Chapter 12: Cell Division and Cycle Regulation in Eukaryotic Cells

What is the primary characteristic that distinguishes living organisms from nonliving matter?

The ability to reproduce and produce more of their own kind.

What is the continuity of life based on?

The reproduction of cells, or cell division.

What are the key roles of cell division in organisms?

Cell division allows single-celled organisms to reproduce, facilitates embryonic development in multicellular eukaryotes, and aids in renewal and repair in fully grown multicellular eukaryotes.

What is the crucial function of most cell division?

The distribution of identical genetic material to the two daughter cells.

What constitutes a cell's genome?

All the DNA in a cell.

How is DNA organized in eukaryotic cells?

DNA is packaged into chromosomes.

What is chromatin?

A complex of DNA and protein that condenses during cell division in eukaryotic cells.

What are somatic cells?

Nonreproductive cells that have two sets of chromosomes.

What are gametes?

Reproductive cells (sperm and eggs) that have half as many chromosomes as somatic cells.

What happens to DNA in preparation for cell division?

DNA is replicated and the chromosomes condense.

What are sister chromatids?

Joined copies of the original chromosome, attached along their lengths by cohesins.

What is the centromere?

The narrow 'waist' of the duplicated chromosome where the two chromatids are most closely attached.

What are the two main processes of eukaryotic cell division?

Mitosis (division of genetic material in the nucleus) and cytokinesis (division of the cytoplasm).

What is meiosis?

A variation of cell division that produces nonidentical daughter cells with half as many chromosomes as the parent cell.

What are the two main phases of the cell cycle?

The mitotic (M) phase and interphase.

What occurs during interphase?

Cell growth and copying of chromosomes in preparation for cell division.

What are the three phases of interphase?

G1 phase (first gap), S phase (synthesis), and G2 phase (second gap).

During which phase are chromosomes duplicated?

During the S phase of interphase.

How many stages is mitosis conventionally broken down into?

Five stages: prophase, prometaphase, metaphase, anaphase, and telophase.

What is the mitotic spindle?

A structure made of microtubules that controls chromosome movement during mitosis.

Where does the assembly of spindle microtubules begin in animal cells?

In the centrosome, which is a type of microtubule-organizing center.

What happens to the centrosome during interphase?

It replicates to form two centrosomes that migrate to opposite ends of the cell during prophase and prometaphase.

What is a kinetochore?

A protein complex associated with centromeres, where spindle microtubules attach during prometaphase.

What occurs during anaphase?

Cohesins are cleaved by separase, allowing sister chromatids to separate and move toward opposite ends of the cell.

How does cytokinesis occur in animal cells?

Through a process known as cleavage, marked by the appearance of a cleavage furrow.

What is binary fission?

A type of cell division in prokaryotes where the chromosome replicates and the cell divides into two.

How is the eukaryotic cell cycle regulated?

By a molecular control system that includes specific signaling molecules and checkpoints.

What are cyclins and cyclin-dependent kinases (Cdks)?

Regulatory proteins involved in cell cycle control; cyclins fluctuate in concentration, while Cdks must be attached to cyclins to be active.

What is MPF (maturation-promoting factor)?

A cyclin-Cdk complex that triggers a cell's passage past the G2 checkpoint into the M phase.

What is the significance of the G1 checkpoint?

It is the most important checkpoint; if a cell receives a go-ahead signal, it will typically complete the cycle and divide.

What is density-dependent inhibition?

A phenomenon where crowded cells stop dividing.

What is anchorage dependence?

The requirement for cells to be attached to a substratum in order to divide.

How do cancer cells differ from normal cells in terms of cell cycle regulation?

Cancer cells do not heed normal signals that regulate the cell cycle and can divide indefinitely.

What is a benign tumor?

A mass of abnormal cells that remains at the original site and typically does not cause serious problems.

What is a malignant tumor?

A tumor that invades surrounding tissues and can undergo metastasis, spreading cancer cells to other parts of the body.

What is metastasis?

The spread of cancer cells to other parts of the body, where they may form additional tumors.

What are some treatments for localized tumors?

High-energy radiation, which damages the DNA in cancer cells.

What are chemotherapeutic drugs used for?

To target the cell cycle in metastatic tumors, though they can also affect normal cells that divide frequently.

What role do growth factors play in cell division?

They are released by certain cells to stimulate other cells to divide.

What is platelet-derived growth factor (PDGF)?

A growth factor required for the division of cultured fibroblasts, made by blood cell fragments called platelets.

What happens if a cell does not receive a go-ahead signal at the G1 checkpoint?

It exits the cycle and switches into a nondividing state called the G0 phase.

What is the significance of internal signals at the checkpoints?

They ensure that processes like anaphase do not begin until all chromosomes are properly attached to the spindle.

What is the relationship between cancer and DNA damage?

The majority of cancer cells have lost the ability to repair DNA damage, contributing to their uncontrolled division.