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The Cell The Basic Unit of Life. The Importance of Cells All organisms are made of cells The cell is the simplest collection of matter that can live.

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Presentation on theme: "The Cell The Basic Unit of Life. The Importance of Cells All organisms are made of cells The cell is the simplest collection of matter that can live."— Presentation transcript:

1 The Cell The Basic Unit of Life

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3 The Importance of Cells All organisms are made of cells The cell is the simplest collection of matter that can live Cell structure is correlated to cellular function All cells are related by their descent from earlier cells

4 Microscopy light microscope (LM) visible light passes through a specimen and then through glass lenses, which magnify the image Magnify up to 1000x

5 LE 6-2 Measurements 1 centimeter (cm) = 10 –2 meter (m) = 0.4 inch 1 millimeter (mm) = 10 –3 m 1 micrometer (µm) = 10 –3 mm = 10 –6 m 1 nanometer (nm) = 10 –3 µm = 10 –9 m 10 m 1 m Human height Length of some nerve and muscle cells Chicken egg 0.1 m 1 cm Frog egg 1 mm 100 µm Most plant and animal cells 10 µm Nucleus 1 µm Most bacteria Mitochondrion Smallest bacteria Viruses 100 nm 10 nm Ribosomes Proteins Lipids 1 nm Small molecules Atoms 0.1 nm Unaided eye Light microscope Electron microscope

6 LE 6-3a Brightfield (unstained specimen) 50 µm Brightfield (stained specimen) Phase-contrast

7 LE 6-3b 50 µm Confocal Differential- interference- contrast (Nomarski) Fluorescence

8 electron microscopes (EMs) are used to study subcellular structures Two types Scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen providing images that look 3D Transmission electron microscopes (TEMs) focus a beam of electrons through a specimen to study the internal structures of cells

9 LE µm Scanning electron microscopy (SEM) Cilia Longitudinal section of cilium Transmission electron microscopy (TEM) Cross section of cilium

10 Basic features of all cells: Plasma membrane Selectively permeable double layer of phospholipids Semifluid substance called the cytosol Includes cytoplasm & organelles Chromosomes (carry genes) Ribosomes (make proteins)

11 LE 6-8 Hydrophilic region Hydrophobic region Carbohydrate side chain Structure of the plasma membrane Hydrophilic region Phospholipid Proteins Outside of cell Inside of cell 0.1 µm TEM of a plasma membrane

12 Prokaryotic Cells Eukaryotic Cells no nucleus DNA is in an unbound region called the nucleoid No membrane-bound organelles Include bacteria and Achaea Have nucleus DNA in nucleus Membrane-bound organelles Usually larger than prokaryotic cells Cell size limited by metabolic activities Include plants, animals, and fungi

13 LE 6-6 A typical rod-shaped bacterium A thin section through the bacterium Bacillus coagulans (TEM) 0.5 µm Pili Nucleoid Ribosomes Plasma membrane Cell wall Capsule Flagella Bacterial chromosome

14 LE 6-7 Total surface area (height x width x number of sides x number of boxes) Total volume (height x width x length X number of boxes) Surface-to-volume ratio (surface area volume) Surface area increases while Total volume remains constant

15 LE 6-9a Flagellum Centrosome CYTOSKELETON Microfilaments Intermediate filaments Microtubules Peroxisome Microvilli ENDOPLASMIC RETICULUM (ER Rough ER Smooth ER Mitochondrion Lysosome Golgi apparatus Ribosomes: Plasma membrane Nuclear envelope NUCLEUS In animal cells but not plant cells: Lysosomes Centrioles Flagella (in some plant sperm) Nucleolus Chromatin

16 LE 6-9b Rough endoplasmic reticulum In plant cells but not animal cells: Chloroplasts Central vacuole and tonoplast Cell wall Plasmodesmata Smooth endoplasmic reticulum Ribosomes (small brown dots) Central vacuole Microfilaments Intermediate filaments Microtubules CYTOSKELETON Chloroplast Plasmodesmata Wall of adjacent cell Cell wall Nuclear envelope Nucleolus Chromatin NUCLEUS Centrosome Golgi apparatus Mitochondrion Peroxisome Plasma membrane

