9-11 Flashcards
What are Dynein and Kinesin?
The proteins that move along the microtubules
- dynein is a dimer and moves towards the negative end of the microtubules—> towards the centrosome (nucleus) - in 9+2 stucture moves along neighbouring doublet of microtubule dragging the other to cause bending
- Kinesin moves away from centrosome
Structure of microtubule
25nm across and made of α and β tubulin
Examples of movement mechanisms
x 7
- Outer hair cell motor
- Invertebrate photoreceptors
- ATP synthase
- RNA polymerase
- Flagella/cilia
- Actin/tubulin axonal transport
- Myosin/actin
Difference between parallel and series muscle unit structure
PARALLEL - each contract and force but then this is additive for each unit pulling so big force if parallel
SERIES - Adding contractile elements in series amplifies degree of movement as each segment shortens
Structure of muscle -
Myofibrils are bundles of protein filaments and then a group of myofibrils makes a muscle fibre (one single muscle cell) and then a bundle of fibres is a fascicle (sheathed in connective tissue) and then the whole skeletal muscle is multiple fascicles
What are the dark and light bands of striated (skeletal) muscle
Dark = A band = ANISOTROPIC
Light = I band = ISOTROPIC
Structure of a sarcomere
- single contractile unit of a muscle cell
- Z to Z line is 2 μm
- middle is m line which is the middle of the H zone, in the middle of the A band
- next to A band is I band and the Z line is in the middle of this
Structure of myosin
6 polypeptide chains
- Main is two supercoiled α helices so dimer with 2 heads and then three of these dimers per section
- the heads have the stiff neck with flexible hinge (each head has a ATP binding site)
- cocked state is the high energy state
- heads at 120 degrees and repeat every 43 nm
Structure of actin - F actin
G actin dimers into filaments
- polarised with + and - ends
- Tropomodulin at negative end
- g dimers to + at 5-10 x faster than loss at -
- 40nm sections and differ from 43 of heads of myosin - maybe purposeful desynchronisation (dont actually know why)
Other proteins of the thin actin filament
Tmod = tropomodulin at negative end
- Tropomyosin - cover myosin binding sites - is a dimer
- Troponin holds tropomyosin in place as its association is weak - moves it out of the way
- nebulin but do not know of function
Troponin structure
2 subunits
TnI inhibitory element and binds to actin
TnT binds to tropomyosin
TnC binds to Ca2+ and this causes the troponin to make a lateral shift of tropomyosin
What is titin?
largest protein in genome
- like a spring and maybe to protect against overstretching of sarcomere
- half life of roughly 3 days so continuously repaired
Structure of sarcomere diagram (so can draw)
diagram
- twice as many thin filaments as thick
What visually changes to sarcomere during contraction?
I band shrinks but the A band is constant size
- H zone reduces as well
What is the cross-bridge cycle?
x 6
- ATP binds to myosin heads and so dissociates from actin
- Break to ADP and Pi which causes head to cock into high energy position
- head attaches to myosin site on actin and releases Pi (strengthens binding and activates power stroke)
- Power stroke
- ADP dissociates from myosin head
- ATP attaches to head to cause dissociation from actin
What causes the start of contraction?
Release of Ca2+ from sarcoplasmic reticulum
- binds to TnC which moves tropomyosin
- force production rises rapidly for only a small rise in Ca2+
How do muscle fibres ensure Ca2+ gets to all sarcomeres?
invaginating membrane as otherwise diffusion would take too long
- so near synchronous activation
- done via t-tubules
Structure and purpose of t -tubules
90nm across and penetrate into fibre
- cause the shallow slope after depolarisation
- small and few ions
has Cl- ions to aid in repolarisation
- is K+ accumulates during intense activity can cause problems-volume
What is myotonia congenita
inherited condition which skeletal muscle goes into contracture
- chloride channel mutation of t-tubules
Where is Ca2+ stored?
sarcoplasmic reticulum
- has a system where wraps around tubule system
- in SR is calsequestrin which is a calcium buffer
- calcium channels are ryanodine receptors
Triadic regions of t tubules
two SR terminal cisternae either side of t-tubule in triad form
- t tubule dihydropyridine receptors are voltage sensors on surface of t tubule and line up with ryanodine receptors on both SR membranes so quick release of Ca2+ when membrane depolarisation
What delays force production in muscles?
