Chapter 10 and 11-4 Cell Growth and Division. Organisms need to grow and reproduce: Both require...
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Transcript of Chapter 10 and 11-4 Cell Growth and Division. Organisms need to grow and reproduce: Both require...
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