Transcript Chapter 6 A Tour of the Cell
Chapter 6 A Tour of the Cell
C A M P B E L L A N D R E E C E
Cell Theory
All living organisms are made of cells Cells are the smallest unit of structure & function in living organisms All cells come from other cells
Microscopes
1665: Hooke sees cell walls
Anton van Leewenhoek
made best lenses of his day pond water:
animalcules
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
Light Microscopy
Electron Microscopy TEM
beam e- thru specimen SEM
beam e- across surfaces
Size Range of Cells
Cell Fractionation
Common to all cells 1.
2.
3.
4.
cytosol ribosomes DNA plasma membrane
Compare & Contrast
Prokaryotic Cell
DNA concentrated in nucleoid smaller simpler (-) internal membranes older asexual reproduction Eukaryotic Cell
DNA in nucleus
larger more complex (+) internal membranes asexual or sexual reproduction
Prokaryotic Nucleoid
Images
Eukaryotic Nucleus
Cell Size Limitations
Prokaryotic Cell Details
Eukaryotic Cell Details: Plant Cell
Eukaryotic Cell Detail: Animal Cell
Nucleus
contains most of the DNA 5 microns across on average enclosed by dbl membrane: nuclear envelope
Chromatin
Nucleus Nucleolus Nucleolus
Ribosomes
rRNA & proteins carry out protein synthesis free ribosomes or ribosomes embedded in membrane polysomes: string of ribosomes
Ribosomes Polysomes
Anatomy of a Ribosome
The Endomembrane System
includes all membranes in cell
nuclear envelope
Endoplasmic reticulum
Golgi apparatus
vesicles, vacuoles
lysosomes
plasma membrane
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
The Endomembrane System
Endoplasmic Reticulum
>50% of membrane in a cell “endoplasmic” means within the cytoplasm” “reticulum” means little net made of network of tubules & sacs
Endoplasmic Reticulum
cisternae spaces contiguous with nuclear envelope
RER & SER Contiguous
RER
ribosomes on outer surface of membrane most proteins made shipped out of cell as polypeptide grows (into cisternae) it folds into its 2’ then 3’ structure most secretory proteins are glycoproteins so that carbohydrate attachment is done by enzymes in RER membrane
RER
protein made for use in cytosol kept separate from those meant for export transport vesicles carry new secretory protein/glycoprotein away from RER
Secretory Vesicles
SER
functions:
lipid synthesis
metabolism of carbohydrates
detoxification of drugs & poisons
storage of Ca++
SER
cells with lots SER:
endocrine glands
synthesize steroid hormones
ovaries, 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)
Detox by SER
SER Stores Ca++ in Muscle Fibers
Golgi Apparatus
receives, sorts, packages, ships also does a little modifying of proteins extensive in cells that secrete made of flattened membranous sacs with a curve (has directionality cis & trans) internal space = cisternae
Golgi Apparatus
Golgi Apparatus
ER products modified on trip thru Golgi
cisternae 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
Golgi Apparatus
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)
Lysosomes
membranous sac filled with hydrolytic enzymes digests macromolecules use acidic pH made in RER
Golgi
cytosol
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
Lysosomes
Lysosmes
Lysosomal Storage Diseases
autosomal recessive diseases lack a functioning hydrolytic enzyme residual body)
with cell functions
whatever that enzyme would have chemically broken down builds up in lysosome (called a lysosomes fill up interferes
example: Tay Sachs disease
lipid-digesting enzyme malfunction
affects neurons
Vacuoles
are large vesicles from ER or Golgi solution inside different from cytosol due to its selectively permeable membrane Types:
food vacuoles
contractile vacuoles
remove excess water
in plant cells act like
lysosomes
storage bins
Large Central Vacuoles in Plant Cells
develops by coalescence of smaller vacuoles solution inside it called cell sap
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
Endosymbiosis Theory
Mitochondria
in nearly all cells, 1- 10 microns # correlates with metabolic activity of cell dbl membrane inner 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
Mitochondrion Structure
Chloroplasts
a plastid dbl membrane separates inside
2 parts 3-6 microns in green parts of plants (chlorophyll) thylakoids: inner membrane folds in disc shapes: 1 stack of discs = granum
fluid in inner folds = stroma
Plastids
group of plant organelles other examples: 1.
amyloplast colorless 2.
in roots & tubers stores starch Chromoplast 1.
pigments that give fruits & flowers their colors
Peroxisomes
specialized metabolic compartment with 1 membrane contain enzymes that remove H atoms from various molecules
to O 2
H 2 O 2 H 2 O 2
2 H 2 O by enzymes in liver peroxisomes
functions:
break down fatty acids
in hepatocytes detoxify alcohol, poisons
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
Cytoskeleton
1.
