Biological Molecules: Structure and Properties

Carbon Chemistry

Carbon is a fundamental element in biological molecules due to its ability to form diverse structures through covalent bonding.

• Shapes of Carbon Molecules: Carbon atoms can form straight chains, branched chains, and rings when making single covalent bonds. Double bonds introduce planar structures.

• Valence Electrons: Carbon has 4 valence electrons, allowing it to form up to 4 covalent bonds.

• Bond Types: Carbon commonly forms single, double, and triple covalent bonds, affecting the molecule's shape and reactivity.

Example: Methane (CH4) is a tetrahedral molecule due to carbon's four single bonds.

Covalent Bonding Capacity

The number of covalent bonds an atom can form depends on its valence electrons.

• Valence Electron Numbers:

  • Carbon: 4

  • Nitrogen: 5

  • Hydrogen: 1

  • Oxygen: 6

• Bonding Capacity: Carbon can form 4 bonds, nitrogen 3, hydrogen 1, and oxygen 2.

Carbohydrates: Structure and Function

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, serving as energy sources and structural components.

• General Formula: Most carbohydrates follow the formula (CH2O)n.

• Structure of Polysaccharides: Multiple glucose units can link to form chains (e.g., starch, cellulose).

• Chain Lengths:

  • Disaccharide: 2 glucose units

  • Trisaccharide: 3 glucose units

  • Polysaccharide: Many glucose units

Example: Starch is a polysaccharide made of many glucose molecules.

Types of Carbohydrates

Carbohydrates are classified based on their structure and function.

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

• Disaccharides: Two monosaccharides joined (e.g., sucrose)

• Polysaccharides: Long chains of monosaccharides (e.g., starch, cellulose, glycogen)

Lipids: Structure and Properties

Fatty Acids and Lipids

Lipids are hydrophobic molecules important for energy storage, membrane structure, and signaling.

• Fat: Composed of glycerol and fatty acids.

• Saturated vs. Unsaturated:

  • Saturated fatty acids have no double bonds; they are solid at room temperature.

  • Unsaturated fatty acids have one or more double bonds; they are liquid at room temperature.

• Structure: Fatty acids are long hydrocarbon chains with a carboxyl group at one end.

Example: Butter contains saturated fats; olive oil contains unsaturated fats.

Proteins: Structure and Function

Amino Acids and Protein Structure

Proteins are polymers of amino acids, performing diverse biological functions.

• Amino Acids: Building blocks of proteins, each with a central carbon, amino group, carboxyl group, and side chain (R group).

• Functional Groups: Amino group (-NH2), carboxyl group (-COOH), and R group.

• Protein Structure Levels:

  • Primary: Sequence of amino acids

  • Secondary: Alpha helix and beta pleated sheet formations due to hydrogen bonding

  • Tertiary: 3D folding due to interactions among R groups

  • Quaternary: Association of multiple polypeptide chains

• Bond Types: Peptide bonds link amino acids together.

• Protein Function: Enzymes, structural support, transport, signaling

Example: Hemoglobin has quaternary structure with four polypeptide chains.

Nucleic Acids: DNA and RNA

DNA Structure and Function

DNA stores genetic information in cells and is composed of nucleotides.

• Nucleotide Components: Phosphate group, deoxyribose sugar, nitrogenous base

• Bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G)

• Base Pairing: A pairs with T, C pairs with G

• Pyrimidines: Cytosine, Thymine

• Purines: Adenine, Guanine

• Structure: Double helix

Example: Human DNA contains about 3 billion base pairs.

RNA Structure and Function

RNA is involved in protein synthesis and gene regulation.

• Nucleotide Components: Phosphate group, ribose sugar, nitrogenous base

• Bases: Adenine (A), Uracil (U), Cytosine (C), Guanine (G)

• Base Pairing: A pairs with U, C pairs with G

• Differences from DNA: RNA is single-stranded, contains ribose, and uses uracil instead of thymine.

Example: Messenger RNA (mRNA) carries genetic information from DNA to ribosomes.

Isomers in Biology

Isomer Definition and Examples

Isomers are molecules with the same chemical formula but different structures.

• Structural Isomers: Differ in the arrangement of atoms.

• Stereoisomers: Same connectivity, different spatial arrangement.

• Examples: Glucose and fructose (C6H12O6) are structural isomers.

Phospholipids

Structure and Function

Phospholipids are major components of cell membranes, forming bilayers due to their amphipathic nature.

• Structure: Glycerol backbone, two fatty acid tails (hydrophobic), phosphate group (hydrophilic)

• Function: Form cell membrane bilayers, regulate membrane fluidity

Example: The plasma membrane of animal cells is composed of a phospholipid bilayer.

Macromolecule Classification

Monomer, Dimer, Polymer

Biological macromolecules are classified by the number of repeating units.

Additional info:

• Enzymes are proteins that catalyze biochemical reactions.

• Hydrolysis and dehydration synthesis are key reactions in macromolecule metabolism.

• Functional groups such as hydroxyl, carboxyl, amino, and phosphate are important in biomolecule chemistry.