Cell cycle control Flashcards
why is cell cycle under strict and complex control?
since its disturbance leads either to cell death or to cancer development
how can cell cycle be distributed?
by chemical or physical agents directly or indirectly
mutation of genes that encode cell cycle regulatory proteins is usually at what origin?
at the origin of abnormal cell cycle
what does alteration of signalling pathways that involve oncogenes also lead to?
may also lead to uncontrolled cell cycle
what is the most important check point in the cell cycle?
at the end of G1, the G1-S transition
what happens if a cell passes this gap? what is its benefit?
it will necessarily continue S, G2 and M simply in order to avoid wasting energy
DNA replication must necessarily be followed by what? what happens to the replicated DNA otherwise?
DNA replication must necessarily be followed by cell division, otherwise the replicated DNA would be useless
What is the other check point?
the G2-M transition
what did cell fusion experiment between cells in different stages of the cycle reveal?
revealed the presence of cytoplasmic factors that control nuclear activity and cell cycle
what do the members of the MPF-like family (maturation promoting factor-like) have?
phosphorylation activity
kinase activity of MPFs is dependent on which family?
the cyclin family
what is concentration of cyclins considered as and what happens to concentration as the cell cycle progresses?
the regulatory subunits of MPFs, rises and falls in a predictable pattern as the cell cycle progresses
why are they named cyclins?
because their amounts vary in a cyclic manner
how many families are known? name them and say when is their peak.
2 families are known, the G1 cyclins whose peak is during G1 and mitotic cyclins whose peak is just prior to mitosis
what do cyclins control?
control the activity of MPFs
what are MPFs therefore referred to as and why?
cyclin-dependent kinases (Cdk or cdc) since they are active only when the 2 subunits are assembled
how does MPF promotes initiation of M phase? what does this MPF consist of?
MPF that promotes initiation of M phase by activating G2-M transition, consists of a first subunit named cdc2-kinase (serine/threonine kinase) and a second regulatory one which is a “mitotic cyclin” whose concentration is maximum in the G2 phase
what does the activated MPF trigger and how? what do these specific proteins initiate?
triggers M phase by phosphorylating specific proteins (whose conformations are changed upon phosphorylation) which initiate mitosis
give example on proteins that are activated by such phosphorylation.
proteins which initiate condensation of chromatin into chromosome and those that induce cytoskeleton change are activated by such phosphorylation
what does the same cdc2-kinase enhance and when?
the same cdc2-kinase enhances the G1-S transition when it dimerizes with one of the G1 cyclins whose maximum concentration is reached by the end of G1
what will the cdc2-kinase assembled with G1 cyclins phosphorylate do?
another set of proteins that induce DNA replication and histone synthesis
