Advanced Cell Biology. Lecture 36 - A....
Transcript of Advanced Cell Biology. Lecture 36 - A....
Advanced Cell Biology. Lecture 36
Alexey Shipunov
Minot State University
May 1, 2013
Shipunov (MSU) Advanced Cell Biology. Lecture 36 May 1, 2013 1 / 39
Outline
Questions and answers
Cytoskeleton
Structure of cytoskeletonMyosin and muscle contraction
Shipunov (MSU) Advanced Cell Biology. Lecture 36 May 1, 2013 2 / 39
Outline
Questions and answers
Cytoskeleton
Structure of cytoskeletonMyosin and muscle contraction
Shipunov (MSU) Advanced Cell Biology. Lecture 36 May 1, 2013 2 / 39
Outline
Questions and answers
Cytoskeleton
Structure of cytoskeletonMyosin and muscle contraction
Shipunov (MSU) Advanced Cell Biology. Lecture 36 May 1, 2013 2 / 39
Questions and answers
Previous final question: the answer
How do researchers use constantly active Ras protein?
I For determining sequence of proteins in a signal pathway
Shipunov (MSU) Advanced Cell Biology. Lecture 36 May 1, 2013 3 / 39
Questions and answers
Previous final question: the answer
How do researchers use constantly active Ras protein?
I For determining sequence of proteins in a signal pathway
Shipunov (MSU) Advanced Cell Biology. Lecture 36 May 1, 2013 3 / 39
Structure of cytoskeleton
Cytoskeleton
I Filament-like: intermediary filaments and actin filamentsI MicrotubulesI All are polymers of proteins
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Structure of cytoskeleton
Intermediate filaments
I Keratin in epithelial cellsI Vimentin in connective-tissue cellsI NeurofilamentsI Nuclear laminsI Strengthening cell
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Structure of cytoskeleton
Strengthening of cell layer
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Structure of cytoskeleton
Microtubules
I Grow from centrosomeI Form flagella or ciliaI Form mitotic spindleI Organize interior of cellI Drive intracellular transport
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Structure of cytoskeleton
Microtubules
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Structure of cytoskeleton
Growth and shrinking of microtubules
I Microtubule is made of 13 tubulin microfilaments, each containpairs of β-tubulin (– end) and α-tubulin (+ end)
I Tubulin dimers bind GTP and form a growing GTP cap ofmicrotubule; if GTP cap is lost, microtubules start to shrink
I Capturing the plus end will stabilize microtubule
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Structure of cytoskeleton
Growing and shrinking of microtubules
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Structure of cytoskeleton
Microtubule-specific drugs
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Structure of cytoskeleton
Centrosomes
I γ-tubulin rings: starting places of microtubule growthI Two perpendicular centrioles (they are similar to basal bodies of
flagella)I Cetrosome has a fisherman-like behavior: microtubules are
constantly growing out of it, then degrading, but some arestabilizing
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Structure of cytoskeleton
Motor proteins
I Kinesins and dyneins are dimers that hydrolyze ATP and moveI They can move molecules and even whole organelles
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Structure of cytoskeleton
Kinesin and dynein
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Structure of cytoskeleton
Kinesin movie
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Structure of cytoskeleton
Organelle movement movie
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Structure of cytoskeleton
Flagella/cilia
I Hairlike structures growing from cytoplasmic basal bodiesI Contain 9×2 + 2 microtubules connected by dynein armsI They are natural oars
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Structure of cytoskeleton
9 × 2 + 2 structure of flagella
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Structure of cytoskeleton
Flagella bending
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Structure of cytoskeleton
Actin filaments
I Fast-growing and unstable, they need to contact with multipleprotein types (e.g., capping proteins stabilize actin ends)
I Actin filaments are polar, but thinner and shorter thanmicrotubules, ATP-binding
I Allow cell to change its form
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Structure of cytoskeleton
Growing and shrinking of actin filaments
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Structure of cytoskeleton
Actin binding proteins
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Structure of cytoskeleton
Cell crawling
I Web of growing actin filament will push the leading edge ofpseudopodium forward
I ARPs are starting poins of new filaments, formins promotefilament growing
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Structure of cytoskeleton
Formation of pseudopodium
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Structure of cytoskeleton
Crawling actin movie
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Structure of cytoskeleton Myosin and muscle contraction
Structure of cytoskeletonMyosin and muscle contraction
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Structure of cytoskeleton Myosin and muscle contraction
Myosin
I Two subfamilies of ATP-binding motor proteinsI Myosin-I have one head and one tail, myosin-II (in muscle cells)
are two-headedI GTP-binding Rho proteins activate actin polymerization and
subsequently the movement of cell
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Structure of cytoskeleton Myosin and muscle contraction
Myosin-I
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Structure of cytoskeleton Myosin and muscle contraction
Myosin-II
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Structure of cytoskeleton Myosin and muscle contraction
Myosin movie
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Structure of cytoskeleton Myosin and muscle contraction
Actin-myosin muscle contraction
I Myofibrils consist of sarcomeres (2 nm long), sarcomeres consistof actin and myosin II
I Myosin filaments start to pull actin filaments; this results in musclecontraction
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Structure of cytoskeleton Myosin and muscle contraction
Muscle cells
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Structure of cytoskeleton Myosin and muscle contraction
Sarcomeres
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Structure of cytoskeleton Myosin and muscle contraction
Muscle contraction
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Structure of cytoskeleton Myosin and muscle contraction
Role of Ca2+
I Calcium signals are released in contacts between neural andmuscle cells, and are going into muscle cells via T-tubules
I In a places where T-tubules are close enough to ER(sarcoplasmatic reticulum), action potential “jumps” from T-tubulemembrane to ER membrane and activate the calcium rush fromER into cytosol
I This is a contraction signal: calcium ions will interact withtroponin-tropomyosin system which unblocks the myosin II
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Structure of cytoskeleton Myosin and muscle contraction
Muscle contraction movie
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Structure of cytoskeleton Myosin and muscle contraction
Final question (2 points)
What will happen with cell if microtubuleswill not be able to grow?
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Structure of cytoskeleton Myosin and muscle contraction
Final question (2 points)
What will happen with cell if microtubuleswill not be able to grow?
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Structure of cytoskeleton Myosin and muscle contraction
Summary
I Intermediary filaments are polymers of ropelike polymers offibrous proteins
I Microtubules are labile hollow tubes of tubulin, kinesins anddyneins move along microtubules
I Actin filaments are helical polymers of actin; myosins move alongactin
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Structure of cytoskeleton Myosin and muscle contraction
For Further Reading
A. Shipunov.Advanced Cell Biology [Electronic resource].2011—onwards.Mode of access:http://ashipunov.info/shipunov/school/biol_250
B. Alberts et al.Essential Cell Biology. 3rd edition.Garland Science, 2009.Chapter 16.
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