17 The Nucleus contains most of the cells genes usually the most conspicuous organelle Enclosed by nuclear envelope

18 LE 6-10 Close-up of nuclear envelope Nucleus Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Pore complex Ribosome Pore complexes (TEM)Nuclear lamina (TEM) 1 µm Rough ER Nucleus 1 µm 0.25 µm Surface of nuclear envelope

19 Ribosomes made of ribosomal RNA and protein protein synthesis In the cytosol (free ribosomes) On the outside of the endoplasmic reticulum (ER) or the nuclear envelope (bound ribosomes)

20 LE 6-11 Ribosomes 0.5 µm ER Cytosol Endoplasmic reticulum (ER) Free ribosomes Bound ribosomes Large subunit Small subunit Diagram of a ribosome TEM showing ER and ribosomes

21 Endomembrane System Regulate protein traffic Perform metabolic functions Components of the endomembrane system: Nuclear envelope Endoplasmic reticulum Golgi apparatus Lysosomes Vacuoles Plasma membrane components are either continuous or connected via transfer by vesicles

22 The Endoplasmic Reticulum (ER) is continuous with the nuclear envelope two distinct regions of ER: Smooth ER, lacks ribosomes Rough ER with ribosomes studding its surface

23 LE 6-12 Ribosomes Smooth ER Rough ER ER lumen Cisternae Transport vesicle Smooth ER Rough ER Transitional ER 200 nm Nuclear envelope

24 Functions of Smooth ER Synthesizes lipids Metabolizes carbohydrates Stores calcium Detoxifies poison

25 Functions of Rough ER bound ribosomes Produces proteins and membranes distributed by transport vesicles

26 The Golgi Apparatus consists of flattened membranous sacs called cisternae Functions of the Golgi apparatus: Modifies products of the ER Manufactures certain macromolecules Sorts and packages materials into transport vesicles

27 LE 6-13 trans face (shipping side of Golgi apparatus) TEM of Golgi apparatus 0.1 µm Golgi apparatus cis face (receiving side of Golgi apparatus) Vesicles coalesce to form new cis Golgi cisternae Vesicles also transport certain proteins back to ER Vesicles move from ER to Golgi Vesicles transport specific proteins backward to newer Golgi cisternae Cisternal maturation: Golgi cisternae move in a cis- to-trans direction Vesicles form and leave Golgi, carrying specific proteins to other locations or to the plasma mem- brane for secretion Cisternae

28 Lysosomes membranous sac of hydrolytic enzymes hydrolyze proteins, fats, polysaccharides, and nucleic acids use enzymes to recycle organelles and macromolecules a process called autophagy

29 LE 6-14a Phagocytosis: lysosome digesting food 1 µm Plasma membrane Food vacuole Lysosome Nucleus Digestive enzymes Digestion Lysosome Lysosome contains active hydrolytic enzymes Food vacuole fuses with lysosome Hydrolytic enzymes digest food particles

30 LE 6-14b Autophagy: lysosome breaking down damaged organelle 1 µm Vesicle containing damaged mitochondrion Mitochondrion fragment Lysosome containing two damaged organelles Digestion Lysosome Lysosome fuses with vesicle containing damaged organelle Peroxisome fragment Hydrolytic enzymes digest organelle components

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32 Vacuoles & Vesicles membrane-bound sacs with varied functions Food vacuoles formed by phagocytosis Contractile vacuoles found in many freshwater protists pump excess water out of cells Central vacuoles found in many mature plant cells hold organic compounds and water

33 LE µm Central vacuole Cytosol Tonoplast Central vacuole Nucleus Cell wall Chloroplast

34 LE Nuclear envelope Nucleus Rough ER Smooth ER

35 LE Nuclear envelope Nucleus Rough ER Smooth ER Transport vesicle cis Golgi trans Golgi

36 LE Nuclear envelope Nucleus Rough ER Smooth ER Transport vesicle cis Golgi trans Golgi Plasma membrane

37 Mitochondria & Chloroplasts Mitochondria Chloroplasts sites of cellular respiration not part of the endomembrane system found only in plants and algae the sites of photosynthesis not part of the endomembrane system

