Ch. 29 - Fungi

Freeman - Biological Science 8th Edition

Freeman8th EditionBiological ScienceISBN: 9780138276263Not the one you use?Change textbook

Freeman 8th Edition

Ch. 29 - Fungi

Problem 7

Chapter 29, Problem 7

Evaluate each of the following defects. Which could lead to uncontrolled growth in cancer? Select True or False for each statement. T/FThe overexpression of MPF activity. T/FA nonfunctional Rb protein. T/FThe overexpression of G1 cyclin. T/FA nonfunctional E2F protein.

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Identify the role of each component in cell cycle regulation: MPF (M-phase promoting factor) triggers the cell's entry into mitosis, Rb (retinoblastoma protein) prevents excessive cell growth by inhibiting cell cycle progression until the cell is ready, G1 cyclin binds to and activates CDKs to promote cell cycle progression, and E2F is a transcription factor that is essential for the progression from G1 to S phase in the cell cycle.

Analyze the impact of overexpression of MPF activity: Overexpression of MPF activity could lead to premature or uncontrolled entry into mitosis, bypassing the normal regulatory mechanisms, which could contribute to uncontrolled cell division seen in cancer. Thus, True.

Evaluate the effect of a nonfunctional Rb protein: Rb normally inhibits the cell cycle; a nonfunctional Rb would fail to regulate the cell cycle properly, potentially allowing for uncontrolled cell division. Thus, True.

Consider the consequences of overexpression of G1 cyclin: Overexpression of G1 cyclin could lead to excessive activation of CDKs, pushing the cell through the G1/S checkpoint inappropriately and contributing to uncontrolled cell growth. Thus, True.

Assess the impact of a nonfunctional E2F protein: A nonfunctional E2F would impair the transition from G1 to S phase, likely reducing cell proliferation rather than causing uncontrolled growth. Thus, False.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

MPF Activity

MPF, or M-phase promoting factor, is a complex of cyclin and cyclin-dependent kinase (CDK) that regulates the cell cycle's transition from G2 to M phase. Overexpression of MPF activity can lead to premature entry into mitosis, disrupting normal cell cycle control and potentially contributing to uncontrolled cell proliferation, a hallmark of cancer.

Rb Protein

The retinoblastoma (Rb) protein is a crucial tumor suppressor that regulates the cell cycle by inhibiting progression from the G1 phase to the S phase. A nonfunctional Rb protein fails to restrain cell cycle progression, allowing cells to divide uncontrollably, which is a significant factor in the development of various cancers.

G1 Cyclin and E2F Protein

G1 cyclins are proteins that promote the transition from the G1 phase to the S phase of the cell cycle by activating CDKs. E2F proteins are transcription factors that, when released from Rb inhibition, drive the expression of genes necessary for DNA synthesis. Overexpression of G1 cyclins or a nonfunctional E2F protein can disrupt normal cell cycle regulation, leading to uncontrolled cell growth and cancer.

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Proteins

Related Practice

Textbook Question

What does it mean to say that a hypha is dikaryotic?

a. Two nuclei fuse during sexual reproduction to form a zygote.

b. Two independent nuclei, derived from different individuals, are present in each cell.

c. The nucleus is diploid or polyploid — not haploid.

d. It is extremely highly branched, which increases its surface area and thus absorptive capacity.

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Textbook Question

The Greek root ecto means 'outer.' Why are ectomycorrhizal fungi, or EMF, aptly named?

a. Their hyphae form tree-like branching structures inside plant cell walls.

b. They are mutualistic.

c. Their hyphae form dense mats that envelop roots but do not penetrate the cell walls.

d. They transfer nitrogen from outside their plant hosts to the interior.

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Textbook Question

Explain why fungi that degrade dead plant materials are important to the global carbon cycle. Do you accept the text's statement that, without these fungi, 'Terrestrial environments would be radically different than they are today, and probably much less productive'? Why or why not?

Textbook Question

Lignin and cellulose provide rigidity to the cell walls of plants. But in most fungi, chitin performs this role. Why is it logical that most fungi don't have lignin or cellulose in their cell walls?

Textbook Question

Lawns are sometimes fertilized with nitrate that can be washed into neighboring woodlots by rain. If the trees in that woodlot are associated with EMF, what effect might the excess nitrate have on the fungi and/or trees?

a. Fungal growth may be stimulated, causing the trees to transport more nitrogen to the fungi.

b. The fungi may secrete more peptidases to break down the nitrate.

c. The trees may take up the nitrate directly into their roots and rely less on the fungi.

d. The excess nitrate may stimulate the fungi to transport more sugar to the trees.

Textbook Question

Table 29.1 mentions that chytrids are responsible for massive die-offs currently occurring in amphibians. Review Koch's postulates; then design a study showing how you would use Koch's postulates to test the hypothesis that chytrid infections are responsible for frog deaths.