Chapter 8: Cell Growth and Division

Cell Growth

Describe cell growthDefine cell divisionRelate cell growth to cell division

Why do cells divide?

To reproduce To grow bigger To repair injuries To become more efficient

Limits of Cell Growth1. Volume grows faster than surface area

2. Therefore a larger cell has a more difficult time getting stuff into (oxygen & nutrients) and out of (wastes) the cell

3. SOLUTION: Cell Division

Rates of Cell Growth

1. Vary depending on cell type

2. E. Coli divide every 30 minutes

3. Some cells take much longer to divide or “stop” dividing for a while

Controls on Cell Growth

1. Some cells rarely/never divide – nervous and heart cells

2. Some cells divide daily – skin and digestive tract cells

3. STOP switch: cells stop growing when they bump into each other

4. ON switch: cut or break in tissue cause cells to grow rapidly (but growth slows as healing reaches completion)

Cell Division: Mitosis & CytokinesisDefine mitosis and cytokinesisDescribe the cell cycle and the

changes that take place during interphase

Discuss the events and significance of mitosis

Chromosomes1. Chromosomes:

o “colored body”o seen only when the cell divideso contain genetic info in the form of

DNAo are coiled chromatin

2. Composition of Chromatino Make up chromosomeso Composed of DNA and protein

called histones (helps to condense the DNA)

o DNA in a chromosome is 10,000x longer than the chromosome itself

o Must condense in order to separate correctly during mitosis

o Can only see chromosomes during division

o Each chromosome replicates and is paired as sister chromatids joined at a centromere

o Human cell = 46 chromosomes (2n)

“n” number = 23 = “haploid”

2n = 46 = “diploid” 4n = 92 (during interphase) Body cells (aka somatic

cells) = 2n = 46 Sex cells (aka eggs & sperm)

= n = 23

Chromosome Structure

The Cell Cycle

1. Growth, prepares for division, divides (anywhere from 6 hours to 100 days)

2. 3 Partso Interphaseo Mitosis (PMAT) - few

minutes to several days

o Cytokinesis

Interphase – 3 stages

More than 90% of the life of a cell is spent in this phase

G1: cell growth, development, and protein production (longest)

S: “Synthesis”, DNA replication

G2: Organelles replicated (shortest)

Note: DNA exists as chromatin (no chromosomes yet)

Mitosis - Prophase

Longest phase of MITOSIS (50-60 % of total time required for mitosis)

Nuclear membrane starts to disintegrate

Chromosomes condense (become visible) – seen as 2 identical chromatids lying side by side held together by centromeres

Centrioles move to opposite poles

Spindle fibers grow from centrioles, attach at centromeres

Mitosis – Metaphase (hint “m”=middle)

Chromosomes attach to the spindle fibers

Chromosomes line up in the middle (aka equator)

Spindle fibers run from centrosomes to centromeres of the chromosomes

Mitosis - Anaphase (hint “a” = away)

Centromeres split Spindles retract and pull

sister chromatids apart Chromosomes move to

opposite poles (toward centrioles)

Mitosis - Telophase

Chromosomes cluster at poles

Chromosomes uncoil – back into chromatin

Nuclear envelope reforms around each new nuclei

Mitosis is done Cell membrane begins to

pinch in the middle

Cytokinesis Cell membrane moves inward and pinches in the middle

forming two identical cells In plant cells – a cell plate (eventually becomes the cell

wall) and cell membrane appear separating the 2 new cells

There are now 2 identical cells – same DNA, etc.

http://media.pearsoncmg.com/bc/bc_campbell_concepts_5/media/assets/interactivemedia/activityshared/ActivityLoader.html?c6e&12&03&8B%20Mitosis%20and%20Cytokinesis%20Animation

http://media.pearsoncmg.com/bc/bc_campbell_concepts_5/media/assets/videos/AnimalMitosis-V.html

Pop Quiz????

1. What is the main goal of cell division?2. What are the 3 phases of interphase?3. What are the 4 phases of mitosis?4. A cell has 12 chromosomes. At the end

of cell division how many cells will there be?

5. A cell has 12 chromosomes. At the end of cell division how many chromosomes will be in each cell?