38 Mitochondria in nearly all eukaryotic cells smooth outer membrane inner membrane folded into cristae creates two compartments: intermembrane space mitochondrial matrix Folding creates more surface area for enzymes that synthesize ATP

39 LE 6-17 Mitochondrion Intermembrane space Outer membrane Inner membrane Cristae Matrix 100 nm Mitochondrial DNA Free ribosomes in the mitochondrial matrix

40 Chloroplasts Type of plastid contain the green pigment chlorophyll contains enzymes and other molecules that function in photosynthesis found in leaves and other green organs of plants and in algae Chloroplast structure includes: Thylakoids membranous sacs Stroma the internal fluid

41 LE 6-18 Chloroplast DNA Ribosomes Stroma Inner and outer membranes Granum Thylakoid 1 µm

42 Plastids Responsible for photosynthesis Storage of products (ie. Starch) Synthesis of molecules (ie. Fatty acids)

43 Peroxisomes specialized metabolic compartments single membrane produce hydrogen peroxide and convert it to water are oxidative organelles Aid in breakdown of lipids

44 LE 6-19 Chloroplast Peroxisome Mitochondrion 1 µm

45 Cytoskeleton network of fibers extending throughout the cytoplasm organizes the cells structures and activities anchors many organelles composed of: Microtubules Microfilaments Intermediate filaments

46 LE 6-20 Microtubule Microfilaments 0.25 µm

47 Roles of the Cytoskeleton support the cell maintain cell shape interacts with motor proteins to produce motility Inside the cell, vesicles can travel along monorails provided by the cytoskeleton may help regulate biochemical activities

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51 Centrosomes and Centrioles microtubules grow out from a centrosome near the nucleus microtubule-organizing center In animal cells, the centrosome has a pair of centrioles

52 LE µm Microtubule Centrosome Centrioles Longitudinal section of one centriole Microtubules Cross section of the other centriole

53 Cilia and Flagella Beating controlled by microtubules sheathed by the plasma membrane Dynein Motor protein drives the bending movements of a cilium or flagellum

54 LE 6-23a 5 µm Direction of swimming Motion of flagella

55 LE 6-23b 15 µm Direction of organisms movement Motion of cilia Direction of active stroke Direction of recovery stroke

56 Microfilaments (Actin Filaments) twisted double chain of actin subunits Also have myosin if the microfilaments are used for movement bear tension, resisting pulling forces within the cell form a 3D network just inside the plasma membrane to help support the cells shape Bundles of microfilaments make up the core of microvilli

57 LE 6-26 Microfilaments (actin filaments) Microvillus Plasma membrane Intermediate filaments 0.25 µm

58 LE 6-27b Cortex (outer cytoplasm): gel with actin network Amoeboid movement Inner cytoplasm: sol with actin subunits Extending pseudopodium

59 Cytoplasmic streaming circular flow of cytoplasm within cells speeds distribution of materials within the cell In plant cells, actin-myosin interactions and sol-gel transformations drive cytoplasmic streaming

60 LE 6-27c Nonmoving cytoplasm (gel) Cytoplasmic streaming in plant cells Chloroplast Streaming cytoplasm (sol) Cell wall Parallel actin filaments Vacuole

61 Intermediate Filaments range in diameter from 8–12 nanometers larger than microfilaments smaller than microtubules support cell shape fix organelles in place

62 Extracellular Structures These extracellular structures include: Cell walls of plants The extracellular matrix (ECM) of animal cells Intercellular junctions

63 Cell Walls of Plants distinguishes plant cells from animal cells protects the plant cell maintains cell shape prevents excessive uptake of water made of cellulose fibers embedded in other polysaccharides and protein

64 Cell Walls of Plants Plant cell walls may have multiple layers: Primary cell wall relatively thin and flexible Middle lamella thin layer between primary walls of adjacent cells Secondary cell wall (in some cells) added between the plasma membrane and the primary cell wall Plasmodesmata are channels between adjacent plant cells

