Colorectal tumors arise as a result of the mutational activation of oncogenes coupled with the mutational inactivation of tumor suppressor genes without a major role for gene amplification or rearrangement. These tumors affect the colon and rectum, and most colorectal cancers arise from adenomatous polyps. The development of colorectal neoplasms is characterized by an ordered series of events that are referred to as the “Dysplasia-Carcinoma Sequence” or “Adenoma-Carcinoma Sequence”. Mutations in at least four to five genes are required for the formation of malignant tumors and fewer changes only suffice for benign tumorigenesis. Although genetic alterations occur according to a preferred sequence, the total accumulation of changes, rather than[..]

Tumors of the Central Nervous System (CNS) are devastating as they are difficult to treat and may cause grave disability or death. CNS Gliomas pose particularly difficult problems because of their tendency toward malignancy, rate of tumor spread, and the lack of effective therapy. Gliomas are the most common intracranial malignant tumors in humans (Ref.1). In vertebrates, the embryonic neural tube (neuroectoderm) gives rise to the main cell types of the CNS, including neurons, astrocytes, oligodendrocytes and ependymal cells. The neural crest derives from the dorsal lip of the neural tube, and its cells migrate extensively during embryonic development, giving rise to various tissues, including the Peripheral Nervous System (PNS). In both the CNS and PNS, the appearance[..]

In humans, roughly 300 million spermatozoa on average are ejaculated in the female reproductive tract, but only about one of every million actually enters the Fallopian tube. Upon entry, these spermatozoa apparently bind strongly to the oviductal epithelium in the isthmus, forming a sperm storage site.  Human spermatozoon formed in the testes via spermatogenesis is morphologically complete but functionally immature and incapable of fertilizing an egg. Spermatozoa to become fertile must undergo maturation in the epididymis followed by capacitation, and acrosome reaction in the female reproductive system. For reaching the oocyte at the fertilization site, the limited number of capacitated spermatozoa in the isthmus has to swim a long way full of obstacles. This[..]

Erectile Dysfunction commonly known as ED or Impotence, affects a large segment of the male population that results in impaired relaxation of the smooth muscle cells in the corpus cavernosum and in the penile arteries. It is an age-related problem that is increasingly common in men aged over 40 years. In the past, ED was often assumed to be either a psychological problem or a normal part of the ageing process, to be tolerated with other signs of aging. However, ED is now known to be primarily organic resulting from vascular, hormonal or neurological complications. The corpus cavernosum (cavernous space) contains sinusoids that are surrounded by trabecular smooth muscle (Ref.1). Upon sexual stimulation, the increase in parasympathetic activity results in dilatation of[..]

Chloroplasts represent a diverse group of essential organelles collectively as the plastids. Plastids are a heterogeneous family of organelles found ubiquitously in plant and algal cells. Chloroplasts perform a variety of biochemical functions within plant cells. They contain the green pigment chlorophyll and are responsible for the light-harvesting and carbon-fixation reactions of photosynthesis, as well as for the synthesis of many essential metabolites, such as fatty acids and amino acids. Other members of the plastid family include the Amyloplasts( contain large quantities of starch and play important roles in energy storage and gravitropism), the Chromoplast ( accumulate the red-orange-yellow), Carotenoid (pigments that act as attractants in flowers and[..]

Chloroplasts are exceptionally complex organelles found ubiquitously in Plant and Algal cells. Chloroplasts contain at least six suborganellar compartments: Outer and Inner membranes, Intermembrane Space, Stroma, and Thylakoid membrane and Lumen, all of which require specific trafficking systems. The Thylakoid membrane of the Chloroplast accounts for the bulk of the Chloroplast lipid content and contains the abundant proteins associated with light capture and photosynthetic electron transport.The targeting systems of the Thylakoid appear to be conserved from the Protein export systems that exist in Gram-negative bacteria. The Thylakoid membrane contains four especially prominent complexes (Photosystems I and II, Cytochrome b/f complex and the ATP Synthase), each of[..]

