Chapter 10 and 11-4

Cell Growth and Division

Cell Growth and DivisionOrganisms need to grow and

reproduce:

• Both require divisions of the nucleus (Mitosis/Meiosis) and the cytoplasm (Cytokinesis)

1. Growth

• Mitosis- the division of the cell’s nucleus into 2 identical copies

2. Reproduction

• Meiosis – the reduction of the chromosomes by ½ to create gametes for sexual reproduction.

I. Cell GrowthA. Limits to Cell Growth

– As a cell grows larger the cell volume increases but the surface area to volume ratio decreases.

– What does this mean?

Cells come in different sizes, in order to make a multicellular organism cells must divide, not just grow larger

Exchanging Material1. Larger cells have more

problems getting materials in and out of the cell.

2. Doubling the cell size; increases the amount of time it takes for materials to enter and leave.

a. O2, nutrients, monomers, water enter

b. waste products such as CO2 leave, also proteins made by the cell leave

3. How rapidly materials pass across the membrane and get to the center of the cell is a function of surface area

Cell Sizes

Ratio of surface area to volume

VolumeLengthxwidthxheight

Surface Arealengthxwidthx6 6 cm2

1 cm3

2:13:16:1

27cm3

8 cm3

54 cm2

24 cm2

4. The relationship of surface area (SA) to volume (V) is expressed

as a SA/V Ratio

5. The higher the SA/V ratio = the more efficient transport of substances

• Example: If you wanted to chill a warm Coke, would you use 3 large ice cubes or crushed ice?

• Answer: crushed ice (more surface area exposed to cool down drink)

vs.

DNA Overload:1. DNA must be able to

be transcribed fast enough to create mRNA to make proteins for the cell to function

2. The DNA is limited to the amount of mRNA that can be produced without significantly slowing down the cells activities.

B. Division of the Cell1. Cellular division solves

both problems. • In order to grow larger,

more cells will be made through the process of cell division.

2. As an organism grows larger, the number of cells increases

3. Conception -1 cell, birth – 1 trillion cells, adult - 65 trillion cells

B. Division of the Cell

4. The DNA must be copied, the cell divides and the daughter cells have increased SA/V ratios

5. This allows for efficient exchange of materials and DNA can fulfill protein manufacturing quota

DNA replication

II. Cell Division: Mitosis and CytokinesisA. Chromosomes: Structure

and Composition1. Prokaryotes: circular form

(plasmids)2. Eukaryotes: form distinct

shapes of chromosomes3. Chromosomes are made

out of a material called chromatin (DNA + histone = nucleosome)

• condenses into chromosomes during cell division (mitosis)

• Coil and supercoiling of nucleosome

http://www.biostudio.com/demo_freeman_dna_coiling.htm

4. Organisms vary in the number of chromosomes:

• Goldfish: 94 Potato: 48

• Dog: 78 Carrot: 18

• Humans: 46 Drosophila: 8

B. The Cell Cycle

1. During a cell cycle, a cell grows, prepares for division, and divides to form 2 daughter cells, each of which begins the cycle anew.

2. 2. Two phases: 1. Interphase = (growth, organelle and DNA replication)

2. M Phase = Mitosis & Cytokinesis

G1

s

G2

M-phase

C. Interphase

1. Normal cellular functions, DNA is not visible (chromatin), growth and replication of DNA.

2. Involves 3 stages: i. G1 (Gap 1) – cell grows, proteins and organelles are

produced

ii. S - DNA synthesis/replication

iii. G2 (Gap 2) – organelles/structures required for cell division are made

D. Mitosis

* Nucleus divides into two identical nuclei

* Four phases include:

Prophase, Metaphase, Anaphase, Telophase (PMAT)

1. Prophase• Longest phase of mitosis (50-

60% of time)• Chromosomes start to become

visible• Chromatin is coiled and

condensed• Centrioles separate from each

other• Spindle fibers begin to form• Nucleolus disappears• Nuclear envelope begins to

break down

2. Metaphase

• Shortest phase of mitosis (a few minutes)

• Chromosomes line up at center of cell (equator)

• Microtubules attach to the centromere & spindle poles which forms an aster

3. Anaphase• Centromeres split which then

separates the sister chromatids• Individual chromosomes move

toward opposite poles• Spindle grows larger• Chromosomes are pulled toward

the poles where the centrioles are located.