65 LE 6-28 Central vacuole of cell Plasma membrane Secondary cell wall Primary cell wall Middle lamella 1 µm Central vacuole of cell Central vacuole Cytosol Plasma membrane Plant cell walls Plasmodesmata

66 The Extracellular Matrix (ECM) of Animal Cells made up of glycoproteins and other macromolecules Functions of the ECM: Support Adhesion Movement Regulation

67 Intercellular Junctions facilitate contact between cells Adhesion Interaction Communication

68 Plants: Plasmodesmata channels that perforate plant cell walls water and small solutes (and sometimes proteins and RNA) can pass from cell to cell

69 LE 6-30 Interior of cell Interior of cell 0.5 µm PlasmodesmataPlasma membranes Cell walls

70 Animals: Tight Junctions, Desmosomes, and Gap Junctions tight junctions membranes of neighboring cells are pressed together prevents leakage of extracellular fluid Desmosomes (anchoring junctions) fasten cells together into strong sheets Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells

71 LE 6-31 Tight junctions prevent fluid from moving across a layer of cells Tight junction 0.5 µm 1 µm 0.1 µm Gap junction Extracellular matrix Space between cells Plasma membranes of adjacent cells Intermediate filaments Tight junction Desmosome Gap junctions

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73 Fluid Mosaic Model Phospholipids hydrophobic fatty acid tails hydrophilic phosphate heads

74 LE 7-2 Hydrophilic head Hydrophobic tail WATER

75 Fluidity of Membranes Phospholipids move within the bilayer Most of the lipids, and some proteins, drift laterally Cool temperatures membranes switch from a fluid state to a solid state Membranes must be fluid to work properly Consistency of oil

76 Cholesterol Steroid present in cell membrane Maintains fluidity At warm temperatures (such as 37°C) restrains movement At cool temperatures prevents tight packing

77 LE 7-5c Cholesterol Cholesterol within the animal cell membrane

78 Membrane Proteins Peripheral proteins not embedded Integral proteins penetrate the hydrophobic core often span the membrane transmembrane proteins

79 LE 7-7 Fibers of extracellular matrix (ECM) Glycoprotein Carbohydrate Microfilaments of cytoskeleton Cholesterol Integral protein Peripheral proteins CYTOPLASMIC SIDE OF MEMBRANE EXTRACELLULAR SIDE OF MEMBRANE Glycolipid

80 Six major functions of membrane proteins: Transport Enzymatic activity Signal transduction Cell-cell recognition Intercellular joining Attachment to the cytoskeleton and extracellular matrix (ECM)

81 LE 7-9a Enzymes Signal Receptor ATP Transport Enzymatic activity Signal transduction

82 LE 7-9b Glyco- protein Cell-cell recognition Intercellular joining Attachment to the cytoskeleton and extra- cellular matrix (ECM)

83 Carbohydrates Cell to cell recognition Bonded to lipids = glycolipids Bonded to proteins = glycoproteins (more common)

84 Selective Permeability Permeability factors Molecular size Solubility in lipids ex. Oxygen, carbon dioxide, steroid hormones Charge of ions Presence of carrier molecules

85 Carrier Molecules transport proteins channel proteins carrier proteins bind to molecules change shape to shuttle them across the membrane

86 Diffusion Net direction of movement from areas of high to low concentration Continues until equilibrium has been met Movement continues at equal rates in both directions Animation: Membrane Selectivity Animation: Membrane Selectivity Animation: Diffusion Animation: Diffusion

87 LE 7-11a Molecules of dyeMembrane (cross section) WATER Net diffusion Equilibrium Diffusion of one solute

88 Osmosis diffusion of water direction of osmosis is determined by a difference in total solute concentration Movement from region of lower solute concentration to the region of higher solute concentration

89 Tonicity the ability of a solution to cause a cell to gain or lose water Isotonic solution: solute concentration is the same as that inside the cell no net water movement across the plasma membrane Hypertonic solution solute concentration is greater than that inside the cell cell loses water Hypotonic solution solute concentration is less than that inside the cell cell gains water

