Apoptosis, Cancer, and Stem Cells

• Apoptosis, Cancer, and Stem Cells
• The learning intention includes describing and explaining apoptosis, how cancer occurs, and the role of stem cells in human development

What is Apoptosis?

• Apoptosis is the controlled death of cells in the body.
• There are roughly 300 million cells that die every minute out of the 30 trillion cells in the body.
• Apoptosis occurs in cells that have been damaged or malfunction and are replaced with healthy cells.

Examples of Apoptosis

• Fingers initially develop in paddles, and cells in the tissue between the fingers must die for a proper hand to form.
• Cells in the tail of a tadpole undergo apoptosis to become superfluous when the animal develops into a frog.

Why does apoptosis occur?

• Remove dangerous or harmful cells such cells exposed to toxins.
• Remove mutated cells that become cancerous.
• It is important for the formation or non-formation of cancer.
• Positive and negative selection occur among immune system cells with cells that attack self, being instructed to die.

Pathways Leading to Apoptosis?:

• Two possible ways apoptosis can occur:
• Mitochondrial pathway (intrinsic)
• Death receptor pathway (extrinsic)

Mitochondrial Pathway

• Damaged components inside the cell allow the mitochondria to detect and release cytochrome.
• Cytochrome c is a protein that activates caspase enzymes.
• Cytochrome c activating caspase enzymes begins the apoptosis process.

Death Receptor Pathway

• An external immune cell detects a damaged or infected cell.
• The immune cell then releases death signaling molecules that bind to death receptor proteins on the infected cell.
• The binding of death signaling molecules to death receptor proteins activates the caspase enzymes which starts the apoptosis process.

Steps of Apoptosis

• The caspase enzyme is activated.
• Caspase signals other proteins inside the cell to break down the organelles and nucleus.
• The cell starts to shrink, and blebs start to form.
• Organelles and cytoplasm fill the blebs to create apoptotic bodies which are then consumed by a phagocyte.

What Do Malfunctions In Apoptosis Cause?

• Too much apoptosis can cause diseases and disorders such as Huntington's disease.
• Huntington's disease is a neurological disorder often has large tissue gaps caused by excessive cell death.
• Too little apoptosis can cause issues with malformation, such as not having fully developed fingers.

What is Cancer?

• Cancer or tumors form when cells replicate uncontrollably.
• Cancer can be caused by genetic mutations that increase the rate of cell division or genetic mutations that cause suppression of apoptosis.
• Benign tumors are unable to spread throughout the body.
• Malignant tumors (cancer) invade other parts of the body.

Characteristics of Tumors

• Self-sufficiency: Cancer cells can create their own signals to begin replication instead of needing a signal to begin replication.
• Antigrowth deactivation: Cancer cells can bypass healthy cells that would otherwise stop replicating when it's not needed.
• Increased survival: The more a tumor divides, the more it increases its survivability.
• Blood supply formation: Tumors can form their own blood vessels, allowing nutrients and oxygen to fuel them.
• Tissue invasion and metastasis: Cancer cells migrate around the body via the bloodstream or lymphatic system (metastasis).

What are stem cells?

• Stem cells are undifferentiated cells with the capability of differentiating into specialised cells with a function.
• Instead of appearing magically, each cell begins as a stem cell, and through the process of differentiation, they develop into specialised cells with a particular function.

Properties of stem cells

• Stem cells self-renew through their ability to replicate without disrupting their ability to differentiate by producing both a differentiated cell and a copy of themselves when they replicate
• Stem cells are potent due to being undifferentiated cells which can give rise to differentiated cells with a specialised function.

Potency of stem cells

• Totipotent: Stem cells that can differentiate into any cell type, such as a zygote.
• Pluripotent: Stem cells that can differentiate into multiple cell types, such as embryonic stem cells.
• Multipotent: Stem cells that can differentiate into a limited number of specialized cell types belonging to a specific tissue or organ, such as the bone marrow that contains blood stem cells (also known as hematopoietic stem cells)
• Unipotent/specialised: Cells that are only capable of differentiating into a single cell type.

Ectoderm, Mesoderm, and Endoderm.

• Ectoderm: nervous system and skin
• Mesoderm: muscle, skeleton, kidneys, and reproductive system
• Endoderm: endocrine glands, lungs, digestive tract, and liver

Activities

• Phagocyte digestion of apoptotic bodies occurs during apoptosis.
• The checkpoints of the cell cycle included in the image are:
• G1
• G2
• Metaphase
• Some cells may resist apoptosis because they express non-functional death receptors.
• Apoptosis is a highly regulated and controlled cell death pathway.
• Death receptor proteins detect the presence of a death signaling molecule.
• During apoptosis, blebbing can be characterized by bulging of the plasma membrane.
• Stem cells are undifferentiated cells that can differentiate into specialised cells.
• A stem cell's ability to produce both a differentiated cell and a copy of itself is known as self-renewal.
• A zygote is a totipotent stem cell.
• To develop organs from an individual's own differentiated skin cells by reprogramming them into pluripotent stem cells, scientists must be able to reverse the process of differentiation.
• Stem cells with a greater potency can differentiate into more cell types.

Scientific Skill Questions

• An investigation was most likely taking place to decide if purchasing antimicrobial gel hand sanitiser for students was worthwhile.
• False diagnosis of pregnancy may occur if female frogs were laying eggs naturally around the time of the injection
• The group receiving standard care only was the control group.
• The qualitative data obtained by the student could be the names of the different colours of the reflected light.