Apoptosis and Stem Cells Flashcards
WHAT IS APOPTOSIS?
- Programmed cell death (“Controlled cell suicide”)
- Tightly controlled process
- Natural and necessary mechanism in multicellular organisms to trigger the death of a cell
how is apoptosis a process of balance?
A process of balance:
- Cells in many of our organs and tissues are in a state of constant turnover, eg skin and gut cells
- In adults, the rates of cell renewal and cell death are balanced
- Apoptosis is a normal healthy process in cells!
CELLS THAT UNDERGO APOPTOSIS?
- Cells at the end of their natural life, eg gut lining cells & skin cells
- Cells infected
Excessive cells: - Immune cells and red blood cells, keeping them in balance
- Embryonic development
- During the development of the brain, lots of excess neurons are formed. Only those that make the best neural connections are maintained – the rest are culled
CHARACTERISTICS OF APOPTOSIS?
An animal cell undergoing apoptosis shows characteristic physical changes:
- the cell shrinks
- its plasma membrane forms bubbles or ‘blebs’
- the nucleus and cytoplasmic organelles condense and fragment
- the cell breaks up and its contents form into parcels called apoptotic bodies.
TWO PATHWAYS OF APOPTOSIS?
- Intrinsic Pathway (Also called mitochondrial pathway)
Initiated from inside the cell - Extrinsic Pathway (Also called the death receptor pathway)
Initiated from outside the cell
Mitochondrial pathway?
When internal components of the cell (such as DNA) are damaged mitochondria detect this damage and release cytochrome c into the cytosol. Cytochrome c binds with cytosolic proteins to form an apoptosome, which activates caspase enzymes, initiating apoptosis.
Death receptor pathway?
Death signalling molecules can be recognised by death receptor proteins on the surface of cells, and are often released by immune cells. When these molecules bind to a death receptor surface protein, caspase enzymes are activated, initiating apoptosis.
STAGES OF APOPTOSIS?
Following the initiation of apoptosis and the activation of caspases, apoptosis is composed of the following stages:
- Activation of caspases – detect internal DNA damage and release cytochrome C.
- Digestion of cell contents – caspases cleave intracellular proteins, which leads to the breakdown of organelles.
- Cell shrinks – the cell and nucleus shrink as intracellular material is broken down.
- Membrane blebbing and breakage – the structural integrity of the cell is weakened and membrane-enclosed vesicles known as apoptotic bodies which contain the broken down intracellular material.
INTRINSIC vs EXTRINSIC PATHWAYS similarities?
- Cell begins to bleb.
- Caspases enter the nucleus via nuclear pores and digest the DNA.
- All organelles except nucleus and mitochondria are preserved.
- Cell fragments are engulfed by phagocytes.
INTRINSIC pathways differences?
- Initiated if serious damage occurs inside a cell
- mitochondria detect this damage and release Cytochrome C into the cytosol.
EXTRINSIC pathways differences?
- Death signalling molecules can be released from healthy cells (e.g immune cells)
- Molecules bind to a death receptor surface protein, caspase enzymes are activated, initiating apoptosis.
what is necrosis?
Necrosis is unplanned cell death such as that occurring when cells suffer trauma and die prematurely.
when does necrosis happen?
Necrotic cell death occurs when cells suffer mechanical damage or chemical trauma, thermal burns, frostbite, and oxygen deprivation.
what happens during necrosis?
During necrosis the cell swells and forms blebs but the cell lyses and its content oozes out of the cell and this initiates an inflammatory response. This is one reason why when we injure ourselves, the area can become inflamed.
MALFUNCTIONS IN APOPTOSIS?
- Cancer is often a case of too little apoptosis
- Autoimmune diseases involve a disruption of apoptosis
- Neurodegenerative disorders, like Parkinson’s and Alzheimer’s diseases, are associated with too much apoptosis
APOPTOSIS & CANCER?
- If errors are detected at any of the G1, G2 or Metaphase checkpoints, the cell should either repair itself or undergo apoptosis.
- Unfortunately this does not always occur and apoptotic mechanisms are disrupted.
- When the rate of apoptosis decreases too much, cell growth can increase exponentially, resulting in the formation of tumours.
Tumours can be classified into two categories?
- benign tumour: a tumour that lacks the ability to spread throughout other tissues and organs
- malignant tumour: abnormal cells with the ability to invade nearby tissue and migrate to other parts of the body. Also known as cancerous cells
CHARACTERISTICS OF CANCER CELLS?
Self-sufficiency -
Typically, cells require chemical growth signals to initiate cell replication. However, in tumour cells, they can replicate without these signals by either producing their own chemical signals, or by permanently activating cell growth and replication pathways.
Antigrowth deactivation -
There are many different mechanisms present in cells to prevent cell replication when it is not needed. In tumour cells, these mechanisms can be disabled, thereby allowing cell replication to initiate.
Increased survival -
Due to mutations in the regulation of the cell cycle, apoptosis no longer functions correctly in tumour cells. Tumour cells are also capable of replicative immortality, which theoretically allows them to divide forever, enhancing their survival. However, in practice, due to limitations such as the inability for blood vessels to form in the centre of tumours and provide the necessary nutrients, tumour cells can still die.
Blood supply formation -
Tumour cells can form new blood vessels when growing to maintain adequate nutrient and oxygen supply.
Tissue invasion and metastasis -
When benign tumour cells become malignant/cancerous they are capable of invading nearby layers of tissue and migrating to other parts of the body away from the primary tumour site, typically via the bloodstream or lymphatic system (metastasis).
define Differentiation
the development of a stem cell into a specialised cell with a particular function
define Specialised
cells which serve a unique, particular function
define Zygote
the diploid cell formed by the combination of two haploid gamete cells
define Embryo
early stage of a developing organism (in humans includes the first 8 weeks of development)
define Embryonic stem cell
a pluripotent stem cell present during the early stages of human development
define Foetus
a human embryo after 8 weeks of development
