Advanced Cell Biology. Lecture 38ashipunov.info/shipunov/school/biol_250/2011_2012/lec_250-38.pdf · Advanced Cell Biology. Lecture 38 Structure of cytoskeleton Actin ﬁlaments I

Advanced Cell Biology. Lecture 38


Alexey Shipunov

Minot State University

April 30, 2012


Outline

Questions and answers

Cytoskeleton

Structure of cytoskeleton


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



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, eachcontain pairs 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 someare stabilizing



Motor proteins

I Kinesins and dyneins are dimers that hydrolyze ATP andmove

I 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 withmultiple protein types (e.g., capping proteins stabilize actinends)

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



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



Final question (1 point)

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



Final question (1 point)

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



Summary

I Intermediary filaments are polymers of ropelike polymersof fibrous proteins

I Microtubules are labile hollow tubes of tubulin, kinesinsand dyneins move along microtubules

I Actin filaments are helical polymers of actin; myosins movealong actin



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 17.

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

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

Documents

Advanced Cell Biology. Lecture 38ashipunov.info/shipunov/school/biol_250/2011_2012/lec_250-38.pdf · Advanced Cell Biology. Lecture 38 Structure of cytoskeleton Actin ﬁlaments I