CELL CYCLE

Cell Cycle

refers to the sequence of phases in the life of the cell. It is the period from the beginning of one cell division to the beginning of the next cell division. It is a precisely timed event that results in cell growth and division, eventually producing two new daughter cells from one mother cell.

• Interphase

• Karyokinesis

• Cytokinesis

3 substages in the cell cycle

Interphase

is the longest phase of the cell cycle, where the cell grows and replicates its DNA, followed by nuclear division, where the cell's nucleus and nuclear materials divide

Cytokinesis

where the cell's cytoplasm divides, producing two new cells from one mother cell

G1 Stage

• is the first stage of interphase that comes before the synthesis of DNA.

• In this stage, the cell increases in mass and/or size, and the organelles increase in number in preparation for cell division.

• This stage is the period when protein and mRNA are produced in high rates

Metabolites

also accumulated as a source of energy and building blocks to prepare for the needs in the succeeding events

S Phase

• is a crucial part of interphase because this is when DNA is synthesized.

• In most cells, there is a narrow time frame for DNA synthesis.

• This stage is characterized by the replication of cellular DNA.

• When the DNA has been replicated, the cell has twice as many chromosomes as before; it is then ready to proceed to the G_2 stage.

G2 Phase

• comes after DNA synthesis.

• The cell synthesizes more proteins needed for nuclear division.

• During this stage, proteins necessary for cell division, such as kinase and histones, are synthesized, including the microtubules that will comprise the spindle fibers

• . The chromosomes start to condense and become visible, and the cell enters prophase, the first phase of the nuclear division, mitosis.

Fruit Fly Embryos

Where can the shortest cell cycle be found?

10 quadrillion

Amount of cell divisions a human undergoes in a lifetime

MPF

• is a protein kinase complex of cyclin-dependent kinase 1 and cyclin B (CDK1/Cyclin B) that is considered the master regulator for cells in G_2 to enter M-phase.

• triggers events like chromosome condensation, disappearance of the nuclear membrane, and the formation of spindle fibers.

• ensures that cells will divide only after DNA replication.

Internal Regulators

• proteins found inside the cell.

• These regulate the processes that happen inside the cell.

• Internal regulatory proteins include the proteins that make sure that mitosis does not occur unless the chromosomes have replicated.

• Other proteins prevent the cells from entering anaphase if the spindle fibers are not properly attached to chromosomes.

External Regulators

• proteins or molecular signals that respond to events outside the cell.

• Examples of these

• outside events are chemical balance and sufficient nutrients of the cell.

• One important external regulator is the growth factor that stimulates the growth and division of cells.

• Cell growth and division are needed in healing wounds and embryonic development.

External Regulators

• proteins or molecular signals that respond to events outside the cell.

• Examples of these outside events are chemical balance and sufficient nutrients of the cell.

• One important external regulator is the growth factor that stimulates the growth and division of cells.

• Cell growth and division are needed in healing wounds and embryonic development.

G2/M Checkpoint

• the checkpoint prior to mitosis.

• It checks the integrity of the DNA and any replication damage.

• It is in this stage that DNA damage due to replication is corrected and repaired.

• Cells that have irreparable DNA damage go to apoptosis, or cell death.

• If the DNA has been correctly replicated, cyclin dependent kinases (CDKs) signal the beginning of mitotic cell division.

M Checkpoint

• the checkpoint that happens during mitosis, particularly at the end of the metaphase stage.

• It is also known as the spindle checkpoint because it determines whether all the sister chromatids are correctly attached to the spindle microtubules or not.

• It also ensures that all of the chromosomes are attached to the spindle in preparation for anaphase.

• Wrong alignment and attachment are irreversible, so mitosis is halted unless strayed chromosomes are captured by spindle fibers.

Cancer

A disease characterized by the uncontrolled division of cells. It happens when the regulators of the cell cycle break down

p53 gene

Culprit of cancer

Tumor-suppressor Gene

By stopping the division of damaged cells, the p53 gene prevents the production of many mutated cells and is, therefore, regarded as a _____

Metastasis

The process by which cancer cells spread from where they originated is called?

Alzheimer’s & Parkinson’s Disease

2 examples of neurodegenerative disease

Atherosclerosis

a chronic and progressive inflammatory condition in which an artery wall thickens as a result of the accumulation of white blood cells (WBCs) and the proliferation of vascular smooth muscle cells, among many other contributing factors.