molecular motors Flashcards
larger objects almost do not
diffuse in the cell–> due to the cytoplasm being crowded
molecular motors ar
mechano-enzymes
mechano enzymes
protein complies that utilise ATP to walk along the cytoskeleton e.g. mechanical motors
what do molecular motors do
walk along the cytoskeleton (F-actin and microtubules), carrying cargo such as organelles
which parts of the cytoskeleton do molecular motors work on
F-actin and microtubules
examples of molecular motors
kinesin, dynen, myosin
without ATP
motors cannot attach tightly
once the motor is attached–> tight binding
hydrolysis and a ‘power stroke’ occur and this causes the movement of the motor and also the release of ADP and pi
initially motors attach
weakly, then ATP binds and tight binding occurs
myosin and kinesis go towards..
the PLUS end of microtubules or F-actin
dynein walks to
the MINUS end
kinesin
dances on the microtubules using several protofilaments
dynein
stays on the same protofilament and walks in a straight line
motor recycling
kinesin and dyneon ind tot he same cargo- they can be active in transport or a passive passenger e.g. kinesis can be carried along with a cargo by myosin V molecular moto
myosin II
muscle myosin
Myosin V
membrane trafficing
how can one prove that motors are mechano enzymes
using microscopes and GFP–> fluorescent microtubules ‘slide’ over a layer of glass attached kinesis motors –> motors move latex beads n ceil-free assays
myosin motors are used in
muscle function
40% of your body is
muscle
20% of the muscle is
protein
12-15%
actin
skeletal muscle mainly consists of
myosin and F-actin- striated
the sarcomere is the reason it looks
striated
muscle organisation
sarcomere–> muscle fibril –> muscle cell–> muscle
why bright and dark parts
think and thick filaments only cross over at some points
thick filaments consists of
myosin 2–> with motor protein heads and tail –> motor head will stick out
z line
the two parts that come closer tofether
dark band
decreases in size during contraction as the filaments cross each other
thin filaments consists of
f-actin and associated proteins
in a relaxed muscle there will be no interaction between
myosin heads and actin filament
tropomyosin
wraps around thin filaments and holds troponin complexes in place
how is contraction controlled
1) stimulus for neutron spreads over the plasma membrane
2) depolarisation of men. Calcium released from sarcoplasmic reticulum into cytoplasm
3) bind of calcium to troponin releases the block of the myosin binding site on actin
4) myosin now binds actin and walks towards the Z-disk–> contraction
5) calcium is removed by calcium pumps and myosin releases the actin filament and slides back –> relaxation
cardiac myocytes
form another type of straight muscle
cardiac muscle
is less order but the structural and mechanistic principles are the same –> spontaneous contraction
flagella and most cilia are
motile structures
cilia
-numerus per cell
- function in fluid and particle movement
-back and forth motion
12-230 beats per second
flagellum
- few or one per cell
- cell locomotion
- propella like motion
- 10-40 beats per second
can be distinguished due to
different movement
- cilia–> back and forth
- Flagellum–> propel like motion
what si the core of cilium/flagellum called
axoneme
axoneme
core of flagellum and cilia made from microtubiles
ultrastructure of the standard cilium
9 microtubules, with outer and inner arm dynein
- structure is hollow
- outer: 3 motor heads
- inner- 2 motor heads
cytoplasmic dynein is different to
dynein found in cilium
outer of cilium
3 motor heads
inner of cilium
2 motor heads
centrioles and flagella
form the basal bodies of the flagella
basal bodies
is a protein structure found at the base of a eukaryotic undulipodium (cilium or flagellum).
centrioles structure
made up of a mother centriole and daughter centriole joined by a flexible linker
axonemal dynein is ..
variable in its molecular structure: having 3 heads (alpha, beta, gamma) on outer and 2 heads on inner (alpha and beta)
flagella dynein
connects adjacent microtubules–> sliding movement similar to in the sarcomere
flagella dynein and movement
B-tubulus slides against A-tubulies and this leads to bending activity against the protein bridges between the tubules
most cells form a
non-motile primary cilium
non-motile primary cilium function
Detects signals that govern cell proliferation. senses flow and bending –> triggering various pathways
–> essential for developmental processes
motile cilia vs non-motel cilia
motile cilia: generating flow and cleaning surfaces- has dynein, nexins, spokes and central microtubule pair
non-motile: sensing environmental cues: chemo, mechano, thermosensation e.g. a stimulus results in mem. depolarisation
examples of non-motile cila
rods and cones in the eye retina
- rhodopsin discs are found in the cilium.
- photoreceptors in the human eye are specialised cilium
IFT
intraflagellar transport
intraflagellar transport
supports the formation and function of cilium
- rafts travel along the axoneme
- kinesin and dynein drive the bidirectional transport
kinesin II in cilia
anterograde
dynein in cilia
retrograde
what supports cell migration
actin treadmilling
examples of cell migration
amoeba and human phagocytes
f-actin in a fibroblast
- f-actin concentrates at the leading edge of the cell–> f actin grows via tread milling–> appears as waves
- overtime cell will grow
- leading edge is at the from of the cell directing the end part of the cell which is called the tail
role of cell motility (3)
1) protects against pathogens–> neutrophil chases bacterium
2) cell motility helps with healing wounds–> when skin tears cells actively move in to close the wound
3) organ development–> neurones that extend neurites
treadmilling
as one unit leaves another joins
actin organisation in a fibroblast
stress fibre nearer the centre of the cell has contractile function. Cell cortex- gel like network. Filopodium- extension from the cell which contain tight parallel bundles
these stress fibres in fibroblasts are
contractile like muscle–> form fibres of f actin and myosin II (muscle myosin)
steps during cell migration
1) extension
2) adhesion
3) translocation
4) de-adhesion
name a cytoskeleton dependent process
intracellular membrane trafficking
motors are responsible for
intracellular motility–> not just vesicles, but entire organelle e.g. they transport organelles along microtubules
cool motor example
motors change the colour of the fish skin. the dispersal and conc depends on kinesis, dynein that move along the microtubules
- change in black part of fish is due to a change in mem. trafficking e.g. organelles containing melanin are moved to the centre and then the vesicles get dispersed outwards and make the whole cell look darker
what shape the ER and make them mobile
motors
- the ER will also form without pro
- ER grows paallel on the microtubules- another way to be distributed
the ER will also form without proteins so..
not just due to molecular motors
axonal transport keeps
the cell alive and connects the synapses in the cell body–> in neurons
why is axonal transport important in neurones
have to cope with long distance
- the synapse must communicate with the cell body in order to keep the neurone alive
- the distance to overcome may be meters! (Giraffes)
axonal transport
is a cellular process responsible for movement of mitochondria, lipids, synaptic vesicles, proteins, and other cell parts (i.e. organelles) to and from a neuron’s cell body, through the cytoplasm of its axon (the axoplasm).
dynein and kinesin in a neurone
In axons there is a MINUS end (cell body) and a PLUS end (synapse)
- ->synapse to cell body is done by dynein proteins (retrograde signaling)
- ->cell body to synapse is done by kinesin (antergrade)
in neutrons growing and shrinking in the axon is suppressed
1) microtubule-binding proteins stabilise dendrite
If microtubules depolarise (shrinking) the transport stops- leading to
the cells death