90 Cells without Cell Walls Special adaptations for osmoregulation Control of water balance Ex. Contractile vacuole in Paramecium

91 LE 7-14 Filling vacuole 50 µm Contracting vacuole

92 Cells with Cell Walls Cell walls help maintain water balance hypotonic solution swells until the wall opposes uptake the cell is now turgid (firm) Isotonic is no net movement of water into the cell the cell becomes flaccid (limp), and the plant may wilt hypertonic environment plant cells lose water the membrane pulls away from the wall a usually lethal effect called plasmolysis

93 LE 7-13 Animal cell Lysed H2OH2O H2OH2O H2OH2O Normal Hypotonic solution Isotonic solutionHypertonic solution H2OH2O Shriveled H2OH2O H2OH2O H2OH2O H2OH2O Plant cell Turgid (normal) FlaccidPlasmolyzed

94 Facilitated diffusion passive solute moves down its concentration gradient Transport proteins Channel proteins Carrier proteins

95 LE 7-15a EXTRACELLULAR FLUID Channel protein Solute CYTOPLASM

96 LE 7-15b Carrier protein Solute

97 Active transport moves substances against their concentration gradient requires energy, usually in the form of ATP Integral proteins Ex. sodium-potassium pump Animation: Active Transport Animation: Active Transport

98 LE 7-17 Diffusion Facilitated diffusion Passive transport ATP Active transport

99 Membrane potential voltage difference across a membrane Electrochemical gradient drives the diffusion of ions across a membrane Includes : A chemical force the ions concentration gradient An electrical force the effect of the membrane potential on the ions movement

100 electrogenic pump transport protein generates the voltage across a membrane main electrogenic pump of plants, fungi, and bacteria is a proton pump

101 LE 7-18 H+H+ ATP CYTOPLASM EXTRACELLULAR FLUID Proton pump H+H+ H+H+ H+H+ H+H+ H+H – – – – –

102 Cotransport active transport of a solute indirectly drives transport of another solute Ex. Plants - gradient of hydrogen ions generated by proton pumps drives active transport of nutrients into the cell

103 LE 7-19 H+H+ ATP Proton pump Sucrose-H + cotransporter Diffusion of H + Sucrose H+H+ H+H+ H+H+ H+H+ H+H+ H+H – – – – – –

104 Exocytosis Type of active transport transport vesicles migrate to the membrane, fuse with it, and release their contents

105 Endocytosis cell takes in macromolecules by forming vesicles from the plasma membrane reversal of exocytosis involves different proteins Three types of endocytosis: Phagocytosis cellular eating Cell engulfs particle in a vacuole Pinocytosis cellular drinking Cell creates vesicle around fluid Receptor-mediated endocytosis Binding of ligands to receptors triggers vesicle formation

106 Figure of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Phagocytosis A phagocytic cell comes in contact with the foreign object and sends pseudopodia (cytoplasmic extensions) around it. Pseudopodium (cytoplasmic extension) EXTRACELLULAR FLUID CYTOPLASM Foreign object Cell membrane of phagocytic cell

107 Figure of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Cell membrane of phagocytic cell Phagocytosis A phagocytic cell comes in contact with the foreign object and sends pseudopodia (cytoplasmic extensions) around it. Pseudopodium (cytoplasmic extension) EXTRACELLULAR FLUID CYTOPLASM Foreign object The pseudopodia approach one another and fuse to trap the material within the vesicle.

108 Figure of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Cell membrane of phagocytic cell Phagocytosis A phagocytic cell comes in contact with the foreign object and sends pseudopodia (cytoplasmic extensions) around it. Pseudopodium (cytoplasmic extension) EXTRACELLULAR FLUID CYTOPLASM Foreign object Vesicle The pseudopodia approach one another and fuse to trap the material within the vesicle. The vesicle moves into the cytoplasm.

