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Chapter 6 - The Cell Outline I. Cell Theory II. Studying cells III. Prokaryotic vs Eukaryotic IV. Eukaryotic A. Animal cells B. Plant cells Cells Cell Theory Cells were discovered in 1665 by Robert Hooke. Cells are the basic unit of life Cells maintain homeostasis They are enclosed in a phospholipid membrane - the Plasma Membrane Cells vary in size but there is a limit on how big a cell can be and survive There are different types of cells – specialized cells Early studies of cells were conducted by - Mathias Schleiden (1838) - Theodor Schwann (1839) Schleiden and Schwann proposed the Cell Theory. 4 Cell Theory Cell Size 1. All organisms are composed of cells. 2. Cells are the smallest living things. 3. Cells arise only from pre-existing cells. Cell size is limited. -As cell size increases, it takes longer for material to diffuse from the cell membrane to the interior of the cell. All cells today represent a continuous line of descent from the first living cells. Small cells have a greater surface area relative to volume Surface area-to-volume ratio: as a cell increases in size, the volume increases 10x faster than the surface area 5 6 1 Figure 6.7 Surface area increases while total volume remains constant Some organisms are just one cell - yeast 5 1 1 Total surface area [sum of the surface areas (height width) of all box sides number of boxes] 6 150 750 Total volume [height width length number of boxes] 1 125 125 Surface-to-volume (S-to-V) ratio [surface area volume] 6 1.2 6 Multi-celled organisms have specialized cells Blood Cells Nerve Cells Figure 6.2a 10 m 10 m Human height Chicken egg 1 cm Human height 1m Frog egg 1 mm 0.1 m Human egg Most plant and animal cells 10 m 1 m 100 nm Nucleus Most bacteria Chicken egg 1 cm Mitochondrion Smallest bacteria Viruses Ribosomes 10 nm Superresolution microscopy Electron microscopy 100 m Length of some nerve and muscle cells Unaided eye 0.1 m Length of some nerve and muscle cells Unaided eye 1m Light microscopy Figure 6.2 Some cells are very small Frog egg 1 mm Proteins Lipids 1 nm Small molecules 0.1 nm 100 m Human egg Atoms 2 Figure 6.2b 1 cm As the size of a cell increase, the surface:volume ratio Frog egg Human egg Most plant and animal cells 10 m 1 m 100 nm Nucleus Most bacteria Mitochondrion Smallest bacteria Viruses Ribosomes 10 nm Superresolution microscopy Electron microscopy 100 m Light microscopy 1 mm 1. Increase 2. Decrease 3. Stays the same 33% 33% 33% Proteins Lipids 1 nm 0.1 nm Small molecules Atoms 1 2 3 Copyright © 2009 Pearson Education, Inc. Studying Cells Microscopes Microscopes 1. Light microscopes Also called compound microscopes because it uses multiple lens 2. Electron microscope Transmission electron microscope Scanning electron microscope Microscopes Two features determine how clearly an object is viewed: 1. Magnification = ocular lens x magnifying lens 2. Resolution – quality of lens and type of light Electron Microscope Light microscopes can resolve structures that are 200nm apart. Transmission Electron Microscopes – specimens are first embedded in plastic then sliced thin Scanning Electron Microscope – specimen is coated with film, scans surface only Electron microscopes can resolve structures that are 0.2nm apart. 17 3 Figure 6.3a Figure 6.3b Brightfield (unstained specimen) 50 m Brightfield (stained specimen) Figure 6.3c Figure 6.3d Phase-contrast Differential-interferencecontrast (Nomarski) Figure 6.3e Figure 6.3i Cilia Fluorescence 10 m 2 m Scanning electron microscopy (SEM) 4 Figure 6.3j Cell fractionation Longitudinal section of cilium Used to study organelles Homogenize the sample Lyse the cells (break open) and the resulting cell extract spun in a centrifuge Cross section of cilium Centrifugal force separates extract Pellet – bottom of tube, contains large components of cell, organelles like nucleus Supernatant – liquid on top of pellet, contains lighter components 2 m Transmission electron microscopy (TEM) Figure 6.4b Figure 6.4a TECHNIQUE (cont.) TECHNIQUE Centrifuged at 1,000 g (1,000 times the force of gravity) for 10 min Supernatant poured into next tube Differential centrifugation 20,000 g 20 min Homogenization Pellet rich in nuclei and cellular debris Tissue cells 80,000 g 60 min 150,000 g 3 hr Pellet rich in mitochondria (and chloroplasts if cells are from a plant) Pellet rich in “microsomes” Homogenate Centrifugation Cell Fractionation 1000 g x 10 min = nuclei in pellet 20,000 g x 30 min = mitochondria, chloroplast 80,000 g x 60 min = microsomal fraction contains: Pellet rich in ribosomes If you centrifuge cells at 80,000 g which fraction will contain the endoplasmic reticulum? 