The cell cycle is the series of events a cell undergoes during its lifetime. It involves four main phases: G1, G2, S phases, and mitosis. Each phase is characterized by a specific set of events. These events include cell growth, genetic material replication, and cell division. Several cellular machineries such as organelles and cytoskeletal elements are involved in each phase. In addition to these phases, the cell cycle has specific checkpoints to ensure that the cell is ready to proceed to the subsequent steps in the cycle. This decreases errors during replication and division. G0 phase is a special phase of the cell cycle that is characterized by a quiescent cell.

Cyclin-dependent kinases are special molecules that facilitate the progression of a cell through the cell cycle. Many molecules such as p53 and kinase inhibitors regulate the cell cycle. Unregulated cell cycle can lead to rapid growth of cells that may, eventually, lead to cancer.

Which of the following is/are true regarding the cell cycle?

The cell cycle is the series of events a cell undergoes during its lifetime. It involves four main phases: G1, G2, S phases, and mitosis. Each phase is characterized by a specific set of events. These events include cell growth, genetic material replication, and cell division. Several cellular machineries such as organelles and cytoskeletal elements are involved in each phase. In addition to these phases, the cell cycle has specific checkpoints to ensure that the cell is ready to proceed to the subsequent steps in the cycle. This decreases errors during replication and division. G0 phase is a special phase of the cell cycle that is characterized by a quiescent cell.

Cyclin-dependent kinases are special molecules that facilitate the progression of a cell through the cell cycle. Many molecules such as p53 and kinase inhibitors regulate the cell cycle. Unregulated cell cycle can lead to rapid growth of cells that may, eventually, lead to cancer.

Which of the following is/are true regarding the cell cycle?

The force generated by a muscle when it contracts involves muscle proteins within muscle cells, namely actin and myosin. Beginning with the arrival of an action potential from the motor neuron’s axon, muscles generate force through a cascade of electrical and biochemical events. The release of acetylcholine at the presynaptic membrane into the synaptic cleft is caused by the action potential which opens calcium channels. Temporary binding of neurotransmitter at the postsynaptic membrane with the muscle’s acetylcholine receptors leads to depolarization of the postsynaptic membrane and opening of calcium channels. Twisting of tropomyosin to expose myosin attachment sites on actin is the result of calcium released from the sarcoplasmic reticulum and binding to troponin molecules. two strands of protein, myosin and actin, attach to each other by forming a cross-bridge which allows them to slide relative to each other to shorten the muscle and generate force. When depolarization ends, is pumped back into the sarcoplasmic reticulum and actin- myosin cross-bridges can no longer form resulting in relaxation.

When a motor neuron is electrically stimulated with a single impulse, a muscle innervated by that neuron produces a force called a twitch. Whereas the impulse might be 1 to 3msec in duration, the twitch is 10 to 100msec long. This is because it takes a long time for the to be pumped back into the sarcoplasmic reticulum. When the rate of impulses is low, the twitches have time to relax (Figure 1A). When the rate of simulation is high, the twitches fuse and the force in the muscle sums (Figures 1B and 1C). Maximal tension in the muscle, a condition known as tetanus (Figure 1D), is generated when the frequency of action potential is raised to the point when all cross- bridge binding sites are continuously activated and force output no longer shows any ripples.

Figure 1

Myasthenia gravis (MG) is a disease in which the number of acetylcholine receptors at the postsynaptic neuromuscular junctions becomes greatly reduced. What is the expected difference between contraction of the muscle of the MG patient and that of a healthy person in response to stimulation by a neuron?

Which of the following is true regarding a transmembrane receptor?

The force generated by a muscle when it contracts involves muscle proteins within muscle cells, namely actin and myosin. Beginning with the arrival of an action potential from the motor neuron’s axon, muscles generate force through a cascade of electrical and biochemical events. The release of acetylcholine at the presynaptic membrane into the synaptic cleft is caused by the action potential which opens calcium channels. Temporary binding of neurotransmitter at the postsynaptic membrane with the muscle’s acetylcholine receptors leads to depolarization of the postsynaptic membrane and opening of calcium channels. Twisting of tropomyosin to expose myosin attachment sites on actin is the result of calcium released from the sarcoplasmic reticulum and binding to troponin molecules. two strands of protein, myosin and actin, attach to each other by forming a cross-bridge which allows them to slide relative to each other to shorten the muscle and generate force. When depolarization ends, is pumped back into the sarcoplasmic reticulum and actin- myosin cross-bridges can no longer form resulting in relaxation.

When a motor neuron is electrically stimulated with a single impulse, a muscle innervated by that neuron produces a force called a twitch. Whereas the impulse might be 1 to 3msec in duration, the twitch is 10 to 100msec long. This is because it takes a long time for the to be pumped back into the sarcoplasmic reticulum. When the rate of impulses is low, the twitches have time to relax (Figure 1A). When the rate of simulation is high, the twitches fuse and the force in the muscle sums (Figures 1B and 1C). Maximal tension in the muscle, a condition known as tetanus (Figure 1D), is generated when the frequency of action potential is raised to the point when all cross- bridge binding sites are continuously activated and force output no longer shows any ripples.

Figure 1

Myasthenia gravis (MG) is a disease in which the number of acetylcholine receptors at the postsynaptic neuromuscular junctions becomes greatly reduced. What is the expected difference between contraction of the muscle of the MG patient and that of a healthy person in response to stimulation by a neuron?

Which of the following is true regarding a transmembrane receptor?

Apoptosis can be induced by mitochondria via the release of which protein from the mitochondrial inner membrane?

A type III secretion system is a mechanism several bacteria use to evade the immune system. They insert a syringe-like structure into a nearby host cell and secrete effector proteins that kill the host cell. What term best describes this kind of signaling?

The cellular membrane is a very important structure. The lipid bilayer is both hydrophilic and hydrophobic. The hydrophilic layer faces the extracellular fluid and the cytosol of the cell. The hydrophobic portion of the lipid bilayer stays in between the hydrophobic regions like a sandwich. This bilayer separation allows for communication, protection, and homeostasis.

One of the most utilized signaling transduction pathways is the G protein-coupled receptor pathway. The hydrophobic and hydrophilic properties of the cellular membrane allows for the peptide and other hydrophilic hormones to bind to the receptor on the cellular surface but to not enter the cell. This regulation allows for activation despite the hormone’s short half-life. On the other hand, hydrophobic hormones must have longer half-lives to allow for these ligands to cross the lipid bilayer, travel through the cell’s cytosol and eventually reach the nucleus.

Cholesterol allows the lipid bilayer to maintain its fluidity despite the fluctuation in the body’s temperature due to events such as increasing metabolism. Cholesterol binds to the hydrophobic tails of the lipid bilayer. When the temperature is low, the cholesterol molecules prevent the hydrophobic tails from compacting and solidifying. When the temperature is high, the hydrophobic tails will be excited and will move excessively. This excess movement will bring instability to the bilayer. Cholesterol will prevent excessive movement.

Which of the following molecules can be found inside of a cell?

I. Cyclic adenosine monophosphate (cAMP)

II. Protein kinase A

III. Protein kinase C

During metaphase, the chromosomes of the cell are __________.