Chapter 5 Notes

20 Hydrolysis and Condensation Reactions

Definitions and Connections

Hydrolysis and condensation are two fundamental chemical reactions involved in the synthesis and breakdown of biological macromolecules.

• Condensation (Dehydration Synthesis): A reaction where two monomers are joined together by removing a molecule of water. This process forms covalent bonds between monomers, resulting in the formation of polymers.

• Hydrolysis: The reverse of condensation; a reaction where a polymer is broken down into monomers by the addition of water. The water molecule splits, with one part attaching to one monomer and the other part to the adjacent monomer.

• Connection: Condensation builds polymers from monomers, while hydrolysis breaks polymers back into monomers. These reactions are essential for the metabolism of macromolecules in living organisms.

• Example: The formation of a peptide bond between amino acids (condensation) and its breakdown during digestion (hydrolysis).

Carbohydrates

Structure, Function, and Key Terms

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen, typically with the formula (CH2O)n. They serve as energy sources and structural components in cells.

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

• Polymer Bond Name: Glycosidic linkage

• Polymers: Polysaccharides (e.g., starch, glycogen, cellulose)

• Functions:

  • Energy storage (e.g., starch in plants, glycogen in animals)

  • Structural support (e.g., cellulose in plant cell walls, chitin in arthropod exoskeletons)

• Examples: Glucose, sucrose, lactose, starch, glycogen, cellulose

Classification Table

Type	Monomer/Polymer	Bond	Example
Monosaccharide	Monomer	—	Glucose
Disaccharide	2 Monomers	Glycosidic linkage	Sucrose
Polysaccharide	Polymer	Glycosidic linkage	Starch, Cellulose

Additional info: Disaccharides are formed by condensation reactions between two monosaccharides, releasing water.

Lipids

Structure, Function, and Key Terms

Lipids are a diverse group of hydrophobic molecules, including fats, oils, phospholipids, and steroids. They are not true polymers but are grouped by their insolubility in water.

• Major Classes: Triglycerides (fats and oils), phospholipids, sterols (e.g., cholesterol), terpenes

• Bond Name: Ester linkage (between fatty acids and glycerol in triglycerides)

• Functions:

  • Energy storage (triglycerides)

  • Membrane structure (phospholipids)

  • Signaling molecules (steroids, some terpenes)

• Examples: Triglycerides, phospholipids, cholesterol, carotenoids

Major Lipid Types Table

Type	Main Components	Function	Example
Triglyceride	Glycerol + 3 fatty acids	Energy storage	Fats, oils
Phospholipid	Glycerol + 2 fatty acids + phosphate group	Membrane structure	Cell membrane
Steroid	Four fused carbon rings	Signaling, membrane fluidity	Cholesterol

Polypeptides (Proteins)

Structure, Function, and Key Terms

Proteins are polymers made of amino acid monomers linked by peptide bonds. They perform a vast array of functions in cells.

• Monomers: Amino acids

• Polymer Bond Name: Peptide bond

• Functions:

  • Enzymatic catalysis

  • Structural support

  • Transport

  • Signaling

  • Movement

• Examples: Hemoglobin, enzymes (e.g., amylase), collagen, actin

Amino Acid Properties: Hydrophobic vs. Hydrophilic

Classification of Amino Acids

Amino acids can be classified based on the properties of their side chains (R groups):

• Hydrophobic (Nonpolar): Side chains are mostly hydrocarbons; do not interact well with water.

• Hydrophilic (Polar): Side chains contain polar groups (e.g., -OH, -NH2); interact with water.

• Hydrophilic (Charged): Side chains are either positively or negatively charged at physiological pH.

How to Tell: Examine the R group. Nonpolar R groups are hydrophobic; polar or charged R groups are hydrophilic. Within hydrophilic, look for full charges (acidic/basic) or partial charges (polar but uncharged).

Levels of Protein Structure

Four Levels of Organization

Proteins have four levels of structure, each contributing to their final shape and function:

• Primary Structure: The linear sequence of amino acids in a polypeptide chain.

• Secondary Structure: Local folding patterns stabilized by hydrogen bonds, such as α-helix and β-pleated sheet.

• Tertiary Structure: The overall 3D shape of a single polypeptide, determined by interactions among R groups (hydrophobic interactions, ionic bonds, disulfide bridges, hydrogen bonds).

• Quaternary Structure: The association of two or more polypeptide chains into a functional protein complex (e.g., hemoglobin).

Denaturation: Loss of protein structure (and function) due to changes in temperature, pH, or chemicals.

Nucleic Acids

Structure, Function, and Key Terms

Nucleic acids are polymers of nucleotide monomers and store and transmit genetic information.

• Monomers: Nucleotides (composed of a five-carbon sugar, phosphate group, and nitrogenous base)

• Polymer Bond Name: Phosphodiester bond

• Types: DNA (deoxyribonucleic acid), RNA (ribonucleic acid)

• Functions:

  • DNA: Stores genetic information

  • RNA: Involved in protein synthesis and gene regulation

• Examples: DNA, mRNA, tRNA, rRNA

5' and 3' Ends; Antiparallel Structure in DNA

Directionality and Double Helix Structure

• 5' End: The end of a nucleic acid strand with a free phosphate group attached to the 5' carbon of the sugar.

• 3' End: The end with a free hydroxyl group attached to the 3' carbon of the sugar.

• Antiparallel: In DNA, the two strands run in opposite directions (one 5' to 3', the other 3' to 5'), allowing complementary base pairing and the double helix structure.

ATP, cAMP, and NAD+

Structure and Cellular Roles

• ATP (Adenosine Triphosphate): The primary energy carrier in cells; stores and transfers energy for cellular processes.

• cAMP (Cyclic Adenosine Monophosphate): A second messenger involved in signal transduction pathways, relaying signals from hormones and other stimuli.

• NAD+ (Nicotinamide Adenine Dinucleotide): An electron carrier involved in redox reactions during cellular respiration and metabolism.

Additional info: ATP releases energy when its terminal phosphate bond is hydrolyzed: $\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{energy}$

5.4 - Notes

• 20 Amino acids that occur in proteins

• Amino acids consist of central or alpha bonds to hydrogen, amino, carboxyl, and R groups