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HbS forms as a result of a single amino acid substitution in the β-chain of Hb. Replacement of the glutamate residue at position 6 in the β-chain by a valine residue is the only chemical difference between HbA and sickle-cell haemoglobin. The residue is present on the outer surface of the molecule. The change produces a sticky hydrophobic spot on the surface that results in the abnormal quaternary association of haemoglobin. This makes the deoxyHbS less soluble than deoxyHbA. Insoluble deoxyHbS forms polymers that aggregate into tubular fibres. The formation of insoluble deoxyHbS fibres distorts the RBC into the elongated sickle-shaped structure which is characteristic of the disease, sickle-cell anaemia. Sickle-cell anaemia and sickle-cell trait are different. Sickle-cell describes a condition in which an individual has one abnormal allele of the β-globin gene(heterozygous). A person with sickle-cell anaemia has two copies of the abnormal β-globin gene(homozygous).

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DNA topoisomerase I (Top1) regulate DNA supercoiling both in the nucleus and mitochondria to enable reliable transmission of our genetic information to the offspring. However, Top1 are toxic when trapped on the DNA (Top1-cleavage complexes; Top1cc) in the presence of anticancer drug camptothecin (CPT), a naturally occurring quinoline alkaloid. Despite the chemical success of Top1 inhibitors like CPT and its derivatives in cancer chemotherapy, inherent resistance has been reported with significant limitations. The cellular role of human tyrosyl DNA phosphodiesterase 1 (TDP1), a key enzyme responsible for the repair of Top1-induced DNA damage and identify TDP1 as a co-target for combinatorial anticancer drug therapy along with Top1 poisons.

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In 1944, Oswald Avery, Colin MacLeod, and Maclyn McCarty revisited Griffith's experiment and concluded that the transforming material was pure DNA, not protein or RNA. These investigators found that DNA extracted from a virulent strain of the bacterium Streptococcus pneumoniae, also known as pneumococcus, genetically transformed an avirulent strain of this organism into a virulent form. 

 

Type IIR cells  ⇒ No transformation

Type IIR cells + Type IIIS DNA extract ⇒ Transformation

Type IIR cells + Type IIIS DNA extract + DNase ⇒ No transformation 

Type IIR cells + Type IIIS DNA extract + RNase ⇒ Transformation 

Type IIR cells + Type IIIS DNA extract + Protease ⇒ Transformation

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Chordates and echinoderms shared a key characteristic of animal taxonomy- that of embryo growth pattern. These two groups comprise the deuterostomes whose embryological development differs greatly from the protostomes ( molluscs, annelids and arthropods). These embryological development patterns are guided by genetic differences in the expression of Hox genes, which suggests that echinoderms and chordates share a key characteristic very distinct from other animal groups. And, although the adult echinoderms look different from the chordates, an early stage in their development looks more closely related to the chordates.

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The three basic body plans of bilaterally symmetrical animals are acoelomates, wherein nobody cavity other than the digestive tract exists; pseudocoelomates, wherein there is a cavity between the mesoderm and the endoderm; and the coelomates, where there is a cavity completely bounded by mesoderm. The internal organs are suspended in coelom by mesodermal double layer mesenteries. In wormlike organisms are found acoelomate and pseudocoelomate body plans; in advance invertebrates and vertebrates only coelomate body plan is found.

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All genes whose epigenetic and genetic changes contribute to the causation of cancer is described as cancer-critical genes. These genes may be involved in the following processes-

1. Cell cycle progression (e.g. Rb, myc)

2. Differentiation process (e.g. Hh, apc)

3. DNA repair (e.g. Atm, Brca)

4. Cell death (e.g. Bcl-2)

Cancer critical genes are grouped into two broad classes, according to whether the cancer risk arises from a gain-of-function mutation of a gene or loss-of-function mutation. Genes for which a gain-of-function mutation drives a cell towards cancer, are called proto-oncogenes, Whereas the genes for which a loss-of-function mutation creates the cancer are called tumour suppressor genes.

Mutation of a critical cancer gene can be either dominant or recessive. Again in function mutation in a single copy of proto-oncogene can drive a cell towards cancer. On the other hand, cancer causing mutation of tumour suppressor genes is generally recessive. It means both copies of the normal gene must be removed or inactivated in the diploid somatic cell before an effect is seen.

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Stem cells are unspecialized(undifferentiated) cells that have the ability to differentiate into other cells, and self-regenerate. These cells divide to produce one daughter cell that remains a stem cell and one that divides and differentiates. Because the division of stem cells produces new stem cells as well as differentiated daughter cells, stem cells are self-renewing populations of cells that can serve as a source for the production of differentiated cells throughout life. Typically, stem cells generate an intermediate cell type or types before they achieve their fully differentiated state.

The intermediate cell is called a precursor or progenitor cell. The ability to differentiate is the potential to develop into other cell types. Depending on the ability to differentiate into other cell types, stem cells can be classified as totipotent, pluripotent and multipotent stem cells. The Totipotent stem cells can give rise to a fully functional organism as well as to every cell type of the body. Pluripotent stem cells can differentiate into all cell types mostly. The multipotent stem cell can differentiate into a limited number of closely related families of cells.

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HCl is a polar covalent compound because in this H+ is a proton having electron affinity and having the tendency to gain the electron but Cl- is act like an anion and having tendency to donate the electron and Cl- is a electronegative atom and as the H+ comes close to Cl- anion then negative charge spreads and polarity begins according to Fazan's Rule and due to this two shared pair electrons of Cl- make the covalent bond with H+ (both the electrons in covalent bond is from Cl- atom. HCl is also called it as hetro-atomic molecule. read less