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October, 2006
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What are Viruses?

JoVE 10821

A virus is a microscopic infectious particle that consists of an RNA or DNA genome enclosed in a protein shell. It is not able to reproduce on its own: it can only make more viruses by entering a cell and using its cellular machinery. When a virus infects a host cell, it removes its protein coat and directs the host’s machinery to transcribe and translate its genetic material. The hijacked cell assembles the replicated components into thousands of viral progeny, which can rupture and kill the host cell. The new viruses then go on to infect more host cells. Viruses can infect different types of cells: bacteria, plants, and animals. Viruses that target bacteria, called bacteriophages (or phages), are very abundant. Current research focuses on phage therapy to treat multidrug-resistant bacterial infections in humans. Viruses that infect cultivated plants are also highly studied since epidemics lead to huge crop and economic losses. Viruses were first discovered in the 19th century when an economically-important crop, the tobacco plant, was plagued by a mysterious disease—later identified as Tobacco mosaic virus. Animal viruses are of great importance both in veterinary research and in medical research. Moreover, viruses underlie many human diseases, ranging from the common cold, chickenpox, and herpes, to more dangerous infection

 Core: Biology

Transgenic Organisms

JoVE 10809

Transgenic organisms are genetically engineered to carry transgenes—genes from a different species—as part of their genome. The transgene may either be a different version of one of the organism’s genes or a gene that does not exist in their genome. Transgenes are usually generated by recombinant DNA and DNA cloning techniques. Transgenic bacteria, plants, and animals allow scientists to address biological queries and design practical solutions. Scientists begin the process of transgenesis—introducing a transgene into an organism’s genome—by selecting an appropriate technique. There are several biological, chemical, and physical methods of transgenesis. A common biological method involves the virus-mediated introduction of foreign DNA into a host cell genome, called transduction. A popular chemical method uses calcium phosphate (Ca3(PO4)2). The method is based on the formation of a Ca3(PO4)2/DNA precipitate to facilitate DNA binding to and entering cells. Physical methods such as microinjection—a technique that uses a thin, glass needle to manually insert genetic material into cells—artificially introduce DNA by force. Once inside the cell, a transgene can either integrate randomly or at a specific site in the genome with the help of DNA repa

 Core: Biology

Types of RNA

JoVE 10800

Three main types of RNA are involved in protein synthesis: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). These RNAs perform diverse functions and can be broadly classified as protein-coding or non-coding RNA. Non-coding RNAs play important roles in the regulation of gene expression in response to developmental and environmental changes. Non-coding RNAs in prokaryotes can be manipulated to develop more effective antibacterial drugs for human or animal use. The central dogma of molecular biology states that DNA contains the information that encodes proteins and RNA uses this information to direct protein synthesis. Different types of RNA are involved in protein synthesis. Based on whether or not they encode proteins, RNA is broadly classified as protein-coding or non-coding RNA. Messenger RNA (mRNA) is the protein-coding RNA. It consists of codons—sequences of three nucleotides that encode a specific amino acid. Transfer RNA (tRNA) and ribosomal RNA (rRNA) are non-coding RNA. tRNA acts as an adaptor molecule that reads the mRNA sequence and places amino acids in the correct order in the growing polypeptide chain. rRNA and other proteins make up the ribosome—the seat of protein synthesis in the cell. During translation, ribosomes move along an mRNA strand where they stabilize the binding of tRNA molecules and catalyze the for

 Core: Biology


JoVE 10682

Hydrolysis is a chemical reaction in which water breaks a bond within a molecule. For example, it breaks peptides into amino acids, carbohydrates into simple sugars and DNA into nucleotides. Enzymes often facilitate these processes.

To break down complex carbohydrates, the linkage between individual sugar units needs to be broken. The reaction that breaks a glycosidic bond is called hydrolysis, as water is added to the compound. The glycosidic bonds between sugar molecules are stable, so hydrolases often catalyze hydrolysis. Hydrolases are enzymes that are specialized in catalyzing hydrolysis. Different types of glycosidic bonds (e.g., 1-4 linkage, 1-6 linkage) require different hydrolases. The type of enzyme needed also depends on the location of the sugar unit within the polymer. For instance, starch primarily consists of 1-4 linked glucose, with a relatively small number of 1-6 glycosidic bonds. While α-amylase can cleave 1-4 glycosidic bonds in the middle of the polymer, the enzyme amyloglucosidase breaks only 1-6 or 1-4 bonds at the terminus (i.e., the last glucose unit at the end of the chain). Human babies produce the enzyme lactase, which catalyzes the hydrolysis of milk sugar, or lactose. Lactose is a disaccharide that consists of glucose and galactose. In many areas of the world, humans stop producing lactase when they reach adul

 Core: Biology

Natural Selection- Concept

JoVE 10632


Widespread variation of phenotypes in natural populations provides the raw material for evolution, which is the change in the inherited traits of populations over successive generations. Natural selection is one of the main mechanisms of evolution and requires variable traits to be heritable and associated with differential survival and/or reproductive success. Phenotypes that…

 Lab Bio

Community Diversity- Concept

JoVE 10607

Populations do not live in isolation; thus, every population interacts with others in certain ways. These interactions give rise to a network of populations. Hence, an ecological community is composed of such population networks of various species interacting with each other within the same area. These biological, or biotic, components may also closely interact with non-living, or abiotic,…

 Lab Bio

Population Growth- Concept

JoVE 10605

Population Models

An ecological population is a group of individuals of a single species living in an area at the same time. To persist, a population must either grow or maintain its size. Population ecology is the study of how population size and age distribution change over time through interactions with other species and the environment as well as with individuals of their own…

 Lab Bio

Enzyme Activity- Concept

JoVE 10585

Biological Catalysts

All living organisms continuously perform numerous biochemical reactions to sustain their presence. Most of these reactions require an input of energy to start, which is called the activation energy. Catalysts are chemicals that lower the activation energy. Even though catalysts facilitate a chemical reaction, they are not consumed by it. This means a catalyst …

 Lab Bio

Diffusion and Osmosis - Prep Student

JoVE 10563

Preparation of Solutions for the Agar Cube Experiment
IMPORTANT: Wear gloves, goggles, and appropriate personal protective equipment – chemicals can be hazardous at high concentrations.
For the diffusion indicator solution, weigh out 1 g of phenolphthalein and add it to a beaker containing 100 mL of 95% ethanol.
To make the basic…

 Lab Bio

Magnetic Activated Cell Sorting (MACS): Isolation of Thymic T Lymphocytes

JoVE 10495

Source: Meunier Sylvain1,2,3, Perchet Thibaut1,2,3, Sophie Novault4, Rachel Golub1,2,3
1 Unit for Lymphopoiesis, Department of Immunology, Pasteur Institute, Paris, France
2 INSERM U1223, Paris, France
3 Université Paris Diderot, Sorbonne Paris Cité, Cellule Pasteur, Paris, France
4 Flow Cytometry Platfrom, Cytometry and Biomarkers UtechS, …

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