The Cell Lecture Notes: Cell Structure and Function

The Cell Lecture 2  The Cell What are the cells’ 3 main parts and their functions? – Overview, plasma membrane, cytoplasm, nucleus What are the stages of the cells’ life cycle and their importance? – Mitosis  Overview Cells are numerou...

The Cell Lecture 2  The Cell What are the cells’ 3 main parts and their functions? – Overview, plasma membrane, cytoplasm, nucleus What are the stages of the cells’ life cycle and their importance? – Mitosis  Overview Cells are numerous and diverse Cells have specific structures and functions. There are 50-100 trillion cells in the body. Cells are diverse (250+ types). Cells are either somatic or sex cells.  Overview: 3 main parts of a generalized cell 1. Plasma membrane - inside from outside 2. Cytoplasm – Cytoskeleton, cytosol, organelles, inclusions 3. Nucleus – control center Nucleu s Plasma membrane Cytoplasm Fig. 2.1  Plasma Membrane Boundary of cell Membrane proteins Membrane lipids – Integral (transmembrane) – Phospholipids – 75% proteins Pass through membrane Bilayer Glycoproteins Hydrophilic Hydrophobic – Peripheral proteins Amphipathic Adhere to either face of membrane – Cholesterol – 20% Fluidity of the membrane – Glycolipids – 5% Contribute to glycocalyx- carbohydrate coating Plays a dynamic role in cellular activity  Plasma Membrane: Fluid Mosaic Model Phospholipid bilayer Extracellular fluid (watery environment) Glycolipid – Hydrophillic head – Hydrophobic tail Cytoplasm (watery environment) This bilayer is fluid. Fig. 2.2  Plasma Membrane: Fluid Mosaic Model Extracellular fluid (watery environment) Membrane proteins: Cholestero l Peripheral Glycoprotein Integral glycocalyx (transmembrane) Glycoproteins (Glycocalyx) Integral proteins HIV virus Periphera l CCR5 Cytoplasm proteinsFilament of cytoskeleton (watery environment) The membrane is a mosaic. Fig. 2.2 Functions of Membrane Proteins: Receptor Transport protein Enzyme Cell-identity marker Channel protein Cell-adhesion molecule Figure 2.9, page  Plasma Membrane Functions: 1.Protective barrier 2.Receptors for communication 3.Selective permeability: membrane transport HIV Lipid virus bilayer CCR5 Cytoplasm Fig. 2.2, 2.3c  Cell Junctions Located at the cell surface Attach cells together and to the extracellular material Enable cells to resist stress, grow and divide normally, communicate with each other, and control the movement of substances.  Cell Junctions 3 types of cell junctions based on their function and purpose: 1. Tight junction: sealant 2. Gap junction: communication 3. Desmosomes: resist stress. Each cell often has two or more type.  Cell Junctions Tight junction – Sealant Desmosomes – Resist stress Gap junction – Communication Figure 2.15, page 38  Cell Junctions Tight Junction: attach neighboring cells tightly; plasma membranes are linked by transmembrane adhesion proteins. The intercellular space is sealed off. Ex: stomach and intestines; digestive juices don’t seep between surface cells and underlying layers.  Cell Junctions Desmosome: a protein patch that holds cells tightly at a specific point. Tight junction is comparable to a zipper; desmosome to a snap. Keeps cells from pulling apart and enables a tissue to resist mechanical stress.  Cell Junctions Gap (communicating) Junction: forms a channel that specific ions and molecules can diffuse directly from the cytoplasm of one cell to another.  Example: In cardiac muscle allows electrical excitation to pass directly from cell to cell so the cells contract in near unison; In the embryo before the circulatory system is formed, it takes over the role of nutrient distribution and allows nutrients to pass from cell to cell. Membrane Transport: Simple Diffusion  Membrane Transport: Osmosis Special case of simple diffusion Movement of water From “more watery” side to “less watery” side  Tonicity Tonicity: The ability of a solution to cause a cell to shrink or swell Isotonic: A solution with the same solute concentration as that of the cytosol Hypertonic: A solution having greater solute concentration than that of the cytosol Hypotonic: A solution having lesser solute concentration than that of the cytosol  Osmolarity and Tonicity Hypotonic solution – Has a lower concentration of nonpermeating solutes than intracellular fluid (ICF) High water concentration – Cells absorb water, swell, and may burst (lyse) Hypertonic solution – Has a higher concentration of nonpermeating solutes Low