concentration gradient – Solutes move down a concentration gradient  Diffusion Figure 3-4  Diffusion Diffusion Across Plasma Membranes – Can be simple or channel mediated: Materials that diffuse through plasma membrane by simple diffusion: – lipid-soluble compounds (alcohols, fatty acids, and steroids) – dissolved gases (oxygen and carbon dioxide) Materials that pass through transmembrane proteins (channels): – are water-soluble compounds – are ions  Diffusion Across the Plasma Membrane Figure 3-5  Diffusion Osmosis: A Special Case of Diffusion – Osmosis is the diffusion of water across the cell membrane More solute molecules, lower concentration of water molecules Membrane must be freely permeable to water, selectively permeable to solutes Water molecules diffuse across membrane toward solution with more solutes Volume increases on the side with more solutes  Osmosis Figure 3–6  Diffusion Osmosis: A Special Case of Diffusion – Osmotic pressure: Is the force of a concentration gradient of water Equals the force (hydrostatic pressure) needed to block osmosis  Diffusion Osmolarity and Tonicity – The osmotic effect of a solute on a cell: Two fluids may have equal osmolarity but different tonicity – Isotonic (iso- = same, tonos = tension): A solution that does not cause osmotic flow of water in or out of a cell – Hypotonic (hypo- = below): Has less solutes and loses water through osmosis – Hypertonic (hyper- = above): Has more solutes and gains water by osmosis  Diffusion Osmolarity and Tonicity – A cell in a hypotonic solution: Gains water Ruptures (hemolysis of red blood cells) – A cell in a hypertonic solution: Loses water Shrinks (crenation of red blood cells) Effects of Osmosis Across Plasma Membranes Figure 3-7  Filtration Hydrostatic pressure pushes on water Water crosses membrane Solute follows water Filtration initiates urine formation 3-4 Carrier-mediated and vesicular transport mechanisms also facilitate membrane passage  Carrier-Mediated Transport Carrier-mediated transport of ions and organic substrates – Facilitated diffusion – Active transport Characteristics – Specificity: One transport protein, one set of substrates – Saturation limits: Rate depends on transport proteins, not substrate – Regulation: Cofactors such as hormones  Carrier-Mediated Transport Cotransport – Two substances move in the same direction at the same time Countertransport – One substance moves in while another moves out  Carrier-Mediated Transport Facilitated diffusion – Passive – Carrier proteins transport molecules too large to fit through channel proteins (glucose, amino acids): Molecule binds to receptor site on carrier protein Protein changes shape, molecules pass through Receptor site is specific to certain molecules  Facilitated Diffusion Figure 3-8  Carrier-Mediated Transport Active Transport – Active transport proteins: Move substrates against concentration gradient Require energy, such as ATP Ion pumps move ions (Na+, K+, Ca2+, Mg2+) Exchange pump countertransports two ions at the same time  Carrier-Mediated Transport Active Transport – Sodium–potassium exchange pump: Active transport, carrier mediated: – sodium ions (Na+) out, potassium ions (K+) in – 1 ATP moves 3 Na+ and 2 K+ The Sodium–Potassium Exchange Pump Figure 3-9  Vesicular Transport Materials move into or out of cell in vesicles – Endocytosis (endo- = inside) is active transport using ATP: Receptor mediated Pinocytosis Phagocytosis – Exocytosis (exo- = outside): Granules or droplets are released from the cell Receptor-Mediated Endocytosis Figure 3-10  Phagocytosis and Exocytosis Figure 3-11  3-5 Organelles within the cytoplasm perform specific functions  Cytosol and Organelles All materials inside the cell and outside the nucleus – Cytosol (fluid): Dissolved materials: – nutrients, ions, proteins, and waste products High potassium/low sodium High protein High carbohydrate/low amino acid and fat – Organelles: Structures with specific functions  The Organelles Membranous Organelles – Covered with plasma membrane – Isolated from cytosol – Include the endoplasmic reticulum (ER), the Golgi apparatus, lysosomes, peroxisomes, and mitochondria Nonmembranous Organelles – No membrane – Direct contact with cytosol – Include the cytoskeleton, microvilli, centrioles, cilia, ribosomes, and proteasomes  Organelles Nonmembranous Organelles – The cytoskeleton — structural proteins for shape and strength: Microfilaments Intermediate filaments Microtubules  The Cytoskeleton Figure 3-12  The Organelles The Cytoskeleton – Microvilli: Increase surface area for absorption Attach to cytoskeleton – Centrioles in the centrosome: Centrioles form spindle apparatus during cell division Centrosome: cytoplasm surrounding centriole – Cilia: Small hair-like extensions Cilia move fluids across the cell surface  The Organelles Ribosomes – Build polypeptides in protein synthesis – Two types: Free ribosomes in cytoplasm: – manufacture proteins for cell Fixed ribosomes attached to ER: – manufacture proteins for secretion Proteasomes – Contain enzymes (proteases) – Disassemble damaged proteins for recycling  The Organelles Membranous Organelles – Five types of membranous organelles: Endoplasmic reticulum (ER) Golgi apparatus