Lsn 4 Biochemistry I: Carbohydrates and Nucleic Acids – Foundations for Microbiology

Biological Macromolecules: The Four Pillars of Life

Overview of Macromolecules

Biological macromolecules are large, complex molecules essential for life. They are primarily organic, containing carbon, and often include hydrogen, oxygen, nitrogen, phosphorus, and sulfur. The four major classes are:

• Carbohydrates – Provide quick energy and structural support.

• Proteins – Function as catalysts (enzymes), provide cell structure, and act as signaling molecules.

• Lipids – Serve in energy storage, membrane structure, and hormone production.

• Nucleic Acids – Store and transmit genetic information.

All macromolecules are built from smaller subunits (monomers) joined by dehydration synthesis and broken down by hydrolysis.

Dehydration and Hydrolysis: How Cells Build and Break Macromolecules

Polymerization and Depolymerization

• Dehydration Synthesis: Water is removed to form a new covalent bond, joining monomers into polymers. Example: formation of polysaccharides, proteins, nucleic acids, and fats.

• Hydrolysis: Water is added to break a covalent bond, splitting polymers into monomers. Example: digestion of starch into glucose.

This process allows cells to build structure, store energy, and encode information.

Functional Groups in Biological Molecules

Role and Types of Functional Groups

Functional groups are specific clusters of atoms that determine the chemical reactivity, interactions with water, and bonding behavior of biological molecules. They are found in all major macromolecules.

• Chemical Reactivity: Dictate how molecules participate in chemical reactions.

• Interactions with Water: Influence solubility and hydrophobic/hydrophilic properties.

• Bond Formation and Breakdown: Enable polymerization and depolymerization.

Functional Group	Structure Style	Function/Behavior	Common Contexts
Hydroxyl	-OH	Polar, forms H-bonds	Alcohols, sugars
Ether	-O-	Links sugar units	Disaccharides
Ketone	-C=O (internal)	Reactive carbonyl	Sugars
Aldehyde	-CHO (terminal)	Reactive carbonyl	Sugars
Carboxyl	-COOH	Acidic, forms ions	Amino acids, fatty acids
Amino	-NH2	Basic, accepts H+	Amino acids
Ester	-COOR	Hydrophobic linkage	Fats, waxes
Sulfhydryl	-SH	Forms disulfide bridges	Protein folding
Phosphate	-PO4	High energy, neg. charge	ATP, nucleotides, phospholipids
Methyl	-CH3	Hydrophobic, nonpolar	Lipids, gene regulation

Carbohydrates: Structure and Function

General Properties

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen in a 1:2:1 ratio (CH2O). They serve several biological functions:

• Ready energy source (e.g., glucose, sucrose)

• Long-term energy storage (e.g., starch, glycogen)

• Form the backbone of nucleic acids (ribose, deoxyribose)

• Can be converted to amino acids

• Structural components (e.g., cellulose in plants, peptidoglycan in bacteria)

• Cell recognition and signaling (glycoproteins, glycolipids)

Classification of Carbohydrates

• Monosaccharides: Single sugar units (e.g., glucose, fructose)

• Disaccharides: Two sugars bonded together (e.g., sucrose, lactose)

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

Structure impacts function, from quick energy to long-term storage and structural support.

Monosaccharides

• Smallest carbohydrate units (CH2O) Typically 5-6 carbon atoms

• Exist in both linear and ring forms

• Serve as building blocks for larger carbohydrates

• α-glucose: Found in starch (digestible by humans)

• β-glucose: Found in cellulose (not digestible by humans)

• N-acetylglucosamine: Modified monosaccharide used in peptidoglycan (bacterial cell walls) and chitin (fungi, arthropods)

Disaccharides and Polysaccharides

• Disaccharides: Formed by dehydration synthesis (e.g., sucrose = glucose + fructose)

• Polysaccharides: Structure drives function

  • Cellulose: Straight chains, β 1-4 bonds, structural support (plants, fungi)

  • Starch (Amylose): Unbranched chains, α 1-4 bonds, energy storage in plants

  • Glycogen: Highly branched chains, α 1-4 and α 1-6 bonds, energy storage in animals

Branching increases energy accessibility; linear structures increase stability and strength.

Nucleotides and Nucleic Acids: The Foundations of Genetic Information

Structure and Function

• Nucleotides are the building blocks of nucleic acids.

• Two major types:

  • DNA (Deoxyribonucleic Acid): Long-term genetic storage

  • RNA (Ribonucleic Acid): Assists with gene expression, protein building, and sometimes acts as an enzyme (ribozyme)

• Key Functions:

  • DNA: Inheritance and genome stability

  • RNA: Protein synthesis, regulation, catalysis

Nucleotide Structure

• Each nucleotide has three parts:

  • Phosphate group

  • Pentose sugar (ribose or deoxyribose)

  • Nitrogenous base (A, T, G, C, U)

• Nucleoside: Sugar + base (no phosphate)

Structure and Bonding in Nucleic Acids

• Covalent bonds (phosphodiester bonds) link the phosphate group of one nucleotide to the sugar of another.

• Hydrogen bonds link bases across two strands:

  • A pairs with T (DNA) or U (RNA) — 2 hydrogen bonds

  • G pairs with C — 3 hydrogen bonds

• DNA structure: Double-stranded (antiparallel), complementary base pairing

DNA and RNA Structures

• DNA: Deoxyribose sugar, double-stranded, stores genetic information

• RNA: Ribose sugar, single-stranded (sometimes double), involved in protein synthesis and regulation

Monomers of Nucleic Acids

• Nucleotides consist of:

  1. Nitrogenous base (purines: adenine, guanine; pyrimidines: cytosine, thymine, uracil)

  2. Pentose sugar (deoxyribose in DNA, ribose in RNA)

  3. One or more phosphate groups

Orientation of Nucleotides (5' and 3' Ends)

• The phosphate group attaches to the 5' carbon of the sugar.

• New nucleotides are added at the 3' carbon of the sugar.

• This defines the 5' → 3' directionality critical for DNA and RNA structure.

General Structure of DNA: The Double Helix

• Antiparallel strands

• Complementary base pairing

• Stable structure for genetic information

Functions of Nucleic Acids: The Central Dogma of Molecular Biology

Central Dogma

• Replication (DNA → DNA): Ensures genetic continuity

• Transcription (DNA → RNA): Converts genetic instructions into a readable format

• Translation (RNA → Protein): Builds functional molecules that drive cell activities

Comparison of Nucleic Acids

Characteristic	DNA	RNA
Sugar	Deoxyribose	Ribose
Purine nucleotides	A and G	A and G
Pyrimidine nucleotides	T and C	U and C
Number of strands	Double stranded in cells and most DNA viruses; single stranded in parvoviruses	Single stranded in cells and in most RNA viruses; double stranded in reoviruses
Functions	Genetic material of all cells and most DNA viruses	Protein synthesis in all cells; genetic material of RNA viruses

Adenosine Triphosphate (ATP)

• ATP is the main short-term energy supply for cells.

• Energy is released when phosphate bonds of ATP are broken:

$\text{ATP} \rightarrow \text{ADP} + \text{P}_i + \text{energy}$

• ATP supply is limited and must be replenished.

Example:

During muscle contraction, ATP is hydrolyzed to ADP, releasing energy for movement.

Additional info: These notes are based on foundational biochemistry concepts relevant to microbiology, focusing on macromolecules, their synthesis and breakdown, functional groups, carbohydrate classification, and nucleic acid structure and function.