Chapter 6 A Tour of the Cell
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Transcript of Chapter 6 A Tour of the Cell
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CAMPBELL AND REECE
Chapter 6A Tour of the Cell
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Cell Theory
All living organisms are made of cellsCells are the smallest unit of structure &
function in living organismsAll cells come from other cells
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Anton van Leewenhoek
made best lenses of his day
pond water: animalcules
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Light Microscopy
light goes through specimen and is refracted by glass lenses so image is magnified as it is projected toward eye
magnification: ratio of image size to real size
resolution: a measure of clarity , the minimum distance 2 pts can be separated & seen as 2 pts (can’t do better than 200 nm)
contrast: accentuate pts in different parts of specimen
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Light Microscopy
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TEM SEM
beam e- thru specimen
beam e- across surfaces
Electron Microscopy
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Common to all cells
1. cytosol2. ribosomes3. DNA4. plasma membrane
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Prokaryotic Cell Eukaryotic Cell
DNA concentrated in nucleoid
smallersimpler(-) internal
membranesolderasexual
reproduction
DNA in nucleuslarger more complex(+) internal
membranesasexual or sexual
reproduction
Compare & Contrast
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ProkaryoticNucleoid
EukaryoticNucleus
Images
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Cell Size Limitations
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Eukaryotic Cell Details: Plant Cell
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Nucleus
contains most of the DNA5 microns across on averageenclosed by dbl membrane: nuclear
envelope
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Chromatin
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Ribosomes
rRNA & proteinscarry out protein synthesisfree ribosomes or ribosomes embedded
in membranepolysomes: string of ribosomes
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Ribosomes Polysomes
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The Endomembrane System
includes all membranes in cellnuclear envelopeEndoplasmic reticulumGolgi apparatusvesicles, vacuoles lysosomesplasma membrane
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The Endomembrane System
functions: synthesis of proteins (ribosomes in
membrane) transport of proteins into membranes &
organelles (or out of cell) movement of lipids detoxification of poisons all membranes “related” either by
proximity or by transfer of membrane segments via vesicles
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The Endomembrane System
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Endoplasmic Reticulum
>50% of membrane in a cell“endoplasmic” means within the
cytoplasm”“reticulum” means little netmade of network of tubules & sacs
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Endoplasmic Reticulum
cisternae spaces contiguous with nuclear envelope
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RER
ribosomes on outer surface of membranemost proteins made shipped out of cellas polypeptide grows (into cisternae) it
folds into its 2’ then 3’ structuremost secretory proteins are glycoproteins
so that carbohydrate attachment is done by enzymes in RER membrane
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RER
protein made for use in cytosol kept separate from those meant for export
transport vesicles carry new secretory protein/glycoprotein away from RER
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Secretory Vesicles
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SER
functions: lipid synthesismetabolism of carbohydratesdetoxification of drugs & poisonsstorage of Ca++
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SER
cells with lots SER: endocrine glands
synthesize steroid hormonesovaries, testes, adrenals
hepatocytes detoxify by adding –OH, increases solubility cleared by kidneys
alcohol, drug abusers (legal or not) have increased amts of SER in their hepatocytes (also increases drug tolerance)
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Detox by SER
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SER Stores Ca++ in Muscle Fibers
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Golgi Apparatus
receives, sorts, packages, ships also does a little modifying of proteinsextensive in cells that secrete made of flattened membranous sacs with
a curve (has directionality cis & trans)internal space = cisternae
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Golgi Apparatus
ER products modified on trip thru Golgicisternae membrane has unique
“team”of enzymes that moves from cis to trans
modifies the monomers in carb part of glycoproteins
modifies phospholipids destined for membrane
makes some macromolecules: polysaccharides
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Golgi Apparatus Vesicles
when leave trans vesicles have molecular ID tags that indicates where they are going
vesicles have receptor proteins on external surface that “recognize” where vesicle is supposed to dock (other organelles, plasma membrane)
