Why do cells divide?
1. Growth-organisms grow by producing more cells
2. cell replacement
3. Reproduction (asexual)
Why do cells increase by number and not size?
cells can not continue to grow larger. #1- larger cell places more demand on the DNA #2 a cell's volume increases faster than its surface area.
-thus before the cell becomes too large, it divides.
what is cell division?
when a cell divides into two new daughter cellls.
describe the two steps of cell division
1-Mitosis-division of the nucleus.
2-Cytokinesis- division of the cytoplasm.
what controls cell division?
1- when cells comes in contact with eachother, they stop growing.
2-Internal regulators make sue the cell dosn't divide until chromosomes have doubled.
3- external regulators are growth factors that stimulate or inhibit growth.
What is cancer?
when a cell loses control over growth, a tumor forms.
causes: genetics, tobacco, UV light, viral infections.
What is the cell cycle?
a series of events that cells go through as they grow and divide.
what is Mitosis?
Mitosis - the division of the cell nucleus
Mitosis has 4 phases:
What is Cytokinesis?
the pinching off of cytoplasm
What is Metaphase?
second step. Chromosomes line up at the center of cell.
Each chromosome is attached to a spindle fiber at the centromere.
What is prophase?
first step. Chromatin condenses into chromosomes.
Centrioles separate and spindle fibers form.
The nucleus (envelope) and nucleolus break down (no longer visible).
What is Interphase?
the time between cell divisions. Nucleus is still intact and the nucleolus is visible.
DNA is in the form chromatin (stringy DNA bound to protein)
Includes G1, S, and G2
What is Anaphase?
third step. The sister chromatids are pulled apart (centromere splits) to opposite ends of the cell.
what is Telophase?
fourth step. Nuclear membrane and nucleolus reform.
Mitotic spindle disappears.
Nuclear division is complete.