1. Pellet 2. Supernate 50% 50% ER, Golgi, plasma membrane pe rn at e Su Pe To separate the ER, Golgi and plasma membrane you can use a density gradient centrifuge ll e t 150,000 g x 3 hr = ribosomes 5 Inner Life of a Cell - Harvard Cell Structures All cells have certain structures in common. Inner life of a cell - short version, music only 1. genetic material – in a nucleoid or nucleus 2. cytoplasm – a semifluid matrix (fluid portion is the cytosol) 3. plasma membrane – a phospholipid bilayer 4. Ribosomes (make proteins) 32 Figure 6.6 Plasma Membrane Outside of cell The plasma membrane is a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell Inside of cell The general structure of a biological membrane is a double layer of phospholipids 0.1 m (a) TEM of a plasma membrane Carbohydrate side chains Hydrophilic region Hydrophobic region Hydrophilic region Phospholipid Proteins (b) Structure of the plasma membrane © 2011 Pearson Education, Inc. The main component of the plasma membrane is: 1. 2. 3. 4. Trigylcerides Cholesterol Protein Phospholipids 25% 25% Prokaryotic vs Eukaryotic 25% 25% Prokaryotic – Pro (before) karyotic (nucleus) Eukaryotic – Eu (true) karyotic (nucleus) The presence or absence of a nucleus is the most obvious difference between these types of cells. 1 2 3 4 Copyright © 2009 Pearson Education, Inc. 6 Eukaryotic cells have internal membranes that compartmentalize their functions The basic structural and functional unit of every organism is one of two types of cells: prokaryotic or eukaryotic Figure 6.5 Fimbriae Nucleoid Ribosomes Plasma membrane Bacterial chromosome Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells Protists, fungi, animals, and plants all consist of eukaryotic cells Cell wall Capsule 0.5 m (a) A typical rod-shaped bacterium Flagella (b) A thin section through the bacterium Bacillus coagulans (TEM) © 2011 Pearson Education, Inc. Figure 6.5a Prokaryotic Cells – Characteristics and Features 1. Include bacteria and archaea 2. Has no nucleus, have nucleoid region 3. Also lack membrane bound compartments (organelles) 4. Many use folds in the plasma membrane to accomplish the tasks of organelles 0.5 m (b) A thin section through the bacterium Bacillus coagulans (TEM) Prokaryotic Cells – Characteristics and Features 5. Many prokaryotic cells have cell walls 6. Some have a capsule Prokaryotic Cells 6. Have a plasma membrane 7. Have cytoplasm 8. Many have flagella for locomotion 9. Contain ribosomes for protein production 10. Have storage granules – contain glycogen, lipids, and phosphate compounds 11. Some can perform photosynthesis 42 7 Do prokaryotic cells contain ribosomes? Prokaryotic cells have a nucleus 50% 1. Yes 2. No 3. Some do 33% Fa ls e 50% Tr ue 1. True 2. False 1 33% 33% 2 3 Copyright © 2009 Pearson Education, Inc. Eukaryotic cells Highly organized, have organelles including a nucleus. Eukaryotic cells are generally much larger than prokaryotic cells Animal cells Plant cells Protists Fungi Major Features of Animal Cells (page 79) Membrane bound Organelles 1. Nucleus – contains the DNA 2. Mitochondria – energy production 3. Endoplasmic reticulum – modifies new polypeptide chains (rough) and synthesizes lipids (smooth) 4. Golgi body – modifies, sorts, ships new proteins and lipids 5. Vesicles – storage, transport, digestion 6. Lysosomes – digestion 7. Peroxisomes – lipid metabolism, detoxification Major Features of Animal Cells Structures: 1. Plasma membrane – controls entry in/out of cell 2. Cytoplasm – semi-fluid matrix outside the nucleus, liquid portion is the cytosol 3. Ribosomes - assembling polypeptide chains 4. Chromosomes - DNA 5. Cytoskeleton - gives shape, structure, transport 6. Flagella - movement Figure 6.8a ENDOPLASMIC RETICULUM (ER) Flagellum Rough ER Nuclear envelope Smooth ER Nucleolus Chromatin NUCLEUS Centrosome Plasma membrane CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Ribosomes Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome 8 Figure 6.8c Nuclear envelope NUCLEUS Nucleolus Chromatin Rough endoplasmic reticulum Smooth endoplasmic reticulum Ribosomes Central vacuole Golgi apparatus Microfilaments Intermediate filaments Microtubules CYTOSKELETON Mitochondrion Peroxisome Chloroplast Plasma membrane Cell wall Plasmodesmata Wall of adjacent cell BioFlix: Tour of an Animal Cell © 2011 Pearson Education, Inc. Cell Membranes 1. Plasma membrane: Divides outside from inside of cell 2. Organelles: specialized membrane bound compartments