The Cell Cycle Flashcards
what is the cell cycle
the cell cycle is a sequence of events where 2 cells are duplicated and divided
What are the 2 main phases in the cell cycle
M phase and interphase
What happens in the m-phase
nuclear division (mitosis)
cytoplasmic division
what happens during interphase
This is defined as the period between cell division
G1 phase
S-phase is where DNA replication occurs
g2 phase
What type of cells only divide when an appropriate stimulus is given
liver cells when they are damaged
What type of cells divide on an ongoing basis
Hematopoietic and epithelial stem cells
How do our cells make sure that each process in each stage has been carried out correctly
The cell-cycle has a control system that will delay later events until earlier events are complete
The 3 major checkpoints:
start point
G2/M checkpoint
metaphase-to-anaphase transition
Start checkpoint
Right before transcription
Checks to see if the environment has the proper nutrients
G2/M checkpoint
checks to see if all DNA is replicated and if DNA damage is repaired
metaphase-to-anaphase transition
sees if all chromosomes are properly attached to the mitotic spindle
Is there a specific mechanism that tells cells to proceed to the next stage
cell cycle is controlled my molecular switches
The switches are cyclin-dependent protein kinases (Cdks)
Interphase
G1: where centrosome duplication is initiated
G2: centrosome duplication is completed
S-phase: chromosomes ae replicated (DNA replication)
Prophase
- replicated chromosomes condense
- mitotic spindle assembly starts
S-Phase
During chromosome replication, cohesins are deposited to hold the sister chromatids together
What will happen at the end of G2? why does this need to happen?
replicated chromosomes will be dispersed, but tangled/
they need to be organized for mitosis
Prophase
most cohesins will be removed
condensins will condense the DNA and the 2 sister chromatids will be organized and connected in the centromere by cohesins
Also the assembly of the mitotic spindle will begin and requires duplicated centrosomes
What is centrosome structure
Contains a pair of centrioles that are organized at right angles
The centrosome is surf by pericentriolar material that the y-tubulin ring complex (y-TuRCs)
Describe the mitotic spindle assembly
- Assembly of microtubules that starts in Prophase
- Microtubules dynamics (assembly and disassembly)
3.stabilize the inter pole microtubules (connected to DNA) through kinesins
- Position astral microtubules (the ones facing outwards) through cytoplasmic dyneins
The completion of the mitotic spindle requires breakdown of nuclear envelop
Where does nuclear envelope breakdown occur
It occurs between prophase and prometaphase
What is nuclear envelope breakdown
This happens to at the beginning of mitosis so that the spindles can capture the condensed chromosomes
Nuclear envelope breakdown
The phosphorylation of Latin’s and nuclear pore proteins triggers the disassembly of the nuclear envelope into small membrane vesicle
Prometaphase
This occurs after the nuclear envelop breakdown
The chromosome are attached to the microtubules and chromosome movement begins
Astral microtubules
Help position the mitotic spindle and cytoplasmic dyenin
Inter pole microtubules
These are anti parallel microtubules that are cross-linked
Provide structural support for spindle poles
Kinetochore microtubules
They attach and position specific chromosomes
What is another name for metaphase-anaphase transition
Spindle assembly checkpoint
Anaphase will not begin until all chromosomes are attached to metaphase plate
Anaphase
Separation of sister chromatids by separate cutting cohesin complex
Anaphase AM
Kinetochore microtubule shortened and sister chromatids are pulled apart
Anaphase B:
Spindle poles move outward
Telophase
Chromosomes are now separated
The mitotic spindle disassembles
Nuclear envelop re-assembles
Chromosomes decondense
How will the nuclear envelop reassemble after anaphase
Dephosphorylation of nuclear pores and Latin’s
It will re-assemble with nuclear laminate and pores
cytokinesis in animal cells
Here the cytoplasm divided in 2 by a contractile ring of actin and myosin filaments
This contractile ring is at the cleavage furrow
This will mark the end of M phase
When is the contractile ring formed
During anaphase actin and myosin filaments assemble
What is the difference between cell division in plant cells
Mitosis is very similar in the two cells but in plant cells there is no centrosome
Cytokinesis will also be different because the membrane vesicles fuse together forming a new cell wall
Cytokinesis in plant cells
Telophase: chromosomes separated. phragmoplasts start to form which will form cell plate
Cytokinesis: nuclear envelope re-assemble and chromosomes are decondensed. The cell plate will form and eventually mature into new cell wall
