The enzyme that catalyzes the conversion of ATP to cAMP is:
A. Protein kinase A
B. Adenylyl cyclase
C. Phosphodiesterase
D. Phospholipase C
Answer: Option B
Solution (By JKExamLibrary)
Adenylyl cyclase converts ATP to cyclic AMP (cAMP), a second messenger. Phosphodiesterase breaks down cAMP, PKA is activated by cAMP, PLC produces IP₃ and DAG.
Explanation:
Salivary amylase (ptyalin) hydrolyzes starch into maltose and dextrins in the mouth. It functions optimally at neutral to slightly alkaline pH. Pepsin digests proteins in the stomach, lipase digests fats, trypsin is a pancreatic protease. Salivary amylase action ceases in the acidic stomach.
Explanation:
An action potential is initiated when a stimulus causes the membrane potential to reach a threshold. This opens voltage-gated sodium channels, leading to a rapid influx of sodium ions (Na+) into the neuron. This makes the inside of the cell positively charged relative to the outside, a process called depolarization. Repolarization follows with the efflux of K+ ions.
Explanation:
The choroid plexus, a network of ependymal cells and capillaries in the ventricles of the brain, continuously produces CSF by filtration and secretion. CSF circulates through ventricles and the subarachnoid space and is reabsorbed by arachnoid villi into the venous system. Dura mater is the outer protective membrane.
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