Question

1) Neurons propagate signals in the form of action potentials that are mediated by:

Answer 1

1. The correct answer is a.
Neurons communicate using action potentials, that travel down neurons using an electrochemical cascade. These action potentials are mediated by changes in the polarity of the cell membrane. At the beginning of the action potential, the Na+ channels open and this causes an influx of Na+ into the nerve cell, triggering, in turn, the depolarization of the membrane.

2. The correct answer is b.
The Krebs cycle (also known as the citric acid cycle) is a process involved in cellular respiration. The Krebs cycle happens in the mitochondria and involves the transformation of Acetyl coA to molecules, that will then be used to create ATP (the energy molecule). Acetyl coA goes through several chemical transformations and the energy released is transferred to NAD and FAD. In a process before the Krebs cycle, Pyruvate (produced by glycolysis) forms the acetyl coA. Therefore, pyruvate does not intervene in the Krebs cycle.

3. The correct answer is b.
The neuromuscular junction is a chemical synapse connecting a motor neuron and a muscle fiber. The signal transmitted from the motor neuron to the muscle fiber triggers the muscle contraction. The process is mediated partly through ion channel linked receptors. When acetylcholine (the ligand) binds to the receptor, the ion channel part of the receptor opens and this produces an influx of ions intracellularly.
 
4. The correct answer is c.
Cystic fibrosis is a inherited disorder that affects mostly the lungs, but also other organs of the body, such as the liver and the pancreas. It is caused by a mutation in the CTFR gene. This gene encodes a protein that is a chloride ion channel and is responsible for the movement of water in and out of the cells. The mutations in this gene result in a disruption of this ion channel, causing a change in the consistency of the mucus and sweat produced by the organism.

5. The correct answer is d.
The CTFR protein (the product of the CTFR gene) is a chloride ion channel regulated by cAMP. This ion channel is activated by phosphorylation, caused by cAMP - dependent protein kinase (PKA). PKA needs to bind two cAMP in order to be activated and able to phosphorylate other proteins.