Phosphatidylserine (or 1, 2-Diacyl-sn-Glycero-3-Phospho-L-Serine) is the only amino acid-containing glycerophospholipid in animal cells. Although it is distributed widely among animals, plants and microorganisms, it is usually less than 10% of the total phospholipids, the greatest concentration being in myelin from brain tissue. It is an acidic (anionic) phospholipid with three ionizable groups, i.e. the phosphate moiety, the amino group and the carboxyl function. As with other acidic lipids, it exists in nature in salt form.In bacteria and other prokaryotic organisms, Phosphatidylserine is synthesized by a mechanism comparable to that of other phospholipids, i.e. by reaction of L-Serine with CDP-DAG (CDP-Diacylglycerol).In contrast in animal tissues, there are two[..]

Sucrose is produced by plants, algae and cyanobacteria as an end product of photosynthesis. It is the primary sugar transported from the source tissues to sink tissues by the phloem in most plants. In other non-photosynthetic tissues, sucrose serve as raw material for many metabolic pathways (Ref.1).Sucrose synthesis starts in the cytosol where two triose-phosphates produce one Fructose-1,6-bisphosphate by the enzyme aldolase. Fructose-1,6-bisphosphate is converted to fructose-6-phosphate by the enzyme Fructose-1,6-bisphosphatase. Then the enzyme phosphohexose isomerase converts fructose-6 phosphate to glucose-6-phosphate. Glucose-6-phosphate then forms glucose-1-phosphate in presence of the enzyme phosphoglucomutase (PGM). The glucose-1-phosphate is converted to[..]

Phosphoglycerides such as phosphatidylethanolamine and phosphatidylserine are the major component of lipid bilayer membranes in which their detergent-like properties help to provide membranes the quality of self-assembly. Phosphatidylglycerol is a precursor in the synthesis of both cardiolipin and PI (Phosphatidylinositol). Cardiolipin is a unique dimeric phospholipid found in the heart and most mammalian tissues. This phospholipid is the only phospholipid localized primarily in the mitochondrial membrane of mammalian cells. In cardiolipin, two phosphatidylglycerol units are joined together. Phosphatidic acid is activated to CDP-DAG (CDP-Diacylglycerol), which is the precursor to PI and cardiolipin. PI is the precursor of PI Phosphates, which have one of more[..]

Plasmalogens are glycerophospholipids of neural membranes containing vinyl ether bonds. Their synthetic pathway is located in peroxisomes and endoplasmic reticulum. About 20% of mammalian Glycerophospholipids are Plasmalogens. The exact percentage varies both from species to species and from tissue to tissue within a given organisms. While Plamalogens comprise only 0.8% of phospholipids in human liver, they account for 23% of those in human nervous tissue (Ref.1). One of the starting materials for plasmalogen biosynthesis is DHAP (Dihydroxyacetone Phosphate) from glycolysis, which is used to form the glycerol backbone of the plasmalogen. The initial steps of plasmalogen biosynthesis are catalyzed by DHAP-AT (Dihydroxyacetone phosphate Acyltransferase) and[..]

The Toll-like receptors (TLRs), 13 types known to-date, are a group of pattern-recognition receptors that play a crucial role in danger recognition and induction of the innate immune response against bacterial and viral infections. The major adaptors that bind to the intracellular domain of TLR to activate the proinflammatory response are the myeloid differentiation primary response MYD88 and TIR-domain-containing adapter-inducing interferon-beta (TRIF). TRIF-dependent signaling is required for TLR-mediated production of type-I IFN and several other proinflammatory mediators (Ref.1 and 2). The TLR adaptor molecule facilitates TLR3 and TLR4 signaling and concomitant activation of the transcription factors, NF-kappaB, AP-1 and IFN regulatory factor 3, leading to[..]

The cellular responses to DNA damage induced by ionizing radiation include activation of cell cycle checkpoints that delay progression of cells through the cell cycle. Ionizing radiation-induced checkpoints are active at the transition from the G1-phase to the S-phase, in the S-phase, and at the transition from the G2-phase to mitosis (G2/M). The surveillance mechanisms responsible for initiating these checkpoints appear to facilitate maintenance of the integrity of the genome, presumably because they ensure that damaged DNA templates are neither replicated nor segregated into the daughter cells until they are repaired. The option to undergo apoptosis can be considered as one of the checkpoint endpoints, and a failure of the cell to die under appropriate circumstances[..]

