Question

Human cells divide every day for normal growth, replacement of cells, and tissue repair. The dividing cells proceed through the three phases of the cell cycle as shown in the figure. When a person experiences a cut, damaged skin cells secrete a protein called epidermal growth factor (EGF). Epidermal (skin) cells in the vicinity of the injury possess proteins in their cell membranes called epidermal growth factor receptors (EGFR)

(a) Identify the THREE major stages of interphase, and describe the sequence in which they occur.

(b) 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.

(c) Cancer can result from disruptions in cell cycle control. Mutations that increase the production of EGFR have been associated with skin cancer of the head and neck. Describe how a mutation outside of the coding region of a gene that encodes EGFR could lead to the overproduction of EGFR protein in a skin cell.

Answer 1

The three stages of interphase are G1 phase, S phase, and G2 phase. EGF and EGFR play a role in cell signaling and tissue repair. Mutations in the gene encoding EGFR can lead to overproduction of EGFR protein in a skin cell, potentially causing skin cancer.

Step-by-step explanation:

(a) The three major stages of interphase are:

1. G1 phase: This is the first gap phase where cells undergo growth and prepare for DNA replication.
2. S phase: This is the synthesis phase where DNA replication occurs and each chromosome is duplicated.
3. G2 phase: This is the second gap phase where cells continue to grow and prepare for cell division.

(b) Epidermal growth factor (EGF) and epidermal growth factor receptors (EGFR) play a role in cell signaling and tissue repair. When a person experiences a cut, damaged skin cells secrete EGF, which binds to EGFR on nearby skin cells. This binding activates a signaling pathway that causes the cells to grow and divide, resulting in tissue repair.

(c) Mutations in the gene that encodes EGFR can lead to the overproduction of EGFR protein in a skin cell. Even if the mutation occurs outside of the coding region of the gene, it can still affect the expression of the gene and increase the production of EGFR protein. This overproduction of EGFR can disrupt the normal cell cycle control and potentially lead to uncontrolled cell growth and skin cancer.

Answer 2

(a) The three major stages of interphase are:

G1 phase: This is the first stage of interphase and is also known as the "growth" phase. During this stage, the cell grows and carries out metabolic functions.

S phase: This is the second stage of interphase and is also known as the "synthesis" phase. During this stage, the cell replicates its DNA in preparation for cell division.

G2 phase: This is the third and final stage of interphase and is also known as the "second growth" phase. During this stage, the cell checks for errors in the replicated DNA and makes any necessary repairs.

The sequence in which these stages occur is G1 phase, S phase, and G2 phase.

(b) EGF and EGFR play a role in a cell signaling pathway. EGF is a growth factor that is secreted by damaged cells, it binds to its receptor (EGFR) on the surface of nearby undamaged cells, this binding triggers a cascade of intracellular signals that lead to the activation of a set of genes responsible for cell proliferation, migration, and survival. This results in the repair of the tissue.

(c) Mutation that occurs outside of the coding region of a gene that encodes EGFR, for example in the promoter region, can lead to the overproduction of EGFR protein in a skin cell. The promoter region is responsible for controlling the expression of a gene, and if a mutation occurs in this region, it can lead to the overproduction of the gene's protein product, in this case, EGFR. This overproduction of EGFR can then lead to uncontrolled cell growth and division, which is a characteristic of cancer.