Contraction of a skeletal muscle cell is initiated by the
A) release of acetylcholine by a neuron terminating at the neuromuscular junction.
B) release of calcium ions by the neuron into the neuromuscular junction.
C) electrical current traveling from the neuron directly into the muscle cell.
D) hormones delivered by the blood supply to the nearby tissue.
E) release of sodium ions by the neuron into the neuromuscular junction.
A
You might also like to view...
Describe the differences between the algae and the cyanobacteria
What will be an ideal response?
How do nastic movements differ from tropisms?
A. Nastic movements are slower than tropisms. B. Nastic movements only occur in the dark. C. Tropisms are directional responses to directional stimuli; nastic movements are the same regardless of the direction of the stimulus. D. Nastic movements happen after a stimulus, tropisms happen during a stimulus. E. Nastic movements are not reversible.
The system of flexing and extending muscles makes movement of appendages easy to understand. But how are some actions possible (sticking out your tongue, beating of your heart) when these structures have no bone structure with opposing flexors and extensors in them?
A. Muscle cells running diagonally or crosswise amidst the longitudinal muscles must contract and force the long relaxed muscle cells to elongate. B. These structures must be empty chambers, and fluids forced into them expand them. C. One set of muscle cells must therefore be able to both contract and expand. D. This cannot be explained at present.
Insulin is a small protein that regulates blood sugar level and is given to patients who suffer from diabetes. Many years ago, diabetics were given insulin that had been purified from pig pancreas
Once recombinant DNA techniques became available, the DNA encoding insulin could be placed into an expression vector and insulin could be produced in bacteria. Which of the following is NOT a reason why purifying insulin from bacteria is a better way to produce insulin for diabetics than using insulin purified from a pig pancreas. (a) Insulin can be easily produced in large quantities from cells carrying the cloned DNA sequence. (b) The creation of transgenic pigs that expressed insulin was very expensive compared to the cost of creating bacteria that expressed insulin. (c) Insulin made from a bacterial culture and then purified will be free of any possible contaminating viruses that pigs (and any other animals) harbor. Since pigs are more closely related to people than bacteria are, their viruses are more likely to be harmful to people than are viruses that might infect bacteria. (d) The pig protein has slight amino acid differences compared to the human protein, so human insulin produced by bacteria will work better in people.