Fundamentals of Microbial Cell Structure and Macromolecules

Microbial Organisms

Major Groups of Microbes

Microbiology studies a diverse array of microscopic organisms, each with unique characteristics and roles in nature and human health.

• Bacteria and Archaea: Prokaryotic cells lacking a nucleus; found in nearly every environment.

• Algae: Photosynthetic eukaryotes, often aquatic.

• Protozoa: Unicellular eukaryotes, often motile and found in water or as parasites.

• Fungi: Includes yeasts, molds, and mushrooms; eukaryotic, non-photosynthetic.

• Parasitic worms: Multicellular organisms (helminths) that can infect hosts.

Example: Escherichia coli (bacterium), Plasmodium (protozoan causing malaria), Aspergillus (fungus).

Characteristics of Organisms

Defining Features of Life

All living organisms share several fundamental characteristics that distinguish them from non-living matter.

• Cellular Structure: Composed of one or more cells.

• Growth: Ability to increase in size.

• Reproduction: Production of new individuals.

• Metabolism: Chemical processes for energy and synthesis.

• Response to Environment: React to stimuli or changes in surroundings.

All organisms possess various cellular structures in common, such as membranes and genetic material.

Macromolecules Form Cell Structures

Biological Macromolecules

Cells are built from large, complex molecules called macromolecules, primarily composed of carbon, hydrogen, oxygen, and nitrogen.

• Carbohydrates: Sugars and polysaccharides; energy storage and structural roles.

• Lipids: Fats, oils, and waxes; form membranes and store energy.

• Amino Acids and Proteins: Proteins are polymers of amino acids; perform structural, enzymatic, and regulatory functions.

• Nucleic Acids: DNA, RNA, and ATP; store and transmit genetic information.

Example: The phospholipid bilayer of cell membranes is made of lipid molecules.

Carbohydrates

Structure and Function

Carbohydrates are organic molecules consisting of carbon, hydrogen, and oxygen, typically in a 1:2:1 ratio. They serve as energy sources and structural components.

• Monosaccharides: Simple sugars (e.g., glucose, C6H12O6).

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

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

Example: Glucose is a primary energy source for cells.

Formula:

$\text{(CH}_2\text{O)}_n$

Complex Carbohydrates

Polysaccharides

Complex carbohydrates are polymers of monosaccharides, providing structural support and energy storage.

• Starch: Energy storage in plants.

• Glycogen: Energy storage in animals and bacteria.

• Cellulose: Structural component in plant cell walls.

Example: Glycogen is stored in the liver and muscles of animals.

Lipids

Structure and Types

Lipids are hydrophobic molecules, including fats, oils, and waxes. They are essential for membrane structure and energy storage.

• Fatty Acids: Long hydrocarbon chains with a carboxyl group.

• Triglycerides: Three fatty acids linked to glycerol.

• Phospholipids: Major component of cell membranes.

Example: Phospholipids form the bilayer of cell membranes.

Formula:

$\text{Fatty acid: CH}_3(\text{CH}_2)_n\text{COOH}$

Amino Acids and Proteins

Protein Structure and Function

Proteins are polymers of amino acids, each with a unique side chain (R group). There are 20 standard amino acids.

• Primary Structure: Sequence of amino acids.

• Secondary Structure: Alpha helices and beta sheets.

• Tertiary Structure: 3D folding of the polypeptide.

• Quaternary Structure: Multiple polypeptides assembled.

Example: Enzymes are proteins that catalyze biochemical reactions.

General Formula for Amino Acid:

$\text{NH}_2\text{-CHR-COOH}$

Nucleotides and Nucleic Acids

Structure and Role

Nucleotides are the building blocks of nucleic acids (DNA and RNA). Each nucleotide consists of a phosphate group, a sugar (ribose or deoxyribose), and a nitrogenous base (A, T, C, G, or U).

• DNA: Deoxyribonucleic acid; stores genetic information.

• RNA: Ribonucleic acid; involved in protein synthesis.

• ATP: Adenosine triphosphate; energy currency of the cell.

Example: ATP provides energy for cellular processes.

General Formula for Nucleotide:

$\text{Phosphate} - \text{Sugar} - \text{Base}$

Details of DNA Structure

Genetic Material and Organization

DNA is a double helix composed of two strands of nucleotides. The sequence of bases encodes genetic instructions. In bacteria, DNA is organized in a single circular chromosome.

• Base Pairing: Adenine (A) pairs with Thymine (T); Cytosine (C) pairs with Guanine (G).

• Genome: The complete set of genetic material in an organism.

• Chromosome: DNA molecule containing part or all of the genetic material.

Example: The Escherichia coli genome consists of a single circular chromosome.

Base Pairing Formula:

$\text{A} = \text{T}, \quad \text{C} = \text{G}$

Cellular Structures and Macromolecules

Organization of the Cell

Cells contain various structures composed of macromolecules, each with specialized functions.

• Cytoplasm: Aqueous environment containing proteins, solutes, metabolites, and macromolecular complexes.

• Cytoskeleton: Network of proteins providing structural support and organization.

• Ribosomes: Complexes of RNA and protein; site of protein synthesis.

• Cytoplasmic Membrane: Phospholipid bilayer with embedded proteins; regulates transport and maintains integrity.

Example: Ribosomes translate mRNA into proteins.

Genetic Material and Flow of Information

Central Dogma of Molecular Biology

The central dogma describes the flow of genetic information from DNA to RNA to protein.

• DNA: Contains instructions for protein synthesis.

• Transcription: DNA is copied into messenger RNA (mRNA).

• Translation: mRNA is decoded by ribosomes to synthesize polypeptides (proteins).

Example: The gene for insulin is transcribed into mRNA and translated into the insulin protein.

Central Dogma Equation:

$\text{DNA} \xrightarrow{\text{transcription}} \text{RNA} \xrightarrow{\text{translation}} \text{Protein}$

Summary Table: Major Biological Macromolecules

Comparison of Macromolecule Types

Macromolecule	Monomer	Main Elements	Function	Example
Carbohydrates	Monosaccharide	C, H, O	Energy, structure	Glucose, cellulose
Lipids	Fatty acid	C, H, O	Membranes, energy storage	Phospholipid, triglyceride
Proteins	Amino acid	C, H, O, N, S	Enzymes, structure, regulation	Hemoglobin, enzyme
Nucleic Acids	Nucleotide	C, H, O, N, P	Genetic information, energy	DNA, RNA, ATP