CELL STRUCTURE V
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Transcript of CELL STRUCTURE V
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Membrane compartments of theMembrane compartments of the
cellcell
CytoskeletonCytoskeleton
Svetlana Lutsenko, Dept. Biochemistry and Mol. BologySvetlana Lutsenko, Dept. Biochemistry and Mol. Bology
MRB 624, Ext. 4-6953, [email protected] 624, Ext. 4-6953, [email protected]
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Reading for the Cytoskeleton portion:
Alberts Essential Cell Biology pp.513-532
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1. Transport of various molecules,including proteins, DNA and RNA
through large protein-lined pores.
Specificity of transport is based on
size exclusion
3. Simple diffusion and protein-mediated transport of ions and small
molecular weight nutrients, such an
amino-acids and sugars
5. Vesicular transport is mediated by
membranes that bud off as a vesiclesfrom their original compartment and
carry out specific cargo (ions,
proteins, neurotransmitters) to
another compartment
Mechanisms by which molecules can pass through membranesMechanisms by which molecules can pass through membranes
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Cellular Compartments and TheirCellular Compartments and Their
FunctionsFunctions
Cytosol ::many biosynthetic pathway;synthesis of cytosolic protein
Nucleus :: DNA and RNA synthesis
Mitochondria :: energy metabolism,urea cycle
Endoplasmic Reticulum: ProteinSecretion; Synthesis of Membrane
Proteins
Golgi :: Distribution and Modification of
Secreted Proteins
Lysosomes :: Degradation of proteinsand other molecules
Peroxisomes: Degradation of CertainFatty Acid
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NucleusNucleus
The nucleus is a membrane
bound structure that
contains the cell's hereditary
information and controls the
cell's growth and
reproduction.
It is commonly the mostprominent organelle in the
cellhttp://biology.about.com/library/weekly/aa032300a.htm
http://biology.about.com/gi/dynamic/offsite.htm?site=http://www.brigadoon.com/%7Eschaffer/biology/nucleus.htmlhttp://biology.about.com/gi/dynamic/offsite.htm?site=http://www.brigadoon.com/%7Eschaffer/biology/nucleus.html -
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Nuclear MembranesNuclear Membranes
The nuclear content is located in thenuclear lumennuclear lumen and is surrounded by a
double membrane ornuclear envelopenuclear envelope,
composed ofinner membraneinner membraneandouterouter
membranemembrane.
The outer membrane is contiguous with
the ER
The nuclear membrane contains nuclearnuclear
porespores, which provide selective access into
and out of the nuclear lumen
The inner membrane has a protein lining
called the nuclear lamina, which binds to
chromatin and other nuclear components.
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The Nuclear Pore ComplexesThe Nuclear Pore Complexesform aform a continuous aqueous channel between cytoplasm & nucleoplasm
-30 different proteins found in pore; basic subunit
repeated 16 times. Central granule" now called
"transporter" functions to move molecules through
pore. There is a ring of proteins that anchors pore
to N.E. and the "basket" of fibers with unknown
function
-no obvious motor proteins were found
Proposed mechanism -transport factors with cargo destined to pass through nuclear pore bind to
pore increasing their local concentration. Higher local concentration allows diffusion across the
diffusion barrier channel
nuclear pore complex is
large about 120 million
Daltons
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The NucleolusThe Nucleolus
The region of the nucleus where portions of chromosomes that contain genescoding for ribosomal RNA are transcribed and ribosomal subunits are
assembled
http://biology.about.com/library/weekly/aa032300a.htm
Stretch of DNA with rRNA genes
nucleolar organizing region =
(NOR)
Ribosomal proteins are synthesized
in cytoplasm and transported into
the nucleus
These proteins self associate withappropriate rRNA during rRNA
synthesis forming immature
ribosomal subunits
Ribosomes finish self assembly in
cytoplasm
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Endoplasmic ReticulumEndoplasmic Reticulum
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The Endoplasmin Reticulum (ER) is an extensive,The Endoplasmin Reticulum (ER) is an extensive,
extra-nuclear membrane system with the followingextra-nuclear membrane system with the following
functions:functions:
ER is a home for various enzymes involved in protein folding , drug
detoxification, membrane lipid biosynthesis, cholesterol and fatty acidmetabolism
ER is an entry point for protein sorting. Targeting of these proteins is
mediated by signal sequence. The membrane proteins are inserted into
the ER membrane in their proper orientation. Secreted proteins aretranslocated into ER lumen and then transported to the destination
place
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The rough ER manufactures membranes and secretory proteins.
The rough and smooth ER are usuallyinterconnected and the proteins andmembranes made by the rough ER move
into the smooth ER to be transferred toother locations.
In leukocytes the rough ER produces antibodies.
In pancreatic cells the rough ER produces insulin.
The cytoplasm has a reducing environment,
while ER lumen is oxidizing . Thisdifference is generated by unequal
distribution of trypeptide glutathione and
is essential for formation of disulfide bonds
in proteins and for proper folding
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MitochondriaMitochondria
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Mitochondria (singular: mitochondrion) are the sites of
aerobic respiration, and generally are the major energy
production center in eukaryotes
The number of mitochondria range from one to thousands per cells.
