Correct statement about two striking structural changes are seen in the enzyme upon isomerization from the closed to the open complex;

A. First, the pincers at the front of the enzyme clamp down tightly on the downstream DNA.

B. Second, there is a major shift in the position of the amino-terminal region of s. When not bound to DNA, s region 3.2 lies within the active center cleft of the holoenzyme, blocking the path that, in the open complex, is followed by the template DNA strand.

C. In the open complex, region 1.1 shifts some 50 A˚ and is now found on the outside of the enzyme, allowing the DNA access to the cleft.

D. Region 1.1 of s is highly negatively charged ( just like DNA).

#Question id: 11211

#Unit 7. System Physiology – Animal

The following steps refer to various stages in transmission at a chemical synapse.

1. Neurotransmitter binds with receptors associated with the postsynaptic membrane.

2. Calcium ions rush into neuron's cytoplasm.

3. An action potential depolarizes the membrane of the presynaptic axon terminal.

4. The ligand-gated ion channels open.

5. The synaptic vesicles release neurotransmitter into the synaptic cleft.

Which sequence of events is correct?

#Question id: 11212

#Unit 7. System Physiology – Animal

The activity of acetylcholine in a synapse is terminated by its ________.

#Question id: 11213

#Unit 7. System Physiology – Animal

An example of ligand-gated ion channels is ________.

#Question id: 11214

#Unit 7. System Physiology – Animal

Neurotransmitters categorized as inhibitory are expected to ________.

#Question id: 11215

#Unit 7. System Physiology – Animal

If excitatory postsynaptic potentials (EPSPs) are produced nearly simultaneously through two different synapses on the same postsynaptic neuron, the EPSPs can also add together creating ________.

#Question id: 11216

#Unit 7. System Physiology – Animal

When two excitatory postsynaptic potentials (EPSPs) occur at a single synapse so rapidly in succession that the postsynaptic neuron's membrane potential has not returned to the resting potential before the second EPSP arrives, the EPSPs add together producing ________.