Which of the following is the correct sequence that describes the excitation and contraction of a skeletal muscle fiber?

A. Tropomyosin shifts and unblocks the cross-bridge binding sites.

B. Calcium is released and binds to the troponin complex.

C. Transverse tubules depolarize the sarcoplasmic reticulum.

D. The thin filaments are ratcheted across the thick filaments by the heads of the myosin molecules using energy from ATP.

E. An action potential in a motor neuron causes the axon to release acetylcholine, which depolarizes the muscle cell membrane.

#Question id: 360

#Unit 1. Molecules and their Interaction Relevant to Biology

Which of the following is considered to be a strong base (alkali)?

#Question id: 361

#Unit 1. Molecules and their Interaction Relevant to Biology

Calculate the percentage of histidine that has its imidazole side chain protonated at pH 7.3. The pKa values for histidine are pK1 = 1.8, pK2 (imidazole) = 6.0, and pK3 = 9.2.

#Question id: 362

#Unit 1. Molecules and their Interaction Relevant to Biology

A 0.01 M solution of a substance has a pH of 2. What can you conclude about this substance?

#Question id: 363

#Unit 1. Molecules and their Interaction Relevant to Biology

What is the pH of a mixture of 0.042 M NaH2PO4 and 0.058 M Na2HPO4? If 1.0 mL of 10.0 M NaOH is added to a liter of the buffer prepared, how much will the pH change? (pKa = 6.86)

#Question id: 364

#Unit 1. Molecules and their Interaction Relevant to Biology

 A solution contains 0.0000001 (10-7) moles of hydrogen ions [H+] per liter. Which of the following best describes this solution?

#Question id: 365

#Unit 1. Molecules and their Interaction Relevant to Biology

Water is a polar molecule: the oxygen atom with its unshared electrons carries a partial negative charge (δ−) of ___________, and the hydrogen atoms each carry a partial positive charge (δ+) of __________, where e is the charge of the electron.