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Basic Cell Structure
Heyer 1
Into the CellInto the CellInto the Cell The Cell TheoryThe Cell Theory““Cell DoctrineCell Doctrine””
1. All organisms are constructed of oneor more cells.
2. The cell is the basic unit of life.¸ Minimum level of complexity that
exhibits all characteristics of life.
3. All cells derive from previous cells.
What does a cell need?
n Selective isolation from environment(plasma membrane)
n Energy (ATP)n Instructions (DNA)n Machinery to carry out instructions and
regulate processes (proteins)n Compartmentalization of incompatible or
specialized activities (organelles)
Isolated activity compartmentsIsolated activity compartments
•• Cell membraneCell membrane••PlasmalemmaPlasmalemma
•• Organelle membranesOrganelle membranes
Cell & Organelle Membranes:More than just a phospholipid bilayer
n Human nerve cell:> 1 meter
n Frog egg: 2 mmn Average animal cell:
50 µmn Human red blood cell:
~8 umn Bacteria: 1–2 µmn Organelle: 1 µmn Virus: 50 nm
Cell Size Varieswith Function
Basic Cell Structure
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Why Must CellsBe Small?
Smaller cells have more total surface arean Increased surface area makes it easier for gasses,
nutrients, etc. to enter a cell
‹ Same volume fi
v Volume controlledby nucleus.
Why Must CellsBe Small?
Upper limits on cellsize are set by
diffusion distance.Molecules must
diffuse through cell.
So, Why Can’t CellsBe Even Smaller?vThey must be big
enough to hold alltheir parts!
vMacromoleculescannot be shrunk.
Early views of cellsEarly views of cells
n Plasma membrane
n “Nucleus” ( “center”)
– filled with “chromatin”(“colored stuff”)
n “Cytoplasm” (“cell fluid”)
unstained
human cheek cell
stained
50µm
Modern views of cellsModern views of cells
5 µm
n Better microscopes andstains– Electron microscope.
n “Cytoplasm” and“chromatin” much morecomplicated, structured,and dynamic thanpreviously appreciated.
Basic Cell Structure
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Two major types of cellsTwo major types of cellsEUKARYOTIC CELL
Membrane
Cytoplasm
Organelles
Nucleus (contains DNA)1 µm
PROKARYOTIC CELL
DNA (no nucleus)
Membrane
Contrastingeukaryotic andprokaryotic cells insize and complexity
I. Prokaryotic — Bacteria• No membranous organelles
II. Eukaryotic — Protists• Single celled or simple colonial
III. Eukaryotic / multicellular— Plant• Organelles present, including chloroplasts• Cellulose cell wall around plasma membrane
IV. Eukaryotic / multicellular—Fungi• No chloroplasts• Chitinous cell wall
V. Eukaryotic / multicellular— Animal• No chloroplasts nor cell wall• Varied cell morphology
Cell-TypeSystematics
Five-Kingdom Model
Prokaryotic Cell Structure
nn Single-celledSingle-celledorganismsorganisms
nn No nucleusNo nucleusnor othernor othermembranousmembranousorganellesorganelles
nn No cytoskeletonNo cytoskeletonnn Most withMost with
cell wallcell walloutside plasmaoutside plasmamembranemembrane
nn Some with capsuleSome with capsuleoutside cell walloutside cell wall
v The plasmamembrane isthe onlymembrane.
Photosynthetic prokaryote
Prokaryotes lack a trueendomembrane system
Eukaryotic Cell Structure—organelles & cytoskeleton
Cytoplasmn Fills cell; contains
– cytosol• fluids and more
• gel & sol state
– membrane-bound organelles• concentrate specific
enzymatic activities
• isolate incompatible reactionsor toxic products
– cytoskeleton• maintain and alter cell shape
• hold and move organelles, etc.
