Molecular Biology Tutorials

Intrinsic Pathway of Apoptosis (Apoptosis Molecular Mechanism Part 1)

Mitochondrial Apoptosis Signaling

Intrinsic Pathway of Apoptosis
(The Mitochondria Mediated Programmed Cell Death Pathway)

Two Types of Apoptosis

In the previous post, we have discussed the characteristic features and significance of programmed cell death or apoptosis. As we discussed, the stimuli for the execution of programmed cell death can be of internal or external to the apoptotic cell.

Based on the source of stimuli, there are two types of apoptosis signaling pathways operate in the cells. They are (1) Intrinsic pathway (stimuli are internal) and (2) Extrinsic pathway (stimuli are external) of apoptosis. Even though both the intrinsic and extrinsic pathways considerably different, there is always cross-talk between these two pathways. In the present post, we will discuss the details of INTRINSIC PATHWAY of apoptosis signalling.

What is meant by Intrinsic Pathway of Apoptosis?

In the intrinsic pathway of apoptosis, the death-inducing stimuli are originated inside the target cell itself. Mitochondria, the powerhouse of the cell, have a significant role in executing the intrinsic pathway of apoptosis. Thus, the intrinsic pathway of apoptosis is also known as the Mitochondria-mediated death pathway.

What are the stimuli for the intrinsic pathway of apoptosis?

Most commonly observed internal stimuli for the initiation of the intrinsic pathway of apoptosis are:

Ø  Severe genetic damage

Ø  Lack of oxygen (hypoxia)

Ø  Very high concentration of cytosolic Ca2+ ions

Ø  Presence of some viral proteins

Ø  Severe oxidative stress due to the production of free radicals

What are Bcl-2 (B-cell lymphoma-2) family proteins?

The intrinsic pathway of apoptosis is facilitated by the members of Bcl-2 family proteins. The members of the Bcl-2 family proteins are characterized by the presence of one or more BH domains (Bcl-2 Homology Domain). The first identified member of Bcl-2 family proteins is Bcl-2 itself. The Bcl-2 was first identified as a cancer-causing oncogene in some human lymphomas. The gene which codes for the Bcl-2 protein was over-expressed in these cancer cells due to translocation. However, later studies have shown that Bcl-2 is not directly acting as an oncogene. They act as the oncogene by promoting the survival of the cancerous cells that would otherwise die by apoptosis.

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Molecular Biology Tutorials

Apoptosis: The Molecular Mechanism of Programmed Cell Death (Short Notes)

Programmed Cell Death Short Notes

Apoptosis: The Programmed Cell Death

What is Apoptosis? Why apoptosis is known as the ‘Programmed Cell Death’?

The total number of cells in an organ or organism is fundamentally fixed to a specific range in all multicellular organisms. In every multi-cellular organism, the cell number is effectively controlled by two strategies- (a) by regulating cell Division and (b) by regulating cell Death. If cells are no longer needed, they commit suicide (self-destruction) by activating an intracellular death signaling programme. Thus, this death process is known as ‘Programmed Cell Death’. This programmed cell death pathway is called Apoptosis.

The term apoptosis in Greek literally mean ‘falling off’. Just like the old leaves ‘falloff’ from the trees without affecting the life of the plant, the apoptotic cell death will not interfere with the functioning of the organ and organism. The most striking feature of apoptosis is that if a cell undergoes the programmed cell death, the neighboring cells are not at all damaged. Apoptotic death of a cell and its subsequent phagocytosis by a neighboring cell or by a macrophage allow the organic components of the death cell to be effectively recycled.

Learn more: Difference between Apoptosis and Necrosis

The apoptosis is better known as the ‘Programmed Cell Death’. It is a natural well-orchestrated, well sequenced and timely executed chain of events leads to the death of a cell.

What are the characteristics of Apoptotic Cell Death?

