Biological Macromolecules: Carbohydrates, Lipids, and Nucleic Acids

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Monosaccharides are the simplest form of carbohydrates and serve as the building blocks for more complex sugars.

Definition: Single sugar molecules, such as glucose, fructose, and galactose.
Functions: Provide immediate energy for cellular processes.
Examples: Glucose (C6H12O6), fructose, galactose.

Disaccharides are carbohydrates composed of two monosaccharide units joined by a covalent bond.

Definition: Sugars formed by the combination of two monosaccharides.
Type of bond formed: Glycosidic bond.
Functions: Serve as energy sources and transport sugars in plants.
Examples: Sucrose (glucose + fructose), lactose (glucose + galactose), maltose (glucose + glucose).

Polysaccharides are large carbohydrate molecules formed by the polymerization of many monosaccharide units.

Definition: Long chains of monosaccharides linked by glycosidic bonds.
Storage polysaccharides: Store energy for organisms.
- Examples and functions: Starch (energy storage in plants), glycogen (energy storage in animals).
Structural polysaccharides: Provide structural support to cells and tissues.
- Examples and functions: Cellulose (plant cell walls), chitin (exoskeletons of arthropods).

Lipids are a diverse group of hydrophobic molecules that play key roles in energy storage, membrane structure, and signaling.

Hydrophobic nature: Lipids are insoluble in water due to their nonpolar characteristics.
Major types: Fats, phospholipids, steroids.

Fats, also known as triglycerides, are composed of glycerol and fatty acids and serve as long-term energy storage molecules.

Structure of triglycerides: One glycerol molecule bonded to three fatty acids.
Type of bonds that form: Ester bonds between glycerol and fatty acids.
Saturated vs. Unsaturated Fatty Acids:
- Saturated fatty acids: No double bonds between carbon atoms; solid at room temperature (e.g., butter).
- Unsaturated fatty acids: One or more double bonds; liquid at room temperature (e.g., olive oil).
Function: Energy storage, insulation, and protection.
Examples: Animal fats (saturated), plant oils (unsaturated).

Phospholipids are essential components of cell membranes, forming bilayers that separate cellular environments.

Structure: Composed of a glycerol backbone, two fatty acids, and a phosphate group.
Function: Form the structural basis of biological membranes.
Behavior in water: Amphipathic nature causes them to arrange into bilayers, with hydrophilic heads facing water and hydrophobic tails facing inward.

Nucleic acids store and transmit genetic information and are involved in the synthesis of proteins.

Types: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
Function: DNA stores genetic information; RNA is involved in protein synthesis and gene expression.

Nucleic acids are polymers made up of nucleotide monomers.

Monomers: Nucleotides, each consisting of a phosphate group, a five-carbon sugar, and a nitrogenous base.
Structure of a nucleotide:
- Purines vs. Pyrimidines: Purines (adenine, guanine) have a double-ring structure; pyrimidines (cytosine, thymine, uracil) have a single-ring structure.
- DNA vs. RNA sugars: DNA contains deoxyribose; RNA contains ribose.

Nucleotides are linked together by covalent bonds to form polynucleotide chains.

Type of bonds: Phosphodiester bonds connect the 3' carbon of one sugar to the 5' carbon of the next.
5' and 3' ends: The 5' end has a phosphate group; the 3' end has a hydroxyl group.
Relationship between nucleic acids and proteins: Nucleic acids encode the information for protein synthesis.

DNA and RNA differ in structure and function, but both are essential for genetic information flow.

Structure of DNA: Double helix with complementary base pairing (A-T, G-C).
Base pairing rules: Adenine pairs with thymine (DNA) or uracil (RNA); guanine pairs with cytosine.
Significance of complementary strands: Ensures accurate replication and transmission of genetic information.
Structure of RNA: Usually single-stranded; contains uracil instead of thymine.
Differences between DNA and RNA: DNA is double-stranded, contains deoxyribose, and uses thymine; RNA is single-stranded, contains ribose, and uses uracil.

Feature	DNA	RNA
Sugar	Deoxyribose	Ribose
Strands	Double-stranded	Single-stranded
Bases	A, T, G, C	A, U, G, C
Function	Genetic information storage	Protein synthesis, gene expression

General formula for monosaccharides:
- $C_nH_{2n}O_n$
Formation of a disaccharide (dehydration synthesis):
- $\text{Monosaccharide}_1 + \text{Monosaccharide}_2 \rightarrow \text{Disaccharide} + H_2O$
Phosphodiester bond formation in nucleic acids:
- $\text{Nucleotide}_1 + \text{Nucleotide}_2 \rightarrow \text{Dinucleotide} + H_2O$