Unit 4: Cell Communication & Cycle
Biology · Unit 4 · Paper 1

Cell Communication & Cycle unit test

A test on this unit alone, marked as a percentage and a letter grade — for the test your class is actually sitting, rather than for May. Answer everything, then submit once: seeing the answer to question 3 before attempting question 4 makes the final percentage meaningless.

Paper 1Paper 2Paper 3
Each paper is built from this unit’s 37 terms and is the same for everyone, so a teacher can assign “Unit 4, Paper 1” and every student sits the identical test. Multiple choice is marked objectively; the written sections you mark yourself against the model answer and rubric.
Suggested time 36 min 33 points0/17 attempted
1

Synapsis and tetrads

2

Signal transduction pathway

3

Centrosome and spindle

4

Quorum sensing

5

Lab: Mitosis and Meiosis

6

Mitosis phases

7

Cytokinesis

8

Tyrosine kinase receptor

9

Crossing over

10

Cancer as checkpoint failure

11

Ligand

12

Ligand-gated ion channel

Short answer 1. Define or explain: Phosphorylation cascade

3 pts

Short answer 2. Define or explain: Sister chromatids vs homologous chromosomes

3 pts

Short answer 3. Define or explain: Apoptosis

3 pts

Short answer 4. Define or explain: Negative and positive feedback

3 pts

Free response

9 pts

In eukaryotic microorganisms the PHO signaling pathway regulates a set of genes, the Pho target genes, whose products control phosphate homeostasis. • When extracellular inorganic phosphate (Pi) is HIGH, the transcriptional activator Pho4 is phosphorylated by a complex of two proteins, Pho80–Pho85. The Pho target genes are then NOT expressed. • When extracellular Pi is LOW, a third protein, Pho81, inhibits the Pho80–Pho85 complex. Pho4 is left unphosphorylated and induces expression of the target genes. Starting from a wild-type strain of yeast, researchers created a strain with a mutant form of Pho81 (pho81mt) and a strain with a mutant form of Pho4 (pho4mt). In each strain they measured the activity of APase — an enzyme that removes phosphate groups from its substrates, encoded by the Pho target gene PHO1 — and the relative amount of PHO1 mRNA. Wild-type PHO1 mRNA in the low-Pi environment was set to 10. TABLE 1. APase ACTIVITY AND RELATIVE AMOUNTS OF PHO1 mRNA (± 2SE of the mean) Strain Mutation APase, high Pi APase, low Pi PHO1 mRNA, PHO1 mRNA, (mU/mL/OD600) (mU/mL/OD600) high Pi low Pi Wild-type none 0.5 ± 0.1 17.3 ± 0.9 0.1 ± 0.0 10 ± 2.0 pho81mt nonfunctional Pho81 0.4 ± 0.1 0.6 ± 0.1 0.7 ± 0.2 0.9 ± 0.8 pho4mt nonfunctional Pho4 0.5 ± 0.0 0.8 ± 0.2 0.6 ± 0.4 0.3 ± 0.1

(a)(i) Describe the effect that the addition of a charged phosphate group can have on a protein that would cause the protein to become inactive.

(a)(ii) Explain how a signal can be amplified during signal transduction in a pathway such as the PHO signaling pathway.

(b)(i) Based on Table 1, identify a dependent variable in the researchers’ experiment.

(b)(ii) Justify the researchers’ using the wild-type strain for the creation of the mutant strains.

(b)(iii) Justify the researchers’ using mutant strains in which only a single component of the pathway was mutated in each strain.

(c)(i) Based on the data in Table 1, identify the yeast strain and growth conditions that lead to the highest relative amount of PHO1 mRNA.

(c)(ii) Calculate the percent change in APase activity in wild-type yeast cells in a high-Pi environment compared with that of wild-type cells in a low-Pi environment.

(d)(i) In a follow-up experiment, researchers created a strain of yeast with a mutation that resulted in a nonfunctional Pho85 protein. Predict the effect of this mutation on PHO1 expression in a high-Pi environment.

(d)(ii) Provide reasoning to justify your prediction in (d)(i).