Download Lecture 1

Introduction to MCB380 2008
• Instructor: Juliet Lee
• Email [email protected]
• Class website: http://web.uconn.edu/mcb380/
• Goal: To understand how the cytoskeleton, integrates
and coordinates cell functions
Whole organism
Large
– How do molecular scale
events affect cellular and
tissue level behavior or
function?
Tissue level
– Major examples: Cell
motility, cell division,
signaling, cancer
Cell level
Molecular
Monomers
Small
Filament
1. What is the nature of the cytoskeleton at the molecular level?
The cytoskeleton is a dynamic structure
• Cytoskeletal filaments can grow
and shrink (or both) as subunits
are assembled or disassembled,
respectively.
• The cytoskeleton can rapidly
reorganize itself in response to its
environment by means of different
signaling mechanisms.
• The structure and dynamics of the
cytoskeleton is intimately linked
to its function.
2. How does the cytoskeleton function in a whole cell?
Cell movement
Protrusion at front
Protrusive force
Adhesion formation
Adhesive force
Forward shift of cell body
Contractile force
Contractile force
De-adhesion
Retraction at rear
Cell division
• 1. The role of microtubules and
motors in generating the forces
necessary for:
• Spindle formation in prophase
• Chromosome alignment –
metaphase
• Separation of duplicated
chromosomes – anaphase
• Separation of daughter nuclei –
telophase
• Separation of daughter cells cytokinesis
How is the cytoskeleton involved in the functioning of
tissues or the whole organism ?
Signaling: Regulation of mitosis and cell motility
Loss of growth control
Increased motility
Cancer
• Course structure:
–
–
–
–
–
Lecture period ~45 min.
Workgroup problem or
Presentation of a research paper
Exams, part I (in class) part II (take home)
Group problems/papers = 30% , exams = 70% of final grade
• Lectures (PowerPoint)/ papers will be posted on the
MCB380 website or HuskyCT (if more space is needed)
Overview of the actin cytoskeleton
• Where is it?
– Methods of visualization,
electron microscopy and
fluorescence microscopy
• What is it ?
– Molecular composition
• How is it assembled?
– dynamics
• What are its functions ?
– Structure,
– Many others…
How was the cytoskeleton discovered?
• The cytoskeleton was first identified
by electron microscopy (EM).
• 3 different filament systems were
identified on the basis of their
diameter and surface texture.
• A major characteristic of the
cytoskeleton is its insolubility in non
ionic detergents - allowing
observation and biochemical
characterization.
• A freeze-dried metal replica of a
fibroblast, viewed by EM provides a
very high resolution image of
cytoskeletal elements.
Why was (EM) important for the discovery of the
cytoskeleton ?
Resolving power of light microscope
compared with EM
200 nm
.
The maximum resolution of a
light microscope is ~ 200 nm
The resolving power of the
electron microscope is much
higher - because the
wavelength of electrons is
much smaller than that of
light ~ 1.5nm.
Immunofluorescence shows the location of
different cytoskeletal filaments
Actin filaments
•
Intermediate filaments
Microtubules
Cytoskeletal proteins can be labeled with fluorescently tagged
(conjugated) antibodies, which bind with high affinity and specificity.
(Usually in fixed cells)
– Can be done in living cells to investigate function of a specific filament system
• Cytoskeletal proteins can be labeled with fluorescent molecules and
injected into living cells - to see where they become localized
The cytoskeleton is a filamentous polymer
meshwork
• The cytoskeleton consists of three different types of filament systems
Actin, diameter 7-9 nm
Sub unit = actin monomer
• Each filament is a polymer built from small
protein subunits, which are held together
non covalently.
Microtubules, 25 nm
Sub unit = tubulin heterodimer
• Note that: proteins are also polymers
composed of amino acid monomers, BUT
they are bound together covalently.
Intermediate 10 nm
Sub unit = α helical subunits
Thermal stability of a single filament is increased
by “side” binding with others
•
A single filament is not strong
enough to avoid breakage from
ambient thermal energy - because
each monomer is linked NONcovalently
•
Lateral binding with other
“protofilaments” increases the
strength of the entire filament
•
Single monomers can be added or
lost from ends more easily than
the filament can be broken in the
middle
The cytoskeleton is multifunctional.
The cytoskeleton can form permanent and transient structures
Microvilli are permanent actin containing
structures
Ruffles on the surface of a moving cell are
transient actin containing structures
EM view of the cytoskeleton in a
gut epithelial cell
Permanent microtubule-containing
structures
• Didinium: A carnivorous ciliate
• One protozoan eating another
• ( Fig. 1-28, Alberts 3rd Ed.)
The mitotic spindle is a
transient microtubulecontaining structure