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Lysosomes
membranous sac filled with hydrolytic enzymes
digests macromolecules use acidic pHmade in RER Golgi cytosol
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Lysosome Functions
digest food vacuoles ingested by phagocytosis in protists or by macrophages (WBCs that ingest bacteria or debris and recycle nutrients in them)
autophagy: hydrolytic enzymes in lysosomes recycle cell’s own organic material in worn out organelles
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Lysosmes
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Lysosomal Storage Diseases
autosomal recessive diseaseslack a functioning hydrolytic enzyme
whatever that enzyme would have chemically broken down builds up in lysosome (called a residual body) lysosomes fill up interferes with cell functions example: Tay Sachs disease
lipid-digesting enzyme malfunction affects neurons
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Vacuoles
are large vesicles from ER or Golgisolution inside different from cytosol due
to its selectively permeable membraneTypes:
food vacuolescontractile vacuoles
remove excess water in plant cells act like
lysosomes storage bins
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Large Central Vacuoles in Plant Cells
develops by coalescence of smaller vacuoles
solution inside it called cell sap
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Endosymbiont Theory
early ancestor of eukaryotic cells engulfed an oxygen-using nonphotosynthetic prokaryotic cell = mitochondrion
over time prokaryotic cell became an endosymbiont (a cell living w/in another cell)
some time later some or 1 of these engulfed a photosynthetic prokaryotic cell and developed same relationship = chloroplast
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Endosymbiosis Theory
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Mitochondria
in nearly all cells, 1- 10 microns# correlates with metabolic activity of celldbl membraneinner membrane folded (cristae) & divides
mitochondria into 2 separate inner compartments (intermembrane space & matrix)
matrix contains enzymes for cellular respiration, DNA, ribosomes
intermembrane has enzymes that make ATP
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Chloroplasts
a plastiddbl membrane separates inside 2 parts3-6 micronsin green parts of plants (chlorophyll)thylakoids: inner membrane folds in disc-
shapes: 1 stack of discs = granumfluid in inner folds = stroma
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Plastids
group of plant organelles other examples:1. amyloplast
colorless in roots & tubers stores starch
2. Chromoplast1. pigments that give fruits & flowers
their colors
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Peroxisomes
specialized metabolic compartment with 1 membrane
contain enzymes that remove H atoms from various molecules to O2 H2O2
H2O2 2 H2O by enzymes in liver peroxisomes
functions:break down fatty acids in hepatocytes detoxify alcohol,
poisons
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Glyoxysomes
specialized peroxisomes in fat-storing tissues of plant seeds
contain enzymes that start catabolism of fatty acids sugars
seed uses these sugars for energy to plant
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Cytoskeleton
organizes the structure & activities of a cell
3 types:1. Microtubules2. Microfilaments3. Intermediate Filaments
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Functions of the Cytoskeleton
1. mechanical support2. maintain cell shape3. provides anchor for organelles & cytosol
enzymes4. cell motility
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Cytoskeleton & Cell Motility
involves interaction between cytoskeleton & motor proteinsboth work with plasma membrane to
move cellmake flagella or cilia movemuscle fiber contractionmigration of neurotransmitter vesicles
to axon tips
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Motor Protein Animation
http://www.sinauer.com/cooper5e/animation1204.html
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Types of Cytoskeleton
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Assembly of Microfilaments
http://www.sinauer.com/cooper5e/animation1201.html
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Cell Surface Projections Formed by Cytoskeleton
http://www.sinauer.com/cooper5e/micrograph1202.html
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Microvilli
http://www.sinauer.com/cooper5e/micrograph1201.html
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Cytoskeleton Animation
http://www.bmc.med.utoronto.ca/bmc/images/stories/videos/eddy_xuan.mov
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Microtubules
in all eukaryotic cellshollow rods 25 nm across, 200 nm – 25
microns longmade from a globular protein: tubulin, a
dimer (made of 2 subunits)
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Microtubules
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Assembly of Microtubules
http://www.sinauer.com/cooper5e/animation1203.html
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Microtubule Functions
shape & support cell (compression-resistant role)
serve as tracks other organelles with motor proteins can move along
guide secretory vesicles from Golgi plasma membrane
in mitotic spindle to separate chromosomes
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in animal cells: microtubules made in centrosome