Ca2+ build in concentration and then the binding of 4 Ca2+ to troponin as require all 4 to be full activation
What is SERCA
the pump that transports Ca2+ back into SR to stop muscle contraction
- activated when ca2+ released
What does temporal summation of calcium concentration
tetanus from multiple action potentials and calcium cannot be taken up quickly enough between AP
Describe a motor unit
the nerve and innervated muscle fibres
- and each motor unit can be low or high force by containing a smaller number of muscle fibres
What is asynchronous activation?
Different motor units recruited one after another usually in order of size when force increases
- controlled by central pattern generations
What are muscle spindles?
Muscle spindles are proprioceptors that consist of intrafusal muscle fibers enclosed in a sheath
- they provide information on muscle length and positioning
Cardiac muscle
striated with no tendons as pull on next cell (the intercalated disks)
- contract around the chambers and the cells have gap junctions between then to allow for conduction between cells
- part between two intercalated disks is a myocyte
Smooth muscle
striation is less obvious and wrapped around vessels and organs
- efficient and long lasting contraction
- dont have an end plate, have gap junctions and are thin and spindle like cells
Insect asynchronous muscle
contraction of antagonist muscle activates contraction in the muscle which then causes antagonist to contract
atrophy vs hypertrophy
at = disuse hyper = with use
What affects the speed of muscle twitches?
Temperature and the types of muscle fibre
4 types of muscle fuel (providing atp)
- ATP store
- Phosphocreatine
- Lactic acid system
- Aerobic respiration
GRAPH (pg 10 lecture14)
How does phosphocreatine work?
can phosphorylate ADP to make more ATP
What is VO2 max?
the max oxygen taken in per kg per minute
What is myoglobin?
the oxygen binding protein in muscles similar to haemoglobin
- a lot in red muscle and not as much in white muscle
Properties of slow oxidative fibres
- type 1 of red muscle
x 8 and example
- small diameter
- low force per area
- low Vmax
- low myosin ATPase activity
- High fatigue resistance
- A lot of mitochondria
- high oxidative capacity
- low number of oxidative enzymes
example = postural muscles in humans
Properties of fast oxidative fibres
- type 2 red muscle
x 8 and examples
- Medium diameter
- medium force per unit area
- medium Vmax
- High myosin ATPase activity
- medium fatigue resistance
- a lot of mitochondria
- high oxidative capacity
- medium number of glycolytic enzymes
example is flight muscles in migratory birds
Properties of fast glycolytic fibres
- white muscle
x 8 and examples
- large diameter
- high force per unit area
- high Vmax
- high myosin ATpase activity
- Low fatigue resistance
- Few mitochondria
- low oxidative capacity
- High number of glycolytic enzymes
example is chicken breast
The length-tension relationship for a whole muscle
graph
Using a single fibre length to explain active tension relationship
graph
What is isometric contraction
Tension increase but not movement so not work done
- lifting something that is too heavy
What is isotonic contraction?
when the muscle shortens and there is the same tension throughout the movement
- bicep curl
what is Work?
Work in joules is force x distance
- force is mass x acceleration
How can isometric contraction still cause fatigue?
as no work but as there is tension then ATP is being used and therefore muscle fatigues
What is power (watts)
joules per second = force x velocity
Force velocity relationship
graph
How do muscle shapes help alter mechanics of movement?
2 examples
different types of movement with different force and speed of contraction
- strap muscle like the bicep has lots of series elements and produces large movement with high velocity but low force
- unipennate like intercostal muscle with lots of parallel elements produce small movement with low velocity but high force
