Term
| What are the names of two ubiquitin ligases that destroy cyclins throughout the cell cycle and what is the purpose of cyclin destruction? |
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Definition
| SCF and APC. They bind at a mitotic destruction box and their purpose is to ensure a unidirectional cell cycle. |
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Term
| What is another name for the G1 checkpoint and what happens then? |
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Definition
| The G1 checkpoint is also called the restriction point. It occurs between G1 and S phases and size, environment, quantity of energy, presence of nucleotides, nutrient level, and growth factor presence is considered. |
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Term
| What happens at the G2 checkpoint? |
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Definition
| The cell makes sure that all DNA is replicated, that the environment is favorable, and that there are sufficient nutrients. |
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Term
| What happens at the exit from M1? |
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Definition
| The cell checks in the chromosomes are alligned at the spindle, that they are paired properly, and that the cell is ready to split. |
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Term
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Definition
| It mediates initiation of the cell cycle at the G1/S transition. |
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Term
| Name the phases of the cell cycle and what happens during each one |
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Definition
M = mitosis, & cytokinesis daughter cells split.
G1 = Longest. G0 resting phase if S not immediate.
S = DNA is replicated.
G2 = prep for division. |
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Term
| Which transcription factors activate Cyclin D1 and what does cyclin D1 do? |
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Definition
| Fos, Jun, & AP1. D1 is a major player in moving the cell cycle past the G1 checkpoint. |
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Term
| What do G1 cyclins do? What about G1/S, S, and M? |
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Definition
| G1 cylins (work on restriction point), G1/S Cyclins (act at end of G1 and commit cell to DNA replication), S-Cyclins (act in S phase to initiate DNA replication), M-Cyclins (promote mitotic events). |
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Term
| Where in the cell cycle does D1-CDK4/6 work? |
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Definition
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Term
| Where in the cell cycle does E1-CDK2 work? |
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Definition
| It moves cell into S phase. |
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Term
| Describe the characteristics of CDKs and cyclins? |
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Definition
| They do not exibit kinase activity unless associated with a cyclin. There are 9 mammalian CDKs. Cyclins are necessary for CDK activity and aid in substrate specifity. There are 20 mammalian cyclins. |
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Term
| How are CDK-cyclin complexes inhibited? |
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Definition
| Phosphorulation by p57, p27, or p21; aka Kip2, Kip1, and Cip1 or binding to inhibitory proteins like INK. This slows the cell cycle in adverse conditions. |
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Term
| What is checked at the checkpoint between S and G2 phase? |
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Definition
| Check for unreplicated DNA between S and G2. |
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Term
| What is MPF and what does it do? |
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Definition
| It is a CDK that activates chromosome condensation, nuclear membrane breakdown, mitotic apparatus assembly, and chromosome alignment. It also activates APC, which degrades cyclins. |
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Term
| Describe how chromosomes separate and what goes wrong when they fail to separate. |
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Definition
| MPF activates APC. APC activates separase (by degrading it's inhibitor, securin). Separase cleaves the cleisin complex and releases sister chromatids during anaphase. A weakening of the kleisin (scc1) linkage complex causes chromosomes to separate at the wrong time and distribute unevenly during cell division. |
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Term
| During which phase are cells most responsive to mitotic growth factors and TGF-beta? |
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Definition
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Term
| Cyclin D-CDK4/6 and Cyclin E-CDK2 control what kind of modification of which protein at which part of the cell cycle? |
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Definition
| Cyclin D-CDK4/6 and Cyclin E-CDK2 control phosphorulation of Rb at the R point of G1. Specifically, CDK4/6 initiates phosphorylation of pRb, and then CDK2 hyperphosphorylates it, making it unable to bind/inhibit TFs. Cell cycle moves forward. |
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Term
| What happens in retinoblastoma? |
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Definition
| When Rb is hypophosphorulated, it acts as a tumor suppressor. When it gets phosphorulated by Cyclin-CDK complexes, it turns off and the cell cycle moves forward. In retinoblastoma, Rb stays phosphorulated and cannot act as a tumor suppressor. In this case, the cell cycle moves forward uninhibited. |
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