2.
3.
organizes the structure & activities of a cell 3 types: Microtubules Microfilaments Intermediate Filaments
Functions of the Cytoskeleton 1.
2.
3.
4.
mechanical support maintain cell shape provides anchor for organelles & cytosol enzymes cell motility
Cytoskeleton & Cell Motility
involves interaction between cytoskeleton &
motor proteins
both work with plasma membrane to move cell
make flagella or cilia move
muscle fiber contraction
migration of neurotransmitter vesicles to axon tips
Motor Protein Animation
http://www.sinauer.com/cooper5e/animation1204.
html
Types of Cytoskeleton
Assembly of Microfilaments
http://www.sinauer.com/cooper5e/animation1201.h
tml
Cell Surface Projections Formed by Cytoskeleton http://www.sinauer.com/cooper5e/micrograph1202 .html
Microvilli
http://www.sinauer.com/cooper5e/micrograph1201.
html
Cytoskeleton Animation
http://www.bmc.med.utoronto.ca/bmc/images/stori es/videos/eddy_xuan.mov
Microtubules
in all eukaryotic cells hollow rods 25 nm across, 200 nm – 25 microns long made from a globular protein: tubulin, a dimer (made of 2 subunits)
Microtubules
Assembly of Microtubules
http://www.sinauer.com/cooper5e/animation1203.
html
Microtubule Functions
shape & support cell (compression-resistant role) serve as tracks other organelles with motor proteins can move along guide secretory vesicles from Golgi
membrane plasma in mitotic spindle to separate chromosomes
in animal cells: microtubules made in
centrosome
Centrioles
pair w/in each centrosome each made of 9 sets of triplet microtubules only in animal cells
Micrograph of Centrioles http://www.sinauer.com/cooper5e/micrograph1206 .html
Cilia
locomotor appendage on some cells move fluid over surface are usually many on cell surface 0.25 microns across & 2 – 20 microns long move like oars (alternating power /recovery strokes) generate force perpendicular to cilium’s axis
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
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
Flagella & Cilia Animation http://biology animations.blogspot.com/2008/02/flagell-and-cilia animation-video.html
Microfilaments
are really actin: globular protein that links with others into chains, which twist helically around each other, forming microfilaments in all eukaryotic cells function: bears tension many found just inside plasma membrane (support cell shape) which gives cytosol gel like consistency just inside plasma membrane make up core of microvilli
Microfilaments
with myosin (another contractile protein) make
muscle fibers contract
Amoeboid movement (pseudopods)
Intermediate Filaments
8 – 12 nm across
tension bearing not assembled/disassembled like microtubules & microfilaments made of proteins, one is keratin line interior of nuclear envelope, axons support framework of cell shape
Intermediate Filaments
Extracellular
materials made by cell but put into extracellular space: Cell Wall Extracellular Matrix Cell Junctions
Plant Cell Walls
functions:
protection
maintains shape
prevents excessive uptake of water Details
exact chemical composition varies from species to species
all have microfibrils made of cellulose
Plant Cell Wall Basic Design
Plant Cell Walls
secreted by cell membrane young plant cell secretes primary cell wall:
thin, flexible
middle lamella: lies between primary cell walls of adjacent cells
made of pectin: glues adjacent cells togeher
Plant Cell Walls
1.
when cell stops growing either: secrete hardening substances into primary wall 2.
secrete a secondary wall between plasma membrane & primary cell wall
has strong & durable matrix wood is mostly secondary cell wall
Primary & Secondary Cell Walls
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
ECM
fibronectin: ECM glycoprotein binds to cell surface receptor proteins called integrins integrins: span plasma membrane transmitting signals from ECM membrane
microfilaments on inner border of plasma
ECM
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
Plasmodesmata
Cell Junctions in Animal Cells 3 main types 1.
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
Tight Junctions
Cell Junctions in Animal Cells
2. Desmosomes
function like rivets
fastens cells together
anchored in cytoplasm by intermediate filaments
example: attach muscle cells to each other
Desmosomes
Cell Junctions in Animal Cells
3. Gap Junctions
cytoplasmic channels from 1 cell to another
made 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
Gap Junctions
Cell Animation http://vcell.ndsu.nodak.edu/animations/flythrough /movie-flash.htm