Basic Cell Structure
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Organelles & Cytosol
n Cytosol: Dense, semisolid aqueous gel containing atremendous variety of solutes and macromolecular machines
Cellular Organellesn Nucleus
– Nuclear envelope
– Nucleolus• Nucleus of nucleus• Transcribes rRNA for
ribosomes
– Chromatin/chromosomes
– Nuclear lamina• Protein scaffolding
underlying theenvelope andsupporting thechromatin
n Double-membranewith pores
n Contains DNA ofchromosomes
n Controls cell– structure– function
n Blueprints for new cells
Nucleus
Nuclearenvelopesurface
Porecomplexes
Nuclearlamina
Nuclear envelope: 2 membranes
Nuclear envelope: 2 membranes Cellular Organelles
n Endoplasmic Reticulum
Smooth E.R.– New membrane synthesis– Lipid synthesis &
processing– Steroid synthesis– Lipophilic detoxification
– Intra-cellular Ca++ store
– Usually tubular appearance
Basic Cell Structure
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Cellular Organelles
n EndoplasmicReticulum
Rough E.R.– Ribosome attachment sites– Synthesis of membrane proteins– Synthesis of proteins for
secretion or intra-organellestorage
– Flattened beaded stacks;Membrane often continuouswith nuclear envelope
Cellular Organelles
n Ribosomes– Free and RER-bound
Cellular Organellesn Golgi Complex
– Further processing and trafficking of proteins from RER
– Receives vesicles from ER; buds off vesicles to plasma membranefor export
Transporting proteins in vesicles
RER to Golgi
Progression of membrane & proteinsCellular Organelles
n Vesicles– Shuttle
betweenorganellesand plasmamembrane
Basic Cell Structure
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Cellular Organelles
n Lysosome– Contains
hydrolyticenzymes
– Digest food,bacteria, oldcell parts
– Apoptosis(cellularself-destruct)?
Lysosomes are digestive compartments
Lysosomes
Lysosomes are digestive compartments
Large storage vessels
Vacuoles
150
µm
Central vacuolein a plant cell
Fat vacuolesin adipose cells
Paramecium lives infresh water— takes on waterby osmosis.
Pumps out waterwith the contractilevacuole.
Contractile vacuole Endomembrane Systemn Continuous exchange of membrane and
membranous contents
Basic Cell Structure
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wNuclear envelope
wEndoplasmic reticulum
wGolgi apparatus
w Lysosomes
wVacuoles & vesicles
Endomembrane System Peroxisomesn May form from ER or autonomouslyn Both produces and removes hydrogen peroxide
– Detoxifies organic compounds, e.g. ethanol– Destroy bacteria
n ß-oxidation offatty acids
n Phospholipidsynthesis— esp. myelin
ChloroplastPeroxisome
Mitochondrion
1 µmFigure 6.19
Cellular Organelles: bioenergetics
n Mitochondria– Double-membrane
– Aerobic respiration• Powerhouse of cell
• Converts chemicalenergy fromcatabolism into ATP
– Have some of ownDNA to maintainactivity whennucleus isunavailable
Cellular Organelles: bioenergetics
n Chloroplast– Triple-membrane– Photosynthesis
• uses sunlight to construct organic molecules (CO2Æ sugar)
– Also have some of their own DNA– Plants
& someprotists
Cytoskeleton
Organizingthe
organelles
protein framework thatextends throughout the
cytoplasm
Cytoskeleton
Basic Cell Structure
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Cell Support Structuresn Cytoskeleton
∅MyosinDynein
(and others)
motorprotein
Keratin
(and others)
ActinTubulin(dimer)
structuralprotein
intermediatefilaments
micro-filaments
micro-tubules
Cytoskeletal structures
Cytoskeleton
Tensegrity:A balance of
tension &compression
Cytoskeleton
Cytoskeleton Cellular Structure:Centrioles
Microtubule organizing centers
Basic Cell Structure
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The nucleus & the cytoskeleton
n Intermediate filaments penetrate envelope toconnect with nuclear lamina
n Microtubule organizing center adjacent to nucleus
Vesicle transport alongmicrotubule “rails”
ATP energy isused to pullvesicles alongmicrotubules.
Cell Mobility Structures
n Flagella
n Cilia
Eukaryotic versions
flagella & cilia
HOW DO CILIA AND FLAGELLA MOVE ?HOW DO CILIACILIA AND FLAGELLAFLAGELLA MOVE ?
n Dynein arms causemicrotubules to bend
Fig. 4.19
Molecularmotors:structure ofcilia &flagella
Basic Cell Structure
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Myosin cross-bridges pullactin filaments along
Crowded networkof cross-linkedmicrofilaments(red) underlyingthe plasmamembrane (blue) .
“cytoplasmic cortex”
Cytoskeletal support ofcell membrane
Cytoplasmic Streaming
n Motor proteins pullcytoplasmicmacromolecularcomplexes andorganelles along themicrofilamentmeshwork
Cytoskeleton and pseudopodia
n Selective growthof themicrofilamentmeshworkproduces a bulge(pseudopodium)in cell membranefor amoeboidmovement orphagocytosis.
The Cell: A Living Unit greater than the sum of Its parts
n Cells rely on the integration of structures and organellesin order to function
5 µ
m
Figure 6.32
Many Variations in Theme