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October, 2006
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What are Carbohydrates?

JoVE 10680

Carbohydrates are essential biological molecules made of carbon, hydrogen, and oxygen atoms, often in the ratio of 1:2:1. They occur as simple or complex structures and are essential for energy metabolism and storage.

All carbohydrates are sugars, also called saccharides. However, depending on their length and complexity carbohydrates can be classified as monosaccharides, disaccharides, and polysaccharides. Monosaccharides are also called simple sugars. Polysaccharides are referred to as complex carbohydrates. They are polymers, as they are built from repeating units of simple sugars. One of the simplest sugars is glucose. It is made of six carbons, 12 hydrogens, and six oxygens (i.e., C6H12O6). Glucose has a single sugar unit and is, therefore, a monosaccharide. Even such a simple molecule has several variants (isomers), depending on the orientation of individual atoms in space. For instance, if the hydroxyl (-OH) group on carbon number five points to the right, we speak of D-Glucose, if it points to the left, it is L-Glucose. The two molecules are enantiomers, mirror images of each other. The representation of a molecule as a ring structure is called Haworth projection. It reveals another option to arrange the atoms in a glucose molecule. Identify the carbon that previously carried the carboxyl group (

 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

Golgi Apparatus

JoVE 10970

As they leave the Endoplasmic Reticulum (ER), properly folded and assembled proteins are selectively packaged into vesicles. These vesicles are transported by microtubule-based motor proteins and fuse together to form vesicular tubular clusters, subsequently arriving at the Golgi apparatus, a eukaryotic endomembrane organelle that often has a distinctive ribbon-like appearance.

The Golgi apparatus is a major sorting and dispatch station for the products of the ER. Newly arriving vesicles enter the cis face of the Golgi—the side facing the ER—and are transported through a collection of pancake-shaped, membrane-enclosed cisternae. Each cisterna contains unique compositions of enzymes and performs specific protein modifications. As proteins progress through the cis Golgi network, some are phosphorylated and undergo removal of certain carbohydrate modifications that were added in the ER. Proteins then move through the medial cisterna, where they may be glycosylated to form glycoproteins. After modification in the trans cisterna, proteins are given tags that define their cellular destination. Depending on the molecular tags, proteins are packaged into vesicles and trafficked to particular cellular locations, including the lysosome and plasma membrane. Specific markers on the membranes of these vesicles allow them to dock

 Core: Biology

Carbohydrate Digestion

JoVE 10834

Carbohydrate digestion and metabolism break down simple and complex carbohydrates from food into saccharides (i.e., sugars) for the body to use as energy. Carbohydrate digestion starts in the mouth during mastication, or chewing. The masticated carbohydrates remain intact in the stomach. Digestion resumes in the duodenum of the small intestine, where pancreatic alpha-amylase and brush border enzymes of the microvilli convert complex carbohydrates to monosaccharides. Finally, the monosaccharides are absorbed by the intestinal epithelium for energy usage. Three basic types of carbohydrates are found in the human diet: simple carbohydrates, complex carbohydrates, and fiber. Simple carbohydrates are monosaccharide molecules such as glucose, fructose, and galactose. Complex carbohydrates, on the other hand, are polysaccharides composed of long chains of glucose. Finally, fiber is a carbohydrate that is found in the cellulose of plant-based foods. It cannot be broken down by the body for energy, but it does play a vital role in healthy digestion by helping ingested food to move along the digestive system.

 Core: Biology

The Extracellular Matrix

JoVE 10695

In order to maintain tissue organization, many animal cells are surrounded by structural molecules that make up the extracellular matrix (ECM). Together, the molecules in the ECM maintain the structural integrity of tissue as well as the remarkable specific properties of certain tissues.

The extracellular matrix (ECM) is commonly composed of ground substance, a gel-like fluid, fibrous components, and many structurally and functionally diverse molecules. These molecules include polysaccharides called glycosaminoglycans (GAGs). GAGs occupy most of the extracellular space and often take up a large volume relative to their mass. This results in a matrix that can withstand tremendous forces of compression. Most GAGs are linked to proteins—creating proteoglycans. These molecules retain sodium ions based on their positive charge and therefore attract water, which keeps the ECM hydrated. The ECM also contains rigid fibers such as collagens—the primary protein component of the ECM. Collagens are the most abundant proteins in animals, making up 25% of protein by mass. A large diversity of collagens with structural similarities provide tensile strength to many tissues. Notably, tissue like skin, blood vessels, and lungs need to be both strong and stretchy to perform their physiological role. A protein called elastin gives p

 Core: Biology

Microscopy and Staining: Gram, Capsule, and Endospore Staining

JoVE 10513

Source: Rhiannon M. LeVeque1, Natalia Martin1, Andrew J. Van Alst1, and Victor J. DiRita1
1 Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, United States of America

Bacteria are diverse microorganisms found nearly everywhere on Earth. Many properties help distinguish them from…


Community DNA Extraction from Bacterial Colonies

JoVE 10218

Source: Laboratories of Dr. Ian Pepper and Dr. Charles Gerba - Arizona University
Demonstrating Author: Luisa Ikner

Traditional methods of analysis for microbial communities within soils have usually involved either cultural assays utilizing dilution and plating methodology on selective and differential media or direct count assays.…

 Environmental Microbiology

Plant Cell Wall

JoVE 11084

The plant cell wall gives plant cells shape, support, and protection. As a cell matures, its cell wall specializes according to the cell type. For example, the parenchyma cells of leaves possess only a thin, primary cell wall.

Collenchyma and sclerenchyma cells, on the other hand, mainly occur in the outer layers of a plant's stems and leaves. These cells provide the plant with strength and support by either partially thickening their primary cell wall (i.e., collenchyma), or depositing a secondary cell wall (i.e., sclerenchyma). Altogether, the varying cell wall compositions determine the function of specific cells and tissues. Some plants, such as trees and grasses, deposit a secondary cell wall around mature cells. Secondary cell walls typically contain three distinct layers: the secondary wall layer 1 (S1) to the outside, the secondary wall layer 2 (S2) in the middle, and the innermost secondary wall layer 3 (S3). In each layer, the cellulose microfibrils are organized in different orientations. The S2 layer may make up to 75% of the cell wall. Regardless of composition, all plant cell walls have small holes, or pits, that allow for the transport of water, nutrients, and other molecules. In a pit, the middle lamella and primary cell wall merely form a thin membrane that separates adjacent cells.

 Core: Biology
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