Biomolecules | Proteins, Carbohydrates, Nucleic Acids & Enzymes

Introduction to Biomolecules

Biomolecules are organic compounds produced by living organisms. They are primarily composed of carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur (CHONPS). These molecules are categorized into:

• Primary metabolites: Necessary for normal growth (e.g., amino acids, sugars)

• Secondary metabolites: Often species-specific (e.g., alkaloids, pigments, essential oils)

The four main categories we’ll explore are:

1. Carbohydrates

2. Proteins

3. Nucleic Acids

4. Enzymes

Carbohydrates: The Energy Source

Carbohydrates are polyhydroxy aldehydes or ketones. They serve as the primary source of energy and are classified based on complexity.

Types of Carbohydrates

1. Monosaccharides: Simple sugars (e.g., glucose, fructose, galactose)

   • General formula: (CH2O)n

   • Glucose is the most abundant monosaccharide in nature

   • Fructose is the sweetest natural sugar

Mnemonic: GLUe For GALAxy
Glucose – Fructose – Galactose

2. Disaccharides: Composed of two monosaccharides

   • Sucrose = Glucose + Fructose

   • Lactose = Glucose + Galactose

   • Maltose = Glucose + Glucose

Mnemonic: Some Lovely Moments
Sucrose – Lactose – Maltose

3. Oligosaccharides: 3–10 sugar units

   • Found on cell membranes for recognition and signaling

4. Polysaccharides: Many sugar units

   • Storage: Starch (plants), Glycogen (animals)

   • Structural: Cellulose (plants), Chitin (fungi/arthropods)

Tests for Carbohydrates

• Benedict’s test for reducing sugars (positive for glucose, maltose)

• Iodine test for starch (blue-black color)

Proteins: The Structural and Functional Molecules

Proteins are polymers of amino acids linked by peptide bonds. They perform a wide range of functions including enzymatic, structural, hormonal, and transport roles.

Amino Acids

• 20 standard amino acids are used in proteins

• Basic structure includes amino group (-NH2), carboxyl group (-COOH), hydrogen atom, and a variable R group attached to a central alpha carbon

• Classified as essential (must be obtained from diet) or non-essential (synthesized in body)

Mnemonic for Essential Amino Acids:
His Lovely TV Took Isoleucine, Methionine, Leucine, and Valine
Histidine, Lysine, Threonine, Valine, Tryptophan, Isoleucine, Methionine, Leucine, Phenylalanine

Levels of Protein Structure

1. Primary: Linear sequence of amino acids

2. Secondary: Alpha helices or beta sheets due to hydrogen bonding

3. Tertiary: 3D folding due to interactions among R-groups

4. Quaternary: Multiple polypeptide chains (e.g., hemoglobin)

Protein Types by Function

• Structural: Keratin, collagen

• Enzymatic: Trypsin, amylase

• Hormonal: Insulin

• Transport: Hemoglobin

• Defensive: Antibodies

Denaturation: Loss of 3D structure due to pH, temperature changes (e.g., egg white cooking)

Nucleic Acids: Information Carriers

Nucleic acids store and transmit genetic information. Two types:

1. DNA (Deoxyribonucleic acid)

2. RNA (Ribonucleic acid)

Components of Nucleic Acids

• Nitrogenous base (purines: adenine, guanine; pyrimidines: cytosine, thymine/uracil)

• Pentose sugar (ribose or deoxyribose)

• Phosphate group

Structure of DNA

• Double helix, antiparallel strands

• Base pairing: A with T (2 H-bonds), G with C (3 H-bonds)

RNA Types

• mRNA (messenger)

• tRNA (transfer)

• rRNA (ribosomal)

Mnemonic for Purines: AG is Pure
Adenine and Guanine are Purines

Mnemonic for RNA Base Pairing: A-U and G-C in RNA Crew
A pairs with U, G pairs with C

Enzymes: The Biological Catalysts

Enzymes are proteins that speed up biochemical reactions by lowering the activation energy.

Characteristics of Enzymes

• Highly specific to substrates

• Reusable

• Affected by temperature, pH, inhibitors

Mechanism of Action

• Lock and Key Model: Substrate fits perfectly into enzyme's active site

• Induced Fit Model: Enzyme changes shape slightly for substrate binding

Factors Affecting Enzyme Activity

1. Temperature: Optimal activity at 37°C for human enzymes

2. pH: Most enzymes work best at specific pH (e.g., pepsin at pH 2)

3. Substrate concentration: Rate increases then levels off (saturation point)

4. Inhibitors:

   • Competitive: Compete with substrate for active site

   • Non-competitive: Bind elsewhere, altering enzyme shape

Coenzymes and Cofactors

• Coenzyme: Organic molecule assisting enzyme (e.g., NAD+, FAD)

• Cofactor: Inorganic ion (e.g., Mg²⁺, Zn²⁺)

Examples of Important Enzymes

• Amylase: Starch to maltose

• Pepsin: Proteins to peptides

• Lipase: Lipids to fatty acids and glycerol

• DNA Polymerase: DNA synthesis

Mnemonic for Enzyme Types:
Over The Hydrants, Little Isomeric Lions Lie
Oxidoreductase, Transferase, Hydrolase, Lyase, Isomerase, Ligase

Tests for Biomolecules

• Biuret test: Proteins (violet color)

• Benedict’s test: Reducing sugars (brick red precipitate)

• Iodine test: Starch (blue-black)

• Sudan III test: Lipids (orange-red)

Conclusion

Biomolecules form the basis of life and are involved in every essential function of living organisms. Carbohydrates fuel cells, proteins build and regulate bodily processes, nucleic acids store and relay genetic information, and enzymes catalyze biochemical reactions.