Organic Molecules and Macromolecules: Structure, Function, and Synthesis in Human Anatomy & Physiology

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Organic Molecules: Structure and Properties

Carbon and Its Unique Role

Organic molecules are defined by the presence of carbon, which is electroneutral and forms four covalent bonds, making it central to the chemistry of life. Carbon's ability to share electrons without gaining or losing them allows for the formation of complex molecules essential to living systems.

Electroneutrality: Carbon shares electrons equally, forming stable covalent bonds.
Bonding: Carbon forms four single covalent bonds, enabling diverse molecular structures.
Exceptions: CO2 and CO are inorganic despite containing carbon.

Formation of four single covalent bonds: Carbon shares four electron pairs with four hydrogen atoms to form methane (CH4)

Synthesis and Hydrolysis of Organic Compounds

Dehydration Synthesis and Hydrolysis

Macromolecules are assembled and broken down through dehydration synthesis and hydrolysis reactions. These processes are fundamental to the formation and degradation of polymers in biological systems.

Dehydration Synthesis: Monomers are joined by removing a water molecule (H2O), forming covalent bonds.
Hydrolysis: Polymers are broken down by adding water, splitting covalent bonds.
Example: Formation and breakdown of sucrose from glucose and fructose.

Dehydration synthesis and hydrolysis reactions, including example reactions with glucose, fructose, and sucrose

Major Organic Compounds (Macromolecules)

Overview

The four major classes of organic compounds are carbohydrates, lipids, proteins, and nucleic acids. Many are polymers, consisting of repeating monomer units.

Carbohydrates: Sugars and starches, energy storage and structural roles.
Lipids: Fats, oils, phospholipids, steroids; energy storage, membrane structure.
Proteins: Structural, enzymatic, contractile, and regulatory functions.
Nucleic Acids: DNA and RNA; genetic information and protein synthesis.

Carbohydrates

Structure and Classification

Carbohydrates are composed of carbon, hydrogen, and oxygen, typically in a 2:1 ratio of hydrogen to oxygen. They are classified based on the number of sugar units.

Monosaccharides: Single sugar units (e.g., glucose, fructose, galactose, deoxyribose, ribose).
Disaccharides: Two monosaccharides linked (e.g., sucrose, maltose, lactose).
Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen, cellulose).
General Formula: where is the number of carbon atoms.

Monosaccharides: Examples of hexose and pentose sugars Disaccharides: Sucrose, maltose, and lactose structures Polysaccharides: Structure of glycogen as a polymer of glucose

Lipids

Structure and Types

Lipids are hydrophobic molecules containing carbon, hydrogen, and oxygen (with less oxygen than carbohydrates), and sometimes phosphorus. They are insoluble in water and serve various functions in the body.

Triglycerides: Three fatty acids bonded to a glycerol molecule; energy storage, insulation, protection.
Saturated Fatty Acids: No double bonds; solid at room temperature (e.g., butter).
Unsaturated Fatty Acids: One or more double bonds; liquid at room temperature (e.g., olive oil).
Phospholipids: Modified triglycerides with a phosphate group; major component of cell membranes.
Steroids: Four-ring structure; includes cholesterol, hormones.

Dehydration synthesis reaction in triglyceride formation Saturated fat: Structure and packing of molecules Unsaturated fat: Structure and effect of double bonds Phospholipid structure and bilayer formation

Lipid Type	Location/Function
Triglycerides	Energy storage, insulation, protection
Phospholipids	Cell membrane structure, lipid transport
Steroids	Cell membrane component, hormones, vitamin D
Other Lipid Substances	Fat-soluble vitamins, prostaglandins, glycolipids

Table of representative lipids found in the body

Proteins

Structure and Function

Proteins are polymers of amino acids, held together by peptide bonds. They are the most functionally diverse macromolecules, serving structural, enzymatic, contractile, transport, communication, and defensive roles.

Amino Acids: 20 types, differing by their R group.
Peptide Bonds: Formed by dehydration synthesis between amino acids.
Functions: Structural (collagen), enzymatic (disaccharidases, proteases), transport (hemoglobin), contractile (actin, myosin), communication (insulin), defensive (antibodies).