Cells are constantly under threat from the cytotoxic and mutagenic effects of DNA damaging agents that result from either endogenous sources (cellular metabolic processes) or exogenous sources (environmental factors). Endogenous sources of DNA damage include hydrolysis, oxidation, alkylation, and mismatch of DNA bases; sources for exogenous DNA damage include ionizing radiation (IR), ultraviolet (UV) radiation, and various chemicals agents (Ref.1). Repairing damage in DNA from anything that causes a mutation, such as UV radiation and tobacco smoke, is a fundamental process that protects our cells from becoming cancerous. The major forms of DNA damage include SSB (Single-strand Breaks), DSB (Double-strand Breaks), alteration of bases, hydrolytic depurination, hydrolytic[..]

An upregulation of cellular signaling pathways is observed in multiple cell types upon HCMV(human cytomegalovirus) infection, suggesting that a global feature of HCMV infection is the activation of the host cell. HCMV initiates and maintains cellular signaling through a multitiered process that is dependent on a series of events: (1) the viral glycoprotein ligand interacts with its cognate receptor, (2) cellular enzymes and viral tegument proteins present in the incoming virion are released and (3) a variety of viral gene products are expressed. Viral-mediated cellular modification has differential outcomes depending on the cell type infected.Human CMV infects a significant portion of the human population and belongs to the family of beta-herpes virus(Ref.1&2).One[..]

Circadian rhythms are daily rhythms of biological processes in behavior or physiology that reoccur approximately every 24 hr. They are determined and modified by environmental cues like light and temperature, but can also persist in the absence of these cues. Although circadian rhythms are present in nearly all living organisms, Drosophila melanogaster is used as model organism to study the phenomena due to many advantages including low genetic redundancy, functional simplicity, its clock regulated behavior including eclosion, olfactory sensitivity, egg laying , courtship, gustatory sensitivity or learning and memory, and the ability to conduct large-scale genetic screens (Ref.1). Circadian clocks consist of 3 parts: input pathway, circadian oscillator[..]

Protein kinases are ubiquitous enzymes that are able to modulate the activities of other proteins by adding phosphate groups to their tyrosine, serine, or threonine amino acids (phosphorylation). MAPKs (Mitogen-Activated Protein Kinases), which are activated by many different signals, belong to a large family of serine/threonine protein kinases that are conserved in organisms as diverse as yeast and humans. MAPKs deliver extracellular signals from activated receptors to various cellular compartments, notably the nucleus, where they direct the execution of appropriate genetic programs, including activation of gene transcription, protein synthesis, cell cycle machinery, cell death, and differentiation. A unique feature of MAPKs is that they themselves can be activated[..]

Phagocytic cells are a critical line of defense against infection. The ability of a pathogen to survive and even replicate within phagocytic cells is a potent method of evading the defense mechanisms of the host. A number of pathogens survive within macrophages after phagocytosis and this contributes to their virulence. Salmonella is one of these pathogens. Salmonella spp are Gram-negative bacteria capable of infecting a wide range of host species, including humans, domesticated and wild mammals, reptiles, birds and insects. They are the etiologic agents of a variety of diseases globally defined as salmonellosis. Salmonellosis is one of the most important human enteric diseases worldwide. Salmonella infections display a broad range of clinical manifestations that are[..]

Circadian clocks are molecular time-keeping mechanisms that reside in a diverse range of cell types in a variety of organisms. The primary role of these cell-autonomous clocks is to maintain their own 24-hour molecular rhythm and to drive the rhythmic expression of genes involved in physiology, metabolism and behavior. The ability of the clock to persist in the absence of environmental cues provides internal temporal organization so that rhythmic activities can occur at characteristic times during the circadian cycle. In addition, two other clock properties, entrainment (that is, setting the clock to local time with respect to environmental cycles) and temperature compensation (that is, the ability of the clock to run at the same rate at different temperatures) ensure[..]