Cell Cycle Control and Cell Division II Flashcards
What are the four checkpoint controls?
- Late G1 or Start Checkpoint
- G2-M Checkpoint
- Metaphase to anaphase transition
- (G0)
What is the function of cell cycle checkpoint controls?
designed to block progression through each of the checkpoints if problems are sensed
What are the steps of the initation phase of DNA replication?
– Late mitosis-early G1: prereplication complex assembles at the origins of replication
– Onset of S phase when prereplication complex nucleates the formation of the preinitiation complex
Where does DNA replication occur?
specific sites or origins of replication
What recruits RNA polymerase?
preinitiation complex
What nucleates the preinitation complex?
phosphorylation of ORC (origin recognition complex)
What CDK triggers S phase?
S-Cdk
What happens at the G2/M checkpoint?
completion of DNA replication
What happens during S phase when S-Cdk activation occurs?
formation of preinitiation complex, initiation, elongation
What happens during M phase when M-Cdk activation occurs?
chromosome segregation
What happens during G1 phase when APC/C activation occurs?
assembly of new prereplicative complexes at origins
What does the G2-M checkpoint ensure?
that all DNA has been properly replicated
What does M-Cdk induce?
- assembly of the mitotic spindle
- chromosome condensation
- promotes breakdown of nuclear envelope
- rearrangments of actin cytoskeleton and golgi
What is prophase?
the mitotic spindle assembles between the two centrosomes which have replicated and moved apart
What is prometaphase?
starts with the abrupt breakdown of the nuclear envelope; chromosomes can attach to spoindle via kinetochores and undergo active movement
What is metaphase?
- chromosomes are aligned at the equoator of the spindle midway between the spindle poles
- kinetochore microtubules attach sister chromatides to opposite poles of the spindle
What is anaphase?
sister chromatids synchronously separate to form two daughter chromosomes and each is pulled slowly toward the spindle pole it faces
What is telophase?
- two sets of daughter chromosomes arrive at the poles of the spindle and decondense
- a new nuclear envelope reassembles around each set, completing the formation of two nuclei and marking the end of mitosis
What is cytokinesis?
the cytoplasm is divided in two by a contractile ring of actin and myosin filaments, which pinches the cell in two to create two daughters, each with one nucleus
What are the symptoms of roberts syndrome?
- prenatal growth retardation
- craniofacial abnormalities (microcephaly and cleft lip/palate and limb malformations)
What mutation is involved in roberts syndrome?
homozygous mutation of ESCO2
What other syndrome is roberts syndrome related to?
Cornelia de Lange Syndrome
What do ESCO2 mutations do in roberts syndrome?
- decreased rDNA transcription and subsequent ribosomal biogenesis and the observed defects in nucleolar morphology (decreased protein synthesis)
What should ESCO2 do in a typical person?
encode an acetyltransferase (important for formation of cohesion complex that binds to chromosomes and creates sister chromatid adhesion)
