Dr. Shataha S. Jumaah/Lecturer _____________________________________________ Genetics – 2nd /2nd Semester

shatha.saadi@tiu.edu.iq https://tiu.edu.iq/

2020 - 2021

TIU - Faculty of Science Medical Analysis Department

• A Greek word : Falling leaves (like in Autumn)

• In the human body about 100,000 cells are produced every second by

mitosis and a similar number die by apoptosis !!!

•The average adult human loses between 50 and 70 billion cells each day due to apoptosis.

•For an average human child between the ages of 8 and 14, approximately 20–30 billion cells

die per day.

CELL SUICIDE

DEFINITION : Apoptosis is a peculiar well

controlled individual cell death that is

caspase (family of protease enzymes

playing essential roles in programmed cell

death) mediated and leads to

fragmentation of the cell and organelles

into numerous small buds, which are then

engulfed by macrophages without

surrounding inflammation

1) Crucial for embryonic development -Errors in Apoptosis can lead to Birth Defects

2) Important for maintaining homeostasis - Cell death is balanced with mitosis to

regulate cell number.

3) Improper regulation contributes to human disease –

Neurodegenerative diseases

Parkinson’s Alzheimer’s

Cancer

Autoimmune diseases e.g. (diabetes type I)

Viral diseases

• Cells die by one of two mechanisms necrosis or apoptosis

Two physiologically different processes –

Necrosis – death by injury

Apoptosis – death by suicide

• If cell killed by things that harm them (such as toxic chemicals or physical injury), a

process called .

• They are triggered to undergo programmed cell death.

• The best-understood form of programmed cell death is .

and occur under different circumstances and involve

different steps. Simply put, necrosis is messy and causes an immune response of

inflammation, apoptosis is tidy and splits the cell into little parcels that

can be taken up and recycled by other cells.

When cells are damaged by harmful factors (such as injury or

toxic chemicals), they usually “spill their guts” as they die.

the damaged cell’s plasma membrane can no longer

control the passage of ions and water, the cell swells up, and

its contents leak out through holes in the plasma membrane.

This often causes inflammation in the tissue surrounding the

dead cell.

Cells that undergo apoptosis go through shrink and develop

bubble-like protrusions (technical name: “blebs”) on their

surface. The DNA in the nucleus gets chopped up into small

pieces, and some organelles of the cell, such as the endoplasmic

reticulum, break down into fragments. In the end, the entire cell

splits up into small chunks, each neatly enclosed in a package of

membrane.

1. They release signals that attract debris-eating (phagocytic)

immune cells, such as macrophages.

2. The fragments of the dying cell display a lipid molecule called

phosphatidylserine on their surface.

3. Phosphatidylserine is usually hidden on the inside of the

membrane, and when it is on the outside, it lets the phagocytes

bind and "eat" the cell fragments.

1. Some cells need to be “deleted” during development – for instance, to

shap an intricate structure like a hand out of a larger block of tissue.

2. Some cells are abnormal and could hurt the rest of the organism if

they survive, such as cells with viral infections or DNA damage.

3. Cells in an adult organism may be eliminated to maintain balance – to

make way for new cells or remove cells needed only for temporary

tasks.

The initiation of apoptosis is tightly regulated by activation mechanisms, because once apoptosis has

begun, it inevitably leads to the death of the cell. The two best-understood activation mechanisms

are the intrinsic pathway (also called the mitochondrial pathway) and the extrinsic pathway.

1. The is activated by intracellular signals generated when cells

are stressed and depends on the release of proteins from the inter membrane

space of mitochondria.

is activated by extracellular ligands binding to cell-

surface death receptors, which lead to the formation of the death-inducing

signaling complex (DISC).

Thanks for your

attention

@tiu.edu.iq