Which of the following structural motifs promotes dimerization?

A. Zinc finger
B. Leucine zipper
C. Helix-turn-helix
D. Helix-loop-helix


B

Biology & Microbiology

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

1. Tropomyosin shifts and unblocks the cross-bridge binding sites. 2. Calcium is released and binds to the troponin complex. 3. Transverse tubules depolarize the sarcoplasmic reticulum. 4. The thin filaments are ratcheted across the thick filaments by the heads of the myosin molecules using energy from ATP. 5. An action potential in a motor neuron causes the axon to release acetylcholine, which depolarizes the muscle cell membrane. A) 1 ? 2 ? 3 ? 4 ? 5 B) 2 ? 1 ? 3 ? 5 ? 4 C) 2 ? 3 ? 4 ? 1 ? 5 D) 5 ? 3 ? 1 ? 2 ? 4 E) 5 ? 3 ? 2 ? 1 ? 4

Biology & Microbiology

Gene expression in developing organisms is regulated on several different levels. In many developing animals, regulation of gene expression is influenced by the action of Hox genes. Which of the following regulatory elements is produced by many Hox genes?

A) transcriptional factors B) cell-surface molecules for cell-cell interactions C) signals from maternal cytoplasm, such as bicoid D) mRNA processing factors

Biology & Microbiology

The internal membranes within the chloroplast are organized into flattened sacs called ________.

Fill in the blank(s) with the appropriate word(s).

Biology & Microbiology

Which symptom is indicative of premenstrual syndrome?

A. Drowsiness B. Headaches C. Water loss D. Fibroids E. Muscle soreness

Biology & Microbiology