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CASA Exam 2
Wed (10/9) through Fri (10/11)
Chapters 5, 6, 7, 11 & 12
~ 50 multiple choice questions
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Eukaryotic genes include coding (exons)
and non-coding (introns) segments
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Prokaryotic mRNA is usually polycistronic
Prokaryotic ribosomes can recognize and bind near start codonsin the middle of an mRNA molecule.
Several related proteins are synthesized simultaneously from asingle mRNA
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The Lac Operon
!-galactosidase !-galactoside permease
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Many antibiotics target prokaryotic translation
Weve been able to borrowmuch of this technology from oureukaryotic cousins, the fungi.
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Many fungal antibiotics block translation
Blocked by Streptomycin
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Many fungal antibiotics block translation
Blocked by Tetracycline
Blocked by Chloramphenicol
Blocked by Cycloheximide
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Translation is terminated at stop codons
UAA, UAG and UGA They signal the
binding of release
factors (proteins). A hydrolysis reaction
then frees the
polypeptide. Nascent proteins are
typically met by
chaperone proteins as
they emerge from the
ribosome
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Posttranslational modifications
After biosynthesis, many proteins undergoposttranslational modificationsthat can
substantially alter protein stability and
function.
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Biomembranes are selectively permeable barriers to diffusion
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Biomembranes
most significantmacromolecular structure of cell
protect cell from environmental
chemistry
allow for the development of
concentration gradients
-- Equilibrium is Death --
must be flexible to allow for
changes in cell shape / motility
*
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In eucaryotic cells, the
plasma membrane
represents only 5% of
the total membrane in
the cell
All membranouselements of the cell
share a common
structure
Animal Cell
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Double MembraneNuclear Envelope
Mitochondria
Chloroplasts
Endomembrane System
Nuclear Envelope
Endoplasmic Reticulum
Golgi ApparatusEndosomes
Lysosomes
Transport Vesicles
Plasma Membrane
Animal Cell
*
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The Endomembrane System *
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Biomembranes are primarily
composed ofphospholipids,
amphipathic molecules thatspontaneously form stable bilayers.
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Amphipathic Membrane Components
*
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Figure 11-10 Essential Cell Biology ( Garland Science 2010)
phospholipidtriglyceride
Fat*
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Phosphatidylcholine is the most common
phosphoglyceridein biomembranes
1 saturated FA2 unsaturated FA3 polar head
*
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Membrane Lipids are Highly Diverse
> 500 Different Lipids
Found in Biomembranes
However, Only 5 Lipids Comprise
65 - 85%(gm/100 gm)
Most Biomembranes
*
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These 5 Lipids Comprise 65 - 85 % of Biomembranes *
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Only phosphatidylserine is (negatively) charged at neutral pH
*
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Sphingomyelin does not contain a glycerol backbone
------ phosphoglycerides ----- -- not--
*
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Sphingomyelin does not contain a glycerol backbone
Sphingosine
Cholinemoiety
amide
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Acetone is miscible with water
Acetone disturbs the structure of water, but is not excluded
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Acetone is miscible with water
Acetone disturbs the structure of water, but is notexcluded
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2-methylpropane is notmiscible with water
2-MP cannot hydrogen bond, and is excluded from waterinto an ice-likecage
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Amphipathic molecules form ordered structures in aqueous media
Detergents work by trapping oily contaminants in the
hydrophobic interior of micelles
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1 FA tail
2 FA tails
O
CO-
RO
O=P-O-
Amphipathic molecules form ordered structures in aqueous media
Minimize aqueous contact with hydrophobic moieties
*
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High concentrations of
phospholipids andrelated amphipathic
substances
spontaneously form
spherical compartments
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Liposomes (TEM)
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Liposomes can be used for drug / gene delivery
yourdrug
here
*
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Blackphospholipid membrane
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The lipid bilayer is a 2 dimensional fluid
Fast (~ 2 m/s)
Very Fast
(~ 5,000 rps)
Very Slow~ 1/month
*
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Membrane fluidityis determined by
temperature and membrane composition
longer fatty acid length shorter
less unsaturation more
high cholesterol intermediate
Liquid Crystal
*
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Table 10-1 Molecular Biology of the Cell( Garland Science 2008)
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PC : SM1 : 1
PC : SM: Chol1 : 1 : 1
Lipid Rafts
*