The process of DNA replication, gene transcription and protein translation combinedly known as central dogma of biology is mainly responsible for the expression and maintenance of every gene in an organism. Transcription is the process through which a DNA sequence is enzymatically copied by an RNA polymerase to produce a complementary RNA. Transcription can also be defined as a process that transcribes genetic information from DNA into RNA. In eukaryotes, it takes place in the nucleus, mitochondria and chloroplast. Transcription is performed by DNA-directed RNA Polymerases. Unlike DNA Polymerases, RNA Polymerases do not need a primer to start the reaction. While Bacteria contain only 1 RNA Polymerase, there are 3 different RNA polymerases in eukaryotic cells, which[..]

The amino-acid derived polyamines have long been associated with cell growth and cancer, and specific oncogenes and tumor suppressor genes regulate polyamine metabolism. Polyamines are organic cations that are derived from amino acids and occur in all organisms. Putrescine, Spermidine and Spermine are the main polyamines found in prokaryotes and eukaryotes. Polyamines are essential for the growth and function of normal cells. They interact with various macromolecules, both electrostatically and covalently and, as a consequence, have a variety of cellular effects. At physiological pH, polyamines carry a positive charge on each nitrogen atom and it has been suggested that polyamines are simply ‘supercations’, equivalent to one or two calcium or magnesium[..]

The Blood-Testes Barrier (abbreviated as BTB) acts as a physical barrier between the blood vessels and the seminiferous tubules of the testes. This barrier is formed by tight and adherens connections between the Sertoli cells, which are sustentacular cells (supporting cells) of the seminiferous tubules, and nourish the spermatogonia (Ref.1). In the testes, tight and adherens junctions are dynamically remodeled to allow the movement of post-meiotic germ cells across the seminiferous epithelium and the timely release of spermatids into the tubular lumen. Three main functions are ascribed to the blood-testes barrier; (i) creates a specialized environment; (ii) regulates the passage of molecules; and (iii) serves as an immunological barrier. When the blood-testes barrier[..]

Cell adhesion and migration is the fundamental feature of multicellular organisms during defense mechanisms, where leukocytes play the central role. They bind bacteria, parasites, viruses, tumor cells etc. Furthermore, their interactions with the endothelium are of special importance. The migration of leukocytes or WBCs (White Blood Cells) from the vascular system to sites of pathogenic exposure is a key event in the process of inflammation. Generally, agranulocyte (which includes Lymphocytes and Monocytes) adhesion and passage from the bloodstream to the lymphatic system occurs in the high endothelial venules of the lymphnodes, also known as the lymphoid endothelial venule. This way the agranulocytes communicate with each other in the lymphatic system and search for[..]

Polyamines are vital for the growth and function of normal cells. The complexity of polyamine metabolism and the multitude of compensatory mechanisms that are invoked to maintain polyamine homoeostasis argue that these amines are critical to cell survival. The regulation of polyamine content within cells occurs at several levels, including transcription and translation (Ref.1). The amino-acid derived polyamines like Putrescine, Spermidine and Spermine that are the main polyamines found in prokaryotes and eukaryotes, have long been associated with cell growth and cancer, and specific oncogenes and tumor suppressor genes regulate polyamine metabolism. Regulation of these polyamines (otherwise known as “organic cations”) is chiefly associated with cancers[..]

rRNA (Ribosomal RNA) is the central component of the Ribosome, the protein manufacturing machinery of all living cells. The synthesis of new ribosomes begins during transcription of the rRNA which is tightly regulated to maintain the right number of ribosomes. In eukaryotes, : ribosomal proteins are synthesized in the cytosol whereas transcription, processing of rRNA, and the assembly of ribosomes take place in the nucleoli, where it follow an orderly 5' to 3' gradient. Only the transcription of the small 5S rRNA occurs in the nucleoplasm. The ribosomal proteins and assembly factors are imported into the nucleus, where they are combined with the appropriate rRNAs. They self-assemble into the two complex folded structures (the large 60S and the small 40S[..]