BIO-241 Chapter 4: Bacteria and Archaea Study Guide

Practice flashcards covering bacterial and archaeal anatomy, external and internal structures, cell wall biochemistry, Gram staining, endospore biology, and cellular morphology based on BIO-241 Chapter 4 notes.

What four cellular structures are present in every bacterium and prokaryote?

A cell membrane, cytoplasm, ribosomes ($70\text{S}$), and one chromosome (usually circular, located in the nucleoid).

How do prokaryotic and eukaryotic ribosomes differ in size and composition?

Prokaryotes have $70\text{S}$ ribosomes composed of $30\text{S}$ and $50\text{S}$ subunits, whereas eukaryotes have $80\text{S}$ ribosomes in their cytoplasm and $70\text{S}$ ribosomes inside mitochondria and chloroplasts.

What are the three structural components of a bacterial flagellum?

The filament (composed of flagellin), the hook (a curved connecting joint), and the basal body (rings anchored in the cell wall and membrane acting as a motor).

What are H antigens, and how are they used in clinical microbiology?

Flagellar proteins are called H antigens, which are used to identify specific bacterial strains, such as in Escherichia coli O157:H7.

What are the characteristics of monotrichous, lophotrichous, amphitrichous, and peritrichous flagellar arrangements?

Monotrichous is one flagellum at one end; lophotrichous is a tuft or cluster at one end; amphitrichous has flagella at both ends; and peritrichous features flagella distributed all over the cell surface.

How does flagellar rotation generate bacterial 'run and tumble' motility?

Counterclockwise rotation results in a smooth run forward, whereas clockwise rotation causes a tumble and a change in direction.

What are periplasmic flagella (axial filaments), and which bacterial group possesses them?

Internal flagella that lie under the outer membrane and impart a corkscrew-like twisting motility; they are characteristic of spirochetes such as Treponema pallidum and Borrelia.

What is the primary function of bacterial fimbriae?

They are short, thin fibers used by bacteria to attach to surfaces (such as host tissues) and facilitate biofilm formation, but they are not used for motility.

What is the role of the bacterial sex pilus in conjugation?

It connects a donor cell ($\text{F}^+$) to a recipient cell ($\text{F}^-$) to allow the horizontal transfer of DNA, such as plasmids carrying antibiotic-resistance genes.

How do slime layers and capsules differ structurally and functionally?

A slime layer is loosely attached, easily washed off, and protects against drying while aiding biofilm formation; a capsule is tightly bound, organized, thicker, blocks phagocytosis by white blood cells, and acts as a major virulence factor (K antigen).

What two alternating sugars form the glycan backbone of peptidoglycan?

N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).

How do penicillin and lysozyme destroy bacterial cell walls?

Penicillin blocks the bacterial enzymes responsible for forming the cross-linking peptide bonds between NAM residues, whereas lysozyme cleaves the chemical bond between NAG and NAM.

What are the primary differences between Gram-positive and Gram-negative cell envelopes?

Gram-positive cells have a thick peptidoglycan layer ($\sim 20\text{--}80\,\text{nm}$) containing teichoic and lipoteichoic acids with no outer membrane; Gram-negative cells have a thin peptidoglycan layer, a large periplasmic space, and an outer membrane containing lipopolysaccharide (LPS) and porins.

What are the three structural components of lipopolysaccharide (LPS)?

The O-antigen (O polysaccharide), the core polysaccharide, and Lipid A (the endotoxin responsible for triggering fever and septic shock).

What are the four reagents used in the Gram stain in order, and which is the decolorizer?

1. Crystal violet (primary stain), 2. Gram's iodine (mordant), 3. Alcohol/acetone (decolorizer), and 4. Safranin (counterstain). Alcohol/acetone is the key decolorizing agent.

What unique lipid component is present in the acid-fast cell wall of Mycobacterium and Nocardia?

Waxy mycolic acid, which resists Gram staining, drying, disinfectants, and causes these bacteria to stain red/pink in the Ziehl-Neelsen acid-fast stain.

Why is Mycoplasma naturally resistant to penicillin?

Mycoplasma species lack a peptidoglycan cell wall entirely (instead stabilizing their membrane with sterols), leaving no target for penicillin to disrupt.

What key physiological roles does the bacterial cytoplasmic membrane serve in the absence of mitochondria?

Selective permeability/nutrient transport, energy generation via the electron transport chain and ATP synthesis, and the secretion of enzymes and wall components.

What are bacterial plasmids, and why are they clinically important?

Small, extra circles of non-essential DNA separate from the chromosome that can replicate independently and carry genes for antibiotic resistance (R plasmids) or toxins.

What are metachromatic (volutin) granules, and which organism do they help identify?

Inclusion bodies that store polyphosphate, which are characteristically seen in and used to identify Corynebacterium diphtheriae.

What biochemical adaptations make bacterial endospores exceptionally resistant to heat and harsh conditions?

A dehydrated core, a thick multilayer protein coat, a specialized peptidoglycan cortex, and dipicolinic acid combined with calcium ions that stabilize proteins and DNA.

Which bacterial genera produce endospores?

Mainly the Gram-positive genera Bacillus and Clostridium (as well as Clostridioides).

What conditions are required to achieve true sterilization of endospores via autoclaving?

Heating at $121^\circ\text{C}$ under pressure for approximately $\sim 15\,\text{min}$.

How do spirilla and spirochetes differ in morphology and locomotion?

Spirilla are rigid spiral cells that move using external flagella, while spirochetes are flexible spirals that move using periplasmic flagella (axial filaments).

What are the structural definitions of streptococci, staphylococci, and palisades arrangements?

Streptococci are cocci organized in chains; staphylococci are cocci organized in irregular grape-like clusters; and palisades are bacilli grouped side by side like a picket fence or 'Chinese letters'.

What is pleomorphism, and what are two bacterial examples?

The variation in cell shape and size among individuals of the same bacterial species; examples include Mycoplasma and Corynebacterium.

What is the function of the 16S rRNA gene in microbiology?

It is the gene encoding ribosomal RNA that is universally utilized to identify, classify, and determine phylogenetic relationships among prokaryotes.