BioFlix: Tour of a Plant Cell © 2011 Pearson Education, Inc. Organelles Protein Production/Synthesis Compartments allow the cells to keep reactive compounds from causing injury Organelle/feature Function Nucleus Contains DNA DNA is copied to make RNA Some membranes form vesicles that are used for transporting things Ribosomes “reads” mRNA to assemble amino acids into a polypeptide chain Some membranes are attached to other membranes Rough Endo Ret Polypeptide chain that are to be exported or membrane bound are processed here Golgi complex Further processes and sorts proteins to be exported or membrane bound Vesicles Transports proteins 9 The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes The nucleus contains most of the DNA in a eukaryotic cell Ribosomes use the information from the DNA to make proteins Nucleus Nucleus protects DNA Separates DNA from rest of cell Place where DNA replicates itself Place where DNA is copied to make RNA © 2011 Pearson Education, Inc. The Nucleus: Information Central The nucleus contains most of the cell’s genes and is usually the most conspicuous organelle The nuclear envelope encloses the nucleus, separating it from the cytoplasm Figure 6.9a Nucleus Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Rough ER The nuclear membrane is a double membrane; each membrane consists of a lipid bilayer Pore complex Ribosome Close-up of nuclear envelope Chromatin © 2011 Pearson Education, Inc. Figure 6.9b Figure 6.9c Nuclear envelope: 0.25 m 1 m Inner membrane Outer membrane Nuclear pore Pore complexes (TEM) Surface of nuclear envelope 10 In the nucleus, DNA is organized into discrete units called chromosomes Pores regulate the entry and exit of molecules from the nucleus The shape of the nucleus is maintained by the nuclear lamina, which is composed of protein Each chromosome is composed of a single DNA molecule associated with proteins The DNA and proteins = histones are together called chromatin Chromatin condenses to form discrete chromosomes as a cell prepares to divide The nucleolus is located within the nucleus and is the site of ribosomal RNA (rRNA) synthesis © 2011 Pearson Education, Inc. Parts of the Nucleus 2. Nucleolus – dense area in the nucleus is where rRNA are produced and ribosomes are assembled 3. Nucleoplasm – area within nucleus © 2011 Pearson Education, Inc. Ribosomes: Protein Factories Ribosomes are particles made of ribosomal RNA and protein Ribosomes carry out protein synthesis in two locations In the cytosol (free ribosomes) On the outside of the endoplasmic reticulum or the nuclear envelope (bound ribosomes) © 2011 Pearson Education, Inc. Ribosomes Has two components: a small subunit and a large subunit Figure 6.10 0.25 m Free ribosomes in cytosol Endoplasmic reticulum (ER) Each subunit is made up of strands of rRNA and many proteins The ribosome is like the workbench for assembling polypeptide chains. It is here that amino acids are bound together with a peptide bond. Ribosomes bound to ER Large subunit TEM showing ER and ribosomes Small subunit Diagram of a ribosome 11 The endomembrane system regulates protein traffic and performs metabolic functions in the cell Components of the endomembrane system Nuclear envelope Endoplasmic reticulum Golgi apparatus Lysosomes Vacuoles Plasma membrane These components are either continuous or connected via transfer by vesicles © 2011 Pearson Education, Inc. Endoplasmic reticulum The Endoplasmic Reticulum: Biosynthetic Factory The endoplasmic reticulum (ER) accounts for more than half of the total membrane in many eukaryotic cells The ER membrane is continuous with the nuclear envelope There are two distinct regions of ER Smooth ER, which lacks ribosomes Rough ER, surface is studded with ribosomes © 2011 Pearson Education, Inc. Figure 6.11 Smooth ER Nuclear envelope Rough ER Network of folded internal membranes located in the cytoplasm ER lumen Attached to nucleus Cisternae Transitional ER Ribosomes Transport vesicle Smooth ER Rough ER 200 nm Lumen = space inside endoplasmic reticulum Functions of Smooth ER The smooth ER Synthesizes lipids Metabolizes carbohydrates Detoxifies drugs and poisons Stores calcium ions © 2011 Pearson Education, Inc. Functions of Rough ER The rough ER Has bound ribosomes Creates transport vesicles © 2011 Pearson Education, Inc. 12 Rough Endoplasmic Reticulum (RER) Ribosomes that are producing polypeptide chains for export or to be embedded in membranes dock with the surface of the RER The growing polypeptide chain enters the lumen of the RER Functions of Rough Endoplasmic Reticulum (RER) In the RER