Stem Cells
Most tissues of the body grow by increasing their cell number
In adults, most cell division is involved in tissue renewal rather than growth
Many types of cells undergo continuous replacement. Skin cells, for example, are constantly being sloughed off and replaced; in this case, the mature differentiated cells do not divide, but their population is renewed by the division of immature stem cells.
Where do cells come from?
All cells come from preexisting cells through the process of cell division
Prokaryotes: Binary fission
Eukaryotes (explant/animal cells): mitosis
Cell Division
Cell division is the process in which one cell, called the parent cell, divides to form two new cells, referred to as daughter cells.
Cell Division in Prokaryotes: Binary Fission (Image Below)
Control of the Cell Cycle
Without regulation, cells might go from one phase to the next before they were ready.
Cell cycle controlled by regulatory proteins.
Proteins signal the cell to start or delay the next phase of the cell cycle.
Regulatory proteins control the cell cycle at key checkpoints.
Cell Cycle & Cancer
Occurs when the cell cycle is no longer regulated.
May happen because a cell’s DNA becomes damaged. Damage can occur due to exposure to hazards such as radiation or toxic chemicals.
Cancerous cells generally divide much faster than normal cells. They may form a mass of abnormal cells called a tumor.
How is it assured that every cell in your body has the same DNA?
The process in which the nucleus divides is called mitosis.
Before mitosis occurs, a cell’s DNA is replicated.
Chromosomes
Chromosomes are the form of the genetic material of a cell during cell division.
During other phases of the cell cycle, DNA is not coiled into chromosomes. Instead, it exists as a grainy material called chromatin.
Chromatids and the Centromere
X-shaped form of a chromosome = condensed & coiled DNA
Because DNA has already replicated, each chromosome actually consists of two identical copies of DNA
The two copies are called sister chromatids.
They are attached to a region called the centromere.
Mitosis occurs in 4 phases:
Prophase: first & longest phase, it’s also when the complex of DNA and proteins contained in the nucleus, known as chromatin, condenses.
Metaphase is a stage in the cell cycle where all the genetic material is condensing into chromosomes. These chromosomes then become visible. During this stage, the nucleus disappears and the chromosomes appear in the cytoplasm of the cell.
Anaphase: the stage of meiotic or mitotic cell division in which the chromosomes move away from one another to opposite poles of the spindle.
Telophase: the final phase of cell division, between anaphase and interphase, in which the chromatids or chromosomes move to opposite ends of the cell and two nuclei are formed.
Cytokinesis: Cytoplasm pinches in half to create the 2 new daughter cells. It created two Identical chromosomes.