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October, 2006
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Lactose: A disaccharide of Glucose and Galactose in human and cow milk. It is used in pharmacy for tablets, in medicine as a nutrient, and in industry.


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

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


JoVE 10984

Prokaryotes can control gene expression through operons—DNA sequences consisting of regulatory elements and clustered, functionally related protein-coding genes. Operons use a single promoter sequence to initiate transcription of a gene cluster (i.e., a group of structural genes) into a single mRNA molecule. The terminator sequence ends transcription. An operator sequence, located between the promoter and structural genes, prohibits the operon’s transcriptional activity if bound by a repressor protein. Altogether, the promoter, operator, structural genes, and terminator form the core of an operon. Operons are usually either inducible or repressible. Inducible operons, such as the bacterial lac operon, are normally “off” but will turn “on” in the presence of a small molecule called an inducer (e.g., allolactose). When glucose is absent, but lactose is present, allolactose binds and inactivates the lac operon repressor—allowing the operon to generate enzymes responsible for lactose metabolism. Repressible operons, such as the bacterial trp operon, are usually “on” but will turn “off” in the presence of a small molecule called a corepressor (e.g., tryptophan). When tryptophan—an essential amino acid—is abundant, tryptophan binds and activates the

 Core: Biology

Macromolecules- Concept

JoVE 10590


Organisms contain a wide variety of organic molecules with numerous functions which depend on the chemical structures and properties of these molecules. All organic molecules contain a carbon backbone and hydrogen atoms. The carbon atom is central in the formation of a vast variety of organic molecules ranging in size, shape and complexity; inorganic molecules on the other…

 Lab Bio

Punnett Squares

JoVE 10772

A Punnett square displays the possible genotypes offspring can inherit from two parental genotypes. If a trait’s inheritance pattern (e.g., dominant or recessive) is known, Punnett squares can also be used to determine the probability of inheriting a phenotype. Punnett squares are applicable in situations where trait inheritance is determined by a single gene locus and traits are independently inherited. However, they cannot predict trait probabilities for more complex genetic inheritance scenarios. Punnett squares are visual representations that display possible offspring genotypes resulting from a cross between two parental genotypes. They can depict inheritance of one or multiple phenotypes, or traits, although other tools are more appropriate for investigating the inheritance of more than two traits. Punnett squares can be used to determine the likelihood of offspring inheriting a specific genotype, or pair of alleles causing a particular characteristic (i.e., phenotype or trait), provided that the phenotype is caused by a single gene locus and is independently assorted during meiosis. In other words, Punnett squares are useful for determining inheritance probabilities in scenarios where the likelihood of inheriting one trait does not affect the probability of inheriting another. Although there are many exceptions to these assumptions (e.

 Core: Biology

An Overview of Gene Expression

JoVE 5546

Gene expression is the complex process where a cell uses its genetic information to make functional products. This process is regulated at multiple stages, and any misregulation could lead to diseases such as cancer.

This video highlights important historical discoveries relating to gene expression, including the…


Combining Single-molecule Manipulation and Imaging for the Study of Protein-DNA Interactions

1LENS - European Laboratory for Non-linear Spectroscopy, University of Florence, 2Chemistry Research Laboratory, University of Oxford, 3Department of Biology, University of Florence, 4Department of Physics and Astronomy, University of Florence, 5National Institute of Optics-National Research Council, Italy, 6International Center of Computational Neurophotonics

JoVE 51446


Scalable High Throughput Selection From Phage-displayed Synthetic Antibody Libraries

1The Recombinant Antibody Network, 2The Banting and Best Department of Medical Research, University of Toronto, 3Antibiome Center, University of California, San Francisco at Mission Bay, 4Department of Biochemistry and Molecular Biology, The University of Chicago

JoVE 51492

 Immunology and Infection
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