Examples of kinase in the following topics:
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- Kinases are a major component of cellular communication.
- Yeasts have 130 types of kinases.
- More complex organisms such as nematode worms and fruit flies have 454 and 239 kinases, respectively.
- Of the 130 kinase types in yeast, 97 belong to the 55 subfamilies of kinases that are found in other eukaryotic organisms.
- The only obvious deficiency seen in yeasts is the complete absence of tyrosine kinases.
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- Signal cascades convey signals to the cell through the phosphorylation of molecules by kinases.
- A major component of cell signaling cascades is the phosphorylation of molecules by enzymes known as kinases.
- For example, phosphatases are enzymes that remove the phosphate group attached to proteins by kinases in a process called dephosphorylation.
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- The transfer of the phosphate is catalyzed by an enzyme called a kinase.
- Various kinases are named for the substrate they phosphorylate.
- The main role of cAMP in cells is to bind to and activate an enzyme called cAMP-dependent kinase (A-kinase).
- A-kinase regulates many vital metabolic pathways.
- Enzymes known as kinases phosphorylate PI to form PI-phosphate (PIP) and PI-bisphosphate (PIP2).
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- Most growth factors bind to cell-surface receptors that are linked to tyrosine kinases.
- These cell-surface receptors are called receptor tyrosine kinases (RTKs).
- Activation of RTKs initiates a signaling pathway that includes a G-protein called RAS, which activates the MAP kinase pathway described earlier.
- The enzyme MAP kinase then stimulates the expression of proteins that interact with other cellular components to initiate cell division.
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- Two groups of proteins, called cyclins and cyclin-dependent kinases (Cdks), are responsible for the progress of the cell through the various checkpoints.
- Like all kinases, Cdks are enzymes (kinases) that phosphorylate other proteins.
- Cyclin-dependent kinases (Cdks) are protein kinases that, when fully activated, can phosphorylate and activate other proteins that advance the cell cycle past a checkpoint.
- To become fully activated, a Cdk must bind to a cyclin protein and then be phosphorylated by another kinase.
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- The last step in glycolysis is catalyzed by pyruvate kinase.
- (Recall that fructose-1,6-bisphosphate is an intermediate in the first half of glycolysis. ) The regulation of pyruvate kinase involves phosphorylation, resulting in a less-active enzyme.
- Pyruvate kinase is also regulated by ATP (a negative allosteric effect).
- Pyruvate dehydrogenase is also regulated by phosphorylation: a kinase phosphorylates it to form an inactive enzyme, and a phosphatase reactivates it.
- The kinase and the phosphatase are also regulated.
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- Additionally, the last step in glycolysis will not occur if pyruvate kinase, the enzyme that catalyzes the formation of pyruvate, is not available in sufficient quantities.
- Thus, pyruvate kinase is a rate-limiting enzyme for glycolysis.
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- Cyclic AMP activates PKA (protein kinase A), which in turn phosphorylates two enzymes.
- The first enzyme promotes the degradation of glycogen by activating intermediate glycogen phosphorylase kinase (GPK) that in turn activates glycogen phosphorylase (GP), which catabolizes glycogen into glucose.
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- This transition, as with all of the major checkpoint transitions in the cell cycle, is signaled by cyclins and cyclin dependent kinases (CDKs).
- If the DNA has been correctly replicated, cyclin dependent kinases (CDKs) signal the beginning of mitotic cell division.
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- Adenylyl cyclase catalyzes the conversion of ATP to cAMP. cAMP, in turn, activates a group of proteins called protein kinases, which transfer a phosphate group from ATP to a substrate molecule in a process called phosphorylation.
- Further amplification occurs as protein kinases, once activated by cAMP, can catalyze many reactions.