An apoptotic cell death is characterized by:

Ø  Shrinkage of the cell

Ø  Shrinkage of the nucleus

Ø  Loss of adhesion to the neighboring cells

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Lecture notes in Microbiology

Bacterial Cell Surface Structures and Appendages (Flagella, Fimbriae and Pili)

Fimbria vs pilus

Cell Surface Appendages of Bacteria
(Flagella vs Fimbriae vs Pili of Bacteria)

What are cell surface appendages?

Cell surface appendages (aka filamentous appendages) are proteinaceous tubular or fibrous structures found on the surface of bacterial cells. They extend from the surface of the bacterial cell wall and can have many functions such as locomotion, attachment, adhesion and assisting in genetic exchange.

What are the three types of cell surface appendages of bacteria?

The THREE types of cell surface appendages are present on bacteria. The classification is based on the relative length of the appendages, composition and function. The three cell surface appendages of bacteria are

(1).  Flagella

(2).  Fimbriae

(3).  Pili

(1). Flagella

Bacterial Flagella definition: Bacterial flagella are long whip-like filamentous structures present in some bacteria. The most important function of flagella is to assist in locomotion. Flagella can also act as a sensory organ to detect temperature and the presence of certain chemicals. Even though the flagella are present in prokaryotes and eukaryotes, both are entirely different in their structure, formation and mechanism of propulsion.

What are the characteristics of bacterial flagella?

Ø  Flagella are long whip-like filamentous structures.

Ø  Flagella are many times longer and thicker than Fimbriae and Pili.

Ø  Approximate length of flagella varies from 15 to 20 µm.

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Lecture notes in Microbiology

Difference between Bacterial Endospores and Vegetative Cells- A Comparison Table

Difference between Vegetative cell and endospores

Vegetative Cells vs Endospores of Bacteria
(Difference between Vegetative Cells and Endospores of Bacteria)

Endospore of bacteria

Bacterial Endospores under Phase-contrast microscope

Bacterial endospores are special tough, dormant and resistant spores produced by some Gram-positive bacteria of during unfavorable environmental conditions. They help the bacteria to endure the unfavorable conditions. The endospores are structurally, metabolically and functionally very different from bacterial vegetative cells. In the previous post, we have discussed about the Structure, Characteristics, Significance and Formation of Endospores.

In this post, we will discuss about the Difference between a Bacterial Endospore and Vegetative Cell with a Comparison Table.

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Lecture notes in Microbiology

Bacterial Endospore: Definition, Characteristics, Structure and its Formation

Bacterial Endospore

Bacterial Endospores
(Structure, Characteristics, Significance, Formation and Germination of Bacterial Endospores)

What are Endospores?

Bacterial endospores are special tough, dormant and resistant spores produced by some Gram-positive bacteria of Firmicute family during unfavorable environmental conditions. Endospores are developed within the vegetative cells (hence the name, endo = inside). They help the bacteria to endure the unfavorable environmental conditions.

Another importance of endospores is that it can be easily dispersed by wind, water and through the gut of animals. Bacillus and Clostridium are the most studied endospore forming bacterial genera. Bacillus enters into endospore formation cycle when the carbon or nitrogen source is getting limited in the growing medium.

Who discovered endospores

John Tyndal (source cc wikipedia)

Who discovered the endospore?

Endospores were discovered by John Tyndall, a 19th century physicist. He discovered endospores as the heat resistant spores of bacteria which survived even after 100oC. He also discovered a simple cost effective process to kill bacterial endospores called Tyndallization.

What are the characteristics of Endospores?

The endospores are structurally, metabolically and functionally very different from bacterial vegetative cells. The main characteristics of bacterial endospores are giving below:

Learn more: Difference between Endospore and Vegetative Cells

Ø  Endospores are exceptionally resistant to stressful environmental conditions such as heat, ultraviolet radiation, gamma radiation, chemical disinfectants and desiccation.

Ø  Most of the endospores are viable for many years, even for 10, 000 years or more.

Ø  Due to this long viability and their adaptations to stress conditions, most of the endospores producing bacteria are notorious pathogens.

Ø  Wiping with alcohol or hydrogen peroxide or boiling at 100oC will not kill the bacterial endospores.

Ø  However, endospores can be killed by autoclaving (at 121oC).

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