4. Telophase• Chromosomes begin to uncoil• Chromatin fibers are reformed• Nuclear envelope reforms• Spindle begins to breakdown• Nucleolus becomes visible in

each daughter nucleus

**MITOSIS IS NOW COMPLETE!!

E. Cytokinesis• Dividing of the cytoplasm and organelles• Plant cells form a cell plate that becomes

the cell wall• Animal cells: membrane pinches inward

Vesicles containingcell wall material

Cell plateforming

Cell plate Daughtercells

Wall ofparent cell

Daughternucleus

Cell wall New cell wall

Chromosomes

Centrioles

Centrioles_______________(paired chromatids)

Nuclear envelope

Nuclear envelope

Centrioles

Chromosomes

Centromere

Centrioles

Chromatin

reforms

Individual

SpindleDaughter Cells

http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter11/animations.html#

Animal Cell Division in White Fish Blastula

III. Rates of Cell Growth & Controls on Cell Growth

• Escherichia coli (E. coli) can divide every 20-30 minutes under ideal conditions.

• Ideal conditions cannot be sustained forever.

• Every organism/type of cell grow at varying rates - p249

• Some cells rarely divide if they divide at all. – Example: nerve cells, heart cells,

muscle cells, red blood cells

• Cells that form linings are frequently replaced which requires cell division– Example: Skin cells, blood cells

(marrow)

E.coli

Skin Cell

A. Controls on Cell Division1. Cells in the Lab:

1. Grown in a petri dish containing nutrient broth (provides food for the cells)

2. Cells will grow until they form a thin layer then stop

3. Cells contact other cells which signals cell division to stop

• We don’t see multiple layer grow

1.

2.

4.

3.

5.

Figure 2: Cells in a petri dish will continue to grow until they come in contact with other cells.

Question: What happens when you cut your finger or break your bone?

Answer: The cells bordering the injury will begin dividing to fill in the gap in the tissues that have been torn or broken. This is the process known as healing.

B. Cell Cycle Regulators1. Scientists wondered what ____________cell division.2. Tim Hunt and Mark Kirschner discovered that cells in mitosis contained a protein that when injected into a cell would cause the formation of spindle fibers.3. Protein group known as ____________ regulates the cell cycle. 4. They rise and fall in time with the ________.5. Cyclins _____________ the timing of the cell cycle in __________cells.

controlled

cyclins

cell cycle

regulateeukaryotic

6. Two main groups of protein regulatorsi. Internal Regulators: respond

to events __________________ . Ex. Make sure cell doesn’t enter mitosis until chromosomes have all replicated

ii. External Regulators: respond to events _________________________.

Ex. Embryonic growth and healing

inside the cell

outside the cell

C. Uncontrolled Cell Growth• Cancer: a disorder in which some

cells have lost the ability to control their own rate of growth

• Malignant Cells (cancer cells) - will grow multiple layers and develop into a tumor which eventually will spread to other areas of the body.

• Benign Tumors (NOT cancerous) - self-contained and will not spread to other areas.

2. Causes of Cancer:a. Exposure to mutagens

(carcinogens)1. chemical – compounds

within tar from cigarettes, asbestos, thalidomide, some pesticides

2. Diet – low fiber, high salt with few veggies

3. Radiation (10%) – UV, gamma

4. Viral (18%) – Hepatitis, HPV

5. genetic defect (5%) – p53 gene

Number of Cells

Field 1 Field 2 Field 3 TOTAL % of Total(Pie Chart)

Time in each stage

(% x 1,440min)

Interphase 1247 1820 1490

Prophase 67 88 101

Metaphase 39 67 53 159 3.1% 44.6 min

Anaphase 26 36 45

Telophase 13 9 19

TOTAL 5120

Consider the that is takes, on average, 24 hours (1,440 minutes) for onion root tip cells to complete the cell cycle. You can calculate the time spent in each phase of the cell

cycle from the percentage of cells in that stage