Biomolecules in Human Physiology: Carbohydrates and Lipids

Introduction to Biomolecules in Human Physiology

Biomolecules such as carbohydrates and lipids are essential for the structure and function of the human body. Understanding their chemical properties and biological roles is fundamental in anatomy and physiology.

Elements Essential to Life

Principal Elements in the Human Body

• Carbon (C), Hydrogen (H), Oxygen (O), and Nitrogen (N) (often abbreviated as CHON) make up approximately 96% of the human body by mass.

• These elements are the primary building blocks of organic molecules.

Example: Proteins, carbohydrates, lipids, and nucleic acids are all composed mainly of CHON elements.

Carbon: The Central Atom in Organic Molecules

Why Carbon is Central

• Carbon atoms can form four covalent bonds, allowing for a diversity of stable, complex molecules.

• This versatility enables the formation of long chains, branched structures, and rings, which are the backbone of biomolecules.

Example: Glucose (C6H12O6) and fatty acids both have carbon skeletons.

Organic Molecules: Structure and Classification

Monomers and Polymers

• Monomer: A small, repeating subunit that serves as a building block for larger molecules.

• Polymer: A large molecule made by joining many monomers together.

• Examples of monomers: monosaccharides (simple sugars), amino acids, nucleotides, fatty acids.

• Examples of polymers: polysaccharides (starch, glycogen), proteins, nucleic acids, triglycerides.

Polymer Synthesis and Breakdown

Dehydration Synthesis (Condensation Reaction)

This is a chemical reaction that joins two monomers by removing a water molecule, forming a covalent bond.

• One monomer loses a hydroxyl group (–OH), the other loses a hydrogen atom (–H).

• The removed –OH and –H combine to form water (H2O).

Equation:

$\text{Monomer}_1 + \text{Monomer}_2 \rightarrow \text{Polymer} + H_2O$

Hydrolysis

This is a chemical reaction that breaks covalent bonds in polymers by adding water, splitting the polymer into monomers.

• Water is split into –OH and –H, which are added to the resulting monomers.

Equation:

$\text{Polymer} + H_2O \rightarrow \text{Monomer}_1 + \text{Monomer}_2$

Carbohydrates

Structure and Types

• Composed of carbon, hydrogen, and oxygen (C, H, O), typically in a 1:2:1 ratio.

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

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

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

Functions:

• Primary source of energy (glucose is used to produce ATP).

• Structural roles (cellulose in plants, glycogen in animals).

• Cell signaling and recognition (glycoproteins on cell surfaces).

Table: Types of Carbohydrates

Type	Example	Function
Monosaccharide	Glucose	Energy source
Disaccharide	Sucrose	Transported sugar in plants
Polysaccharide	Glycogen	Energy storage in animals
Polysaccharide	Cellulose	Structural support in plants

Lipids

Structure and Types

• Composed mainly of carbon and hydrogen, with much less oxygen than carbohydrates.

• Non-polar and hydrophobic (insoluble in water).

• Main types: triglycerides, phospholipids, steroids.

Fatty Acids

• Saturated fatty acids: No double bonds between carbon atoms; straight chains; solid at room temperature.

• Unsaturated fatty acids: One or more double bonds; bent chains; liquid at room temperature.

Example: Butter (saturated fat), olive oil (unsaturated fat).

Triglycerides

• Consist of one glycerol molecule bonded to three fatty acids.

• Main form of stored energy in animals.

Phospholipids

• Composed of a glycerol backbone, two fatty acids, and a phosphate group.

• Amphipathic: have both hydrophilic (phosphate head) and hydrophobic (fatty acid tails) regions.

• Major component of cell membranes, forming a bilayer.

Example: In water, phospholipids arrange themselves into bilayers, with hydrophobic tails inward and hydrophilic heads outward.

Steroids

• Lipids with four fused carbon rings.

• Cholesterol is a key steroid, important for cell membrane structure and as a precursor for steroid hormones.

Table: Types of Lipids

Type	Structure	Function
Triglyceride	Glycerol + 3 fatty acids	Energy storage, insulation
Phospholipid	Glycerol + 2 fatty acids + phosphate	Cell membrane structure
Steroid	4 fused carbon rings	Hormones, membrane stability

Summary

• Carbohydrates and lipids are essential biomolecules with diverse structures and functions in the human body.

• Understanding their chemical properties helps explain their biological roles in energy storage, cell structure, and signaling.