The cell cycle Flashcards
Many cells require — to a substrate. how did experiments show this?
anchorage. a cell suspended in agar had very low chance of entering S phase, a cell spread on a large adhesive patch had high prob of entering S phase
what are integrins?
transmembrane proteins that function as dimers to bind cell to ECM. principle receptors for anchorage to ECM substrate (with help from other proteins like focal adhesions)
Cell growth, division, and survival are inhibited by extracellular signaling proteins such as (3)
- TGF-Beta: inhibits proliferation and blocks progression at G1
- Bone Morphogenetic Protein (BMP): member of TGF fam. triggers apoptosis that sculpts vertebrate paw
- Myostatin (GDF-8): another TGF fam member. inhibits myogenesis and muscle growth
what does a myostatin deficiency cause?
uncontrolled muscle growth known as double muscling
what does ploidy have to do with cell size?
cell size is proportional to ploidy, higher number of copies of genome causes larger cells. This is still balanced though, eg salamanders with different ploidy have same sized organs but cells making up those organs are larger/smaller
why do cells need to replicate?
needed during development of organisms. Then needed to replace cells that don’t live long. without ongoing division, adults die
what are the phases of cell cycle?
Interphase (G1, S, G2)
G1: cell growth and monitoring of intracellular and extracellular conditions
S: DNA is synthesized during the process of duplication
G2: cell growth and monitoring of intracellular and extracellular conditions
M: Mitosis, nuclear division
G0: specialized resting state can last days-years. many cells stay in G0 permanently (neurons)
what role do cytoskeletal filaments have in cell replication?
they are essential. microtubules are necessary for alignment/separation of chromosomes. actin is important at end of mitosis separation
how is entry into phases of cell cycle regulated?
by Cell Cycle Control System (CCCS) which is an orderly series of biochemical switches
what does the CCCS respond to? what does it prevent?
Responds to intracellular and extracellular signals
prevents later events from starting before earlier events are complete
what are the three main checkpoints in the CCCS?
G2/M transition: ready to enter mitosis
Metaphase to Anaphase: trigger anaphase and proceed to cytokinesis
Start transition: enter cell cycle and proceed to S phase
What are Cdk’s?
Cyclin dependent kinases. they are evolutionary conserved in all eukaryotes. They function to control the CCCS by being activated by cyclin in waves that allow checkpoints to be passed
Why does Cdk concentration oscillate?
there is a dynamic balance between cyclin synthesis and cyclin degradation. cyclin conc increases gradually but kinase activity increases abruptly when cyclins reach critical conc (remember the figure on slide 36)
what did the experiment with xenopus oocyte tell us?
the oocyte is driven to M phase when injected with M phase cytoplasm but not when injected with interphase cytoplasms. this is because there is not sufficient M-cyclin conc in interphase
when would you expect to see each type of Cdk present in a cell?
G1/S-Cdk is activated during G1 and tapers off as S starts.
S-Cdk is activated at S phase and stays active until anaphase starts
M-Cdk is activated slowly through G2 and is high during M until anaphase
