What is the Biological Molecule and Structure?
Molecular and structural formula:
The molecular formula for a hexose is written as C, H,, O,. It is useful to show the arrangement of atoms in a molecule by a diagram known as a structural formula.
Ring structure:
Pentoses and hexoses usually form rings in water. In pentoses and hexoses, the chain of carbon atoms is long enough to close up on itself and form a stable ring structure e.g. glucose. When glucose forms a ring, carbon atom No. 1 joins to the oxygen on carbon atom No.5. The ring, therefore, contains oxygen and the last carbon of glucose is not part of the ring.
The hydroxyl group, (OH) on carbon atom number one may be above or below the plane of the ring. If it is below the string is known as alpha glucose (a-gluc; and if it is a, it is known as an isomer. They form glucose (Beta glucose). The two different forms of the same chemical
Trioses:
is C, H, O, for example, glyceraldehyde, dihydroxy acetone. These are intermediate substances in cellular respiration and photosynthesis.
Pentoses:
Their formula is C, H,, O, e.g. ribose, deoxyribose, and ribulose. Ribose is the component of RNA, ATP, NAD, FAD, NADP, etc. Deoxyribose is the component of DNA while ribulose is the component of RUBP which is the CO, acceptor in photosynthesis.
Hexoses:
Their formula is C, H,, O, e.g., glucose, fructose, galactose. Glucose is the most common respiratory substrate and also the most common monosaccharide.
Comparison between Structural Isomers and Stereoisomers:
Isomers (Gk. Iso: equal, meros: part) are molecules with the same molecular formula but different chemical structures. It means that isomers contain the same number of atoms of each element but have different arrangements. Isomers do not generally share similar properties,
unless they also have the same functional group. There are two main forms of isomerism, structural isomerism, and stereoisomers.
structural isomers:
In structural isomers (also called constitutional isomers) the atoms and functional groups are joined together in different ways, glucose and fructose are
structural isomers.
Stereo-isomerism:
In stereo-isomerism, the bond structure is the same but the geometrical positioning of atoms and functional groups in space differs e.g., D-glucose and L-glucose.
The Laboratory Manufactured Sweeteners are "Left-handed" Sugars:
Two forms of chemical compounds may exist, that are mirror images of each other. A suitable analogy is a pair of gloves, they can be either left-handed or right-handed. Sugar is also left-handed and right-handed molecules.
Our digestive enzymes can only digest the right-handed sugar molecules but generally do not digest the left-handed that allow t digestion.
The LH sugar has the same physical property to pass through the body as D-glucose, therefore, may be used instead of D-glucose e.g., for baking and also making ice cream.
Left-handed sugars are not commonly used because they are expensive, and not commonly available, and their overuse causes serious disturbance for diarrhea patients.
The laboratory-manufactured sugars such as tagatose, sucralose, etc. are examples of LH sugar. These sugar molecules can not be digested because mostly the enzymes for their digestion are not synthesized in the body and our cells do not have receptors for them. LH sugar is not converted into fats.
Oligosaccharide:
They are made up of 2 to 10 monosaccharides. Some examples of oligosaccharides are Disaccharides, Trisaccharides, and Tetrasaccharides. The most common oligosaccharides are disaccharides.
Disaccharide:
It is made up of two monosaccharides (usually hexoses) combined using a chemical reaction known as condensation. Disaccharides are less sweet in taste and less soluble in water as compared to monosaccharides.
0 Comments