Cell cycle & Mitiosis Flashcards
Why is cell division is important ?
- important in growth and repair of tissues in multicellular organism
- reproduction of all organisms
What four events must occur for cell division ?
- a reproductive(intra/extracellular) signal initiates cell division
- replication of DNA
- Segregation :Distribution of DNA into 2 new cells
- Cytokinesis: separation of cellular material into 2 new cells
How does binary fission occur ?
- Replication occurs as the DNA is threaded through ‘ Replication complex’ of proteins
-Rapidly dividing prokaryotes the entire time is DNA replication between cell divisions
Binary fission how 2?
When replication is complete the daughter DNA molecules are segregated at opposite ends
The ORI regions move towards opposite ends of cells aided by special protein
3 binary fission ?
Cytokinesis begins by a pinching in of a plasma membrane ; protein fibres (mostly Ftsz) form ring
New Cell wall materials are synthesised resulting in a separation of 2 cells being formed
Cell cycle in eukaryotes consist of ?
MITOSIS
CYTOKINESIS
INTERPHASE
Interphase ?
nucleus is visible & cell functions,including DNA replication,occur
Begins after cytokinesis ends when mitosis starts
Interphase subspaces ?
G1: (Gap 1) between cytokineses and S phase ;chromosomes are single , unreplicated structures
- Duration varies from minutes to years
Some cells enter resting phase (G0)
Interphases 2 nd sub stage ?
G1 TO S transition the commitment is made to DNA replication and subsequent cell division .
Called Restriction (R )point
Describe S phase & G2 Phase ?
S phase -(synthesis ) DNA replicates forming 2 sister chromatids stay together
G2 :(gap 2 ) cell prepares for mitosis
By synthesising structures to move the chromatids
How do transitions occur from 1 stage to the next ?
Specific signals trigger this-add more
What do these signals act through ?
through proteins called cyclin-dependant kinases (Cdk’s)
Kinase catalyse transfer of a phosphate group from ATP to a protein (Phosphorylation)
A Cdk must be activated by binding to a cyclin protein
Allosteric regulation altering the shape of Cdk thus exposing its active site to allow it to transfer a phosphate
Is there 1 cyclin-CD-R complex ?
no there ar many. At diff stages
1.) G2 PHASE
2.) MITOSIS
3.)G1
4.) S PHASE
What does the Cyclin Cdk do at the G1-S transition ?
Progress between the restriction point depends on Retinoblastoma protein (RB)
RB usually inhibits cell cycle BUT when phosphorylated by cyclin Cdk in a lot of places ,RB becomes inactive (changing 3D structure) and thus allows cell cycle
What are cell cycle checkpoints ?
G1- DNA damage
S - incomplete replication or DNA damage
G2 - DNA damage
M - chromosomes unattached to spindle
Mitosis
Newly replicated chromosomes-SISTER CHROMATIDS
-separates into 2 new nuclei
Sepeerating many large liner chromosomes would be diffifvutl
How is DNA packed ?
Eukaryotic DNA molecule are “packed” and organised by histone proteins even uncondensed DNA is wound around histones to form nucleosomes.
When the chromosomes condense these Hilton’s begin to pack together
The phases of mitosis ?
PROPHASE
The chromatin condenses and distinct chromatids become visible under a microscope
PROMETAPHASE?
Nucleus envelope breaks down and chromosomes attach to the ‘spindle ‘ of microtubles
ANAPHASE
The chromatids seperate and move to opposite poles by the spindle
TELOPHASE
Nuclear envelope reforms,spindle disappears,chromosomes become less compact
Interphase
- Orientation is determined but the centrosome an organelle near the nucleus
Prophase in depth
Each centrosome can consist of 2 centrioles- hollow tubes formed by microtubules at right angles
The centrosome doubles during S phase ;during prophase they move to oppposite ends of the nuclear envelope
PROMETAPHASE
Late in prophase ,the spindle attachment points called kinetochores develop on each chromatid
Microtubules form between the poles and the chromosomes to make up the spindle fibres
Nuclear envelope breaks down and chromosome attach to a spindle of microtubule
METAPHASE
2 types of microtubules in the spindle
Chromosomes line up in the middle of/ equatorial plate
- polar microtubules form spindle framework; run from one pole to the other
- Kinetochore microtubules attach to kinetochores on the sister chromatids and to microtubules in opposite halves of the spindle
ANAPHASE
After separation ,the chromatids are called daughter chromosomes
- chromatids share a centromere
- chromosomes have their own centromere
During the separation of SC -controlled by M phase Cyclin-Cdk; it activates ANAPAHSE -PROMOTING COMPLEX(APC)
Cohesion that hold the chromatids together is hydrolysed by seperase.
Chromatids separate and move to opposite poles of spindle
Anaphase 2
Kinetochores have motor proteins; energy from ATP moves chromosomes along the microtubules
Kinetochores microtubules also shorten ,drawing chromosomes towards pole
Telophase
Nuclear envelope reforms spindle fibres disappear chromosomes become less compact
Cytokineses
Division of the cytoplasm follows mitosis
In animal cells the plasma membrane pinches in between the nuclei
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Cytokinesis in plant cells
The membrane bound vesicles appear along the plane of cell division .
These fuse to form a new plasma membrane
Contents of vesicles form a cell plate -the beginnings of new cell wall.
