* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Resolving power
Survey
Document related concepts
Model lipid bilayer wikipedia , lookup
Cell culture wikipedia , lookup
Cellular differentiation wikipedia , lookup
Cytoplasmic streaming wikipedia , lookup
Extracellular matrix wikipedia , lookup
Cell growth wikipedia , lookup
Organ-on-a-chip wikipedia , lookup
Cell nucleus wikipedia , lookup
Cytokinesis wikipedia , lookup
Signal transduction wikipedia , lookup
Cell membrane wikipedia , lookup
Transcript
Structure and Function of the Cell Chapter 3 3-1 How we learn about cells. • Brightfield Microscopy – visible light passes through the specimen and then through glass lenses. (magnification up to 1000x) • Magnification is the ratio of an object’s image to its real size. • Resolving power is a measure of image clarity. – It is the minimum distance two points can be separated and still viewed as two separate points. – Resolution is limited by the shortest wavelength of the source, in this case light. – Resolution of a light microscope is about 0.2um. 3-2 • The minimum resolution of a light microscope is about 2 microns, the size of a small bacterium • Light microscopes can magnify effectively to about 1,000 times the size of the actual specimen. – At higher magnifications, the image blurs. Fig. 7.1 3-3 • While a light microscope can resolve individual cells, it cannot resolve much of the internal anatomy, especially the organelles. • To resolve smaller structures we use an electron microscope (EM), which focuses a beam of electrons through the specimen or onto its surface. – Electron microscopes with shorter wavelengths than visible light have finer resolution. – The resolution of a modern EM is about 2 nm. 3-4 • Transmission electron microscopes (TEM) are used mainly to study the internal ultrastructure of cells. – A TEM aims an electron beam through a thin section of the specimen. – The image is focused and magnified by electromagnets. – To enhance contrast, the thin sections are stained with atoms of heavy metals. Fig. 7.2a 3-5 • Scanning electron microscopes (SEM) are useful for studying surface structures. – The sample surface is covered with a thin film of gold. – The beam excites electrons on the surface. – These secondary electrons are collected and focused on a screen. • The SEM has great depth of field, resulting in an image that seems three-dimensional. Fig. 7.2b 3-6 Cell Characteristics • Plasma Membrane – Outer cell boundary • Cytoplasm – Cytosol – Cytoskeleton – Cytoplasmic inclusions • Organelles – Specialized structures that perform specific functions 3-7 3-8 Plasma Membrane • • • • Intracellular versus extracellular Membrane potential Glycolipids and glycoproteins Fluid-mosaic model 3-9 Membrane Lipids • Phospholipids form a lipid bilayer – Hydrophilic (water-loving) polar heads – Hydrophobic (water-fearing) nonpolar heads • Cholesterol: Determines fluid nature of membrane 3-10 Membrane Proteins • Integral or intrinsic – Extend from one surface to the other • Peripheral or extrinsic – Attached to either the inner or outer surfaces of the lipid bilayer 3-11 Plasma membrane 3-12 Membrane Proteins 1. Marker Molecules • Allow cells to identify on another or other molecules • Glycoproteins – Also Glycolipids • Examples: – Immune system – Recognition of oocyte by sperm cell 3-13 2. Attachment Sites Integrins: Proteins in the plasma membrane attach to extracellular molecules. 3-14 3. Channel Proteins • Nongated ion channels – Always open • Ligand gated ion channel – Open in response to small molecules that bind to proteins or glycoproteins • Voltage-gated ion channel – Open when there is a change in charge across the plasma membrane 3-15 4. Receptors • Receptor molecules – Exposed receptor site • Linked to channel proteins – Acetylcholine • Linked to G proteins – Alter activity on inner surface of plasma membrane 3-16 5. Enzymes and Carrier Proteins 3-17 Nucleus • DNA dispersed throughout • Consists of : – Nuclear envelope: Separates nucleus from cytoplasm and regulates movement of materials in and out – Chromatin: Condenses to form chromosomes during cell division – Nucleolus: Assembly site of large and small ribosomal units 3-18 Nucleus 3-19 Cytoplasm • Cellular material outside nucleus but inside plasma membrane • Cytosol: Fluid portion • Cytoskeleton: Supports the cell – Microtubules – Microfilaments – Intermediate filaments • Cytoplasmic inclusions 3-20 The Endomembrane System Nuclear Endoplasmic Golgi Envelope Reticulum Apparatus Secretory Vesicle If you stick your finger in the hole of a doughnut is it inside or outside the doughnut? 