Carbohydrates

Carbohydrates

Characteristics of Enzymes
i. Almost all enzymes are proteins. Enzymes follow the physical and chemical reactions of proteins.
ii. They are heat labile.
iii. They are water-soluble.
iv. They can be precipitated by protein precipitating reagents (ammonium sulfate or trichloroacetic acid
v. They contain 16% weight as nitrogen.
CLASSIFICATION OF ENZYMES
When early workers isolated certain enzymes, whimsical names were given. Some of these, such as Pepsin, Trypsin, Chymotrypsin, etc. are still used. Later, it was agreed to call the enzymes by adding the suffix "-ase" to the substrate. Thus, enzyme Lactase acts on the substrate lactose, and the products glucose and galactose are formed. Enzymes that hydrolyse starch (amylose) are termed as amylases; those that dehydrogenate the substrates are called dehydrogenases. These are known as the trivial names of the enzymes.
Factors affecting enzyme activity
1-Enzyme concentration
2- Substrate concentration
3- Product concentration
4-Temperature
5- Hydrogen ion concentration (pH)
6- Presence of activators
7- Presence of inhibitors
8- Presence of repressor or derepressor
9- Covalent modification.
Carbohydrates
Molecules having only one actual or potential sugar group are called monosaccharides (Greek, mono = one; saccharide = sugar). They cannot be further hydrolyzed into smaller units. When two monosaccharides are combined together with elimination of a water molecule, it is called a disaccharide (e.g. C12H22O11). Trisaccharides contain three sugar groups. Further addition of sugar groups will correspondingly produce tetrasaccharides, pentasaccharides and so on, commonly known as oligosaccharides (Greek, oligo = a few). When more than 10 sugar units are combined, they are generally named as polysaccharides (Greek, poly = many). Polysaccharides having only one type of monosaccharide units are called homopolysaccharides and those having different monosaccharide units are heteropolysaccharides. Sugars having aldehyde group are called aldoses and sugars with keto group are ketoses. Depending on the number of carbon atoms, the monosaccharides are named as triose (C3), tetrose (C4), pentose (C5), hexose) C6), heptose (C7) and so on.
Functions of Carbohydrates
1- Carbohydrates are the main sources of energy in the body. Brain cells and RBCs are almost wholly dependent on carbohydrates as the energy source. Energy production from carbohydrates will be 4 kcal/g.
2- Storage form of energy (starch and glycogen) .
3- Excess carbohydrate is converted to fat.
4- Glycoproteins and glycolipids are components of cell membranes and receptors.
5- Structural basis of many organisms: Cellulose of plants; exoskeleton of insects, cell wall of micro- organisms, mucopolysaccharides as ground substance in higher organisms. The general molecular formula of carbohydrate is Cn(H2O)n For example, glucose has the molecular formula C6H12O6. Carbohydrates are polyhydroxy aldehydes or ketones or compounds which yield these on hydrolysis .