water concentration – Cells lose water + shrivel (crenate) Isotonic solution – Concentrations in cell and ICF are the same – Cause no changes in cell volume or cell shape – Normal saline  (a) Isotonic solutions (b) Hypertonic solutions (c) Hypotonic solutions Cells lose water by osmosis and Cells retain their normal size and shrink in a hypertonic solution Cells take on water by osmosis until shape in isotonic solutions (same (contains a higher concentration they become bloated and burst (lyse) solute/water concentration as inside of solutes than are present inside in a hypotonic solution (contains a cells; water moves in and out). the cells). lower concentration of solutes than are present in cells).  Carrier-Mediated Transport Uniport – Carries only one solute at a time Symport – Carries two or more solutes simultaneously in same direction (cotransport) Antiport – Carries two or more solutes in opposite directions (countertransport) – Sodium-potassium pump brings in K+ and removes Na+ from cell Carriers employ two methods of transport – Facilitated diffusion – Active transport  Carrier-Mediated Transport Facilitated diffusion— transport down its concentration gradient Does not consume ATP Solute attaches to binding site on carrier. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ECF ICF 1 A solute particle enters 2 The solute binds to a receptor 3 The carrier releases the the channel of a membrane site on the carrier and the solute on the other side of protein (carrier). carrier changes conformation. the membrane. Membrane Transport: Active Transport Figure 2.10d  Vesicular Transport transport—processes that move large particles, fluid droplets, or numerous molecules at once through the membrane in vesicle: Endocytosis—transport into cell Exocytosis—transport out of cell Transcytosis—transport into, across, and then out of cell  1 Phagocyte adheres to pathogens or debris. 2 Phagocyte forms pseudopods that Phagosome eventually engulf the (phagocytic particles forming a vesicle) Lysosome phagosome. 3 Lysosome fuses with the phagocytic vesicle, forming a phagolysosome. Acid hydrolase enzymes 4 Lysosomal enzymes digest the particles, leaving a residual body. 5 Exocytosis of the vesicle removes indigestible and residual material. (b) Events of phagocytosis.  Endocytosis Pinocytosis —Cell drinking by in folding the plasma membrane  Vesicular Transport Receptor-mediated endocytosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Extracellular molecules Receptor Coated pit Clathrin- coated Clathrin vesicle 1 2 3 Extracellular molecules bind to Plasma membrane sinks inward, Pit separates from plasma receptors on plasma membrane; forms clathrin-coated pit. membrane, forms clathrin-coated receptors cluster together. vesicle containing concentrated molecules from ECF.  Vesicular Transport Exocytosis Secreting material Replacement of plasma membrane removed by endocytosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Dimple Fusion pore Secretion Plasma membrane Linking protein Secretory vesicle (a) 1 A secretory vesicle approaches 2 The plasma membrane and (b) the plasma membrane and docks vesicle unite to form a fusion on it by means of linking proteins. pore through which the vesicle The plasma membrane caves in contents are released. at that point to meet the vesicle. Courtesy of Dr. Birgit Satir, Albert Einstein College of Medicine  Glycocalyx Carbohydrate component belonging to membrane’s glycolipids and glycoproteins Fuzzy, sugary coat external to the plasma membrane Functions – Protection – Cell identity – Binds tissues – Fertilization – Defense against cancer  Cell Summary I The plasma membrane has a structure consisting mainly of phospholipids and proteins which function to protect, communicate and transport selectively.  Overview: 3 main parts of a generalized cell 1. Plasma membrane - inside from outside 2. Cytoplasm – cytosol, organelles, inclusions, cytoskeleton 3. Nucleus – control center Nucleu s Plasma membrane Cytoplasm  Cytoplasm: 4 main parts 1. Cytosol: jellylike fluid with proteins 2. Organelles: functional units 3. Inclusions: temporary structures mainly for storage 4. Cytoskeleton Fig. 2.4  Organelles: 9 main types Ribosomes Endoplasmic reticulum Golgi apparatus Lysosomes Peroxisomes Mitochondria Cytoskeleton Centrosomes and centrioles  Ribosomes Structure: proteins bound to rough ER or free in cytoplasm Function: synthesize proteins Rough ER Nuclear envelope Rough ER