3. Cell Cycle
the series of growth and development steps
a cell undergoes between its “birth”—
formation by the division of a mother cell—
and reproduction—division to make two
new daughter cells
6. - Gap 1 (G1): cell growth
and normal functions
- DNA synthesis (S): copies
DNA
- Gap 2 (G2): additional
growth
- Mitosis (M): includes
division of the cell nucleus
(mitosis) and division of
the cell cytoplasm
(cytokinesis)
8. Interphase
G1 : Gap One
1st phase
Growth and normal processes
take place
No division occurs
Longest phase of interphase
9. Interphase
S or Synthesis phase
DNA replicates
At the end of this phase, the
nucleus will contain 2 complete
sets of DNA
Condensed, duplicated chromosome
chromatid
telomere
centromere
telomere
10. Interphase
G2 : Gap Two
Cells prepare for division
Shortest stage of interphase
Spindle fibers, centrioles, etc –
are prepared for the next stage.
Parent cell
centrioles
spindle fibers
centrosome
nucleus with
DNA
11.
12. Mitosis
Division of the cell nucleus and its
contents.
Has 4 main stages:
Prophase
Metaphase
Anaphase
Telophase
13. Cytokinesis
the cytoplasm of the cell is split in two,
making two new cells.
usually begins just as mitosis is ending,
with a little overlap.
20. Checkpoint
is a stage in the eukaryotic cell cycle at which the
cell examines internal and external cues and
"decides" whether or not to move forward with
division
21. 3 Important Checkpoints
The G1 checkpoint, at the
G1/S transition.
The G2 checkpoint, at the
G2/M transition.
The spindle checkpoint, at the
transition from metaphase to
anaphase
Cells have distinct phases of growth, reproduction, and normal functions.
The rate of cell division varies with the need for those types of cells.
The cell cycle has four main stages.
Mitosis occurs only if the cell is large enough and the DNA undamaged.
Making another copy of chromosomes
In mitosis, the nuclear DNA of the cell condenses into visible chromosomes and is pulled apart by the mitotic spindle, a specialized structure made out of microtubules. Mitosis takes place in four stages: prophase (sometimes divided into early prophase and prometaphase), metaphase, anaphase, and telophase. In cytokinesis, the cytoplasm of the cell is split in two, making two new cells. Cytokinesis usually begins just as mitosis is ending, with a little overlap. Importantly, cytokinesis takes place differently in animal and plant cells.
In mitosis, the nuclear DNA of the cell condenses into visible chromosomes and is pulled apart by the mitotic spindle, a specialized structure made out of microtubules. Mitosis takes place in four stages: prophase (sometimes divided into early prophase and prometaphase), metaphase, anaphase, and telophase. In cytokinesis, the cytoplasm of the cell is split in two, making two new cells. Cytokinesis usually begins just as mitosis is ending, with a little overlap. Importantly, cytokinesis takes place differently in animal and plant cells.
During the mitotic (M) phase, the cell divides its copied DNA and cytoplasm to make two new cells. M phase involves two distinct division-related processes: mitosis and cytokinesis.
Importantly, cytokinesis takes place differently in animal and plant cells.
During prophase, chromosomes condense and spindle fibers form.
mitotic spindle, a specialized structure made out of microtubules.
During metaphase, chromosomes line up in the middle of the cell.
During anaphase, sister chromatids separate to opposite sides of the cell.
During telophase, the new nuclei form and chromosomes begin to uncoil.
G0 Phase While some cells are constantly dividing, some cell types are at rest. These cells may exit G1 and enter a resting state called G0. In G0, a cell is performing its function without actively preparing to divide. G0 is a permanent state for some cells, while others may re-start division if they get the right signals
A checkpoint is a stage in the eukaryotic cell cycle at which the cell examines internal and external cues and "decides" whether or not to move forward with division.
main decision point for a cell – that is, the primary point at which it must choose whether or not to divide.
Once the cell passes the G1 checkpoint and enters S phase, it becomes irreversibly committed to division.
That is, barring unexpected problems, such as DNA damage or replication errors, a cell that passes the G1 checkpoint will continue the rest of the way through the cell cycle and produce two daughter cells.
At the G1 checkpoint, a cell checks whether internal and external conditions are right for division.
Size. Is the cell large enough to divide?
• Nutrients. Does the cell have enough energy reserves or available nutrients to divide?
• Molecular signals. Is the cell receiving positive cues (such as growth factors) from neighbors?
• DNA integrity. Is any of the DNA damaged?
If a cell doesn’t get the go-ahead cues it needs at the G1 checkpoint, it may leave the cell cycle and enter a resting state called G0 phase. Some cells stay permanently in G0, while others resume dividing if conditions improve.
To make sure that cell division goes smoothly (produces healthy daughter cells with complete, undamaged DNA), the cell has an additional checkpoint before M phase, called the G2 checkpoint. At this stage, the cell will check:
DNA integrity. Is any of the DNA damaged? Source: https://www.khanacademy.org
DNA replication. Was the DNA completely copied during S phase?
If errors or damage are detected, the cell will pause at the G2 checkpoint to allow for repairs. If the checkpoint mechanisms detect problems with the DNA, the cell cycle is halted, and the cell attempts to either complete DNA replication or repair the damaged DNA. If the damage is irreparable, the cell may undergo apoptosis, or programmed cell death. This self-destruction mechanism ensures that damaged DNA is not passed on to daughter cells and is important in preventing cancer.
The M checkpoint is also known as the spindle checkpoint: here, the cell examines whether all the sister chromatids are correctly attached to the spindle microtubules. Because the separation of the sister chromatids during anaphase is an irreversible step, the cycle will not proceed until all the chromosomes are firmly attached to at least two spindle fibers from opposite poles of the cell.