109 Figure of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Cell membrane of phagocytic cell Phagocytosis A phagocytic cell comes in contact with the foreign object and sends pseudopodia (cytoplasmic extensions) around it. Pseudopodium (cytoplasmic extension) EXTRACELLULAR FLUID CYTOPLASM Foreign object Vesicle Lysosomes The pseudopodia approach one another and fuse to trap the material within the vesicle. The vesicle moves into the cytoplasm. Lysosomes fuse with the vesicle.

110 Figure of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Cell membrane of phagocytic cell Phagocytosis A phagocytic cell comes in contact with the foreign object and sends pseudopodia (cytoplasmic extensions) around it. Pseudopodium (cytoplasmic extension) EXTRACELLULAR FLUID CYTOPLASM Foreign object Vesicle Lysosomes The pseudopodia approach one another and fuse to trap the material within the vesicle. The vesicle moves into the cytoplasm. Lysosomes fuse with the vesicle. This fusion activates digestive enzymes.

111 Figure of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Cell membrane of phagocytic cell Phagocytosis A phagocytic cell comes in contact with the foreign object and sends pseudopodia (cytoplasmic extensions) around it. Pseudopodium (cytoplasmic extension) EXTRACELLULAR FLUID CYTOPLASM Foreign object Vesicle Lysosomes The pseudopodia approach one another and fuse to trap the material within the vesicle. The vesicle moves into the cytoplasm. Lysosomes fuse with the vesicle. This fusion activates digestive enzymes. The enzymes break down the structure of the phagocytized material.

112 Figure of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Cell membrane of phagocytic cell Phagocytosis A phagocytic cell comes in contact with the foreign object and sends pseudopodia (cytoplasmic extensions) around it. Pseudopodium (cytoplasmic extension) EXTRACELLULAR FLUID CYTOPLASM Foreign object Vesicle Lysosomes Undissolved residue The pseudopodia approach one another and fuse to trap the material within the vesicle. The vesicle moves into the cytoplasm. Lysosomes fuse with the vesicle. This fusion activates digestive enzymes. The enzymes break down the structure of the phagocytized material. Residue is then ejected from the cell by exocytosis.

113 LE 7-20c Receptor RECEPTOR-MEDIATED ENDOCYTOSIS Ligand Coated pit Coated vesicle Coat protein Coat protein Plasma membrane 0.25 µm A coated pit and a coated vesicle formed during receptor- mediated endocytosis (TEMs).

114 Figure of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings EXTRACELLULAR FLUID Ligands binding to receptors Ligand receptors CYTOPLASM Ligands Receptor-Mediated Endocytosis Target molecules (ligands) bind to receptors in cell membrane.

115 Figure of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings EXTRACELLULAR FLUID Ligands binding to receptors Ligand receptors CYTOPLASM Ligands Endocytosis Receptor-Mediated Endocytosis Target molecules (ligands) bind to receptors in cell membrane. Areas coated with ligands form deep pockets in membrane surface.

116 Figure of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings EXTRACELLULAR FLUID Ligands binding to receptors Ligand receptors CYTOPLASM Coated vesicle Ligands Endocytosis Receptor-Mediated Endocytosis Target molecules (ligands) bind to receptors in cell membrane. Areas coated with ligands form deep pockets in membrane surface. Pockets pinch off, forming vesicles.

117 Figure of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings EXTRACELLULAR FLUID Ligands binding to receptors Ligand receptors CYTOPLASM Coated vesicle Ligands Endocytosis Lysosome Fused vesicle and lysosome Fusion Receptor-Mediated Endocytosis Target molecules (ligands) bind to receptors in cell membrane. Areas coated with ligands form deep pockets in membrane surface. Pockets pinch off, forming vesicles. Vesicles fuse with lysosomes.

118 Figure of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings EXTRACELLULAR FLUID Ligands binding to receptors Ligand receptors CYTOPLASM Coated vesicle Ligands Endocytosis Lysosome Fused vesicle and lysosome Fusion Receptor-Mediated Endocytosis Target molecules (ligands) bind to receptors in cell membrane. Areas coated with ligands form deep pockets in membrane surface. Pockets pinch off, forming vesicles. Vesicles fuse with lysosomes. Ligands are removed and absorbed into the cytoplasm.