Ribosomes Fig. 2.6  Endoplasmic Reticulum (ER) Structure: interconnected membranes continuous with the nuclear and cell membrane Functions: synthesize, store, transport, detox 1. Rough ER: binds ribosomes, synthesize proteins 2. Smooth ER: synthesize lipids, break down drugs Smooth ER Nuclear Membrane/envelope Rough ER Ribosomes Fig. 2.6  Golgi apparatus Structure: flattened membrane sacs (cisternae) continuous with rough ER Function: modify, pack and deliver proteins in vesicles Transport vesicle from rough ER Where do the Secretory vesicles go? vesicle Fig. 2.7  Golgi apparatus Vesicles go to 3 destinations Rough ER Phagosom Plasm ER e membran a e mem- brane A) Leave cell by Pathway C: Lysosome exocytosis Vesicle B) To plasma becomes lysosome membrane C) Stay in cell as Secretor Golgi apparatus y vesicle Pathway B: Vesicle lysosome membrane to be Pathway A: incorporated Vesicle contents Secretion by into plasma destined for Extracellular exocytosis membrane exocytosis fluid Fig. 2.8  Lysosomes and Peroxisomes Organelle Structure Function Lysosomes Spherical Digest waste, membranes with “garbage disposal” Peroxisomes enzymes Detoxify harmful substances lysosome Fig. 2.9  Mitochondria Structure: double membrane Function: produce energy in the form of ATP (uses oxygen), “power plants” Fig. 2.10  Inclusions Not essential to cell survival Stored cellular products – Pigments – Fat droplets – Granules of glycogen Foreign bodies – Dust particles – Viruses – Intracellular bacteria  Cytoskeleton Structure: series of rods (proteins) throughout cytosol Function: “cell skeleton” for structure and support 3 types of rods: Microfilaments Intermediate filaments Microtubules  Centrosome and Centrioles Structure: centrosome is near nucleus containing centrioles (microtubule bundles) Function: forms spindle during mitosis for division of nucleus Fig. 2.12  Surface Extensions Microvilli – Plasma membrane extensions – Increase surface area – Brush border Cilia – Primary cilium – Motile cilia – Axoneme – microtubules – Dynein – motor protein Flagella – Long axoneme – Propels sperm cell  Overview: 3 main parts of a generalized cell 1. Plasma membrane - inside from outside 2. Cytoplasm – cytosol, organelles, inclusions 3. Nucleus – control center Nucleu s Plasma membrane Cytoplasm Fig. 2.1  The Nucleus Structures: – Nuclear envelope (membrane) DNA helix double – Nucleolus: synthesizes ribosomes – Chromatin: DNA + proteins Histones Function: control center chromatin (proteins) Nuclear Nuclear pores envelope Nucleus chromosome Nucleolu s Chromatin (condensed) Fig 2.13, 14  Cell Summary II The cytoplasm contains cytosol, inclusions and many organelles, each with a specific structure and function. The nucleus contains DNA and controls the cell. Cellular Terminology  Cell Life Cycle The cell life cycle consists of Interphase Mitosis (prophase, metaphase, anaphase, telophase) Fig. 2.16 (review 2.17) Fig. 2.16  The Cell Cycle, continued Interphase – First gap phase (G1) Growth and normal metabolic roles – Synthesis phase (S) DNA replication – Second gap phase (G2) Growth and preparation for mitosis DNA proofreading The Cell Cycle, continued Mitotic Phase (M) – Division of Nuclear material – Prophase – Anaphase Chromatin condenses Daughter chromosomes Nuclear envelope breaks move to opposite poles down – Telophase Nucleolus disappears Chromatids at each pole Spindle fibers form to decondense connect to kinetochore Surrounded by new – Metaphase nuclear membrane Nucleoli reformed Chromosomes align at center of cell Aster attached to plasma membrane  The Cell Cycle, continued Cytokinesis – Division of cytoplasm – Begins in anaphase – Cleavage furrow developed – Cell pinches into two identical daughter cells  Mitosis Figure 2.23  Cell Life Cycle Cancer is uncontrolled cell division and can cause a tumor growth. Normal cells (with hairlike cilia)) Comparision Breast cancer cell mitosis Cancer cells  Stem Cells Immature cells that can develop into one or more types of mature, specialized cells – Developmental plasticity Adult stem (AS) cells – In most body organs – Produce cells for normal turnover – Multipotent (e.g. bone marrow cells) Embryonic stem (ES) cells – Embryo up to 150 cells – Pluripotent – Excess of in vitro fertilization  Cell Summary III The cell life cycle includes interphase and mitosis, which is the division of the nucleus into two. Altering normal cell division can lead to cancer and can be used in stem cells.