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Uric Acid: An oxidation product, via Xanthine oxidase, of oxypurines such as Xanthine and Hypoxanthine. It is the final oxidation product of purine catabolism in humans and primates, whereas in most other mammals Urate oxidase further oxidizes it to Allantoin.

Comparative Excretory Systems

JoVE 10998

Animals have evolved different strategies for excretion, the removal of waste from the body. Most waste must be dissolved in water to be excreted, so an animal’s excretory strategy directly affects its water balance.

Nitrogenous wastes are some of the most significant forms of animal waste. Nitrogen is released when proteins and nucleic acids are broken down for energy or conversion into carbohydrates and fats. Proteins are broken down into amino acids and nucleic acids into nitrogenous bases. The nitrogen-containing amino groups of amino acids and nitrogenous bases are then converted into nitrogenous wastes. Typical nitrogenous wastes released by animals include ammonia, urea, and uric acid. These excretory strategies involve tradeoffs between conserving energy and water. The various nitrogenous wastes reflect distinct habitats and evolutionary histories. For example, most aquatic animals are ammonotelic, meaning they directly excrete ammonia. This approach is less energy-intensive than converting ammonia into urea or uric acid before excretion, but also requires more water. For terrestrial organisms, which face perhaps no more significant regulatory threat than dehydration, water conservation is worth the extra energy cost. Ureotelic animals, like mammals and sharks, convert ammonia into urea before excretion. Urea is less toxic

 Core: Regulation and Excretion

Osmoregulation in Insects

JoVE 10990

Malpighian tubules are specialized structures found in the digestive systems of many arthropods, including most insects, which handle excretion and osmoregulation. The tubules are typically arranged in pairs and have a convoluted structure that increases their surface area.

Malpighian tubules extend from the digestive tract, typically the area between the midgut and hindgut, into the hemolymph—a mixture of blood and interstitial fluid found in insects and other arthropods, as well as most mollusks. Unlike other excretory systems, the excretory processes of Malpighian tubules lack a filtration step. Metabolic wastes, like uric acid, diffuse into the tubules from the hemolymph. The tubules are lined with a layer of transport epithelia. These specialized epithelial cells contain pumps that actively transport ions, like sodium (Na+) and potassium (K+), from the hemolymph into the interior of the tubule, called the lumen. Osmosis allows water to follow ions into the tubules passively. From the tubule lumen, water, ions, and waste travel from the intestine to the rectum. Tiny, protruding microvilli lining the inside of the tubules help maximize solute-water coupling and the propulsion of uric acid crystals through the tubules. In the rectum, specialized glands pump many of the ions back into the hemolymph. Osmosis

 Core: Regulation and Excretion

What is Metabolism?

JoVE 10725

Metabolism represents all of the chemical activity in a cell, including reactions that build molecules (anabolism) and those that break molecules down (catabolism). Anabolic reactions require energy, whereas catabolic reactions provide it. Thus, metabolism describes how cells transform energy through a variety of chemical reactions, which are often made more efficient with the help of enzymes. Metabolism is the management of energy in cells and provides three key functions: converting food into energy to run various cellular processes, producing energy to build cell components, and removing waste products. To produce energy, macromolecules from food must be broken down into smaller molecules—through a catabolic pathway. This, in turn, provides energy to construct larger molecules from smaller building blocks—through an anabolic pathway. In other words, the potential energy in food—comprised of the chemical energy stored in the bonds between atoms—can be converted into kinetic energy that can be used for cellular reactions. Enzymes are essential molecular tools in metabolic pathways, as they greatly speed up many chemical reactions by reducing the amount of required energy. Catabolism is the breakdown of macromolecules for any purpose. This inc

 Core: Metabolism

What Are Osmoregulation and Excretion?

JoVE 11001

Organisms must keep bodily fluids at a constant temperature and pH while maintaining specific solute concentrations in order to support life functions. Osmoregulation is the process that balances solute and water levels.

