Chap 12 - Cell Cycle Flashcards
Centrosome vs Centromere
CentroSOME - cytoskeleton component in animals.
CentroMERE - the bit that connected sister chromatids.
Centromere structure
Repetitive DNA sequences that are recognised by proteins and used to bind the chromatids together.
Cohesins
Complexes along the length of sister chromatids that attach them even more.
5 phases of cell cycle
Mitosis (M):
- Mitosis
- Cytokinesis
Interphase:
- G phase
- S phase
- G2 phase
Phases of mitosis
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
Prophase
- Chromosomes condense and cohesins form.
- Nucleoli gone.
- Centrosomes (which duplicated in interphase) move apart, with spindles beginning to form.
Asters
Radial “stars” of microtubules extending from the centrosomes.
Prometaphase
- Nuclear envelope fragmented
- Chromosomes fully condensed
- Kinetochores form at centromere of chromatids, which microtubules begin to attach to.
Kinetochore
Large protein complex on the centromere that spindles attach to.
Cell lengthening during mitosis
Spindles from opposing centrosomes are pushed apart while also lengthening.
Metaphase
- All kinetochores attached.
- Centromeres lined up on the metaphase plate as they at pulled to both cell poles.
- Centrosomes in contact with plasma membrane at the poles.
Metaphase plate
‘Imaginary’ plane at equator of cell that chromosomes line up in.
Anaphase
Very short!
- Cohesin proteins are cleaved, chromosomes pulled apart.
- The cell is lengthened by non-kinetochore spindles.
How chromosomes are pulled to poles
- Motor proteins walk the kinetochores up the spindle towards poles.
- Other motor proteins at the poles reel in the spindle.
Telophase
- New nuclear envelope begins to form.
- Nucleoli reappear.
- Spindles depolymerised
[End of mitosis]
Cytokinesis
The division of cytoplasm with a plasma membrane inbetween.
Usually well underway during telophase, finished quickly after mitosis ends.
Cleavage
One method of cytokinesis (in animals)
A shallow groove (cleavage furrow) forms where metaphase plate used to be. The ring contracts with myosin proteins until the cell pinches into two.
Cytokinesis in plants
- Vesicles containing cell wall materials produced (from Golgi)
- Move to middle of cell and coalesce into a cell plate.
- Cell plate enlarges until it fuses with plasma membrane.
Binary fission
Doubling in size and then splitting of single celled organisms.
Involves mitosis in eukaryotes, no mitosis in prokaryotes.
Binary fission in prokaryotes (bacteria)
- DNA replication starts at origin of replication on the chromosome.
- Two duplicated origins move to opposite ends of cell.
- Cell elongates.
- Plasma membrane pinched in with a protein similar to tubulin (evolutionary origin?!) and new cell wall formed.
Weird eukaryote binary fission #1 - Dinoflagellates
Microtubules pass THROUGH the nucleus, then the nucleus divides similarly to prokaryotic binary fission.
Weird eukaryote binary fission #2 - Diatoms
The spindles are formed and separate chromosomes inside nucleus, and nucleus then splits in two.
G phase
Growth, mostly.
S phase
DNA synthesis, also growth too.
G2 phase
Woah growth again, and ‘preparation’ for mitosis such as centrosome duplication.
Checkpoints in cell cycle control system
Important control points where triggers/inhibitors regulate the cell cycle.
Location of important cell cycle checkpoints(3)
- Near the end of G1
- At the start of M
- Near the end of M
