18. TRUE or FALSE. If False, write the correct statement A) During skeletal-musc

Question

18. TRUE or FALSE. If False, write the correct statement A) During skeletal-muscle contraction, the distance between the Z lines of a sarcomere decreases because of shortening of the filaments. B) Actin is an ATPase enzyme. C) The phenomenon of rigor mortis demonstrates that myosin can remain bound to actin in the absence of additional ATP, but the bond cannot then be broken (at least for several hours). 19. Calculate the mean arterial pressure (MAP) for each example listed. A. a person with a systolic blood pressure of 120 mmHg and pulse pressure of 35 mmHg B. a person with a blood pressure of 130/95 mm Hg

Explanation / Answer

18A. The Z line is the dark line within I band formed by thin filaments composed of actin. The two Z lines at the ends of sarcomeres delimit the unit of muscle contraction. The sarcomeres shorten during muscle contraction. Hence, the distance between the lines also decreases. Muscle contraction occurs due to cross bridge formation between actin and myosin (thick) filaments. Actin is pulled between the spaces of myosin filaments. Hence the I band will decrease, but the A band doesn’t change. There is only overlap between filaments. There is no shortening of filaments.

Option is False.

True statement: During skeletal muscle contraction, the distance between the Z line decreases because of overlap between the thick and thin filaments that decreases the I and H bands.

B. Actin is an ATPase enzyme as it can cleave ATP to ADP and Pi. When monomeric G actin is converted to filamentous F actin, the ATP bound to G actin is dephosphorylated. F actin has ATPase activity, which is minimal in G actin. Formation of F actin involves assembly and disassembly known as threadmilling. Actin units are added at plus end and dissociate at the minus end. When an ATP bound actin binds, ATP is hydrolyzed to ADP and Pi. Loss of Pi results in formation of ADP-actin state. ADP –actin units are depolymerized at minus end and recycled to ATP-actin for polymerization at the plus end.

Right option is True.

C. Rigor mortis is the stiffening of the body after death. It is caused by cessation of heartbeat and cessation of breathing. Muscle cells build up electrical potential in resting state due to pumping of calcium ions. These calcium are pumped into the sarcoplasmic reticulum and triggers cross bridging between actin and myosin due to release of binding sites on actin. The cross bridge formation is reversed when ADP is replaced by ATP. After death, breathing stops. Hence, muscle cells cannot produce ATP due to lack of aerobic respiration. So muscle cells will become short of ATP. Thus, actin and myosin cannot be released from their contracted state. Further, calcium cannot be pumped back into muscle cells. All muscle cells remain in a tense contracted state in rigor mortis. This state remains for several hours after death.

Right option is true.

19. Pulse pressure (PP)= Systolic (SBP) and Diastolic blood pressure (DBP) difference.

PP= SBP-DBP

DBP=SBP-PP= 120-35= 85 mmHg

In order to calculate mean arterial pressure, double the diastolic blood pressure (DBP) and add the sum to the systolic blood pressure (SBP).

MAP= SBP +2(DBP)/3= 120+2*85/3= 99.67= 100 mmHg

B. In order to calculate mean arterial pressure, double the diastolic blood pressure (DBP) and add the sum to the systolic blood pressure (SBP).

SBP= 130mm Hg, DBP= 95 mmHg

MAP=SBP +2(DBP)/3= 130 +2*95/3= 106.67= 107 mmHg

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