1. Cell Growth and Division
Biology Ch. 5

2. 5.1 The Cell Cycle Growth DNA duplication Cell division Gap 1
The cell cycle is the pattern of:
Growth
DNA duplication
Cell division
The cell cycle only occurs in eukaryotic cells
The cell cycle has 4 main stages:
Gap 1
Synthesis Originally called interphase
Gap 2
Mitosis

3. Gap 1 (G1)
Cell carries out normal functions
Cell grows
Organelles increase in number
Stage that a cell spends most of it’s time in
In order to pass to the next stage, the cell must pass a checkpoint
Enough nutrition, adequate size, and undamaged DNA

4. Synthesis (S)
Cell makes of copy of DNA
The DNA is located in the nucleus
By the end of the S phase, the cell nucleus contains 2 complete sets of DNA

5. Gap 2 (G2)
Cell continues to carry out normal functions
Additional growth occurs
Includes a checkpoint to make sure everything is functioning properly.

6. Mitosis (M)
Includes 2 processes:
Mitosis
Division of the nucleus and its contents
The nuclear membrane dissolves
The duplicated DNA condenses around 2 proteins and separates
2 new nuclei form

7. Cytokinesis
Division of the cell cytoplasm
The result is 2 daughter cells that are genetically identical to the original cell.

8. The Cell Cycle

9. Prokaryotic cells divide faster than eukaryotic cells because prokaryotes do not have membrane bound organelles.
The rate at which cells divide is linked to the body’s need for those cells.
In humans, the S, G2, and M phases usually take about 12 hours.
The rate of cell division is greater in embryos and children than in adults.
Children have a shorter cell cycle and many of their organs are still developing.

10. The rate of cell division varies in adults.
Cells in areas that receive a lot of wear and tear will have the fastest rates of cell division.
Other cells in the body only divide occasionally.
Cells that divide rarely enter a stage called the G0 stage.
During the G0 stage, cells are unlikely to divide but continue to carry out normal functions.

11. Skin cells and the cells that line the intestines and stomach are subject to wear so they divide rapidly.
Muscle cells and cells that make up many of your internal organs such as the lungs, kidneys, and liver divide occasionally.
Neurons and white blood cells are very unlikely to divide unless a need arises.

12. Cell size is limited.
The limit on cell size is due to the ratio of cell surface area to volume.
As a cell increases in size, its volume increases faster than its surface area.
If the size of the cell continues to increase, the surface area would be too small for adequate exchange of materials.
To maintain a suitable cell size, growth and division must be coordinated.

13. 5.2 Mitosis and cytokinesis
DNA is a double stranded molecule made of subunits called nucleotides.
A chromosome is a long continuous thread of DNA that consists of genes.
Your body cells have 46 chromosomes each.
The DNA in one cell would be about 10 feet long if it were stretched out.

14. In order for DNA to fit inside the nucleus, it wraps around proteins.
DNA is loosely organized until mitosis. This allows proteins to access specific genes.
During mitosis, the chromosomes are tightly condensed. This allows for the chromosomes to be divided.
During the entire cell cycle, each chromosome is associated with a group of proteins called histones.
The DNA wraps around the histones allowing the DNA to be compacted.

15. The loose refers to how much the DNA is folded.
As the cell move into mitosis, the chromatin condenses even more eventually forming small thick rods.
Because the chromosome has already been copied, it looks like an X.
The loose combination of DNA and histones is called chromatin.
Each half of the X contains two identical DNA double helixes.

16. One half of the duplicated chromosome is called a chromatid.
The 2 identical chromatids are called sister chromatids.
The sister chromatids are held together by a centromere.
The ends of the DNA molecules form structures called telomeres which don’t code for anything.
Telomeres prevent the ends of chromosomes from attaching to each other and help prevent the loss of genes.

17. Interphase provides time for duplication of organelles and for DNA replication.
By the end of interphase, a cell has 2 full sets of DNA, or chromosomes, and is large enough to divide.
Mitosis divides the cell nucleus into 2 genetically identical nuclei.
Each cell has a full set of DNA.
Mitosis prepares the cell for cytokinesis.

18. Mitosis is divided into phases:
Prophase
Chromatin condenses into chromosomes
Each chromosome consists of 2 sister chromatids
The nuclear envelop breaks down
Centrosomes move to opposite sides of the cell
Spindle fibers grow and move toward the center of the cell.

19. Metaphase
Spindle fibers attach to the centromere of each chromosome
Chromosomes line up along the center of the cell
Anaphase
Chromatids separate from each other
Spindle fibers shorten and pull the sister chromatids away from each other toward opposite sides of the cell

20. Telophase
Identical chromosomes are positioned at each pole of the cell.
The nuclear membrane starts to form
Chromosomes begin to uncoil
Spindle fibers fall apart

21. Mitosis

22. Cytokinesis begins during late anaphase or telophase
Cytokinesis divides the cytoplasm into 2 cells and completes the cell cycle.
In animals, the cell membrane forms a trench that is pulled inward and gradually pinches closed. This forms a separate cell around each nucleus.

23. During cytokinesis in plant cells a cell plate forms between the two nuclei.
The cell plate is made by the golgi apparatus.
A new cell wall grows as cellulose is laid down.
Cytoplasm is divided evenly between daughter cells
The formation of new cells is used for growth, development, and repair.

24. 5.3 Regulation of the cell cycle
External factors the come from outside the cell
Cell to cell contact
Once one cell touches another cell it stops growing
Growth factors
Proteins that stimulate cell division and growth
Platelets & Erythropoietin are examples
Growth hormone
Results in bone growth and affects protein and fat metabolism

25. Internal factors come from inside the cell
Kinases
Enzymes that transfer a phosphate group to a specific target molecule.
This action increases energy of the molecule or changes its shape.
Cyclins
Responsible for activating kinases
Helps the cell advance to different stages of the cell cycle

26. Apoptosis is programmed cell death
It occurs when signals activate genes to produce self-destructive enzymes.
The nucleus of an apoptopic cell shrinks and breaks apart.
These cells are recognized by immune cells.
The immune cells gobble up the apoptopic cell and recycle its parts.

27. Cancer is uncontrolled cell division.
It occurs when regulation of the cell cycle breaks down.
Cancer cells continue to divide when regulating factors are present.
A benign tumor forms when cancer cells are clustered together which makes them relatively harmless and curable by removal.
A malignant tumor forms when some of the cancer cells break away or metastasize. These cells can enter the blood stream and moves to other parts of the body.

28. Tumors are harmful because the cells do not perform the functions needed by the body.
The tumors are basically large clumps of rapidly dividing cells that require lots of food and blood but contribute nothing to the body.
A growing tumor can put pressure on surrounding organs and may keep those organs from performing their functions.
Cancer cells come from normal cells that have suffered damage to their genes that make proteins involved in regulation.

29. Most cancer cells carry mutations in two types of genes which can be inherited.
Oncogenes which accelerate the cell cycle
Cell cycle breaks
Some mutations are caused by exposure to radiation or chemicals.
Substances that promote the development of cancer are called carcinogens.

30. Standard cancer treatment involves radiation and chemotherapy
Radiation damages a cell’s DNA so it cannot divide. It is usually localized.
Chemotherapy uses certain drugs to kill actively dividing cells. It is systemic meaning it travels through the whole body.
Most research and study of cancer cells have come from a cell line called HeLa cells.