module 5 - 13.10 the sliding filament model Flashcards
What is me sliding filament theory?
When skeletal muscles contract longitudinally by the actin filaments and myosin filaments in each myofibril slide past each other
What is the result of a sarcomere contracting?
- Lighter band becomes narrower
- The z-lines move closer
- The h-zone becomes narrower
What is me darker area or an election micrograph of related and connected sarcomere?
The darker area is myosin and actin overlapping
What is the structure of myosin molecules?
- Have flexible and globular head and long tail
- made of many myosin molecules arranged in a bundle
- heads of myosin molecules have binding site for ATP and separate binding site for actin (actin-myosin birding site)
- myosin heads prodded along length of me myosin filament.
What is the structure or actin filaments and actin molecules?
- Made of 2 actin molecules twisted around each other forming a loose double helix
- actin-myosin binding sites are blocked by tropomyosin
- tropomyosin is held in place by a globular protein called troponin
What is a neuromuscular junction?
- The synapses between a motor neurone and muscle fibres
- found in motor end plates
- many neuromuscular junctions along a muscle to ensure au muscle fibres contract simultaneously
- a single motor neurone will connect all muscle fibres in a motor unit
When is a strong muscle contraction achieved?
When motor units are stimulated
What happens when an action potential arrives at the neuromuscular junctions?
It causes voltage gated calcium ion channel proteins to open
How do calcium ions diffuse through the synaptic knob? And what does mis cause?
- Through facilitated diffusion
- causes synaptic vesicles to fuse with presynaptic membrane by exocytosis
Where do acetylcholine molecules diffuse across?
Synaptic cleft
Where are the receptor proteins that acetylcholine birds to? And what does this cause?
- The sarcoma
- causes sodium ion channels in the receptor protein to open and sodium ions diffuse into the sarcoplasm
- depolarisation of the sarcolemma occurs
Where does the depolarisation of the sacolemma travel?
Travels deep into the muscle fibre by travelling along t-tubules
What does depolarisation of t-tubules cause?
Causes sarcoplasmic reticulum to release calcium ions that diffuse down their concentration gradient
What does calcium binding to troponin cause?
Causes conformational change which stops tropomyosin from blocking myosin binding sites on actin filaments.
Where is ADP bound to?
Myosin head
Where does the myosin head bind to after ADP is bound to the head?
Myosin head birds to actin filaments at myosin-actin binding site, forming an actin-myosin cross bridge
What happens after an actin-myosin cross-bridge is formed?
- Myosin head changes angle and pulls actin filament along
- ADP is released from myosin head.
What does ATP birding to ATP binding site on myosin head cause?
Causes myosin head to detach from myosin-actin binding site
What are the ATPase enzymes activated by, and what do they do to the ATP on the myosin head?
- Activated by increased concentration of calcium ions in sarcoplasm
- the ATPase enzymes hydrolyse the ATP on myosin head to ADP
What does the hydrolysis of ATP on myosin head to ADP cause?
Causes myosin head to change angle again, back to its original position
What is the energy supply in aerobic respiration during a muscular contraction?
- produces most ATP in muscle contraction
- requires oxygen
- happens in mitochondria
- used for low intensity and long term cycles of muscle contraction & relaxation
What is the energy supply in anaerobic respiration during a muscular contraction?
- Fast way of producing ATP
- used at stat of muscle that are doing rapid cycles of contraction & relaxation
- doesn’t require oxygen
- produces lactic acid and is a short term solution
What is the energy supply in Creatine phosphate during a muscular contraction?
- Very short term supply of phosphate
- used for bursts of very vigorous exercise
What is creatine phosphate?
Store of phosphate groups that can be quickly used to produce ATP from ADP
Why do muscles need ATP?
- ATP is required for movement of globular myosin head and the active transport
- also required for accumulation or calcium ions from sacoplasm into sarcoplasmic reticulum
