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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Lecture notes in Microbiology

Difference between Pili and Flagella of Bacteria- A Comparison Table


Fimbria vs pilus

Flagella vs Pili of Bacteria: A Comparison Table
(Similarities and Differences between Pili and Flagella of Bacteria)

Both Flagellum (plural Flagella) and Pilus (plural Pili) are the filamentous proteinaceous structures found on the surface of some bacterial cells. They extend from the surface of the bacterial cell wall and can have many functions such as motility, attachment, adhesion and assisting in genetic exchange.

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 in the external environment of the cell. Even though the flagella are present in prokaryotes and eukaryotes, both are entirely different in their structure, formation and mechanism of propulsion.

Pili definition: Pili are long hair like tubular micro-fibres like structures present on the surface of some Gram-negative bacteria. They are comparatively shorter filamentous structures than flagella and their number per cell is very limited. There are many classes of pili based on their structure and function. Most of the pili can act as the receptors of some viruses.

The present post describes the Similarities and Differences between Flagella and Pili with a Comparison Table

Similarities between Flagella and Pili

Ø  Both flagella and pili are filamentous structures.

Ø  Both are cell surface appendages.

Ø  Both are made up of proteins.

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