Cell Reproduction and the Cell Cycle

Study Notes

All cells are derived from pre-existing cells.
New cells are produced for growth and to replace damaged or old cells.
Cell reproduction processes differ in prokaryotes (bacteria) and eukaryotes (protists, fungi, plants & animals).

The cell cycle is an orderly sequence of stages from the first division to the time the resulting daughter cells divide.
Just prior to the next division, the cell grows larger, the number of organelles doubles, and the DNA is replicated.
The three major stages of the cell cycle:
Interphase
- Many stages including G1 (growth), S (growth and DNA replication), G2 (growth and final preparations for division)
  - G1 checkpoint: The main checkpoint of the cell cycle.
  - G1: If DNA is damaged, apoptosis will occur. Otherwise, the cell is committed to divide when growth signals are present.
  - G2 checkpoint: G2 mitosis will occur if DNA has replicated properly. Apoptosis will occur otherwise.
Mitotic Stage
- The stage where the cell divides into two identical daughter cells.
Cytokinesis
- The stage where the cytoplasm divides, separating the two new cells.

The instructions for making cell parts are encoded in the DNA, so each new cell must get a complete set of the DNA molecules.

Asexual reproduction involves a single cell dividing to make 2 new, identical daughter cells.
Mitosis & binary fission are examples of asexual reproduction.
Sexual reproduction involves two cells (egg & sperm) joining to make a new cell (zygote) that is NOT identical to the original cells.
Meiosis is an example.

The DNA of prokaryotes (bacteria) is one, circular chromosome attached to the inside of the cell membrane.

Prokaryotes such as bacteria divide into 2 identical cells by the process of binary fission.
The single chromosome makes a copy of itself.
A cell wall forms between the chromosomes dividing the cell.