the polypetide chain is folded Enzymes called molecular chaperones aid in the folding of the polypeptide chains into proteins Some of the polypeptide chains may get modified here “tagged” with carbohydrate chain = glycoproteins The polypeptide chains/proteins are put into transport vesicles The Golgi Apparatus: Shipping and Receiving Center The Golgi apparatus consists of flattened membranous sacs called cisternae Figure 6.12 cis face (“receiving” side of Golgi apparatus) 0.1 m Cisternae Functions of the Golgi apparatus Modifies products of the ER Manufactures certain macromolecules Sorts and packages materials into transport vesicles Produces lysosomes trans face (“shipping” side of Golgi apparatus) TEM of Golgi apparatus © 2011 Pearson Education, Inc. V Cell Movie Golgi – Protein Trafficking All polypeptide chains go to the RER 1. True 2. False 50% 1 50% 2 Copyright © 2009 Pearson Education, Inc. 13 Protein Production - Overview 1. DNA in the nucleus are the instructions for making protein 2. A copy of the DNA is made = mRNA 3. mRNA leaves the nucleus 4. mRNA docks with a ribosome to assemble a chain of amino acids. 5. tRNA brings amino acids to ribosomes 6. At the ribosome the amino acids are linked together with a peptide bond to form a polypeptide chain Protein Production Cont 10. The golgi processes, sorts, packages proteins and lipids from the RER and SER 11. Proteins that are exported are shipped in transport vesicles to the plasma membrane Protein Production Cont 7. Ribosome with the growing polypeptide chain docks with the rough endoplasmic reticulum if the protein is to be exported or embedded in a membrane 8. The polypeptide chain enters the lumen of the RER where they are folded and may get a carbohydrate “tag” attached to it 9. The RER buds off a transport vesicles that can carry the newly formed proteins to the golgi Cytosolic proteins Proteins that are not shipped out of cell are made on free floating ribosomes Chaperone proteins fold the proteins in the cytosol 12. Proteins may be put into lysosomes 13. Proteins that are membrane bound are embedded in the transport vesicles membrane Lysosomes Produced by the Golgi Lysosomes 1. Contain strong acids and enzymes 2. Engulf molecules and digest them or Lysosomes are small membrane bound sacs that contain digestive enzymes. The pH is relatively acidic (pH 5) in the lysosomes. Because the lysosomes are acidic and contain digestive enzymes, their contents must be kept separate from the rest of the cell 3. Fuse with other organelles and vesicles to destroy them 4. Can fuse with plasma membrane to expel waste 5. Destroy bacteria 14 Fig. 4.14 Some types of cell can engulf another cell by phagocytosis; this forms a food vacuole A lysosome fuses with the food vacuole and digests the molecules Lysosomes also use enzymes to recycle the cell’s own organelles and macromolecules, a process called autophagy © 2011 Pearson Education, Inc. Figure 6.13 Vesicle containing two damaged organelles 1 m Nucleus 1 m Mitochondrion fragment Peroxisome fragment Lysosome Digestive enzymes Lysosome Lysosome Plasma membrane Peroxisome Digestion Food vacuole Mitochondrion Digestion Vesicle (a) Phagocytosis (b) Autophagy Animation: Lysosome Formation Right-click slide / select “Play” © 2011 Pearson Education, Inc. Scavenger cells Tay-Sachs Disease Throughout the body there are scavenger cells that engulf bacteria, foreign material or old cellular material Tay-Sachs is a hereditary disease – people with this disease don’t have an enzyme normally found in lysosomes that breaks down lipids in nerve cells. 15 Vacuoles: Diverse Maintenance Compartments Plant cell, protists, and fungal cells may have one or several vacuoles, derived from endoplasmic reticulum and Golgi apparatus Vacuoles: Diverse Maintenance Compartments Food vacuoles are 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 © 2011 Pearson Education, Inc. © 2011 Pearson Education, Inc. Figure 6.14 Central vacuole Cytosol Nucleus Central vacuole Cell wall Chloroplast 5 m Video: Paramecium Vacuole © 2011 Pearson Education, Inc. Central Vacuole in Plants Plant central vacuoles Large area of cell space – up to 90% Fluid filled with water, amino acids, sugars, H+ ions, and wastes. Stores nutrients Digests wastes – similar to lysosomes in animal cells The Endomembrane System: A Review The endomembrane system is a complex and dynamic player in the cell’s compartmental organization © 2011 Pearson Education, Inc. 16 Figure 6.15-1 Figure 6.15-2 Nucleus Nucleus Rough ER Smooth ER Rough ER Smooth ER cis Golgi Plasma membrane Figure 