Download Biological membranes, cell compartments

Biological membranes,
cell compartments
Bruno Sopko
Content
• Introduction
• Plasma membrane
– Lipid rafts
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Nucleus
Mitochondria
Endoplasmic reticulum
Golgi apparatus
Lysosoms
Peroxisoms
Cytoplasm and cytoskeleton
Introduction - Advantages of the
compartmentalisation
• Maintaining of the high local concentration of the chemical
components in one compartment – higher reaction rates
• Controlling the transport of intermediates among
compartments is other effective regulation system of metabolic
pathways, localized in more than one compartment
• Protection from the environment
• Protection from the “aggressive” compartment interior
Introduction – subcellular compartments
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Nucleus
Nucleolus
Golgi apparatus
Mitochondrion
Lysosoms
Peroxisoms
Cytoskeleton
Cytosol
Centriols
Plasma membrane
Endoplasmic
reticulum
Introduction – Transport across membrane
• Diffusion
• Assisted diffusion
• Active transport
Plasma membrane
• Plasma membrane (plasmalemma) is biologic membrane
separating inner parts of the cell from the environment.
• Plasma membrane is the surface of all cells and is
selectively-permeable. This is the regulation part for the
intake and excretion of the chemical substances.
• Composed of lipids (phospholipids, glycolipids and
cholesterol esters) and proteins, participating in many cell
processes as, for instance, cell adhesion, ion channels
transport and cell signaling.
• Inner part contains specific sites, binding components of
intercellular cytoskeleton.
• Organized in subcompartments – microdomains, rafts
Plasma membrane - forming
Lipid Rafts
Lipid rafts are small (10-200nm), heterogeneous,
highly dynamic, sterol- and sphingolipid-enriched
domains that compartmentalize cellular processes.
Lipid Rafts
• Cholesterol and sphingolipid-enriched membrane
microdomains or platforms
– Cholesterol of double concentration
– Sphingomyelin concentration elevated by 50%
• Concentrate and segregate proteins within the
membrane
• More ordered and tightly packed than surrounding
bilayer
• Float freely in the surrounding membrane
Types of lipid rafts
• Caveolae: small, flask-shaped
invaginations of the plasma
membrane enriched in
caveolin
• Planar lipid rafts: found in
neurons and enriched in
flotillin
• Caveolin and flotillin recruit
signaling proteins
• Signaling can be promoted or
dampened
Lipid Raft Proteins
• “True resident proteins”
– GPI-anchored proteins-prion protein (PrPc)
– Caveolin
– Flotillin
• Signaling proteins
– G-protein, non-receptor tyrosine kinases
• Cytoskeletal/Adhesion proteins
– actin, myosin, vinculin, cofilin, cadherin, ezrin
GPI-anchored proteins
Lipid Raft formation
Lipid Rafts and Viruses
• HIV virus
– Budding may occur from lipid rafts
• Influenza virus
– Raft-associated glycoproteins in envelope
Nucleus
• DNA replication
• Transcription, synthesis of mRNA, tRNA, rRNA,
ribosomes
• Surrounded by double membrane connected to
ER
• Transport of cytosolic compounds (active and
passive) only via nuclear pores
• Specialized subcompartments (nucleolus –
ribosomes formation, DNA replication is localized
etc.)
Nucleus
Nucleus – transport across nuclear
envelope
Nucleus –protein transfer
Transfer into nucleus
Transfer from nucleus
Nucleus – RNA export
Mitochondria
• Two membranes – inner and
outer are highly different in
composition and enzymatic
activity
• Matrix of the mitochondria
(mitosol) exhibits different
biochemical functions
• Majority of the mitochondrial
proteins is coded in nucleolar
DNA (and synthesized by free
ribosomes in cytosol), but 13
mitochondrial proteins and
some RNA are coded in
circular mitochondrial DNA
(mtDNA)
Mitochondria
• Synthesis of more then 90% ATP – oxidative phosphorylation
(inner membrane)
• Heat production
• Apoptosis – inner mitochondrial pathway
• Oxidative decarboxylation of pyruvate (pyruvate
dehydrogenase complex)
• ß-oxidation of fatty acids (shorter then 24-C)
• Kreb’s cycle - mitosol
• P450 - in inner membrane
Mitochondria – protein import
Mitochondria – elektron import from cytosolic NADH
Michael W. King, Ph.D / IU School of Medicine / miking at iupui.edu
Mitochondria – ATP export to cytosol
Mitochondria – import of fatty acids for oxidation
Mitochondria – acetyl-CoA export for synthesis of
lipids and cholesterol
Michael W. King, Ph.D / IU School of Medicine / miking at iupui.edu
Mitochondria – the urea cycle
• Only ornithin
transcarbamoylase is
located in mitosol
• Carbamoylphosphate is
synthetized in
mitochondria from
bicarbonate and
ammonia, utilizing 2
ATP
• Citrullin is exported
via antiport with
ornithine
Endoplasmic reticulum
• Proteosynthesis (rough ER = RER)
• Primal steps of polysaccharides chains synthesis
(N-bound glycoproteins (RER))
• Synthesis (smooth ER = SER) - phospholipids,
triglycerides
• Cholesterol and steroids (SER) synthesis (on the
surface)
• Hydroxylation of endogenous a exogenous
