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High Quality Content by WIKIPEDIA articles! In biochemistry, a receptor is a protein molecule, embedded in either the plasma membrane or the cytoplasm of a cell, to which a mobile balls signaling molecule may attach. A molecule which binds to a receptor is called a ligand, and may be a peptide or other small molecule, such as a neurotransmitter, a hormone, a pharmaceutical drug, or a toxin. When such binding occurs, the receptor undergoes a conformational change, which ordinarily initiates a cellular response. However, some ligands (e.g. antagonists) merely block receptors without inducing any response. Ligand-induced changes in receptors result in cellular changes which constitute the biological activity of the ligands.

The barndoor skate, Dipturus laevis, is a species of marine cartilaginous fish in the skate family (family Rajidae) of the order Rajiformes. It is native to the northwestern Atlantic Ocean, and is found from the Grand Banks of Newfoundland and the southern side of the Gulf of St. Lawrence south to North Carolina. The fish is one of the largest skates found in the North Atlantic Ocean, reaching lengths of up to 1.5 metres (5 ft). It is carnivorous, feeding on invertebrates and other fish found near the sea floor.

High Quality Content by WIKIPEDIA articles! Parallel evolution is the development of a similar trait in different not closely related species (that is in species of a different clade), but descending from the same ancestor. For a particular trait, proceeding in each of two lineages from a specified ancestor to a later descendant, parallel and convergent evolutionary trends can be strictly defined and clearly distinguished from one another.[2] When both descendants are similar in a particular respect, evolution is defined as parallel if the ancestors considered were also similar, and convergent if they were not.

Paul Singleton

This Third, Revised Edition of a unique, encyclopaedic reference work covers the whole field of pure and applied microbiology and microbial molecular biology in one volume.

High Quality Content by WIKIPEDIA articles! Protein targeting or protein sorting is the mechanism by which a cell transports proteins to the appropriate positions in the cell or outside of it. Sorting targets can be the inner space of an organelle, any of several interior membranes, the cell's outer membrane, or its exterior via secretion. This delivery process is carried out based on information contained in the protein itself. Correct sorting is crucial for the cell; errors can lead to diseases.

High Quality Content by WIKIPEDIA articles! High Quality Content by WIKIPEDIA articles! A taxis (plural taxes, pronounced /?t?ksi?z/) is an innate behavioral response by an organism to a directional stimulus or gradient of stimulus intensity. A taxis differs from a tropism (turning response, often growth towards or away from a stimulus) in that the organism has motility and demonstrates guided movement towards or away from the stimulus source. It is sometimes distinguished from a kinesis, a non-directional change in activity in response to a stimulus that results in the migration toward or away from a stimulus.

David W. Cameron, Colin P. Groves

Bones, Stones and Molecules provides some of the best evidence for resolving the debate between the two hypotheses of human origins. The debate between the 'Out of Africa' model and the 'Multiregional' hypothesis is examined through the functional and developmental processes associated with the evolution of the human skull and face and focuses on the significance of the Australian record. The book analyzes important new discoveries that have occurred recently and examines evidence that is not availableelsewhere. Cameron and Groves argue that the existing evidence supports a recent origin for modern humans from Africa. They also specifically relate these two theories to interpretations of the origins of the first Australians. The book provides an up-to-date interpretation of the fossil, archaeological and the molecular evidence, specifically as it relates to Asia, and Australia in particular. * Readily accessible to the layperson and professional * Provides concise...

Gerald Thiel

This first book to cover neural development, neuronal survival and function on the genetic level outlines promising approaches for novel therapeutic strategies in fighting neurodegenerative disorders, such as Alzheimer?s disease. Focusing on transcription factors, the text is clearly divided into three sections devoted to transcriptional control of neural development, brain function and transcriptional dysregulation induced neurological diseases. With a chapter written by Nobel laureate Eric Kandel, this is essential reading for neurobiologists, geneticists, biochemists, cell biologists, neurochemists and molecular biologists.

High Quality Content by WIKIPEDIA articles! Spermatogenesis is the process by which male spermatogonia develop into mature spermatozoa, also known as a sperm cell. Spermatozoa are the mature male gametes in many sexually reproducing organisms. Thus, spermatogenesis is the male version of gametogenesis. In mammals it occurs in the male testes and epididymis in a stepwise fashion, and for humans takes approximately 64 days. Spermatogenesis is highly dependent upon optimal conditions for the process to occur correctly, and is essential for sexual reproduction. It starts at puberty and usually continues uninterrupted until death, although a slight decrease can be discerned in the quantity of produced sperm with increase in age.

High Quality Content by WIKIPEDIA articles! The prokaryotes are a group of organisms that lack a cell nucleus (= karyon), or any other membrane-bound organelles. They differ from the eukaryotes, which have a cell nucleus. Most are unicellular, but a few prokaryotes such as myxobacteria have multicellular stages in their life cycles. The word prokaryote comes from the Greek ???- (pro-) "before" + ?????? (karyon) "nut or kernel", referring to the cell nucleus, + suffix -???? (-?t?s) (pl. -???? (-?tes)). It is also spelled "procaryote".