Term
| What two factors control cell size? |
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Definition
1. Genetics
2. Nutrient availability |
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Term
| What is the main determinant in organism size? |
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Definition
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Term
| What are the effects of accelerating the rate of division? |
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Definition
1. more cells present
2. smaller cells present
Accelerating the rate of division does not enlarge an organ |
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Term
| What are the effects of decelerating the rate of division? |
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Definition
1. less cells
2. bigger cells
Note: This does not cause the organ size to shrink |
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Term
| Describe the relationship between growth and division |
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Definition
| Growth is NOT a consequence of division. However, division is sensitive to growth |
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Term
| What are intrinsic factors? |
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Definition
Factors predetermined by the organ, independent of outside signals
Organ goes through life with a set of "blinders" to outside circumstances |
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Term
| What are extrinsic factors? |
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Definition
| Communication between the organ and cells and the external environment that affect its development |
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Term
| Describe the IGF-1 Pathway |
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Definition
1. IGF-1 binds to surface receptors
2. Triggers PIP2 to become PIP3
3. PIP3 activates PDK1 and Akt
4. Akt suppresses EIF-4EBP and PDK1 activates S6K
5. This allows growth of ribosomes and translation of mRNA |
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Term
| How does the Tsc/Tor pathway work? |
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Definition
1. Tsc1 and Tsc are stimulated by the presence of nutrients in the cell and bind together
2. The complex serves to turn the GTPase Rheb off
3. When deactivated Rheb binds to Tor
4. Tor activates S6K and inhibits eIF-4EBP (same as IGF-1 pathway)
5. Allows growth of ribosomes and translation of mRNA
Note: This pathway intertwines with the IGF-1 pathway via S6K and eIF-4EBP |
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Term
| Which of the two pathways (IGF-1 vs. Tsc/Tor) is older and how do we know this? |
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Definition
Tsc/Tor
It is found in more primitive organisms where IGF-1 is not |
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Term
| Where do cells stop in the cell cycle if lack of nutrition occurs or they are not of sufficient size to divide yet? |
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Definition
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Term
| Describe the mechanism of how nutritional availability affects cell division |
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Definition
| Low nutrient availability leads to low biosynthesis of ribosomes, whereas high availability leads to more ribosomes. An increased number of ribosomes leads to increased cyclin production |
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Term
| Describe the hypothesized method of how extrinsic factors work |
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Definition
Cell-cell communication
Cells secrete factors and signals that feedback to inhibit further growth of that tissue. When concentration becomes high enough, growth stops |
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Term
| What type of cells is myostatin present in and what function does it serve? |
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Definition
1. Skeletal muscle cells
2. Inhibits further growth |
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