Cell Cycle Regulation and Cancer

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Questions and Answers

What happens when tumor suppressor genes are inactivated?

Cancer may develop due to uncontrolled cell proliferation. (correct)

Cells undergo apoptosis normally.

Cells are always ready to enter S phase.

E24 cannot function as a transcription factor.

How does the retinoblastoma protein (RB) contribute to cell cycle regulation?

It inhibits E24, preventing S phase entry if the cell is not ready. (correct)

It allows prematurely entering the S phase.

It initiates apoptosis when the cell is damaged.

It promotes the expression of genes needed for G2 phase.

What is a consequence of P53 gene inactivation?

E24 expression is inhibited.

Cell cycle checkpoints are strictly maintained.

Ubiquitination processes are enhanced.

Cells become resistant to apoptosis. (correct)

What role does ubiquitination play in cancer development?

It speeds up the degradation of cell cycle checkpoints. Signup and view all the answers

Which statement regarding E24 is true in the context of cell cycle regulation?

It can function as a transcription factor even if the cell is not prepared for S phase. Signup and view all the answers

What is the primary role of oncogenes in cell biology?

To stimulate excessive cell proliferation Signup and view all the answers

Which protein is involved in inhibiting apoptosis and is associated with cancer development?

Bcl-2 Signup and view all the answers

What effect does Mdm2 have on the P53 protein?

Promotes degradation of P53 Signup and view all the answers

What genetic alteration is primarily associated with oncogenes?

Point mutation Signup and view all the answers

How does P53 promote apoptosis in the presence of Bcl-2?

By inhibiting Bcl-2 through PUMA activation Signup and view all the answers

Which of the following is NOT a role of cohesin molecules?

Promoting cell proliferation Signup and view all the answers

What is the consequence of the overactivity of the KRAS protein?

Excessive cell proliferation Signup and view all the answers

What is meant by the term 'gatekeeper gene' in the context of cancer?

Genes that prevent excessive cell growth and division Signup and view all the answers

What is the primary difference in the growth behavior of cancer cells compared to normal cells when deprived of growth factors?

Cancer cells continue to grow in the absence of growth factors. Signup and view all the answers

What role do mutations play in the manifestation of retinoblastoma?

Two mutations must occur in two homologous chromosomes. Signup and view all the answers

In the context of inherited retinoblastoma, what must occur during fertilization and subsequent mitosis?

The presence of normal egg and sperm leads to cells with the RB gene. Signup and view all the answers

What is the main effect of oncogenes, such as E7 from the human papilloma virus, on the retinoblastoma protein?

They promote degradation of the retinoblastoma protein. Signup and view all the answers

Which phase of the cell cycle is primarily affected in normal cells deprived of growth factors?

G1 phase. Signup and view all the answers

What is the typical requirement for cancer development concerning genetic mutations?

Two mutations are usually necessary across both homologous chromosomes. Signup and view all the answers

How does serum deprivation signify growth factor dependency in cell cultures?

Normal cells will stop the cell cycle without serum, while cancer cells persist. Signup and view all the answers

What is the primary distinction between hereditary and non-hereditary retinoblastoma?

Both forms require two mutations but differ in the timing of mutations. Signup and view all the answers

Study Notes

Cell Cycle Regulation, Apoptosis, and Cancer

Cell division progresses to the next stage (S).
Some cells enter a G0 stage, a non-dividing state.
Some cells can re-enter the cell cycle.
Stages in the cell cycle are regulated by signals.
DNA replicates in the S phase.
Other synthesis and translation of proteins occurs.
Cells prepare for division in the G2 phase.

Variations in Cell Cycle

Certain cell types divide continuously to replace dying cells (e.g., epithelial cells in the gut).
Cells in mature tissues like nerve and muscle tissue generally don't divide after maturity.
Liver cells and lymphocytes divide only when prompted.

Cell Cycle Duration

Adult tissues have a cell cycle of approximately 20 hours.
Embryonic cells have a very short cycle (< 30 minutes).

Cleavage of a Fertilized Egg

Zygotes divide rapidly without significant cell growth, resulting in smaller cells.

Regulation of Cell Cycle by TOR

TOR (Target of Rapamycin) regulates cell growth and cell cycle progression.
Increasing protein synthesis leads to increased cell mass.
Cell growth is regulated by TOR.
TOR inhibits protein synthesis and prevents excessive proliferation.

G2-M Transition

Cell size, DNA replication status, and DNA damage are checked.
Growth factors also play a role.

G2-M Transition Checkpoints

Check for DNA damage or errors in replication.
Ensure proper cell size.

G1-S Transition

A cell is checked for growth factors and nutrients before proceeding.
Presence of sufficient nutrients and growth factors is crucial.
DNA damage is checked for.

Cell Cycle Checkpoints

G1 checkpoint: Checks if the cell is healthy and adequate resources are present.
G2 checkpoint: Checks for DNA replication completion and DNA repair.
Spindle checkpoint: Ensures all chromosomes are attached to spindle fibers before mitosis proceeds.

Mitotic Spindle Checkpoint

Prevents anaphase initiation if all chromosomes are not properly attached to the spindle fibers.
This prevents mis-segregation of chromosomes.