3-21 Organelles • Small specialized structures for particular functions • Most have membranes that separates interior of organelles from cytoplasm • Related to specific structure and function of the cell 3-22 Ribosomes • Sites of protein synthesis • Composed of a large and small subunit • Types – Free – Polyribosomes – Attached to endoplasmic reticulum 3-23 Endoplasmic Reticulum • Types – Rough • Attached ribosomes • Proteins produced and modified – Smooth • Not attached ribosomes • Manufacture lipids • Cisternae: Interior spaces isolated from rest of cytoplasm 3-24 Golgi Apparatus • Modification, packaging, distribution of proteins and lipids for secretion or internal use • Flattened membrane sacs stacked on each other 3-25 Function of Golgi Apparatus 3-26 Action of Lysosomes 3-27 Peroxisomes and Proteasomes • Peroxisomes – Smaller than lysosomes – Contain enzymes to break down fatty and amino acids – Hydrogen peroxide is a by-product of breakdown • Proteasomes – Consist of large protein complexes – Include several enzymes that break down and recycle proteins in cell 3-28 Mitochondria • Provide energy for cell • Major site of ATP synthesis • Membranes – Cristae: Infoldings of inner membrane – Matrix: Substance located in space formed by inner membrane 3-29 Centrioles • In specialized zone near nucleus: Centrosome • Each unit consists of microtubules • Before cell division, centrioles divide, move to ends of cell and become spindle fibers 3-30 Cilia • Appendages projecting from cell surfaces • Capable of movement • Moves materials over the cell surface 3-31 Flagella • Similar to cilia but longer • Usually only one exists per cell • Move the cell itself in wavelike fashion • Example: Sperm cell 3-32 Microvilli • Extension of plasma membrane • Increase the cell surface • Normally many on each cell • One tenth to one twentieth size of cilia • Do not move 3-33 Movement through the Plasma Membrane • • • • Diffusion Osmosis Filtration Mediated transport mechanisms – Facilitated diffusion – Active transport – Secondary active transport 3-34 Diffusion • Movement of solutes from an area of higher concentration to lower concentration in solution – Concentration or density gradient • Difference between two points – Viscosity • How easily a liquid flows – Temperature – Size of the diffusing molecule 3-35 Diffusion 3-36 Osmosis • Diffusion of water (solvent) across a selectively permeable membrane • Important because large volume changes caused by water movement disrupt normal cell function • Cell shrinkage or swelling – Isotonic: cell neither shrinks nor swells – Hypertonic: cell shrinks (crenation) – Hypotonic: cell swells (lysis) 3-37 Osmosis 3-38 Osmosis 3-39 Filtration • Works like a sieve • Depends on pressure difference on either side of partition • Moves from side of greater pressure to lower – Example: In kidneys in urine formation 3-40 Mediated Transport Mechanisms • Involve carrier proteins • Characteristics – Specificity • To a single type of molecule – Competition – Saturation • Rate of transport limited to number of available carrier proteins 3-41 Saturation of a Carrier Protein 3-42 Mediated Transport Mechanisms • Facilitated diffusion – Higher to lower concentration without metabolic energy • Active transport – Requires ATP • Secondary active transport – Ions or molecules move in same (symport) or different direction (antiport) 3-43 Secondary Active Transport 3-44 Endocytosis • Internalization of substances by formation of a vesicle • Types – Phagocytosis – Pinocytosis – Receptor-mediated endocytosis 3-45 Pinocytosis and Receptor-Mediated Endocytosis 3-46 Exocytosis • Accumulated vesicle secretions expelled from cell • Examples – Secretion of digestive enzymes by pancreas – Secretion of mucus by salivary glands – Secretion of milk by mammary glands 3-47 Overview of Cell Metabolism 3-48 Chromosome Structure 3-49 3-50 3-51 3-52 Overview of Protein Synthesis 3-53 Overview of Protein Synthesis • Transcription – Copies DNA to form mRNA – tRNA carries amino acids to ribosome • Translation – Synthesis of a protein at ribosome 3-54 Translation 3-55 3-56 3-57 3-58 3-59 3-60 3-61 3-62 3-63 3-64 3-65 3-66 3-67 Cell Life Cycle • Interphase – Phase between cell divisions • Mitosis – – – – Prophase Metaphase Anaphase Telophase • Cytokinesis – Division of cell cytoplasm 3-68 RNA primer made by RNA polymerase 3' Newly synthesized DNA DNA polymerase adds complimentary base pairs to 3’ end. 5' Leading strand (Continuous replication) 3' 5' Lagging strand: (Okazaki fragments ) Helicase unwinds DNA 5' 3' 3' 1. Unwinding - Helicase 2. Complimentary base pairing - RNA polymerase makes RNA primer 5' - DNA polymerase adds nucleotides to 3' end 3. Joining -DNA polymerase removes RNA sequences. -Ligase joins DNA fragments Mitosis 3-70 Mitosis 3-71 Meiosis 3-72 Comparison of Mitosis and Meiosis 3-73 Cellular Aspects of Aging • • • • • Cellular clock Death genes DNA damage Free radicals Mitochondrial damage 3-74