Advanced Cell Biology. Lecture...

Advanced Cell Biology. Lecture 38

Advanced Cell Biology. Lecture 38

Alexey Shipunov

Minot State University

April 30, 2012

Advanced Cell Biology. Lecture 38

Outline

Questions and answers

Cytoskeleton

Structure of cytoskeleton

Advanced Cell Biology. Lecture 38

Outline

Questions and answers

Cytoskeleton

Structure of cytoskeleton

Advanced Cell Biology. Lecture 38

Outline

Questions and answers

Cytoskeleton

Structure of cytoskeleton

Advanced Cell Biology. Lecture 38

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

Advanced Cell Biology. Lecture 38

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

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

Cytoskeleton

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

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

Intermediate filaments

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

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

Strengthening of cell layer

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

Microtubules

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

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

Microtubules

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

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

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

Growing and shrinking of microtubules

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

Microtubule-specific drugs

Advanced Cell Biology. Lecture 38

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 someare stabilizing

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

Motor proteins

I Kinesins and dyneins are dimers that hydrolyze ATP andmove

I They can move molecules and even whole organelles

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

Kinesin and dynein

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

Kinesin movie

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

Organelle movement movie

Advanced Cell Biology. Lecture 38

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

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

9 × 2 + 2 structure of flagella

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

Flagella bending

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

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

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

Growing and shrinking of actin filaments

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

Actin binding proteins

Advanced Cell Biology. Lecture 38

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

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

Formation of pseudopodium

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

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

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

Myosin-I

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

Myosin-II

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

Myosin movie

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

Final question (1 point)

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

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

Final question (1 point)

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

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

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

Advanced Cell Biology. Lecture 38

Structure of cytoskeleton

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.