6.15-3 Nucleus Rough ER Smooth ER trans Golgi Plasma membrane Mitochondria and chloroplasts change energy from one form to another • Mitochondria are the sites of cellular respiration, a metabolic process that uses oxygen to generate ATP cis Golgi Chloroplasts, found in plants and algae, are the sites of photosynthesis trans Golgi Plasma membrane © 2011 Pearson Education, Inc. The Evolutionary Origins of Mitochondria and Chloroplasts Mitochondria and chloroplasts have similarities with bacteria Enveloped by a double membrane Contain free ribosomes and circular DNA molecules Grow and reproduce somewhat independently in cells © 2011 Pearson Education, Inc. The Evolutionary Origins of Mitochondria and Chloroplasts The Endosymbiont theory An early ancestor of eukaryotic cells engulfed a nonphotosynthetic prokaryotic cell, which formed an endosymbiont relationship with its host The host cell and endosymbiont merged into a single organism, a eukaryotic cell with a mitochondrion At least one of these cells may have taken up a photosynthetic prokaryote, becoming the ancestor of cells that contain chloroplasts © 2011 Pearson Education, Inc. 17 Figure 6.16 Endoplasmic reticulum Engulfing of oxygenusing nonphotosynthetic prokaryote, which becomes a mitochondrion Nucleus Nuclear envelope Most all Eukaryotic cells (plants, animals, fungi and protists) contain mitochondria Ancestor of eukaryotic cells (host cell) Mitochondrion Nonphotosynthetic eukaryote Mitochondria At least one cell Engulfing of photosynthetic prokaryote Chloroplast Produces energy for the cell (ATP) Cells that require lots of energy have lots of mitochondria (liver cells can have over 1000 mitochondria Requires oxygen = site of aerobic respiration Mitochondrion Important in apoptosis (programmed cell death) Photosynthetic eukaryote Mitochondria - Structure Bound by a double membrane Forms two compartments Outer membrane faces cytoplasm Inner membrane folded forming cristae which increases surface area The cristae contain many enzymes and other proteins important for cellular respiration Intermembrane space is between outer and inner membrane Mitochondria The double membrane structure is important in its function (cellular respiration) and to keep dangerous oxygen species and free radicals from damaging the cells. Mitochondria contain its own DNA Apoptosis Apoptosis is planned cell death In contrast, necrosis is uncontrolled cell death When a cell is no longer needed or is not functioning properly, the cell will undergo apoptosis. Apoptosis Mitochondria can initiate apoptosis in several ways – one way is through a cascade of enzymatic reactions. When the mitochondria gets the signal to begin apoptosis it releases cytochrome c, which activates a group of enzymes called caspases 18 Figure 6.17 Apoptosis Video 10 m Apoptosis Intermembrane space Mitochondria Outer membrane DNA Free ribosomes in the mitochondrial matrix Inner membrane Mitochondrial DNA Cristae Nuclear DNA Matrix (a) Diagram and TEM of mitochondrion 0.1 m (b) Network of mitochondria in a protist cell (LM) Chloroplasts: Capture of Light Energy Chloroplasts contain the green pigment chlorophyll, as well as enzymes and other molecules that function in photosynthesis Chloroplasts: Capture of Light Energy Chloroplast structure includes Thylakoids, membranous sacs, stacked to form a granum Stroma, the internal fluid Chloroplasts are found in leaves and other green organs of plants and in algae © 2011 Pearson Education, Inc. The chloroplast is one of a group of plant organelles, called plastids © 2011 Pearson Education, Inc. 19 Figure 6.18 Chloroplasts 50 m Ribosomes Stroma Inner and outer membranes Granum Chloroplasts (red) DNA Thylakoid Intermembrane space (a) Diagram and TEM of chloroplast 1 m (b) Chloroplasts in an algal cell 115 Peroxisomes Peroxisomes are membrane bound vesicles that contain oxidative enzymes These enzymes function by oxidizing their substrates (many of their substrates are fatty acids) Peroxisomes Oxidation is when a substance loses an electron RH2 + O2 → RH + H2O2 This produces H2O2 which is dangerous therefore another enzyme, catalase, removes the H2O2 2 H2O2 → O2 + 2H2O Functions of Peroxisomes Fig. 4.15 Involved in lipid metabolism and detoxification Contain enzymes that produce and degrade hydrogen peroxide 20 What organelle produces energy (ATP)? 1. 2. 3. 4. 5. Ribosomes Golgi complex Mitochondria SER Lysosomes 20% 1 20% 2 20% 20% 3 4 Where are polypeptide chains assembled? 20% Ribosomes Golgi complex Peroxisomes SER Lysosomes 20% 1 20% 2 Ribosomes Golgi complex SER RER 25% 5 1 25% 25% 2 3 25% 4 These are membrane bound sacs with digestive enzymes Where are lipids synthesized? 