Osmosis is the tendency of water to move from solutions with lower ion concentrations, or osmolarities, to those with higher ion concentrations. Osmosis occurs in response to differences in the molecular concentrations of solutions separated by a semipermeable membrane. Bodily fluids, which are separated by such membranes, contain water, non-electrolytes, and electrolytes—solutes that dissolve into ions in water. Both electrolytes and non-electrolytes influence osmotic balance. However, since the more important factor to osmosis is solute number, rather than size, the contribution of electrolytes is more significant. Unlike water, electrolytes cannot diffuse passively through membranes but rely on facilitated diffusion and active transport. In facilitated diffusion, protein-based channels move solutes across membranes. Conversely, energy is used to move ions against concentration gradients in active transport. When animals ingest food, material that cannot be used is excreted from the body. Excretory systems in nature involve tradeoffs between conserving energy and water. Nitrogen is among the most significant

 Core: Regulation and Excretion

The Nitrogen Cycle

JoVE 10934

Nitrogen atoms, present in all proteins and DNA, are recycled between abiotic and biotic components of the ecosystem. However, the primary form of nitrogen on Earth is nitrogen gas, which cannot be used by most animals and plants. Thus, nitrogen gas must first be converted into a usable form by nitrogen-fixing bacteria before it can be cycled through other living organisms. The use of nitrogen-containing fertilizers and animal waste products in human agriculture has greatly influenced the natural nitrogen cycle. About 78% of the air we breathe is nitrogen gas. However, in this form, N2, few organisms are able to use it. Nitrogen makes up essential molecules in all organisms, like proteins and DNA. Unable to use the atmospheric form of nitrogen, most organisms use the byproducts of nitrogen-fixing and nitrifying prokaryotes. Nitrogen fixation converts nitrogen gas (N2) into ammonia (NH3), whereas nitrification converts NH3 into nitrites (NO2-) and nitrates (NO3-). Plants can directly use the ammonia and nitrates, and plant-eating organisms obtain nitrogen by ingesting plants. When these organisms die, bacteria in the soil are able to convert the organic nitrogen into ammonia in a process called ammonification. Through denitrification, aerobic bacteria can then convert a

 Core: Ecosystems

A Convenient Method for Extraction and Analysis with High-Pressure Liquid Chromatography of Catecholamine Neurotransmitters and Their Metabolites

1School of Public Health of Southeast University, Laboratory of Environment and Biosafety Research Institute of Southeast University in Suzhou, 2Key Laboratory of Child Development and Learning Science (Ministry of Education), School of Biological Science & Medical Engineering, Southeast University, 3School of Public Health, Tianjin Medical University, 4British Columbia Academy, Nanjing Foreign Language School

JoVE 56445

 Chemistry

Application of Genetically Encoded Fluorescent Nitric Oxide (NO•) Probes, the geNOps, for Real-time Imaging of NO• Signals in Single Cells

1Institute of Molecular Biology and Biochemistry, Medical University of Graz

JoVE 55486

 Biology

Consensus Brain-derived Protein, Extraction Protocol for the Study of Human and Murine Brain Proteome Using Both 2D-DIGE and Mini 2DE Immunoblotting

1Team Alzheimer & Tauopathies, Jean-Pierre Aubert Research Centre, Inserm UMR 837, 2EA 4308-Department of Reproductive Biology-Spermiology-CECOS, CHRU-Lille, 3EA2686-Laboratorie d'Immunologie, Faculté de Médecine - Pôle Recherche, 4Department of Neurology, CHRU-Lille

JoVE 51339

 Neuroscience

Performing Vaginal Lavage, Crystal Violet Staining, and Vaginal Cytological Evaluation for Mouse Estrous Cycle Staging Identification

1Department of Biochemistry, Microbiology and Immunology, Neural Regeneration Laboratory and Ottawa Institute of Systems Biology, 2Department of Cellular and Molecular Medicine, University of Ottawa, 3CIHR Program in Neurodegenerative Lipidomics, University of Ottawa, 4Carleton Immersive Media Studio, Azrieli School of Architecture and Urbanism

JoVE 4389

 Biology

Non-surgical Intratracheal Instillation of Mice with Analysis of Lungs and Lung Draining Lymph Nodes by Flow Cytometry

1Department of Immunology, University of Colorado School of Medicine, 2Division of Cell Biology, Department of Pediatrics, National Jewish Health, 3Department of Microbiology, Immunology, and Pathology, Colorado State University, 4Department of Immunology, National Jewish Health

JoVE 2702

 Immunology and Infection
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