Bio Unit 4 FRQ's

#8: Predict how each of the following mutations in the OR4 gene would most likely affect the sensitivity of mosquitos to sulcatone. Justify each prediction. (a) A mutation that results in the removal of the intracellular domain of the receptor protein. (b) A mutation that results in the substitution of a small hydrophobic amino acid for another small hydrophobic amino acid in the ligand-binding site of the receptor protein.

(a) It would cause mosquitos to be less sensitive to elements such as the sulcatone produced by humans and guinea pigs. This would also cause mosquitos to be unable to initiate intracellular signals that cascade through the cell. (b) It would not change the sensitivity of the mosquitos because the ligand can still bind to the receptor and the shape of the ligand binding domain does not change.

#1: Drawings of samples of plant cells collected from two locations in a woody plant during the spring. (a) Describe the role of mitosis in the growth of a plant (b) Explain why there are more cells observed in mitosis in the root tip than in the woody stem. (c) Refine the model in the space provided for your response by using the letters from four of the cell labels of sample 2 to represent the sequential steps of mitosis. d) Explain how the arrangement of cellular components during the step of mitosis portrayed by cell D in sample 2 facilitates the proper distribution of chromosomes to the two daughter cells.

(a) Mitosis helps the plant grow by creating genetically identical daughter cells. More cells means more plant growth. (b) The root tip shows more cells undergoing mitosis because the root tip needs to grow more than the woody stem and the root tip cells divide more frequently. (c) E, D, B, C, A (d) Cell D is an example of metaphase as some of the cellular components shown are spindle fibers that will eventually split the sister chromatids, if the cell passes the spindle checkpoint. The spindle checkpoint makes sure the chromosomes are lined up correctly and that everything is good to go before splitting.

#4: The cell cycle is fundamental to the reproduction of eukaryotic cells. (a) Describe the phases of the cell cycle. (b) Explain the role of THREE of the following in mitosis or cytokinesis: Kinetochores, Microtubules, Motor Proteins (c) Describe how the cell cycle is regulated and discuss ONE consequence of abnormal regulation.

(a) The cell cycle is a four-stage process in which the cell increases in size in G1, copies its DNA is S, prepares to divide in G2, and divides in M. Stages G1, S, and G2 make up interphase, which accounts for the span between cell divisions. (b) Kinetochores connect chromosomes to microtubules of mitotic spindles. Microtubules pull chromosomes to the poll of the cell. Motor proteins are required for spindle formation and chromosome alignment. (c) The cell cycle is regulated by checkpoints and one abnormal regulation could be the continuous division of cancer cells.

#9: Acetylcholine is a neurotransmitter that can activate an action potential in a postsynaptic neuron. A researcher is investigating he effect of a particular neurotoxin that causes the amount of acetylcholine released from presynaptic neurons to increase. (a) Describe the immediate affect of the neurotoxin on the number of action in a postsynaptic neuron. Predict whether the maximum membrane potential of the postsynaptic neuron will increase, decrease, or stay the same. (b) The researcher proposes two models, A and B, for using acetyl-cholinesterase (AChE), an enzyme that degrades acetylcholine, to prevent the effect of the neurotoxin. In model A, AChE is added to the synapse. In model B, AChE is added to the cytoplasm of the postsynaptic cell. Predict the effectiveness of EACH proposed model. Provide reasoning to support your predictions.

(a) The immediate effect would be that the number of action potentials would increase. I predict that the maximum membrane potential will stay the same. (b) Model A would be effective because acetylcholine is in the synapse. Model B would not be effective because acetylcholine is not in the cytoplasm of the postsynaptic cell.

#7: Describe the most likely role of EGF and the role of EGFR in a cell signaling pathway. Describe how the cellular response to EGF results in tissue repair.

In a cell signaling pathway, EGF is a ligand that binds to EGFR to activate the receptor. The receptor initiates the cell signaling pathway. Cellular response initiates cell division. Cell division results in new cells that result in tissue repair.

#2: The figure above represents a generalized hormone-signaling pathway. Briefly explain the role of each numbered step in regulating target gene expression.

In the figure above, representing a generalized hormone signaling pathway, step one shows the stage of reception, in which bonding between a signal molecule a receptor occurs, causing a shape change in the receptor. Binding initiates signaling. The second step is transduction, in which cascades of molecular interactions relay signals from receptors to target molecules in the cell. The third step shows translation where cell signaling activates cellular response. The target cell is stimulated.

#5: Describe how the cell cycle is regulated and discuss ONE consequence of abnormal regulation.

The cell cycles regulated by checkpoints, which block cell cycle progress unless specific molecular and physical conditions are satisfied. One abnormal regulation could be the continuous division of cancer cells. Cancer cells do to require a signaling for division to proceed.

#3: Acetylcholinesterase is an enzyme that breaks down acetylcholine in the synapse. Describe the effect of inhibiting acetylcholinesterase on the muscle cells with AChR type 2.

The cell will be unable to break down the acetylcholine molecule which will cause the receptor proteins to be constantly stimulated, forcing the Na+ ion to stay open. Since the opening of Na+ channels causes muscle contractions, the inhibition of acetylcholinesterase would force repeated muscle contractions without end, like a seizure.

#6: Identify the THREE major stages of interphase, and describe the sequence in which they occur.

The three stages of interphase are G1, S, and G2. During G1, the cell grows longer and copies organelles to make the building blocks needed for later stages. During S, DNA replication takes place and the copying of the centrosome to separate the two sister cells. During G2, the cell grows, makes proteins, and duplicates more organelles in preparation for mitosis.