compounds by cytochromes P450 (SER)
• Calcium ions storage (SER , sarcoplasmic
reticulum)
• Connected with nucleolar envelope
Golgi apparatus
• Cooperates with endoplasmic reticulum
• Enzymatic postranslation protein
modifications (glycosylation, sulfatation)
• Synthesis of new plasma membrane and
participation in creation of primal lysosoms
and peroxisoms
Lysosoms
• Intracellular digestion of
intracellular, and
extracellular compounds
• Lysosomal enzymes are
hydrolases with maximal
activity at pH 5 (inside of
lysosoms)
• Hydrolysis of intracellular
material – proteins
nucleic acids, lipids
together with organelles
– autofagia
• Extracellular material is
hydrolyzed after the
transport into the cell by
endocytosis (pinocytosis
and phagocytosis) heterofagia
Lysosoms
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Substances are in membrane
enclosed vesicle
2. By fusion of the vesicle with
primal lysosom secondary
lysosom is formed
3. Lysosomal hydrolases digest the
content of secondary lysosoms
4. Digested parts of the
hydrolysate are transferred to
cytosol for reuse
5. Non-digested material is
accumulated in residual body
and is excreted by exocytose
6. Remaining (nonexocytosed)
residual bodies contain
lipofuscin („age pigment“)
Peroxisoms
• Produce or use hydrogen peroxide
• Differ in function and in number in different types of cell
• More then 50 types of enzyme catalyzing oxidative and
reductive biosynthetic reactions
• oxidation of very long fatty acids chains (a- and boxidation)
• synthesis glycerolipids, glycerol ether lipids
(plasmalogens) and isoprenoids
• enzymes for oxidation of D-aminoacids, 2-hydroxy acids
and uric acid (uricase is absent at higher apes)
• catalase
• Known more then 25 perixosomes biogenesis disorders
(Zellweger‘s syndrome = absence of peroxisomes and
death occurs by age 6 months)
• Some xenobiotics induce peroxisom proliferation
Peroxisoms - -oxidation of long fatty
acids
Peroxisoms –plasmalogens synthesis
Cytoplasm/cytoskeleton
• Keeps phenotype (morphology) of the cell and participate
in intracellular transport, cell mobility and cell division
• Is formed by microtubules, intermedial filaments and
actin filaments (microfilaments)
Cytoplasm/cytoskeleton - microtubules
• diameter 25 nm and
length from 200 nm to
25 mm
• Polymers of α- and βtubulin dimmers,
polymerized end to end
to protofilaments.
Protofilaments form
hollow microtubules
Cytoplasm/cytoskeleton - intermedial filaments
• diameter 10 nm
• Domain structure of IF is conserved. Each protein contains
non-a-helix domain at N and C-ends, which frame a-helix
domain of the „stick“
• Basic unit of the intemedial filaments (IF) is dimmer
• Known more then 70 gens for six basic types(I - VI) IF :
– I a II - keratins (epithelial and higher)
– III – e.g. desmin (sarcomers of muscle cells) and vimentin (e.g.
fibroblasts - correct localization of organelles
– V - nucleolar IF
Cytoplasm/cytoskeleton - intermedial filaments
Cytoplasm/cytoskeleton - microfilaments
• The most dynamic part of cytoskeleton are
microfilaments (actin filaments).
• Diameter is 6nm
• Formed by two linear polymers of actin subunits
Cytoplasm/cytoskeleton - Centrosom and centriols
• Centrosom is organell, main organisation centre of
microtubules and regulates cell cycle
• Centrosom is the cell region, forming microtubules
• Centrioles are important parts of centrosomes.
Cytoplasm/cytosol
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54% cell volume
Many reaction chains are located in parts of cytosol
glycolysis (NAD+/ NADH)
PPP - pentosophosphate pathway (NADPH)
glycogenolysis
glycogenesis (synthesa glykogenu)
biosynthesis of fatty acids (fatty acid synthase)
synthesis of active saccharides
Proteosynthesis support
Forming „subcompartments“ with different enzyme
concentrations-> many reactions are carried out only in
certain parts of cytosol
Examples of pathways localized in a single
compartment only
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Kreb’s cycle
Glycolysis
Proteosynthesis
DNA replication
Literature
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Gabriel Schlenstedt, Protein import into the nucleus, FEBS Letters 389 (1996) 7579
Walter Nickel and Catherine Rabouille, Mechanisms of regulated unconventional
protein secretion, NATURE Reviews, Molecular cell Biology volume 10, february
2009
Marks´ Basic Medical Biochemistry, A Clinical Approach, third edition, 2009 (M.
Lieberman, A.D. Marks)
David A. Jans, Chong-Yun Xiao, and Mark H.C. Lam, Nuclear targeting signal
recognition: a key control point in nuclear transport?, BioEssays 22:532-544, 2000
John Wiley & Sons, Inc
The Cell: A Molecular Approach, Fourth Edition, GEOFFREY M. COOPER , ROBERT
E. HAUSMAN, 2007, ASM Press, Washington, D.C. USA
Yoshihiro Yoneda, How Proteins Are Transported from Cytoplasm to the Nucleus,
J. Biochem. 121, 811-817 (1997)
Alwin Köhler and Ed Hurt, Exporting RNA from the nucleus
to the cytoplasm, NATURE Reviews, Molecular cell Biology volume 8, october
2007