Advanced Cell Biology. Lecture 36 - A. Shipunovashipunov.info/shipunov/school/biol_250/lec_250_37.pdf · · 2013-05-03Shipunov (MSU)Advanced Cell Biology. Lecture 36May 1, 2013

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


Outline


Cytoskeleton



Outline


Cytoskeleton




Previous final question: the answer

How do researchers use constantly active Ras protein?

I For determining sequence of proteins in a signal pathway



Previous final question: the answer

How do researchers use constantly active Ras protein?

I For determining sequence of proteins in a signal pathway


Structure of cytoskeleton

Cytoskeleton

I Filament-like: intermediary filaments and actin filamentsI MicrotubulesI All are polymers of proteins



Intermediate filaments

I Keratin in epithelial cellsI Vimentin in connective-tissue cellsI NeurofilamentsI Nuclear laminsI Strengthening cell



Strengthening of cell layer



Microtubules

I Grow from centrosomeI Form flagella or ciliaI Form mitotic spindleI Organize interior of cellI Drive intracellular transport



Microtubules



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



Growing and shrinking of microtubules



Microtubule-specific drugs



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



Motor proteins

I Kinesins and dyneins are dimers that hydrolyze ATP and moveI They can move molecules and even whole organelles



Kinesin and dynein



Kinesin movie


mov/17.7-kinesin.wmv


Organelle movement movie


mov/17.6-organelle_movement.wmv


Flagella/cilia

I Hairlike structures growing from cytoplasmic basal bodiesI Contain 9×2 + 2 microtubules connected by dynein armsI They are natural oars



9 × 2 + 2 structure of flagella



Flagella bending



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



Growing and shrinking of actin filaments



Actin binding proteins



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



Formation of pseudopodium



Crawling actin movie


mov/17.9-crawling_actin.wmv

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



Myosin-I



Myosin-II



Myosin movie


mov/17.10-myosin.wmv


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



Muscle cells



Sarcomeres



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



Muscle contraction movie


mov/17.8-muscle_contraction.wmv


Final question (2 points)

What will happen with cell if microtubuleswill not be able to grow?



Final question (2 points)

What will happen with cell if microtubuleswill not be able to grow?



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



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.


http://ashipunov.info/shipunov/school/biol_250

Documents

Advanced Cell Biology. Lecture 36 - A. Shipunovashipunov.info/shipunov/school/biol_250/lec_250_37.pdf · · 2013-05-03Shipunov (MSU)Advanced Cell Biology. Lecture 36May 1, 2013