sliding filament theory

Question 1

what are the thick and thin filaments

Answer 1

thin filaments= made of actin= light band

thick filament= made of myosin= dark band

Question 2

describe the thin filament actin

Answer 2

-globular protein
-form two long chains that twist forming helical strands
-thin threads of tropomyosin are wound around strands
-troponin attached to tropomyosin
-troponin-tropomyosin complex control muscle contraction

Question 3

describe the thick filaments myosin

Answer 3

-shaped like a golf club with 2 head
-heads stick out from cross bridges
-many of these myosin molecules stick together to form a thick filament

Question 4

what is the I and A band

Answer 4

I band= thin actin filament, light
A band= dark band, myosin and actin

Question 5

what is the Z line

Answer 5

sarcomere boundary= where 2 sarcomeres meet

Question 6

what is the H zone

Answer 6

middle of the dark band where only myosin is

Question 7

what is the M line

Answer 7

point from where the myosin fibres are joining, in the middle

Question 8

what happens to the I band, Z lines, H zone and A band during muscle contraction when sarcomere get shorter

Answer 8

I band= shortens
Z lines= closer together
H zone= gets smaller/ disappears
A band= stays the same, fixed

Question 9

explain the control of sliding filament

Answer 9

1.arrival of an action potential causes the release pf Ca2+ ions from the sarcoplasmic reticulum into sarcoplasm due to depolarisation down t tubule
2. Ca2+ bind to troponin altering the shape and causing tropomyosin to move and expose the myosin binding site on actin
3. the myosin head binds actin forming an actin-myosin cross-bridge
4.the Ca2+ ions also activate ATPase to hydrolyse ATP to ADP and Pi= releases energy to tilt the myosin head and ‘power stroke’ actin forwards (ratchet action)
5. after power stroke new ATP molecule attaches to the myosin head, ATP binding releases the myosin from actin
6. hydrolysis of ATP returns the myosin head to the ‘cocked’ position ready to bind the next binding site on actin
7. as the actin filament is moved along the I bands shorten, the Z lines move closer together and the muscle contracts

Question 10

what are the 3 ways energy is supplied for muscle contraction

Answer 10

1. aerobic respiration= oxidative phosphorylation= ATP

2.anaerobic respiration= little ATP produced but muscles will become fatigued by build up of lactate/ lactic acid

3. creatine phosphate stored in muscle sarcoplasm acts as a reserve phosphate source to recombine with ADP to form ATP, involving phosphotransferase enzyme, replenished using phosphate from ATP when muscle is at rest