week 4 - cytoskeleton Flashcards
why does a vertebrate need a skeleton
- Structure
- Protection
- Localisation
- Movement
what does the cytoskeleton provide?
- Structure
- Protection
- Localisation
- Movement
- Transport
- communicaton
the cytoskeleton is a…
dynamic structure inside the cell
the cytoskeleton allows cells to…
move
the cytoskeleton mediates…
intracellular transport
(membrane bound vesicles)
the cytoskeleton facilitates…
cell division
cytoskeleton components
- actin filaments
- microtubules
- intermediate filaments (IF)
cytoskeleton components
- actin filaments
Cell movement, provides force
- ~7nm
- Also known as microfilaments
- Two strand polymers of actin protein
cytoskeleton components
- microtubules
Cell organization, cell movement, transport network
- ~25nm
- Long tubes made of tubulin proteins
cytoskeleton components
- intermediate filaments
Strength, protection
- ~8-12nm
- Thick rope-like fibres made of
heterogenous fibrous proteins
what does the cytoskeleton enable
cells to have complex structures
cells to move
cells to be protected from damage
to form an organized function whole cell
ACTIN CYTOSKELETON
what does actin allow?
cells to move
how:
disassembly of filaments and rapid diffusion of subunits
reassembly of filaments at a new site
(interaction with other proteins control structure and polymerisation and depolymerisation)
this pushes the membrane in the direction it wants to go
so cell needs to disassemble and assemble actin very quickly
ACTIN CYTOSKELETON
actin monomer
G-actin
globular
bound to ATP
ACTIN CYTOSKELETON
actin polymer
F-actin
minus end - pointed - shrink
plus end - barbed - growth
ACTIN CYTOSKELETON
is actin abundant?
yes
one of the most abundant proteins in our body
ACTIN CYTOSKELETON
staggering
- Going into each other
- Creates a helical structure
When in ADP form less stable
When bound to ADP interaction between plus and minus ends are weakened, so they fall off
But new ones are added
* Can regulate this
MICROTUBULE CYTOSKELETON
microtubules are made of?
alpha-beta-tubulin dimers
MICROTUBULE CYTOSKELETON
microtubule structure
tubulin heterodimer –> alpha and beta together as building block
(instead of a monomer)
form hollow tubes
Built into a protofilament (single strand of tubulin heterodimers)
These protofilaments are then organised into a microtubule (so lots of protofliaments next to each other kinda making a sheet)
MICROTUBULE CYTOSKELETON
Tubulin binds…
GTP
- Both alpha and beta bind to GTP
- But only the beta subunit can hydrolyse GTP to GDP
MICROTUBULE CYTOSKELETON
role of GTP
GTP hydrolysis regulates stability of MTs
- GTP –> GDP
Only the beta subunit can hydrolyse GTP to GDP
(very similar to the actin strand)
Conversion of GTP to GDP the microtubules become less stable
Protofilaments become more flexible and the microtubules falls apart
* This is known as shrinking
Ways to stabilise this
GTP gap
- Prevent GTP from being hydrolysed
- This stabilises the whole microtubule
MICROTUBULE CYTOSKELETON
intracellular transport
- Motor proteins use the microtubule network to move vesicles and organelles
Different motor proteins travel in different directions by recognising the polarity of microtubules
Plus end is the growing end of the microtubule
Microtubules are the pathways for vesicles
Motor proteins move vesicles
MICROTUBULE CYTOSKELETON
SUMMARY
structure
- Microtubules are hollow tubes made up of protofilaments that are formed from a-b tubulin dimers, which are asymmetrical proteins containing GTP
MICROTUBULE CYTOSKELETON
SUMMARY
role of GTP
- In b-tubulin within a microtubule, GTP is hydrolysed over time causing the potofilaments to bend and separate, destabilizing the microtubule
MICROTUBULE CYTOSKELETON
SUMMARY
dynamic nature enables?
- This polar and dynamic nature of microtubules enables cells to organize their contents in time and space via different motor proteins that track in specific direction along microtubules
INTERMEDIATE FILAMENTS
provide…
strength and flexibility
INTERMEDIATE FILAMENTS
dynamic?
much less dynamic
INTERMEDIATE FILAMENTS
can form specialist structures?
yes
e.g.
Nuclear envelope (lamins)
Keratins
- Hair
- Skin
INTERMEDIATE FILAMENTS
assembly and disassembly speed?
not as rapid as actin and microtubules
INTERMEDIATE FILAMENTS
mutation?
Some inherited skin conditions are caused by mutations in intermediate filament genes
e.g. epidermolysis bullosa – mutations in keratin genes
INTERMEDIATE FILAMENTS
structure
- Head and tail domain with long helical domain
- Form dimers which associate with one another in antiparallel fashion
Start with a monomer
The monomer assembles into a dimer and coil together
These dimers associate with each other and go anti parallel
End up with a structure that is really good at resisting force
cell division coordinated by…
the cytoskeleton
e.g. animal mitosis
nuclear Lamins (Ifs) break down
Microtubules separate chromatids (organisation and transport
Cytokinesis: actin drives cell division (movement of membrane)
Other proteins help (e.g. motor proteins
do bacteria have a cytoskeleton?
yes
FtsZ – microtubule-like structure
MreB – actin-like structure
Crescentin and others related proteins – intermediate filament-like structure
CYTOSKELETON SUMMARY
Actin and microtubules have the same structure in…
all eukaryotes
CYTOSKELETON SUMMARY
Actin and microtubules perform…
similar functions in all eukaryotes
CYTOSKELETON SUMMARY
do some eukaryotic groups lack filament fibres?
yes
e.g. yeast
CYTOSKELETON SUMMARY
prokaryotes have a cytoskeleton made of…
proteins structurally related to those in eukaryotes