1. 2. 3. 4. 5. 1. 2. 3. 4. 20% 20% 3 4 Inner Life of a Cell - Harvard Inner Life of a Cell Narrated, long version 20% 1. 2. 3. 4. 5. Ribosomes Golgi complex Mitochondria SER Lysosomes 5 20% 1 20% 2 20% 20% 3 4 20% 5 Cytoskeleton Interconnected system of fibers and lattices Gives cells their organization, shape, ability to move, transport things in cell, important in cell division Some permanent others only present when needed Microtubules Microfilaments Intermediate filaments 21 Fig. 4.20 Components of the Cytoskeleton Three main types of fibers make up the cytoskeleton Microtubules are the thickest of the three components of the cytoskeleton Microfilaments, also called actin filaments, are the thinnest components Intermediate filaments are fibers with diameters in a middle range © 2011 Pearson Education, Inc. Table 6.1a Microtubules 10 m Thickest type of cytoskeleton Important in The structure of cell Cell division – separates the chromosomes Transport of organelles in the cell Movement of cells (cilia and flagella) Column of tubulin dimers 25 nm Tubulin dimer Microtubules Composed of two proteins that form a dimer: α-tubulin and β-tubulin. Dimer -Tubulin Plus end -Tubulin These assemble by adding dimers and disassemble by removing them Structural microtubule-associated proteins (MAPs) regulate microtubule assembly Dimer on (a) Minus end Dimers off 22 Microtubule Anchoring 10 m Microtubules may be anchored in the microtubule-organizing centers (MTOCs) In animal cells the main MTOC is the centrosome – this is important in cell division Column of tubulin dimers 25 nm Tubulin dimer The centrosome is composed of two centrioles The centrioles have nine sets of three microtubules Fig. 4.21 Figure 6.22 Centrosome Microtubule Centrioles 0.25 m Longitudinal section of one centriole Microtubules Cross section of the other centriole Microtubules – cell division During cell division much of the cytoskeleton breaks down and microtubule form that will help in cell division = spindles Spindles move the chromosomes so when the cell divides the chromosomes are evenly divided 23 Microtubule – transport of organelles Fig. 4.22 Microtubule can be used to transport vesicles and other structures. The microtubule is stationary, transport proteins (kinesin and dynein) move the item. Kinesin moves items in one direction (+) and Dynein moves items in the opposite direction (-) Cilia and flagella Cilia and Flagella Microtubules important in movement of the cell Project from cell surface Flagella are long microtubules Cilia are short microtubules Flagella are found on sperm and many one celled organisms Cilia found on many one celled organisms and on cells that line passageways in multi-celled organisms 142 Flagella and Cilia Both flagella and cilia have nine pairs of microtubules in an outer ring and a pair in the center (9 + 2). Anchored by a basal body A motor protein called dynein, which drives the bending movements of a cilium or flagellum Animation: Cilia and Flagella Right-click slide / select “Play” © 2011 Pearson Education, Inc. 24 Figure 6.24 0.1 m Outer microtubule doublet Dynein proteins Central microtubule Radial spoke Microtubules Plasma membrane Plasma membrane Flagella and Cilia How dynein “walking” moves flagella and cilia Cross-linking proteins between outer doublets (b) Cross section of motile cilium Dynein arms alternately grab, move, and release the outer microtubules Protein cross-links limit sliding Forces exerted by dynein arms cause doublets to curve, bending the cilium or flagellum Basal body 0.1 m 0.5 m (a) Longitudinal section of motile cilium Triplet (c) Cross section of basal body © 2011 Pearson Education, Inc. Figure 6.25 Microtubule doublets ATP Dynein protein (a) Effect of unrestrained dynein movement Cross-linking proteins between outer doublets ATP Anchorage in cell (b) Effect of cross-linking proteins 1 3 2 (c) Wavelike motion Fig. 4.24b 25 Figure 6.23 Cilia Direction of swimming (a) Motion of flagella 5 m Direction of organism’s movement Power stroke Recovery stroke (b) Motion of cilia 15 m Microfilaments Microfilaments are made two chains of actin protein molecules Important in: 1. providing support for cell structures 2. movement of cells (ameoba-like movement) 3. dividing cells in two Microfilaments (Actin Filaments) Microfilaments are solid rods about 7 nm in diameter, built as a twisted double chain of actin subunits The structural role of microfilaments is to bear tension, resisting pulling forces