APOPTOSIS

Apoptosis is a form of programmed cell death. It is a process of cellular dismantling that avoids inflammation and this is also called "cellular suicide". It is the essential part of life for every multicellular organism and plays a major role from embryonic development to aging.

It is essential as it is required for the proper developments like: 

(i) the formation of fingers and toes of fetus

(ii) the formation of connections between  neurons in the brain, and as well as needed to destroy cells for e.g,

(i) cells with DNA damage

(ii) cells infected with viruses.

When we look at the causes that makes cell suicide there are two simple reasons which is withdrawal of the positive signals(growth factor), receipt of negative signals (this included DNA damage, increased level of oxidants).

Now, what are the characteristics of apoptosis?

Well, the characteristics are, the dying cells shrinks and starts blebbing . The nucleus breakdown and the cells breaks into small membrane wrapped fragments. Then the further process began and the phagocytic signals are received by other cells which then engulf these dying cells. They do not leave any traces and it does not result in harmful outcomes.

Apoptosis occurs in stages:

i) The cell receipts the signal that triggers the pathway to apoptosis.

ii) The transcription factors stimulate and Ca+ release which deplete ATP. The cell can be rescued if it is exposed to survival factors.

iii) In the third stage the cell dismantles, DNA degrade. But from now the rescue is not possible.

iv) Last stage involves disassemble of the cell into membrane enclosed vesicle.

  

Lets's discuss about the mechanism. This is mediated by a proteolytic enzyme caspase which triggers cell death by cleaving specific proteins in the cytoplasm and nucleus.

Now the question is , what is CASPASE?

So, it's a proteolytic enzyme which is one of the major player in apoptosis. It is a single chain of pro-enzymes. It contains an N- terminal domain, a small sub-unit and a large sub-unit (just like ribosome).

 

   

CHROMOSOME

Chromosomes are microscopic thread like structure which are present in the nucleus of both plant and animal cell. These are present in both eukaryotes and prokaryotes but we will discuss about eukaryotic chromosomes in this blog.

The main function of the chromosome is to pass the hereditary information from one generation to other in the form of GENE. Chromosomes are the vessels of genes,(genes, which are made up of DNA), which are arranged on the chromosomes.

Chromosomes are condensed and is visible only during cell division in multicellular organism. These are present as pairs, one of the pair is maternal and the other is of the paternal.

Talking about the nature of these chromosomes, they are constant, i.e,

(i) constant for all members of a species for e.g, - Human [46], House mouse[40], Maize [20].

(ii) constant throughout the life i.e, we don't lose or gain chromosome throughout our life.

(iii) constant for each cell in an organism's body (except sex cell).{The sex cells only have half set}.

Now let's talk about the structure of chromosome.

Structurally, chromosomes have three parts:

1. Pellicle - is a very thin outer envelope around the substance of chromosome

2. Matrix - is made of nongenic material. It is the ground substance of chromosome that contains chromonemata.

3. Chromonemata - is embedded in the matrix of chromosome. These are two identical, spirally coiled thread like structure. 

NUCLEAR  LAMINA

The Nuclear Lamina is a protein meshwork lining of the inner surface of the nuclear envelope of animal cells and forms the part of the nuclear skeleton network anchoring the chromatin. 

It's a structure near the inner nuclear membrane and the peripheral chromatin. It provides mechanical support to the nuclear envelope, serves as a site of attachment for chromatin fibers at the nuclear periphery. 

The Nuclear Lamina is involved in various nuclear activities like DNA replication, RNA transcription, nuclear and chromatin organisation, cell cycle regulation, cell development and differentiation, nuclear migration and apoptosis.

LAMINS 

The filaments of the nuclear lamina are approximately 10nm in diameter and composed of polypeptides called LAMINS . These are members of the same superfamily of polypeptides that assemble into the 10 nm intermediate filaments of the cytoplasm.

The increasing number of proteins that interact with lamins and the compound interaction between these proteins and chromatin associated proteins make the nuclear lamina a highly complex but also a very exciting structure.

The disassembly of the nuclear lamina prior to mitosis is induced by phosphorylation of the lamins.