Cell Cycle, Mitosis, and Meiosis
Why do cells divide?
Most cells go through a series of changes in order
to maintain homeostasis.
Cells need to reproduce (divide) when their surface area
can no longer supply the much larger volume with
nutrients and get rid of wastes.
Cell Division
• The process by which a cell divides into two new
daughter cells
Chromosomes
• Made of DNA (carries the cell’s genetic information)
and proteins
▫ Every organism has a specific number of
chromosomes
 Humans have 46
Chromosomes
• Only visible during cell division
• Each chromosome is copied before cell division
▫ Each chromosome is made of two identical “sister”
chromatids
 Each pair of chromatids is attached by a centromere
The Cell Cycle
• The series of events that cells go through as they
grow and divide
The Cell Cycle
• Interphase – the period of growth in between
cell divisions
• Three phases of interphase
▫ G1
▫S
▫ G2
Interphase – G1 phase
• Phase where cells do the most growing
• Cells increase in size and make new proteins and
organelles
Interphase – S phase
• Chromosomes are replicated (copied)
• Synthesis (making) of DNA molecules occurs
Interphase – G2
• Organelles and other molecules required for cell
division are produced.
• Once completed, the cell will enter mitosis
Mitosis
• The division of the cell nucleus
• Divided into four phases (PMAT):
▫
▫
▫
▫
Prophase
Metaphase
Anaphase
Telophase
Prophase
•
•
•
•
Chromosomes become visible
Nuclear envelope breaks down
Centrioles separate
Spindles form
Metaphase
• Chromosomes line up along the center of the cell
Anaphase
• Sister chromatids separate
• Individual chromosomes are moved apart
Telophase
• Chromosomes gather at opposite ends of the cell
• Two new nuclear envelopes form
Cytokinesis
• The cytoplasm pinches in two – two new
daughter cells are formed
• In plants a cell plate divides the cytoplasm
before the cell wall forms
Cancer Cells
1. Normal cells contain check points to regulate
the cell cycle, & stop at appropriate check points.
2. Cancerous cells do not respond to check points
and continue rapidly through the cell cycle. This
results in masses of undefined cells called tumors.
3. Cancer cells do not mature; they become more immature.
Binary Fission
• The asexual reproduction of a bacterial cell