within the cell They form a 3-D network called the cortex just inside the plasma membrane to help support the cell’s shape Bundles of microfilaments make up the core of microvilli of intestinal cells © 2011 Pearson Education, Inc. Microfilaments are in green Microfilaments Actin molecules will assemble to form microfilaments Microfilaments are important in formation of microvilli 26 Figure 6.26 Microfilaments Role in Movement - Muscle Microvillus Microfilaments that function in cellular motility contain the protein myosin in addition to actin Plasma membrane In muscle cells, thousands of actin filaments are arranged parallel to one another Microfilaments (actin filaments) Thicker filaments composed of myosin interdigitate with the thinner actin fibers Intermediate filaments 0.25 m © 2011 Pearson Education, Inc. Microfilaments Role in Movement - Pseudopodia Figure 6.27a Muscle Cells Localized contraction brought about by actin and myosin also drives amoeboid movement Muscle cell 0.5 m Actin filament Myosin filament Myosin head Pseudopodia (cellular extensions) extend and contract through the reversible assembly and contraction of actin subunits into microfilaments (a) Myosin motors in muscle cell contraction © 2011 Pearson Education, Inc. Figure 6.27b Cortex (outer cytoplasm): gel with actin network 100 m Inner cytoplasm: sol with actin subunits Extending pseudopodium (b) Amoeboid movement 27 Microfilaments Role in Movement – Cytoplasmic streaming Figure 6.27c Cytoplasmic streaming is a circular flow of cytoplasm within cells This streaming speeds distribution of materials within the cell In plant cells, actin-myosin interactions drive cytoplasmic streaming Chloroplast 30 m (c) Cytoplasmic streaming in plant cells © 2011 Pearson Education, Inc. Intermediate filaments Do not self assemble/disassemble – permanent Important in cell shape Tough but flexible fibers Found in high amounts in cells that are subjected to mechanical stress (in skin) Video: Cytoplasmic Streaming © 2011 Pearson Education, Inc. Intermediate filaments Fig. 4.20.c Amyotrophic lateral sclerosis (ALS) is caused by abnormal intermediate filaments in nerve cells 28 Cilia and flagella are composed of this type of cytoskeleton 1. Microtubules 2. Microfilaments 3. Intermediate filaments Kinesin Actin Tubulin Dynein 33% 25% 25% 2 3 25% fil a te rm ed ia te In 1 This type of cytoskeleton is more permanent 1. Microtubules 2. Microfilaments 3. Intermediate Fibers 25% m en t ts s ic ro f il am en ub ul e M ic ro t M 1. 2. 3. 4. s 33% 33% 33% Microfilaments are composed of: 33% 33% 4 Extracellular components and connections between cells help coordinate cellular activities Most cells synthesize and secrete materials that are external to the plasma membrane These extracellular structures include Cell walls of plants The extracellular matrix (ECM) of animal cells Intercellular junctions 1 2 3 Copyright © 2009 Pearson Education, Inc. Cell Walls of Plants The cell wall is an extracellular structure that distinguishes plant cells from animal cells Prokaryotes, fungi, and some protists also have cell walls The cell wall protects the plant cell, maintains its shape, and prevents excessive uptake of water © 2011 Pearson Education, Inc. Cell Wall Composed of : 1. 2. 3. 4. Cellulose Lignins Sticky polysaccharides Glycoproteins Plant cell walls are made of cellulose fibers embedded in other polysaccharides and protein © 2011 Pearson Education, Inc. 29 Figure 6.28 Cell Wall - Layers Secondary cell wall Primary cell wall Middle lamella 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 1 m Central vacuole Cytosol Plasmodesmata are channels between adjacent plant cells Plasma membrane Plant cell walls Plasmodesmata © 2011 Pearson Education, Inc. Figure 6.28a The Extracellular Matrix (ECM) of Animal Cells Plasma membrane Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM) Secondary cell wall Primary cell wall The ECM is made up of glycoproteins such as collagen, proteoglycans, and fibronectin Middle lamella ECM proteins bind to receptor proteins in the plasma membrane called integrins 1 m © 2011 Pearson Education, Inc. Figure 6.30a Collagen Functions of the Extracellular Matrix (ECM) of Animal Cells EXTRACELLULAR FLUID Proteoglycan complex Fibronectin Integrins Functions of the ECM Support Adhesion Movement Regulation Plasma membrane CYTOPLASM Microfilaments © 2011 Pearson Education, Inc. 30 Cell Junctions Plasmodesmata in Plant Cells Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact Plasmodesmata are channels that perforate plant cell walls Intercellular junctions