Cell Cycle and Interphase

10 Questions

What is the primary function of polar microtubules during cell division?

To interlock with polar microtubules from opposite poles to push spindle poles apart

What is the result of mitosis occurring without cytokinesis following?

Formation of a coenocyte

During anaphase, what happens to the centromeres?

They split simultaneously

What is the purpose of cell cycle checkpoints?

To detect abnormalities and trigger a temporary cell cycle stop

What is the term for the process by which a fertilized Drosophila egg undergoes 13 rounds of mitosis without cytokinesis?

Syncytial blastoderm formation

What is the primary function of the G1 phase in the cell cycle?

To allow for cell growth and prepare for DNA replication

What is the main function of the kinetochores during mitosis?

To attach to spindle fibers and facilitate chromosome separation

Which type of microtubules extends from the centrosome towards the cell periphery during mitosis?

Astral microtubules

What is the primary function of the centrioles in the cell?

To organize microtubules in the cytoplasm

What is the term for the phase of the cell cycle where cells stop dividing and arrest?

G0 phase

Study Notes

Cell Cycle

The cell cycle is a repeating pattern of cell growth and division, where nuclear division divides chromosomes equally into genetically identical daughter cells.
Cell growth and DNA replication occur between cell divisions.

Interphase

Consists of three parts: G1, S, and G2 phases.
G1 phase: cell growth occurs, and it is the gap before DNA duplication.
S phase: chromosomes duplicate to form sister chromatids through synthesis.
G2 phase: cell growth and synthesis of proteins needed for mitosis occur, and it is the gap before mitosis.
Most cell growth occurs during G1 and G2 phases.
Terminally differentiated cells, such as mature neurons, stop dividing and arrest in G0 phase.

Microtubules and Centrosome

Formation of microtubules occurs in the cytoplasm.
Centrosome is the microtubule organizing center near the nuclear envelope.
Centrioles, present in non-plant cells, are the core of centrosome, where microtubules extend from, surrounded by pericentriolar material.

M Phase (Mitosis and Cytokinesis)

Consists of five parts: prophase, prometaphase, metaphase, anaphase, and telophase.

Prophase

Chromosomes condense to stop transcription.
Centrosomes move to opposite poles.
Nucleoli begin to disappear, stopping ribosome production.

Prometaphase

Nuclear envelope breaks down.
Microtubules from centrosomes connect to kinetochores in the centromere of each chromatid.
Mitotic spindle forms, consisting of astral, kinetochore, and polar microtubules.

Metaphase

Sister chromatids face opposite poles, lining up on the metaphase plate.
Forces pushing and pulling chromosomes to or from each pole create a balanced equilibrium.

Anaphase

Centromeres split simultaneously.
Kinetochore microtubules shorten, pulling sister chromatids to opposite poles.

Telophase

Nuclear envelope forms around chromatids.
Nucleoli reform.
Spindle fibers disappear.
Chromosomes uncoil into chromatin.

Cytokinesis

Cytoplasm divides, beginning during anaphase but not completed until after telophase.
In animal cells, a contractile ring contracts to form a cleavage furrow.
In plant cells, a cell plate forms near the equator.

Consequences of Abnormal Mitosis

If mitosis occurs without cytokinesis, it leads to multi-nucleated cells.
Syncytium: multi-nucleated cells, usually early in development.
Coenocyte: multi-nucleated cells other than early development.

Cell Cycle Checkpoints

A system of sensor proteins recognizes abnormalities or damage to cells or DNA.
If damage is detected, the cell cycle stops temporarily to allow repair.
If damaged beyond repair, the cell undergoes apoptosis (programmed cell death) or senescence (permanent cell arrest).
Cancerous cells are mutated, with uncontrolled growth.