Download Chapter 6: A Tour of the Cell The Cell Theory • All living organisms

Chapter 6: A Tour of the Cell
The Cell Theory
 All living organisms are made of cells
 Cell is the basic functional unit of life
 All cells arise from previously existing cells
Microscopy
 Light microscope (LM) – visible light passes thru specimen & then glass lenses
 Electron microscopes – for subcellular structures
o Scanning EM (SEM) – focus beam of electrons onto surface of specimen; 3D surface shot
o Transmission EM (TEM) – focus beam of electrons thru a specimen; cross section
 Microscopy Factors
o Magnification – ratio of object’s image size to real size
o Resolution – measure of clarity of image, or minimum distance of two distinguishable points
o Contrast – visible differences in parts of sample
Cell Types
 Prokaryotes
o Domains (& Kingdoms) Bacteria & Archaea
 Eukaryotes
o Domain Eukarya
 Kingdoms Protista, Fungi, Animalia, & Plantae
 All Cells
o DNA – genetic code
o Ribosomes – make proteins
o Plasma membrane – layer surrounding cell
o Cytoplasm – fluid region inside cell membrane
 Prokaryotic Cells
o No nucleus
 DNA in region called nucleoid
o No membrane-bound organelles
o Cytoplasm everything inside plasma membrane
 Eukaryotic Cells
o DNA in nucleus
o Have membrane-bound organelles
o Cytoplasm – region b/w plasma membrane & nucleus
 Cytosol – liquid outside organelles
o Generally much larger than prokaryotic cells (1-5 vs 10-100 micrometer)
Cell Parts
 Plasma Membrane
o Selective barrier allowing passage of oxygen, nutrients, & waste
o General structure – double layer of phospholipids
 Amphipathic – hydrophilic head & hydrophobic tail
 Nucleus
o Has most of cell’s genes & usually most visible organelle
o Nuclear envelope – double membrane enclosing nucleus
 Separates it from cytoplasm
 Nuclear Pores – regulate what enters & leaves nucleus
o Nuclear Lamina – structural protein that maintains shape of nucleus
o Chromatin – DNA + histones
 Histone – proteins that aid in condensing of DNA
 Chromosomes – condensed chromatin
 Cellular Division
o Diploid – two chromosome sets
o Haploid – one chromosome set
o Mitosis – one diploid cell divides into 2 diploid cells (everywhere)
o Meiosis – one diploid cell divides into 4 haploid cells (gonads)
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Nucleolus
o Located in nucleus; makes ribosomal RNA (rRNA)
o Ribosome Formation
 Proteins from cytoplasm enter nucleus & combine w/ rRNA
 Forms small & large subunits
 Subunits leave thru nuclear pores, form ribosomes in cytoplasm
Ribosomes
o rRNA & protein; synthesize proteins
 Cytosol (free ribosomes)
 Proteins used in cytosolic (e.g. enzyme)
 Bound to outside of ER or nuclear envelope (bound ribosomes)
 Proteins used in membrane, inside organelles, or secreted
Endomembrane System
o Components attached or connected via transfer by vesicles
o Consists of:
 Nuclear envelope, Endoplasmic reticulum, Golgi apparatus, Lysosomes, Vacuoles, Plasma
membrane
o Endoplasmic Reticulum
 Network of membranous tubules & sacs (cisternae)
 ER membrane is continuous w/ nuclear envelope
 Inside called ER lumen
 Two distinct types…
 Smooth ER (no ribosomes)
o Synthesize lipids
 Steroids, phospholipids
o Metabolize carbohydrates
o Store calcium (muscle)
o Detoxify poisons
 Liver – adds hydroxyl group to make more soluble
 Rough ER (ribosomes on surface)
o Make/secrete glycoproteins
 Proteins covalently bonded to carbs (Insulin & glucagon)
o Distributes transport vesicles
o Membrane factory for cell
 Makes phospholipids
o Golgi Apparatus
 Center of manufacturing, warehousing, sorting, & shipping
 Made of membranous sacs stacked together (cisternae)
 Modifies products of ER
 Manufactures some macromolecules
 Sort & package materials into transport vesicles
 Cis face – receiving
 Trans face – transporting
o Lysosome
 Stomach of cell; membranous sac of hydrolytic enzymes (digestion)
 Enzymes made by rough ER, transferred & processed by golgi, shipped to lysosome
 Hydrolyze proteins, fats, polysaccharides, & nucleic acids
 Lysosome Digestion
 Phagocytosis – ‘cellular eating’; cell engulfs another cell or particle; forms food
vacuole
o Lysosome fuses w/ vacuole & digests it
 Autophagy – lysosome digests & recycles cell’s own organelles & macromolecules
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Vacuoles
 Large membrane-bound vesicle; different functions in different cells
