Official Guide to the MCAT Exam

Official Guide to the MCAT Exam Questions and Answers (Solved Papers) BB section What is the difference between Type I and Type II muscle fibers? - Correct Answers ✅Understand the difference between Type I and Type II Muscle fibers.Type I (slow-twitch) - mitochondria rich, slow twitch (slow conduction velocity), slow contraction speed, aerobic, long, low power, long duration, fatigue-free.Type II fibers - two types, Type IIA, and Type IIB. Type IIA are intermediate between I and IIB.Type IIB are white, fast contraction speed, fast-twitch (fast conduction velocity), anaerobic, short, easily fatigue, power, ATP from creatine phosphate.

QUESTION 1:

The muscle subtype represented by Culture C is LEAST likely

to be characterized by:

• a fast rate of muscle contraction.
• the ability to engage in oxidative and anaerobic

respiration.

• the presence of medium-sized motor units.
• low densities of mitochondria and capillaries. - Correct

Answers ✅D. got this wrong because i did not understand 1 / 4

Official Guide to the MCAT Exam Questions and Answers (Solved Papers) which culture (A, B or C) related to which muscle type in the table in the passage.Don't be fooled by this answer choice. Even though in the "Activity used for" section it states anaerobic. The type IIA muscle fiber still exhibits "high oxidative capacity" which means it would be able to perform BOTH anaerobic and aerobic processes.Based on the passage, it can be inferred that Culture B is I, Culture A is Type IIx. Further, Culture C is then Type IIa. There are many clues to figure this out. If this is the case, Type IIa will have HIGH density of mitochondria for oxidative phosporylation (which is indicated as being high for IIA).make sure to look at LEAST likely in the passage.

QUESTION 2:

Which steps involved in the contraction of a skeletal muscle require binding and/or hydrolysis of ATP?

• Dissociation of myosin head from actin filament

II. Attachment of myosin head to actin filament III. Conformational change that moves actin and myosin filaments relative to one another IV. Binding of troponin to actin filament

• Release of calcium from the sarcoplasmic reticulum

VI. Reuptake of calcium into the sarcoplasm 2 / 4

Official Guide to the MCAT Exam Questions and Answers (Solved Papers)

• I, II, and III only
• II, III, and IV only
• I, III, and VI only
• III, IV, and VI only - Correct Answers ✅C. got it wrong,

chose A, bc did not know that ca reuptake required ATP Also known as "cross bridge dissociation". This occurs after the power stroke to put the myosin head into a low energy position II. Calcium is required to expose the myosin binding sites through the conformational change in tropomyosin III.The conformational change among actin and myosin requires the hydrolysis of ATP which is what allows the power stroke a.k.a. the muscle contraction caused when myosin pulls actin towards the middle of the sarcomere VI. Reuptake of calcium requires ATP because the ions are moving against their concentration gradient into the SR What are the steps for muscle contraction? - Correct Answers ✅

QUESTION 3:

Does the release of Ach in skeletal muscle cells, cause depolarization or hyperpolarization?The addition of acetylcholine to the medium most likely

induced: 3 / 4

Official Guide to the MCAT Exam Questions and Answers (Solved Papers)

• depolarization of the cell membrane that resulted in

contraction.

• repolarization of the cell membrane that resulted in

relaxation.

• hyperpolarization of the cell membrane that resulted in

contraction.

• depolarization of the cell membrane that resulted in

relaxation. - Correct Answers ✅A. because we know ach causes contractions also according to the passage it states that ach caused a cell culture to retain contractile activity for longer than 30 mins.

Acetylcholine is released at the neuromuscular junction where it binds to receptors on the muscle cells and, depending on the type of muscle cell, causes depolarization or hyperpolarization of the cell membrane. In skeletal muscles, acetylcholine binds to its receptors, which leads to depolarization of the muscle cell membrane and muscle contraction.

QUESTION 4:

The terminal electron acceptor in lactic acid fermentation is:

• pyruvate.
• oxygen.
• NAD+.
• water. - Correct Answers ✅A.
• / 4