Where does cell division take place?
-Development -Growth -Repair and maintenance -Cell diseases -Reproduction
What must happen before a cell divide?
1-There must be a reproductive signal 2-There must be growth (the cell double in size) 3-Replication of DNA 4-Chromosome segregation
What is cell cycle?
The period between cell divisions
What are the two main components of cell cycle?
Interphase and mitosis/cytokinesis
In which phase does the majority of cells spends their time?
What are the three phases in interphase?
G1, S and G2
Describe G1 phase
In G1 the cell double in size and prepare for DNA replication.
How many chromatid there are in the chromosome in G1 phase?
In G1 phase there's only one chromatid per chromosome.
What is nuclear envelope?
The double membrane that separates the nuclear content from the cytoplasm.
What are Microtubules?
Dynamic scaffolding poles that form the cytoskeleton and the mitotic spindle.
Which are the two kind of microtubules in the mitotic spindle?
1-Polar Microtubules 2-Kinetochore Microtubules
Describe polar microtubules:
Polar Microtubules form the framework of the spindle and run from one pole to the other.
Describe kinetochore microtubules:
Kinetochore microtubules attach to the kinetochore of the chromosomes.
What is a centrosome?
Centrosomes are organelles located near the nucleus that orientate the spindle apparatus in the right direction.
What's the function of Restriction?
To activate or arrest the cell cycle. The cell can only progress to the S phase if it has sufficiently grown during the G1 phase.
Describe how the activation/arrest of the cell cycle works at checkpoints:
The cell cycle is controller by CDKs. CDKs phosprylate RB in order to inactivate it. Inactivated RB allows the cell cycle to proceeds.
Why are cyclins important?
Cyclin phosphorylate CDK so that CDK can phosphorylate RB.
Describe S phase
In S phase the DNA Replication begins. Each chromosome starts duplicating from many origins of duplication located along its structure. Centrosomes duplicates as well.
How are sister chromatids held together?
Sister chromatids are held together by a protein called cohesin.
Describe G2 phase:
In G2 phase the cell prepare for mitosis and duplicates its organelles. Centrosome diverge to opposite ends of the cell.
What happens at G2/M transition?
At G2/M transition the two centrosomes separate from each other, their position will determine the spatial disposition of the daughter cells.
Describe what happens during Mitosis?
During mitosis a single nucleus give rise to two genetically-identical nuclei.
How do the chromosomes appear throughout interphase?
They appear as their uncondensed state called chromatin which looks like yarn in a ball of yarn.
Where do microtubules originate and extend from?
Microtubules extend from MTOC (Microtubules organizing centre).
Name the five stages of the M phase in the correct order.
Prophase Metaphase Anaphase Telophase Cytokinesis
The chromatin starts to condense. Th chromosomes are becoming visible, shorter and thicker. Coesin is partially removed. Nuclea envelope breaks down. Kinetochores MT connect kinetochores to centrosomes.
Chromatin is fully condensed and visible as separate elements. The chromosomes are moved by the MT mitotic spindle to the metaphase plate.
Sister chromatids are segregate to the opposite pole of the cell. Coesin is hydrolized by separase.
Where does the energy that moves the daughter chromosomes comes from?
75% comes from the hydrolisation of ATP made by cytoplasmic dynein located in the kinetochores. 25% comes from the shorten of kinetochores microtubules from the poles.
The two separate bundle of chromatids begin to decondense. Centrosomes nucleated MT asters. Mitotic spinde disappear. Two nuclear envelopes form around the chromosomes.
After chromosome have been segregated and organelles have been distributed the cell split apart.
Describe cytokinesis in animal cells:
In animals cells a contractile ring forms on the equatorial plane and pinch off to form two daughter cells.
Describe cytokinesis in plant cells:
Since plant cells have a rigid cell wall a septum grwos down along the equatorial plane to form form two daughter cells.
What are the three main checkpoints in the cell cycle?
1) Restriction point (G1) 2) G2 phase 3) M checkpoint
Describe G2 checkpoint:
G2 checkpoint - this one occurs at the end of G2 and it checks to see if DNA replication has been completed.
Describe M checkpoint:
It occurs at the end of metaphase. It checks to see whether the chromatids are arranged correctly on the metaphase plate ensuring that each daughter cell receives the same number of chromosomes before anaphase.
What are CDKs and what do CDKs do?
CDKs stand for cyclin-dependent kinases. CDKs phosphorylate RBs, helping the cell to progress to the next stages of the cell cycle.
What happens when DNA is damaged during a stage in the cell cycle?
DNA damage triggers the activation of several proteins that can stimulate DNA repair, arrest the cell cycle or induce the cell to undergo apoptosis.
Give a brief description of binary fission:
1-The cell increases in size. 2-DNA replication occurs 3-Cytoplasm and nuclei separate to form two new cells.
Name common external factors that act as reproductive signals in prokaryotes.
Environmental factors and nutrient factors.
What is apoptosis?
Programmed cell death