Dehydration synthesis and hydrolysis of peptide bonds Structural proteins: Collagen Enzyme proteins: Catalysis Transport proteins: Hemoglobin Contractile proteins: Actin and myosin Communication proteins: Insulin and receptors Defensive proteins: Antibodies

Levels of Protein Structure

Protein function is determined by its structure, which is organized into four levels:

Primary: Linear sequence of amino acids.
Secondary: Alpha helices and beta sheets formed by hydrogen bonding.
Tertiary: Folding of secondary structures into a compact shape.
Quaternary: Association of two or more polypeptide chains.

Primary structure: Sequence of amino acids Secondary structure: Alpha helices and beta sheets Tertiary structure: Folding of polypeptide Quaternary structure: Association of polypeptides

Protein Denaturation

Denaturation is the loss of a protein's functional shape due to changes in pH or temperature. This process is usually reversible unless the changes are extreme.

Active Sites: Loss of structure deactivates functional sites.
Example: Cooking an egg irreversibly denatures proteins.

Enzymes and Enzyme Activity

Enzymes are globular proteins that act as biological catalysts, speeding up chemical reactions by lowering activation energy. They are highly specific and often named for the reactions they catalyze.

Enzyme Action: Substrate binds to active site, undergoes rearrangement, and product is released.
Example: ATP-ase hydrolyzes ATP to ADP.

Enzyme action: Substrate binding, rearrangement, and product release

Optimum Conditions for Enzyme Activity

Enzyme activity depends on optimal temperature and pH, which vary for different enzymes. Deviations can lead to denaturation and loss of function.

Optimal temperature and pH for enzyme activity

Nucleic Acids

DNA and RNA

Nucleic acids store and transmit genetic information. DNA is double-stranded and located in the nucleus, while RNA is single-stranded and functions in protein synthesis.

DNA: Genetic blueprint, double helix, base pairing (A-T, G-C).
RNA: Messenger, transfer, and ribosomal types; base pairing (A-U, G-C).

Characteristic	DNA	RNA
Major cellular site	Nucleus	Cytoplasm
Major functions	Genetic material, directs protein synthesis	Genetic instructions for protein synthesis
Structure	Double strand, double helix	Single strand
Sugar	Deoxyribose	Ribose
Bases	A, G, C, T	A, G, C, U

DNA and RNA structure and base pairing DNA double helix and nucleotide structure

Macromolecules That Are Polymers

Summary Table

Class of Organic Molecule	Monomers (Building Blocks)	Polymer
Carbohydrates	Monosaccharides (e.g., glucose)	Polysaccharides
Proteins	Amino acids	Polypeptides or proteins
Nucleic acids	Nucleotides	DNA or RNA

Summary of monomers and polymers of organic molecules

ATP (Adenosine Triphosphate)

Structure and Function

ATP is the primary energy carrier in cells, capturing energy released from glucose breakdown and providing immediate, usable energy for cellular processes.

Structure: Adenine-containing RNA nucleotide with three phosphate groups.
Energy Release: Hydrolysis of terminal phosphate releases energy, converting ATP to ADP or AMP.
Equation:

Structure of ATP: Adenine, ribose, and phosphate groups Energy coupling involving ATP ATP hydrolysis reaction

Clinical Terms

Alkalosis and Acidosis

These terms refer to disturbances in the body's acid-base balance, which can affect protein structure and function.

Alkalosis: Condition where blood pH is above normal.
Acidosis: Condition where blood pH is below normal.

Chapter Review

Key Concepts

Organic molecules are central to life, with carbon's unique bonding properties enabling complex structures.
Macromolecules are synthesized and degraded by dehydration synthesis and hydrolysis.
Carbohydrates, lipids, proteins, and nucleic acids each have distinct structures and functions in the body.
Enzymes catalyze biochemical reactions, and their activity depends on optimal conditions.
ATP is the universal energy currency of cells.