They are often positioned in cells nearest to sites of energy utilization
One of the richest sources of mitochondria is a hummingbird flight
muscle
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Mitochondria are a double membrane organelle in which the
inner membrane is in-folded to form cristae.
The outer membrane is a fairlysimple phospholipid bilayer,
containing porins,proteins that
render it permeable to molecules
of about 10 kilodaltons or less.
Ions, nutrient molecules, ATP,ADP, etc. easily pass through the
outer membrane and enterthe
intermembrane space
The inner membrane is more
complex and contains respiratorychains and transporters
The matrix lies within the inner membrane. The access to this compartment
often requires specific transporters
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Four possible localization for mitochondrial enzymes
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The Golgi ComplexThe Golgi Complex
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Located near cell nucleus, consists of flattened,
membrane-bounded sacs (cisternae) forming a stack
Each stack has:
cis-face is an entry face - adjacent to ER to acceptincoming vesicles
trans-face is an exit face points towards plasma membrane, produces vesicles for
forward flow
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The function of the Golgiis to transport and processsecreted and membrane proteins from ER to the cell surface
Cis removal of mannose,
phosphorylation
Medial removal of mannose,
addition of N-acetylglucosamine
Trans Removal of galactose,
addition of sialic acid
TGN addition of sialic acid,
Sorting
Cisternae segregated intoconvex ("cis"), medial
(middle), and concave
("trans") compartments.
ER
cys
medial
trans
TGN
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Vesicular TransportVesicular Transport
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The Endocytic PathwayThe Endocytic Pathway
Endosomes and LysosomesEndosomes and Lysosomes
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LysosomesLysosomes
Lysosomes are active in recycling the cell's organic material and in the intracellular
digestion of macromolecules.Lysosomes contain various hydrolytic enzymes that are capable of digesting nucleic
acids, polysaccharides, fats and proteins.The inside of a lysosome is acidic.In humans, a variety of inherited conditions can affect lysosomes. These defects are
called storage diseases and include Pompe's disease and Tay-Sachs disease. People with
these disorders are missing one or more of the lysosomal hydrolytic enzymes.
http://www.pompe.org.uk/http://www.pompe.org.uk/http://www.ninds.nih.gov/patients/disorder/taysachs/taysachs.htmhttp://www.ninds.nih.gov/patients/disorder/taysachs/taysachs.htmhttp://www.ninds.nih.gov/patients/disorder/taysachs/taysachs.htmhttp://www.ninds.nih.gov/patients/disorder/taysachs/taysachs.htmhttp://www.pompe.org.uk/http://www.pompe.org.uk/ -
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The CytoskeletonThe Cytoskeleton
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Cytoskeleton is a network of protein
filaments in the cytoplasm
Main functions:
Supports large volume of the cytoplasm
Participates in large-scale movements associated
with the changes in cell shape and cell motility
Provides machinery for organelle transport,
chromasome segregation during mitosis, and celldivision
M j t f t k l tM j t f t k l t
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Actin filaments Microtubules
Intermediate filaments
Major components of cytoskeletonMajor components of cytoskeleton
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The cytoskeletal filamentsThe cytoskeletal filaments
Common Features :
Linear polymers of protein subunits
Actin ( ~8 nm in diameter)
Intermediate Filaments ( ~10 nm in diameter)
Microtubules ( ~24 nm in diameter)
Filaments are dynamic, i.e. they can assemble
and disassembleHighly conserved
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Intermediate Filaments
Intermediate filaments enablecells to withstand mechanical
stress when cells are stretched.
They can span the entire
cytoplasm and are anchored to
the plasma membrane.
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The Microtubule CytoskeletonThe Microtubule Cytoskeleton
Also penetrates the entire
volume of the cell
Whereas actin fibers areconcentrated at the periphery,
most microtubules radiate from
a central location in the cell
Main functions: intracellulartransport and mitosis
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Microtubules provide anorganizational structure in aninterphase cell and separatechromosomes in a dividing cell
http://www.circs.neu.edu/external/Frank.Gibbons/spindle.html
MicrotubulesMicrotubules
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Microtubules Provide Tracks for Transport
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MicrotubulesMicrotubules are long hollow cylinders made oftubulin
Protofilaments are linear chains of tubulin
dimers, a parallel bundle of 13 protofilaments
forms a microtubule
There are three kinds of tubulins, each with
many subtypes:
-tubulin-tubulin and -tubulin-tubulin form / tubulindimers and represent the basic building block of
microtubules
-tubulin-tubulin is involved in more specializedprocesses, such as nucleation
Microtubules have a GTP cap stabilizing the
ends.
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Motor
Proteins
Motor proteins bind to
microtubules and move
by cycles of
conformational changesusing energy from ATP.
One end of the proteincan bind to specific
cellular components.
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Actin is the most common protein in
the cytoplasm
Actin filaments are concentrated
beneath the plasma membrane and
give the cell mechanical strength
Assembly of actin filaments can
determine cell shape and cause cell
movement
Association of actin filaments withmyosin can form contractile structures
Actin filaments = microfilamentsActin filaments = microfilaments
S i
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SpectrinSpectrinPrincipal component of the cytoskelton(protein meshwork underlying surface ofthe red cell)
Maintains structural integrity of the redcell (e.g. biconvave shape)
Long thin flexible rod
Necessary as red cells go through smallcapillaries