1. Chapter 9: Cell Cycle and Cell Reproduction

2. Why do cells need to divide?
Growth and development
You started as 1 cell and now you’re made up of roughly 40 TRILLION cells
Repair and regeneration of tissue
Reproduction

3. What happens when cells divide?
We go from one functional cell to two functional and identical cells
All the organelles need to double
All the genetic material needs to be replicated
The plasma membrane needs to encapsulate both cells
All of these events are controlled in the cell cycle

4. What is the cell cycle?
Cell cycle – orderly set of stages that take place between the time a eukaryotic cell divides and the time the resulting two daughter cells divide
Cells are always at some stage of the cell cycle

5. Stages of the cell cycle
Interphase – cell performs usual functions and prepares for division
Longest stage at about 20 hours, or 90% of cell cycle
Consists of three separate phases:
G1 – growth phase after previous division, organelles replicate and proteins are translated for DNA synthesis
S phase – DNA is synthesized, or copied
G2 –cell continues to grow and replicate organneles, translation of proteins necessary for mitosis

6. Mitotic Stage Mitosis – Nuclear division
Division of nucleus and DNA
Cytokinesis – Division of cytoplasm

7. Mitosis Mitosis is nuclear division
Nuclear division means we need to create two identical nuclei, including all the genetic material inside of them
Genetic material = DNA
DNA is wrapped around histones, or proteins that help store the DNA
Chromosomes-strands of packaged DNA
Eukaryotic cells contain roughly 2m of DNA and pack it into a nucleus that is only 6um in diameter!

8. Cytokinesis in animals
SEM 140
Daughter cells
Cleavage furrow
Contracting ring of microfilaments
Cytokinesis in animals
Cleavage furrow- indentation of membrane between the two daughter nuclei
Contractile ring – Actin filaments that tighten around the cell

9. Cytokinesis in animals
where the cell
pinches in
“belt” made of
microfilaments (actin)

10. Cell Cycle Regulation Signals – Agent that influences cell growth
Checkpoints occur at G1, G2 and Mitosis
If the cell is ready to proceed, the appropriate signals are released
If not, it stops

11. Apoptosis Apoptosis – Programmed cell death Normal development
To make complicated structures from a single cell, some cells have to die in the process
Prevention of the spread of disease
Cells are constantly becoming damaged and usually they die when they are beyond repair, but sometimes they ignore these cues and replicate uncontrollably
Apoptosis in Normal Development
Apoptosis Overview

12. Cancer
Cancer – cell growth disorder that occurs when cells divide uncontrollably
Happens through a series of mutations that disrupt cell cycle checkpoints and apoptosis
Normal cells cooperate to benefit the whole organism, cancer cells compete to benefit only themselves

13. Characteristics of cancer cells
Cancer cells are no longer specialized cells
they do not perform any useful function
Cancer cells have large nuclei due to extra chromosomes
Cancer cells do not undergo apoptosis
they don’t die when they should
Cancer cells form tumors, or abnormal growths
Cancer cells trigger blood vessel growth (angiogenesis) and travel throughout the body (metastasis)
Essentially, normal cells cooperate to help the body function. Cancer cells only care about themselves and compete with everything