facilitate this contact There are several types of intercellular junctions Plasmodesmata Tight junctions Desmosomes Gap junctions © 2011 Pearson Education, Inc. Through plasmodesmata, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell © 2011 Pearson Education, Inc. Figure 6.31 Cell Junctions in Animal Cells Cell walls Interior of cell At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid Desmosomes (anchoring junctions) fasten cells together into strong sheets Interior of cell Plasmodesmata 0.5 m Plasma membranes Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells © 2011 Pearson Education, Inc. Figure 6.32 Tight junctions prevent fluid from moving across a layer of cells Tight junction TEM 0.5 m Tight junction Intermediate filaments Desmosome TEM 1 m Gap junction Space between cells Plasma membranes of adjacent cells Extracellular matrix TEM Ions or small molecules Animation: Tight Junctions Right-click slide / select “Play” 0.1 m © 2011 Pearson Education, Inc. 31 Tight junctions Tight junctions: prevent substances from leaking across tissues Found in high concentration between cells: Lining the intestine Lining capillaries in the brain Animation: Desmosomes Right- click slide / select “Play” © 2011 Pearson Education, Inc. Desmosomes Anchoring junctions Desmosomes - Anchoring junctions: hold adjacent cells together (like glue) and allow tissues to be flexible Found in high concentration in skin epithelial cells Integrin and Cadherin proteins Attach to cytoskeleton Animation: Gap Junctions Right-click slide / select “Play” © 2011 Pearson Education, Inc. Communicating Junctions Gap junctions – open channels between cells allowing rapid communication due to quick transfer of ions and small molecules between neighboring cells These junctions can be opened or closed High concentration of gap junctions are found in heart tissue Animal and Plant cells Both animal and plant cells have: Plasma membrane Nucleus Smooth and rough endoplasmic reticulum Ribosomes Golgi complex Vesicles Peroxisomes Mitochodria Cytoskeleton Lysosomes 32 Plant Cells Found only in Animal Cells Main Plant cell components not present in animal cells Animal cells have centrioles, plants have a different type of MTOCs Cell wall Vacuoles (usually central) Plastids including Chloroplast Glyoxysomes Not present in plant cells: centrioles Glyoxysomes Plastids Plants also have a type of organelle called glyoxysomes Chromoplasts – contain pigments, give plant color, attract pollinators Glyoxysomes contain enzymes that convert stored fatty acids to sugar that is used for energy, this is especially important in germinating seedlings. Amyloplasts – store starch Chlorplasts – contain a green pigment, chlorophyll and carotenoids – yellow and orange pigments. Site of photosynthesis. Animal cells do not have these type of peroxisomes (we can’t convert fatty acids to sugar) Plant cells do not contain: Important Concepts Know the vocabulary in the lecture 1. 2. 3. 4. Mitochondria Centrioles Nucleus Ribosomes 25% 25% 25% 25% Be able to describe cell theory and the properties of cells and structures common to all cells. Know how cells are studied, the types of microscopy, the centrifugation techniques. How would you separate the organelles of the cell? What are the main difference between prokaryotic cells and eukaryotic cells, and examples of each type? 1 2 3 4 33 Important Concepts What are the features and characteristics of prokaryotic cells? What is apoptosis and what organelle is an important player in the process? What molecules are released and activated during apoptosis? What are the major features of eukaryotic cells, their location, features, structure, and their function – both plants and animals? Important Concepts Describe the steps needed to make a protein and ship it out of the cells, or embed the protein in a membrane, or have the protein stay in the cytosol. What is the cause of Tay Sachs disease? What are the differences between plant and animal cells? Be able to describe the endosymbiont theory Important Concepts What are the types of cytoskeleton – what are their functions, structure, what proteins are they composed of, and how they are assembled? How are microtubules assembled, anchored, how do they transport items and what proteins are used by microtubles to transport items. Important Concepts Know the types of cell junctions, their functions and locations where there are found in high concentration Know the role and components of extracellular matrix What is the cause of ALS? What are cell walls composed of, what are the layers? 34