Lecture 27 Flashcards Preview

Medical Biochem and Genetics > Lecture 27 > Flashcards

Flashcards in Lecture 27 Deck (10):

What are the differentiating characteristics of Necrosis and Programmed Cell Death?

Necrosis typically occurs in large areas (many cells) and is initiated my injury and leads to cell swelling/lysing. The cell contents leak out leading to inflammation. These things do not happen in PCD. In PCD, which typically occurs in one cell or small clusters of cells, the cell shrinks rather than swells, and the membrane blebs but does not rupture. The shrunken cell fragments into intact pieces called apoptotic bodies that are phagocytized.


What are the biochemical characteristics of apoptotic cells?

- Extensive protein cleavage.
- DNA cleavage leading to DNA ladder effect on gel.
- Extensive protein cross-linkage via activation of
- Externalization of phosphatidylserine.


Where does the term Caspase come from?

C - because they have Cysteine in their active sites, and Asp - because they cleave proteins at C-terminus side of aspartate residues.


In what form are caspases synthesized?

They are synthesized as proenzymes so as to regulate their activity.


Which organelle plays a critical role in the "Suicide" or intrinsic PCD pathway?

The mitochondria


What are the steps in the Suicide/intrinsic pathway?

Without trophic factors, cytosolic Bad is dephosphorylated and can outcompete Bax from binding with Bcl2 on the mitochondrial membrane. That allows Bax to complex with itself forming pores in the mitochondrial membrane --> Cytochrome C can leak out of the mitochondria and combine with Apaf-1 which can then form the septameric Apoptosome using dATP and ATP --> the CARD (caspase recruitment domain) recruits Procaspase 9 --> Procaspase 9 undergoes conformational change and autocleavage to form tetrameric .Caspase 9 --> Caspase 9 cleaves/activates Caspase 3


What are the steps in the Murder/Extrinsic PCD pathway?

FasL (death signal) binds Fas (death receptor) which trimerizes and undergoes conformational change --> Fas then binds Death Domain containing adaptor proteins (Disc) --> recruits and activates Caspase 8 --> cleaves and activates Caspase 3 --> cleaves ICAD from CAD --> CAD cleaves DNA.


How does the Perforin Granzyme Pathway work, and which cells are implicit to this pathway?

This pathway involves Cytotoxic T Lymphocytes (CTLs) that insert Perforin into cell membranes --> perforin forms a pore through which the CTL injects granzymes that activate Caspase 10 and directly activate Caspase 3 --> Caspase 10 also activates Caspase 3 --> ICAD cleavage from CAD --> CAD cleaves DNA.


What does Caspase 3 act on?

1. ICAD (Inhibitor of Caspase Activated DNase) -->
cleaves ICAD from CAD --> CAD cleaves DNA
2. Nuclear Lamins --> Fragmentation of Nucleus
3. Cytoskeletal proteins --> disrupts cell signaling + transport and leads to cell fragmentation/blebbing


What is p53's role in the Intrinsic PCD pathway?

In response to excessive cell damage, p53 acts as a TRANSCRIPTION FACTOR and upregulates production of Bax, such that there is much more Bax than Bcl2 --> Bax can complex with itself rather than binding Bcl2 --> forms pores for Cytochrome C to leak out and combine with Apaf-1, so on and so forth.