Introduction to Microbiology and Bacterial Cell Structure

Comprehensive vocabulary flashcards reviewing key concepts, historical milestones, and cell structures from Chapter 1 and Chapter 3.

Microbe

A small living organism (typically requiring a microscope to be seen) that metabolizes food, grows, and reproduces, with the exception of noncellular viruses. Bacterial sizes range from $0.125\,\mu\text{m}$ to $750\,\mu\text{m}$, with an average bacterial size of $1\,\mu\text{m}$ wide by $2\text{ to }4\,\mu\text{m}$ long.

Prokaryote

A unicellular organism, belonging to the domains Archaea or Bacteria, that lacks a membrane-bound nucleus and membrane-bound organelles.

Eukaryote

A unicellular or multicellular organism (such as protists, algae, or fungi) whose cells contain a distinct membrane-bound nucleus and specialized membrane-bound organelles.

Virus

A noncellular particle containing genetic material (DNA or RNA) wrapped in protein that infects a host cell and usurps cellular machinery to generate new viral particles.

Florence Nightingale

A nurse who founded the science of medical statistics and recognized the significance of disease in warfare by collecting data showing that more soldiers died of microbial infections than of battle wounds.

Robert Hooke

The scientist who built the first compound microscope (1635-1703), observed microscopic mold, published the first manuscript illustrating objects under a microscope, and coined the term cell.

Antonie van Leeuwenhoek

The scientist (1632-1723) who was the first to observe single-celled microorganisms using a handheld single-lens microscope.

Spontaneous Generation

The disproved hypothesis that living microbes arise spontaneously from nonliving matter, which was disproved in 1861 by Louis Pasteur using swan-necked flasks.

Endospore

A dormant, heat-resistant structure formed by certain bacteria (such as Bacillus subtilis) that allows them to survive standard ten-minute boiling treatments.

Ignaz Semmelweis

A physician who demonstrated between 1841 and 1850 that postpartum maternal mortality from sepsis dropped from $15\%$ to $2\%$ when doctors instituted handwashing with chlorine solution before attending births.

Germ Theory of Disease

The scientific theory formulated by Louis Pasteur proposing that infectious diseases are caused by the transmission and growth of specific microorganisms.

Koch's Postulates

A set of four criteria established by Robert Koch in 1876 using Bacillus anthracis to experimentally prove that a specific microorganism causes a specific disease.

Edward Jenner

The physician who developed the first smallpox immunization in 1788 by inoculating individuals with fluid from cowpox sores.

Pasteurization

A heat-treatment process created by Louis Pasteur to kill unwanted bacterial interlopers in fermented liquids like wine and beer after fermentation is complete.

Carl Woese

The scientist who analyzed ribosomal RNA ($rRNA$) gene sequences to establish that Archaea constitute a unique domain of life distinct from Bacteria and Eukarya.

Nucleoid

A non-membrane-bound region in the prokaryotic cytoplasm where chromosomal DNA is organized into approximately 50 supercoiled loops by DNA-binding proteins.

Cell Envelope

The outer structural boundary of a bacterial cell consisting of the inner cell membrane, peptidoglycan cell wall, and in some species, an outer membrane.

Amphipathic

Describing a lipid molecule, such as a phospholipid, that possesses both a polar, charged hydrophilic head and a nonpolar, uncharged hydrophobic tail.

Fluid Mosaic Model

The model describing cell membranes as a dynamic, two-dimensional fluid structure in which proteins float within a sea of phospholipids.

Hopanoid

A pentacyclic, steroid-like lipid present in prokaryotic cell membranes that stiffens the membrane and reduces fluidity in warmer environments.

Simple Diffusion

The passive transport of small nonpolar molecules (such as $O_2$ and $CO_2$) directly across a lipid bilayer down their concentration gradient without transport proteins or ATP.

Facilitated Diffusion

Passive transport across a membrane down a concentration gradient that requires dedicated membrane transport proteins for ions, sugars, or amino acids, without requiring ATP.

Active Transport

The energy-dependent transport of molecules across a membrane against their concentration gradient (from low to high concentration) utilizing transport proteins and ATP hydrolysis.

Peptidoglycan

A mesh-like polymer component of bacterial cell walls (sacculus) composed of alternating sugar chains ($N$-acetylglucosamine / NAG and $N$-acetylmuramic acid / NAM) cross-linked by short amino acid peptides.

Gram-Positive Cell Envelope

A bacterial cell boundary consisting of a single inner cell membrane surrounded by a thick cell wall composed of multiple layers of peptidoglycan reinforced by teichoic acids.

Gram-Negative Cell Envelope

A bacterial cell boundary composed of an inner cell membrane, a thin peptidoglycan layer enclosed within a periplasmic space, and an outer membrane containing lipopolysaccharides (LPS).

Lipopolysaccharide (LPS)

A complex molecule located on the outer membrane of Gram-negative bacteria that acts as an endotoxin, capable of causing a fatal host immune overreaction when released.

Mycolic Acids

Exceptionally dense, waxy lipids present in the outer envelope of Mycobacteria (such as Mycobacterium tuberculosis) that hinder antibiotic uptake and immune clearance.

Septation

The step in bacterial cell division where the cell membrane and cell wall grow inward at the equator to form a dividing septum between daughter cells.

Replisome

A multiprotein complex containing DNA polymerase that bidirectionally replicates bacterial DNA starting at the origin of replication (ORI) and ending at the termination site.

Bacterial Cytoskeleton

Internal protein structures in bacteria, such as FtsZ (forming a Z-ring), MreB (rod shape), and crescentin (vibrio shape), that direct cell wall synthesis and organize shape.

Bacterial Morphologies and Arrangements

Variations in bacterial cell shapes and multicellular groupings observable by Gram staining, including diplobacilli, streptococci, staphylococci, and rods.

Chemotaxis

The movement of a bacterium in response to chemical gradients, where counterclockwise (CCW) flagellar rotation causes smooth 'runs' and clockwise (CW) rotation causes 'tumbles'.

Biased Random Walk

A chemotactic behavior where increasing concentrations of a chemical attractant prolong forward runs, leading to net movement toward the attractant source.

Pili

Hair-like protein filaments extending from the bacterial surface that facilitate adherence to host mucous membranes or mediate genetic transfer during conjugation.