Basics of Monosaccharides and Carbohydrates

Monosaccharides

• Carbohydrates that can't be broken down further into simpler units
• Classified based on the number of carbon atoms and the functional group present
• Aldoses contain an aldehyde group
• Ketoses contain a keto group
• Further classified by the number of carbon atoms. For example:
• Ketotriose: 3 carbon ketose
• Aldotriose: 3 carbon aldose

### Reducing Sugars

• Carbohydrates that reduce Fehling's solution and Tollen's reagent.
• Include all monosaccharides and disaccharides except sucrose.

### Carbohydrate Function in Plants

• Polysaccharides like starch serve as storage molecules
• Cellulose, a polysaccharide, forms the cell wall.

### Hydrophilic Properties of Carbohydrates

• Glucose and sucrose have multiple -OH groups, allowing for extensive hydrogen bonding with water, making them soluble
• Cyclohexane and benzene lack -OH groups, preventing hydrogen bonding and making them insoluble in water.

### Hydrolysis of Lactose

• Lactose is composed of β-D galactose and β-D glucose.
• On hydrolysis, it yields these two monosaccharides.

### Glycosidic Linkage

• The bond formed between two monosaccharide units by the loss of a water molecule.
• For example, in a sucrose molecule, ∝-glucose and β-fructose are linked by a glycosidic linkage.

### Glycogen vs. Starch

• Both are carbohydrates
• Glycogen is stored in animals
• Starch is composed of amylose (15-20%) and amylopectin (80-85%)
• Glycogen is similar in structure to amylopectin, but highly branched

### Hydrolysis Products of Sucrose and Lactose

• Sucrose hydrolysis yields one molecule of ∝-D glucose and one molecule of β-D fructose.
• Lactose hydrolysis yields β-D-galactose and β-D-glucose.

### Starch and Cellulose: Structural Differences

• Starch consists of:
• Amylose: linear chain of ∝−D−(+)−glucose units linked by C1−C4 glycosidic linkage
• Amylopectin: branched-chain polymer of ∝-D-glucose units linked by C1−C4 and C1−C6 glycosidic linkages
• Cellulose: straight-chain polysaccharide of β-D-glucose units joined by C1−C4 glycosidic linkage.

### D-glucose Reactions

• HI: Prolonged heating produces n-hexane
• Bromine water: Produces D-gluconic acid
• HNO3: Oxidizes D-glucose to saccharic acid

### D-glucose: Open Chain Structure

• D-glucose does not show typical aldehyde reactions: 2, 4-DNP test, Schiff's test, or reaction with NaHSO4
• Pentaacetate of glucose does not react with hydroxylamine, indicating an absence of a free -CHO group
• Two crystalline forms of glucose ∝ and β, exist, not explainable with its open chain structure.

### Essential and Non-Essential Amino Acids

• Essential: required by the body but cannot be synthesized (e.g., valine, leucine).
• Non-Essential: Required by the body but can be synthesized (e.g., glycine, alanine).

### DNA Structure

• Double-stranded helix
• Each strand consists of a sugar-phosphate backbone, alternating between deoxyribose and phosphate groups.
• Bases attached to the sugar molecules project inward
• Bases on opposite strands pair through hydrogen bonding: adenine (A) with thymine (T), cytosine (C) with guanine (G)

### DNA vs. RNA Structure and Function

• DNA*
• Sugar: β-D-2'deoxyribose
• Bases: adenine (A), guanine (G), cytosine (C), thymine (T)
• Double-stranded helix
• Functions:
  • Chemical basis of heredity
  • Carries genetic information
• RNA*
• Sugar: β-D-Ribose
• Bases: adenine (A), guanine (G), cytosine (C), uracil (U)
• Single-stranded
• Functions:
  • Protein synthesis
  • Carries coded message for protein synthesis
  • Transmits genetic information from DNA to ribosomes

### RNA Types

• Messenger RNA (mRNA): carries genetic code from DNA to ribosomes for protein synthesis
• Ribosomal RNA (rRNA): structural component of ribosomes, essential for protein synthesis
• Transfer RNA (tRNA): carries amino acids to the ribosomes during protein synthesis