Lysosomes Peroxisomes Mitochondria  The Organelles Endoplasmic Reticulum (ER) – Functions: Synthesis of proteins, carbohydrates, and lipids Storage of synthesized molecules and materials Transport of materials within the ER Detoxification of drugs or toxins  The Organelles Endoplasmic Reticulum (ER) – Smooth endoplasmic reticulum (SER): No ribosomes attached Synthesizes lipids and carbohydrates: – phospholipids and cholesterol (membranes) – steroid hormones (reproductive system) – glycerides (storage in liver and fat cells) – glycogen (storage in muscles)  The Organelles Endoplasmic Reticulum (ER) – Rough endoplasmic reticulum (RER): Surface covered with ribosomes: – active in protein and glycoprotein synthesis – folds polypeptide protein structures – encloses products in transport vesicles  The Endoplasmic Reticulum Figure 3-13  Organelles and the Cytoplasm Golgi Apparatus – Vesicles enter forming face and exit maturing face: Secretory vesicles: – modify and package products for exocytosis Membrane renewal vesicles: – add or remove membrane components Lysosomes: – carry enzymes to cytosol  The Golgi Apparatus Figure 3-14  The Organelles Lysosomes – Powerful enzyme-containing vesicles Functions of Lysosomes – Clean up inside cells: Break down large molecules Attack bacteria Recycle damaged organelles Eject wastes by exocytosis – Autolysis Auto- = self, lysis = break Self-destruction of damaged cells: – lysosome membranes break down – digestive enzymes are released – cell decomposes – cellular materials recycle  The Organelles Peroxisomes – Are enzyme-containing vesicles: Break down fatty acids, organic compounds Produce hydrogen peroxide (H2O2)  The Organelles Mitochondria – Have smooth outer membrane and inner membrane with numerous folds (cristae) – Matrix: Fluid around cristae – Mitochondrion takes chemical energy from food (glucose): Produces energy molecule ATP  The Organelles Mitochondria – Aerobic metabolism (cellular respiration) Mitochondria use oxygen to break down food and produce ATP glucose + oxygen + ADP carbon dioxide + water + ATP Glycolysis: – glucose to pyruvic acid (in cytosol) Tricarboxylic acid cycle (TCA cycle): – pyruvic acid to CO2 (in matrix) Electron transport chain – inner mitochondrial membrane  Mitochondria Figure 3-15 3-6 The nucleus contains DNA and enzymes essential for controlling cellular activities Nuclear Structure and Contents Nucleus – Largest organelle – The cell’s control center Nuclear Envelope – Double membrane around the nucleus Perinuclear Space – Between the two layers of the nuclear envelope Nuclear Pores – Communication passages  The Nucleus Figure 3-16  Nuclear Structure and Contents DNA – All information to build and run organisms Nucleoplasm – Fluid containing ions, enzymes, nucleotides, and some RNA Nucleoli – Are related to protein production – Are made of RNA, enzymes, and histones – Synthesize rRNA and ribosomal subunits Chromatin – Loosely coiled DNA (cells not dividing) Chromosomes – Tightly coiled DNA (cells dividing)  Chromosome Structure Figure 3-17 Information Storage in the Nucleus DNA – Instructions for every protein in the body Gene – DNA instructions for one protein Genetic Code – The chemical language of DNA instructions: Sequence of bases (A, T, C, G) – Triplet code: 3 bases = 1 amino acid 3-7 DNA controls protein synthesis, cell structure, and cell function  Protein Synthesis The Role of Gene Activation in Protein Synthesis – The nucleus contains chromosomes – Chromosomes contain DNA – DNA stores genetic instructions for proteins – Proteins determine cell structure and function  Protein Synthesis Transcription – Copies instructions from DNA to mRNA (in nucleus) Translation – Ribosome reads code from mRNA (in cytoplasm) – Assembles amino acids into polypeptide chain Processing – By RER and Golgi apparatus produce protein  Transcription A gene is transcribed to mRNA in three steps – Gene activation – DNA to mRNA – RNA processing  Transcription Figure 3-18  Protein Synthesis Translation – mRNA moves: From the nucleus through a nuclear pore – mRNA moves: To a ribosome in cytoplasm Surrounded by amino acids – mRNA binds to ribosomal subunits: tRNA delivers amino acids to mRNA  Protein Synthesis Translation – tRNA anticodon binds to mRNA codon 1 mRNA codon translates to 1 amino acid – Enzymes join amino acids with peptide bonds Polypeptide chain has specific sequence of amino acids – At stop codon, components separate  Translation Figure 3-19  Translation Figure 3-19  Translation Figure 3-19  Tumors and cancers are characterized by abnormal cell growth and division  Tumors and Cancers Abnormal cell growth Tumors (also called, neoplasm) – Benign: Encapsulated – Malignant: Invasion Metastasis Cancer — Disease that results from a malignant tumor  Differentiation is cellular specialization as a result of gene activation or repression  Cell Differentiation All cells carry complete DNA instructions for all body functions Cells specialize or differentiate – To form tissues (liver cells, fat cells, and neurons) – By turning off all genes not needed by that cell All body cells, except sex cells, contain the same 46 chromosomes Differentiation depends on which genes are active and which are inactive