 Food vacuoles – made by phagocytosis (amoebas, WBCs)
 Contractile vacuoles – pump excess water out of cell; maintains nutrient & ion
concentration (freshwater protists)
 Central Vacuoles
 Large vacuole in plant cells
 Hydrolysis in plants/fungi (both lack lysosomes)
 Stockpiles proteins, ions (K+ & Cl-)
 Waste dump site
 Can contain poisons for defense
 Pigment proteins attracting pollinators
Energy Production: Mitochondria & Chloroplasts
o Have double membrane
o Contain own DNA to make proteins
o Proteins made by free ribosomes & by ribosomes inside organelle
o Endosymbiont Theory
 Early ancestor of eukaryotes engulfed a non-photosynthetic prokaryote forming a
endosymbiotic relationship
 At a later time, photosynthetic prokaryote uptaken in similar way
 Endosymbiont Evidence
 Both organelles have:
 Their own round DNA
 Ribosomes smaller than eukaryotes (similar to prokaryotes)
 Self Replication (binary fission)
o Chloroplast
 Has chlorophyll (green pigment), enzymes, & other molecules for photosynthesis
 Found in leaves & other green organs of plants & algae
 Thylakoids – membranous sacs (poker chips)
 Granum – stacks of thylakoids
 Stroma – internal fluid w/ chloroplast DNA, ribosomes, & enzymes
 Photosynthesis: 6 CO2 + 6 H20 + sunlight → C6H12O6 + 6 O2
o Mitochondria
 Have smooth outer membrane & inner membrane folded into cristae (surface area)
 Inner membrane creates two compartments:
 Mitochondrial matrix
o Mitochondrial DNA, ribosomes, & enzymes to catalyze steps of cellular
respiration (makes ATP)
 Intermembrane space
 Cristae – create large surface area for enzymes to make ATP
 Cellular Respiration
 Glucose to ATP
 C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ATP
Cytoskeleton
o Network of fibers in cytoplasm that help support cell & maintain shape
o Organize cell’s structures & activities; anchors many organelles
o Interact w/ motor proteins to produce motility
o Inside cell, vesicles travel along ‘monorails’ made of cytoskeleton
o Cytoskeleton Components
 Microtubules
 Thickest fiber; made of tubulin
 Cell motility (w/ dynein)
 Separates chromosomes in cell division
 Moves organelles
 Structural component
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Centrosome
o AREA near nucleus that acts as a “MT-organizing center”
 MTs grow out from a centrosome near nucleus
o 2 centrioles make up centrosome
 Structure made of 9 sets of MT triplets
 Cilia & Flagella
o Hair & tail-like structures
 Flagella long; normally 1-2
 Cilia short; normally many
o MTs & Dynein control beating of cilia & flagella
 Beating patterns different
 Dynein – Motor Protein
 Dynein arms alternately grab, move, & release outer MTs
o Powered by ATP
 Protein cross-links limit sliding
 Forces exerted by dynein arms cause MT doublets to
curve = Bends cilium or flagellum
 Intermediate Filaments
 Middle-sized fibers
 Made of diff. types of keratin
 Support cell shape & fix organelles in place
 More permanent cytoskeleton fixtures than other two classes
 Microfilaments or Actin Filaments
 Thinnest fiber; solid rods
 Made of a twisted double chain of actin subunits
 Form network (cortex) just inside cell membrane; supports shape
 Cellular & muscle movement
 Muscle Movement
o Actin works w/ myosin (motor protein)
o Thousands of actin filaments lined up parallel to each other
o Thick filaments of myosin interlock w/ thin actin fibers
 Actin-Myosin Elsewhere
o Amoeboid movement
o Cytoplasmic streaming – circular flow of cytoplasm in cells speeding up
distribution of materials
Extracellular Components
 Most cells synthesize & secrete materials outside of cell membrane
 Cell Wall
o Cellulose fibers embedded in other polysaccharides & protein
o Protects cell, maintains shape, & prevents excessive water uptake
o Prokaryotes, fungi, & some protists also have cell walls
 Extracellular Matrix (ECM)
o Glycoproteins bind to integrins (receptor protein) in plasma membrane
 GPs = Collagen, proteoglycans, fibronectin
o Functions: support, adhesion, movement, regulation
 Intercellular Junctions
o Neighboring cells adhere, interact, & communicate thru physical contact
o Plasmodesmata
 Connect plant cells
 Cytosol can pass thru
 Water, small solutes, RNA, & protein
o Animal Cell Junctions
 Gap junctions (communicating) – provide cytoplasmic channels b/w 2 cells
 Tight junctions – 2 cell membranes pressed together; prevent leakage of extracellular fluid
 Desmosomes (anchoring) – fasten cells together into strong sheets