BIOCHEMISTRY: INFORMATION ON CARBOHYDRATES

1. Glucose:

• Structure: Glucose exists in 3 forms:

• Linear form: An open chain, linear structure.

• Cyclic form: A 6-membered (pyranose) or 5-membered (furanose) ring. This is the most common form in solution.

• Chair form: A conformational change of the cyclic form, providing stability to the molecular structure.

• Note:

• Glucose is the most abundant monosaccharide, playing a crucial role in the metabolism of living organisms.

• The cyclic form of glucose is more stable than the linear form.

• The chair form of glucose provides stability due to the chemical bonds within the molecule.

2. Lactosazone and Glucosazone:

• Lactosazone: A derivative of lactose, having a structure similar to a hedgehog.

• Glucosazone: A derivative of glucose, having a structure similar to a pumpkin.

• Note:

• Lactosazone and Glucosazone are formed by the reaction of lactose and glucose with phenylhydrazine, respectively.

• The structure of Lactosazone and Glucosazone helps distinguish different types of sugars.

3. Oxidation of Glucose and Galactose:

• Oxidation by HNO3:

• Glucose is oxidized by HNO3 to form saccharic acid.

• Galactose is oxidized by HNO3 to form mucic acid.

• Note:

• This oxidation reaction occurs at the aldehyde group of glucose and galactose.

• Saccharic acid and mucic acid are organic acids that play significant roles in biology.

4. Acid Derivatives:

• 3 types of acid derivatives of carbohydrates:

• Aldonic acid: Formed when the aldehyde group is oxidized to a carboxyl group.

• Aldaric acid: Formed when both the aldehyde group and the hydroxyl group at the end of the chain are oxidized to carboxyl groups.

• Uronic acid: Formed when the hydroxyl group at position C6 is oxidized to a carboxyl group.

• Note:

• These acid derivatives have different structures and properties, contributing to the diversity of carbohydrate functions.

5. Important Monosaccharides:

• D-Ribose:

• A structural component of nucleic acids (DNA and RNA) and coenzymes such as ATP, NAD, and NADP.

• D-Ribulose:

• An intermediate metabolite in the Calvin cycle of photosynthesis.

• D-Arabinose:

• Source: Gum arabic, plum gum, cherry.

• Role: Component of glycoprotein.

• D-Xylose:

• Source: Proteoglycan, glycoaminoglycan.

• D-Lyxose:

• Source: Heart muscle.

• Role: Component of lyxoflavin.

6. Polysaccharides:

• Amylose:

• Linear chain structure.

• Gives a blue-violet color when reacted with iodine.

• Accounts for about 25% of starch.

• Amylopectin:

• Branched chain structure.

• Gives a red-violet color when reacted with iodine.

• Accounts for about 75-85% of starch.

• Glycogen:

• Branched chain structure.

• Gives a red-brown color when reacted with iodine.

• The primary form of energy storage in animal bodies.

• Dextran:

• Produced by the bacteria Leuconostoe mesenteroides.

• Highly viscous, can be used as a plasma substitute.

• Chitin:

• Forms the exoskeleton of arthropods and mollusks.

• A polymer of N-acetylglucosamine.

• Pectin:

• Abundant in fruits.

• Used as a gelling agent and stabilizer in the food industry.

7. Glucosaminoglycans (GAGs):

• Function:

• Provide a matrix for attaching protein components, creating the structure of connective tissues.

• Maintain the viscosity and elasticity of tissues.

• Participate in metabolism and cell signaling.

8. Glycoproteins:

• LH, FSH, TSH: Are glycoproteins in nature.

• Note: These hormones play crucial roles in reproduction and the regulation of endocrine gland activity.

9. Cell Membrane Structure:

• Outer surface of Gram-positive bacteria:

• Composed of a polysaccharide-peptide layer.

• Inner surface of Gram-positive bacteria:

• Composed of a lipid layer.

10. Structure of Starch and Cellulose:

• Starch:

• Branched and unbranched chain structure.

• Cellulose:

• Linear chain structure.

• The main component of plant cell walls.

11. Chemical Reactions:

• Molish test:

• To identify glucidic substances.

• Inulin test:

• To probe kidney function.

General Note:

• Carbohydrates are a vital group of organic compounds in biology.

• Carbohydrates have numerous diverse functions, ranging from energy provision to structure and protection.

• Understanding the structure, properties, and functions of carbohydrates is essential for research and applications in fields such as medicine, agriculture, and industry.