119 Figure of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings EXTRACELLULAR FLUID Ligands binding to receptors Ligand receptors CYTOPLASM Coated vesicle Ligands Endocytosis Lysosome Fused vesicle and lysosome Ligands removed Fusion Detachment Receptor-Mediated Endocytosis Target molecules (ligands) bind to receptors in cell membrane. Areas coated with ligands form deep pockets in membrane surface. Pockets pinch off, forming vesicles. Vesicles fuse with lysosomes. Ligands are removed and absorbed into the cytoplasm. The membrane containing the receptor molecules separates from the lysosome.

120 Figure of 8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings EXTRACELLULAR FLUID Ligands binding to receptors Exocytosis Ligand receptors CYTOPLASM Coated vesicle Ligands Endocytosis Lysosome Fused vesicle and lysosome Ligands removed Fusion Detachment Receptor-Mediated Endocytosis Target molecules (ligands) bind to receptors in cell membrane. Areas coated with ligands form deep pockets in membrane surface. Pockets pinch off, forming vesicles. Vesicles fuse with lysosomes. Ligands are removed and absorbed into the cytoplasm. The membrane containing the receptor molecules separates from the lysosome. The vesicle returns to the surface.

121 Cell to Cell Communication signal-transduction pathway A signal on a cells surface is converted into a specific cellular response chemical messengers cell junctions directly connect the cytoplasm of adjacent cells local signaling communicate by direct contact Some animal cells

122 LE 11-3 Plasma membranes Gap junctions between animal cells Cell junctions Cell-cell recognition Plasmodesmata between plant cells

123 local regulators messenger molecules that travel only short distances Some animal cells long-distance signaling Hormones plants and animals

124 LE 11-4 Paracrine signaling Local regulator diffuses through extracellular fluid Secretory vesicle Secreting cell Target cell Local signaling Electrical signal along nerve cell triggers release of neurotransmitter Neurotransmitter diffuses across synapse Endocrine cell Blood vessel Long-distance signaling Hormone travels in bloodstream to target cells Synaptic signaling Target cell is stimulated Hormonal signaling Target cell

125 Cell Signaling Cells receiving signals went through three processes: Reception Transduction Response

126 LE 11-5_1 EXTRACELLULAR FLUID Reception Plasma membrane Transduction CYTOPLASM Receptor Signal molecule

127 LE 11-5_2 EXTRACELLULAR FLUID Reception Plasma membrane Transduction CYTOPLASM Receptor Signal molecule Relay molecules in a signal transduction pathway

128 LE 11-5_3 EXTRACELLULAR FLUID Reception Plasma membrane Transduction CYTOPLASM Receptor Signal molecule Relay molecules in a signal transduction pathway Response Activation of cellular response

129 Reception binding between a signal molecule (ligand) and receptor highly specific conformational change in a receptor Often the initial transduction of the signal Most signal receptors are plasma membrane proteins

130 LE 11-7c Signal molecule (ligand) Gate closed Ions Ligand-gated ion channel receptor Plasma membrane Gate closed Gate open Cellular response

131 Transduction Multistep pathways can amplify a signal opportunities for coordination and regulation

132 Multistep pathways have two important benefits: Amplifying the signal (and thus the response) Contributing to the specificity of the response

133 LE 11-8 Signal molecule Activated relay molecule Receptor Inactive protein kinase 1 Active protein kinase 1 Inactive protein kinase 2 Active protein kinase 2 Inactive protein kinase 3 Active protein kinase 3 ADP Inactive protein Active protein Cellular response Phosphorylation cascade ATP PP P i ADP ATP PP P i ADP ATP PP P i P P P

134 Cyclic AMP (cAMP) one of the most widely used second messengers Adenylyl cyclase enzyme in the plasma membrane converts ATP to cAMP in response to an extracellular signal

135 Terminating the Signal signal molecules leave the receptor receptor reverts to its inactive state


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