Bacterial Classification, Structure, and Replication

Flashcards covering concepts from Bacterial Classification, Structure, and Replication, including microscopy metrics, cell wall composition, Gram stain mechanisms, structural organelles, peptidoglycan synthesis pathways, and sporogenesis.

What are the diameters of the smallest bacteria, Chlamydia and Rickettsia?

They are $0.1\text{ to }0.2\text{ }\frac{1}{1000}\text{ mm}$ (or $0.1\text{ to }0.2\text{ }\frac{1}{10^6}\text{ m}$) in diameter, specifically $0.1\text{ to }0.2\text{ }\frac{1}{10^6}\text{ m}$ ($0.1\text{ to }0.2\text{ }\frac{1}{1000}\text{ mm}$).

What is the resolution of a light microscope, and what is the typical diameter of most bacterial species?

The light microscope has a resolution of $0.2\text{ }\frac{1}{10^6}\text{ m}$, and most bacterial species are approximately $1\text{ }\frac{1}{10^6}\text{ m}$ in diameter.

How does the single circular chromosome of Escherichia coli compare to human chromosomes in terms of base pair count and physical length?

Escherichia coli has a single circular chromosome of approximately $5\text{ million}$ base pairs ($5000\text{ kb}$ pairs) with a length of $1.3\text{ mm}$, whereas humans have two copies of 23 chromosomes representing $2.9 \times 10^9$ base pairs with a length of $990\text{ mm}$.

What are the sedimentation coefficients of prokaryotic and eukaryotic ribosomes and their respective subunits?

Prokaryotes utilize a $70\text{S}$ ribosome composed of $50\text{S}$ and $30\text{S}$ subunits, while eukaryotes utilize an $80\text{S}$ ribosome composed of $60\text{S}$ and $40\text{S}$ subunits.

What are the four sequential steps involved in performing a Gram stain?

1. Heat-fix or dry bacteria onto a slide and stain with crystal violet. 2. Precipitate the stain with Gram iodine. 3. Wash unbound stain with an acetone-based decolorizer and water. 4. Apply the red counterstain, safranin.

Why do gram-positive bacteria retain crystal violet and appear purple, whereas gram-negative bacteria appear red?

Gram-positive bacteria trap crystal violet within a thick, cross-linked peptidoglycan layer. Gram-negative bacteria have a thin peptidoglycan layer that loses the crystal violet during decolorization, allowing them to take up the red counterstain safranin.

Which two bacterial groups cannot be classified using Gram staining, and why?

Mycobacteria, which have a waxy outer shell containing mycolic acid and require an acid-fast stain, and Mycoplasmas, which completely lack a peptidoglycan cell wall.

What bacterial strain is associated with hemorrhagic colitis and identified by specific antigenic serotyping?

Escherichia coli serotype O157:H7.

What structural component present in eukaryotic cytoplasmic membranes is absent in most bacterial membranes, with the exception of Mycoplasmas?

Sterols (e.g., cholesterol).

What hydrophobic lipid molecule serves as the molecular conveyor belt for transporting prefabricated peptidoglycan precursors across the cytoplasmic membrane?

Bactoprenol (undecaprenol, a $\text{C}_{55}$ isoprenoid).

What alternating disaccharide units form the glycan backbone of bacterial peptidoglycan?

N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc).

Between which specific positions of the peptide chains does transpeptidation cross-linking occur in peptidoglycan synthesis?

Between the free amine of the diamino amino acid at the third position (such as lysine or diaminopimelic acid) of one chain and the D-alanine at the fourth position of an adjacent chain.

What membrane-bound enzymes catalyze the cross-linking of peptidoglycan and serve as targets for penicillin and other beta-lactam antibiotics?

Penicillin-binding proteins (PBPs), which include transpeptidases and D-carboxypeptidases.

Which specific glycosidic linkage in the peptidoglycan backbone is cleaved by the human antimicrobial enzyme lysozyme?

The $\beta\text{-1,4}$ disaccharide linkage between GlcNAc and MurNAc.

What are the three structural sections of a lipopolysaccharide (LPS) molecule?

Lipid A, core polysaccharide (rough core), and O antigen.

Which component of lipopolysaccharide (LPS) is responsible for its toxic endotoxin activity?

Lipid A.

What unique 8-carbon sugar is contained within the core polysaccharide region of lipopolysaccharide?

2-keto-3-deoxy-octanoate (KDO).

How does lipooligosaccharide (LOS) found in Neisseria species differ from classic LPS?

LOS lacks the long O-antigen repeat units found in classic LPS, making Neisseria species more susceptible to host-mediated complement control.

What specific outer membrane channel proteins allow the passive diffusion of hydrophilic molecules less than $700\text{ Da}$ in mass through the gram-negative cell wall?

Porin proteins (porin channels).

Which bacterium is an exception to the rule of polysaccharide capsules by producing a capsule made of polypeptide?

Bacillus anthracis.

How do bacterial fimbriae (pili) morphologically differ from flagella in diameter?

Fimbriae are smaller in diameter ($3\text{ to }8\text{ nm}$) compared to flagella ($15\text{ to }20\text{ nm}$).

What organic compound bound to calcium accumulates in high concentrations inside bacterial endospores to stabilize their internal contents?

Dipicolinic acid.

Which genera of gram-positive bacteria are capable of forming dormant endospores under harsh conditions?

Bacillus (e.g., Bacillus anthracis) and Clostridium (e.g., Clostridium tetani or Clostridium botulinum).

What are the approximate durations required for sporogenesis and spore germination?

Sporogenesis requires $6\text{ to }8\text{ hours}$ to complete, whereas germination requires approximately $90\text{ minutes}$.