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Centrioles
pair w/in each centrosomeeach made of 9 sets of triplet
microtubulesonly in animal cells
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Micrograph of Centrioles
http://www.sinauer.com/cooper5e/micrograph1206.html
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Cilia
locomotor appendage on some cellsmove fluid over surfaceare usually many on cell surface0.25 microns across & 2 – 20 microns
longmove like oars (alternating power
/recovery strokes)generate force perpendicular to cilium’s
axis
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Cilia & Flagella Structure
locomotor appendage share common structure with cilia: 9
doublets of microtubules in ring with 2 single microtubules in center then covered with plasma membrane
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Cilia & Flagella Structure
dyneins: large motor proteins extending from one microtubule doublet to adjacent doublet
ATP hydrolysis drives changes in dynein shape so cilia or flagella bend
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Flagella & Cilia Animation
http://biology-animations.blogspot.com/2008/02/flagell-and-cilia-animation-video.html
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Microfilaments
are really actin: globular protein that links with others into chains, which twist helically around each other, forming microfilaments
in all eukaryotic cellsfunction: bears tensionmany found just inside plasma
membrane (support cell shape) which gives cytosol gel-like consistency just inside plasma membrane
make up core of microvilli
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Microfilaments
with myosin (another contractile protein) make muscle fibers contractAmoeboid movement (pseudopods)
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Intermediate Filaments
8 – 12 nm acrosstension bearingnot assembled/disassembled like
microtubules & microfilamentsmade of proteins, one is keratinline interior of nuclear envelope, axonssupport framework of cell shape
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Intermediate Filaments
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Extracellular
materials made by cell but put into extracellular space:
Cell WallExtracellular MatrixCell Junctions
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Plant Cell Walls
functions:protectionmaintains shapeprevents excessive uptake of waterDetailsexact chemical composition varies
from species to speciesall have microfibrils made of cellulose
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Plant Cell Wall Basic Design
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Plant Cell Walls
secreted by cell membraneyoung plant cell secretes primary cell
wall: thin, flexiblemiddle lamella: lies between primary
cell walls of adjacent cells made of pectin: glues adjacent cells togeher
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Plant Cell Walls
when cell stops growing either:1. secrete hardening substances into
primary wall2. secrete a secondary wall between
plasma membrane & primary cell wall has strong & durable matrix wood is mostly secondary cell wall
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Primary & Secondary Cell Walls
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Extracellular Matrix (ECM)
in animals main ingredient: glycoproteins
collagen embedded in proteoglycans (protein with many carbohydrates attached) 40% of all the protein in human body is collagen
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ECM
fibronectin: ECM glycoprotein binds to cell-surface receptor proteins called integrins
integrins: span plasma membrane transmitting signals from ECM microfilaments on inner border of plasma membrane
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ECM
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Cell Junctions
1. plasmodesmata: perforations in plant cell walls lined with plasma membrane, filled with cytoplasm
cytosol flows from cell to cell plasma membranes of adjacent
cells contiguous
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Plasmodesmata
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Cell Junctions in Animal Cells
3 main types1. Tight Junctions
plasma membranes of adjacent cells tightly pressed against each other
bound together by proteins form continuous seal around cell example: tight jcts around skin cells
make skin water proof
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Tight Junctions
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Cell Junctions in Animal Cells
2. Desmosomes function like rivets fastens cells together anchored in cytoplasm by
intermediate filamentsexample: attach muscle cells to each
other
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Desmosomes
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Cell Junctions in Animal Cells
3. Gap Junctionscytoplasmic channels from 1 cell to
anothermade of membrane proteins that
surround a pore open to ions, sugars, a.a.
necessary for communication between cells like cardiac muscle and in animal embryos
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Gap Junctions
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Cell Animation
http://vcell.ndsu.nodak.edu/animations/flythrough/movie-flash.htm
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