F.3 Biology ~

A reducing sugar is any sugar which in basic solution forms some aldehyde or ketone. This allows the sugar to act as a reducing agent, for example in the Maillard reaction and Benedict's reaction. Reducing sugars include glucose, glyceraldehyde, lactose, arabinose and maltose. All monosaccharides which contain ketone groups are known as ketoses, and those which contain aldehyde groups are known as aldoses. Significantly, sucrose is not a reducing sugar. It is in fact known as a non reducing sugar.

Benedict's reagent is used to determine if a reducing sugar is present. If it is a reducing sugar, the mixture will turn green/orange/red. Fehling's solution can also be used for the same purpose, as both contain copper (II) ions which are reduced to a brick red precipitate of copper (I) oxide when the solution is heated.

A reducing sugar occurs when its anomeric carbon is free. Since sugars occur in a chain as well as a ring structure, it is possible to have an equilibrium between these two forms.


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Digestive enzymes are enzymes in the alimentary tract with a purpose of breaking down components of food so that they can be taken up by the organism. The main sites of action are the oral cavity, the stomach, the duodenum and the jejunum. They are secreted by different glands: the salivary glands, the glands in the stomach, the pancreas, and the glands in the small intestines.


Stomach
The enzymes that get secreted in the stomach are called gastric enzymes. These are the following:

Pepsin is the main gastric enzyme. As it breaks proteins into smaller peptide fragments, it is a peptidase.
Gelatinase, degrades type I and type V gelatin and type IV and V collagen, which are proteoglycans in meat.
Gastric amylase degrades starch, but is of minor significance.
Gastric lipase is a tributyrase by its biochemical activity, as it acts almost exclusively on tributyrin, a butter fat.


Pancreatic enzymes
The pancreas is the main digestive gland in our body. It secretes the enzymes:

Trypsin, is a peptidase, like pepsin in the stomach.
Chymotrypsin, also a peptidase
Steapsin, is also a carbohydrate digesting enzyme
Carboxypeptidase, splits peptide fragments into individual amino acids. It is a protease.
Several elastases that degrade the protein elastin and some other proteins.
Several nucleases that degrade nucleic acids,like DNAase and RNAase
Pancreatic amylase that, besides starch and glycogen, degrades also most other hydrocarbons, but not cellulose. Disaccharides and trisaccharides form.
Bile from the liver, which emulsifies fat, allowing more efficient use of lipases in the duodenum; in converting lipids to their component fatty acid and glycerol molecules

Proper small intestine enzymes
Several peptidases.
The jejunum and ileum secretes a juice called succus entericus which contains the following:
Six types of enzymes degrade disaccharides into monosaccharides:

Sucrase, which breaks down sucrose into glucose and fructose
Maltase, which breaks down maltose into glucose.
Isomaltase, which breaks down maltose and isomaltose
Lactase, which breaks down lactose into glucose and galactose
Intestinal lipase, which breaks down fatty acids
Erepsin, also a protein-digesting enzyme