Cell Cycle and Mitosis

Study Notes

The cell cycle consists of three phases: Mitotic (M) phase, Interphase, and Cytokinesis
Interphase can be divided into three subphases: G1 (first gap), S (synthesis), and G2 (second gap)
The cell grows during all three phases, but chromosomes are duplicated only during the S phase

Mitosis is divided into five phases: Prophase, Prometaphase, Metaphase, Anaphase, and Telophase
Cytokinesis is well underway by late Telophase

In animal cells, a ring of actin filaments forms at the metaphase plate, which contracts and divides the cell in two
In plant cells, Golgi vesicles coalesce at the former metaphase plate, forming a phragmoplast, which grows into a cell plate that divides the cell in two

The cell cycle control system is regulated by both internal and external controls
The cell cycle stops at specific checkpoints (G1, G2, and M) until a go-ahead signal is received
If a cell receives a go-ahead signal at the G1 checkpoint, it will usually complete the S, G2, and M phases and divide

A chromosome consists of a DNA molecule packed together with proteins
Bacterial chromosomes are double-stranded, circular DNA molecules associated with a small amount of protein
Eukaryotic chromosomes have linear DNA molecules associated with a large amount of protein
In eukaryotic cells, DNA is precisely combined with proteins in a complex called chromatin
Chromatin undergoes changes in packing during the cell cycle
Most chromatin is loosely packed in the nucleus during interphase and condenses prior to mitosis

Nucleosomes are the basic units of DNA packaging
Each nucleosome is composed of two each of the four basic histone types, with DNA wrapped twice around the core of the eight histones
Histone tails protrude from the nucleosome and are involved in the regulation of gene expression
Chromatin is organized into a 10-nm fiber, which is further compacted into a 30-nm fiber through folding and looping
During interphase, chromosomes occupy specific restricted regions in the nucleus, and the fibers of different chromosomes do not become entangled

During mitosis, sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell
In anaphase, the microtubules shorten by depolymerizing at their kinetochore ends

The kinetochore is a structure composed of several proteins that associate with the centromere region of a chromosome and can bind to spindle microtubules
The kinetochore is responsible for chromosome movement during mitosis### Cell Division and the Cell Cycle
The centromere region of a metaphase chromosome is where DNA binds with spindle proteins.

Loss of cell cycle control can lead to unregulated cell growth and cancer.
Important terms related to loss of cell cycle control:
- Transformation: a process by which a normal cell becomes cancerous.
- Benign tumor: a non-cancerous growth that does not invade nearby tissues.
- Malignant tumor: a cancerous growth that invades nearby tissues.
- Metastasis: the spread of cancer cells from one part of the body to another.