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Figure 10-14a Molecular Biology of the Cell( Garland Science 2008)
AFM image of lipid rafts *
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Atomic Force Microscopy (AFM)
Lifted from Wikipedia
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Figure 10-14b Molecular Biology of the Cell( Garland Science 2008)
Some signaling proteins concentrate at lipid rafts*
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Figure 10-17c Molecular Biology of the Cell( Garland Science 2008)
Phosphatidylinositol
Minor phospholipid
Localized to cytoplasmic
leaflet
Important docking &
signaling molecule
Phosphorylated by specific
lipid kinases
H
H
*
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Phosphatidylinositol (4,5) bis-phosphate
Important signaling molecule = PI(4,5)P2
Converted to PI(3,4,5)P3by PI 3-kinase
PI(3,4,5)P3serves as docking site for
certain signaling proteins (PH domain)
Pleckstrin Homology (PH) Domain
*
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glycolipidsPC SM
PS PE
In healthycells, PS is found exclusively on the inner leaflet
Lipids are asymmetrically distributed
across biological membranes
*
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plasma membrane is
made in the endoplasmicreticulum
new phospholipids are
inserted into thecytoplasmic side of the
ER membrane
enzymes (flippases)transfer phospholipids
across the plasma
membrane
*
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Figure 11-19 Essential Cell Biology ( Garland Science 2010)
Newmembrane is distributed throughout the
endomembrane system through vesicular transport
lumen
Cytoplasmic Surface
extracellular
*
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Figure 11-2 Essential Cell Biology ( Garland Science 2010)
Membrane proteins perform these essential functions
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Figure 11-20 Essential Cell Biology ( Garland Science 2010)
4 functional classes of membrane proteins
glucose transporterNa-K ATPase
integrinsankyrin
!-adrenergic recInsulin rec
adenylyl cyclasephospholipase C
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Figure 11-21 Essential Cell Biology ( Garland Science 2010)
Proteins constitute ~ 50% of the mass of biomembranes
(myelin = 25 % ; inner mito memb = 75%)
~ 1/3 of all proteins are membrane associated
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Figure 11-21 Essential Cell Biology ( Garland Science 2010)
Integral vs Peripheral Membrane Associations
Integral membrane proteins
peripheralmembrane
proteins
*
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Figure 11-21 Essential Cell Biology ( Garland Science 2010)
Membrane Associated Protein Strategies
transmembrane"helical proteins
transmembrane
!barrel proteins
tetheredproteins
*
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Figure 11-23 Essential Cell Biology ( Garland Science 2010)
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Figure 11-24 Essential Cell Biology ( Garland Science 2010)
*
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Figure 11-25 Essential Cell Biology ( Garland Science 2010)
A Bacterial Porin
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Figure 11-27 Essential Cell Biology ( Garland Science 2010)
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Figure 11-26 Essential Cell Biology ( Garland Science 2010)
Ionic detergent Non-ionic detergent
Useful detergents for isolation of membrane proteins
*
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Figure 11-38 Essential Cell Biology ( Garland Science 2010)
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Figure 10-31 Molecular Biology of the Cell( Garland Science 2008)
*
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Figure 10-32 Molecular Biology of the Cell( Garland Science 2008)
Halobacterium salinarum *
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Figure 11-28 Essential Cell Biology ( Garland Science 2010)
Bacteriorhodopsin is a light-powered proton pump
*
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Figure 11-31 Essential Cell Biology ( Garland Science 2010)
Spectrin-rich cortical network supports erythrocyte membrane
**
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Figure 11-32 Essential Cell Biology ( Garland Science 2010)
Demonstration of lateral movement of proteins in cell membrane
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*Fluorescence RecoveryAfter Photobleaching
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Membrane proteins are usually restricted to specific regions
guinea pig sperm
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Four ways to restrict the distribution of membrane proteins
Stabilized by
cell-cell junctions
Tether to cortex Tether to ECM
Restricted by
tight junctions
*
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Figure 11-34 Essential Cell Biology ( Garland Science 2010)
Epithelial cells use tight junctionsto prevent movementbetween apicaland basolateralmembrane domains *
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Figure 10-28a Molecular Biology of the Cell( Garland Science 2008)
*The Glycocalyx
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Figure 11-35 Essential Cell Biology ( Garland Science 2010)
The Glycocalyx
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Figure 10-27 Molecular Biology of the Cell( Garland Science 2008)
Lots of glycosylated residuesSer, Thr, Asn
Structure stabilized by
disulfide bridges
Most cysteine side chainsexist in the reduced state
-SH Not -S-S-
Glycosylation is absent
Its a Jungle out there !! *
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Figure 11-39 Essential Cell Biology ( Garland Science 2010)
*Leukocyte Extravasation
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