Lecture 11 - Excitation-Contraction Coupling and the Cross-Bridge Cycle

Question 1

what is the sliding filament?

Answer 1

regards the fact that individual thick or thin filaments do not get shorter they just slide over each other so the overall skeletal muscle gets shorter and this applies for excitation-contraction coupling

Question 2

what is heat production in muscles?

Answer 2

a by-product of muscle activity

Question 3

what produces heat in muscles?

Answer 3

• substrate catabolism of ATP –> ADP + Pi produces heat

- hydrolysis of ATP –> ADP + Pi also converts NADH to O2 in the mitochondria producing heat

Question 4

why are the muscles required to produce heat?

Answer 4

to maintain body temperature

Question 5

what is hyperthermia?

Answer 5

when the body temperature is raised (exceeds) normal body temperature

Question 6

what is malignant hyperthermia?

Answer 6

a pathological condition that can result from skeletal muscle over-producing heat that is a life-threatening autosomal dominant disorder

Question 7

what causes malignant hyperthermia?

Answer 7

occurs due to mutations in the ryanodine receptor (RYR) or the dihydropyridine receptor (DHPR)

Question 8

what happen when malignant hyperthermia is trigged by violatile anaesthetics?

Answer 8

if triggered by halothane it causes muscle rigidity, a hyper-metabolic state and increased CO2 production resulting in the body temp passing 41’C very rapidly

Question 9

what is the function of anaesthetics?

Answer 9

increase the function of Ca2+ release from the SR

Question 10

what does the myosin complex contain?

Answer 10

contains the myosin head that can either be in a flexed or energised state depending on if ATP is hydrolysed
-energised state occurs when ATP is hydrolysed to ADP + Pi and this is done by ATPase activation protein

Question 11

what is the actin helix intertwined with?

Answer 11

intertwined with the proteins tropomyosin and troponin

Question 12

what is the function of tropomyosin?

Answer 12

tropomyosin normally blocks the myosin binding sites on actin but it is hidden by tropomyosin

Question 13

what is troponin?

Answer 13

a molecule that is a part of tropomyosin that has a Ca2+ binding site on it

Question 14

what is the function of troponin?

Answer 14

has a Ca2+ sensor that causes a conformational change in tropomyosin to expose the myosin binding sites

Question 15

what is Mg2+ protein important for in the cross bridge cycle?

Answer 15

important for ATP hydrolysis

Question 16

what does Ca2+ initiate?

Answer 16

muscle contraction

Question 17

what is the myosin thick filament composed of?

Answer 17

composed of 2 myosin heads with 2 actin binding sites and 2 ATP binding sites

Question 18

why can actin not bind under resting conditions?

Answer 18

actin cannot bind under resting conditions as tropomyosin is blocking the myosin binding sites

Question 19

what is rigor mortis?

Answer 19

in a dead organism there is no ability to regenerate ATP and if there is no ATP the myosin head can not detach from actin and this results in stiff muscles