Brock Biology of Microorganisms Chapter 2: Microbial Cell Structure and Function

Flashcards covering microbial cell structure and function, including prokaryote types, cell size, morphology, cell envelopes, staining techniques, surface structures, locomotion, and cellular inclusions.

How many microbial cells are estimated to be on Earth?

2x10^30 microbial cells.

What are extremophiles?

Microorganisms that live in habitats too harsh for other life, such as hot springs, glaciers, or high salt environments.

Which two domains are classified as prokaryotes?

Bacteria and Archaea.

What is the primary genetic evidence used to distinguish between Bacteria and Archaea?

16s rRNA evidence.

Who pioneered the use of 16s rRNA for classifying living things?

Carl Woese in the 1970s.

What is the 'molecular clock' concept related to 16s rRNA?

The amount of variation in the rRNA gene sequence can be used to track evolutionary divergence among living things.

What is the typical size range for prokaryotes in diameter and length?

0.2-600+ µm diameter and 0.5-10 µm length.

What is an example of a very large prokaryote?

Thiomargarita namibiensis, which can be up to 750 µm in diameter.

Why is the surface-to-volume (s:v) ratio important for small cells?

Smaller cells have a higher s:v ratio, allowing for faster nutrient uptake, waste removal, environmental sensing, and generally quicker and more efficient growth.

What are common shapes for bacteria?

Coccus (spherical), Rod/bacillus (cylindrical), Spirillum (flexible spiral), and Spirochete (rigid spiral).

How do prokaryotes typically divide?

By binary fission.

What are the common arrangements of cocci after cell division?

Diplococci (pairs), streptococci (chains), sarcinae (cubes), and staphylo- (grapelike clusters).

What is the function of the prokaryotic cell wall?

It maintains cell shape and rigidity, withstands osmotic pressure, and prevents cell lysis.

What is the main component of the bacterial cell wall?

Peptidoglycan.

What differentiates Gram-positive from Gram-negative bacteria in terms of cell wall structure?

Gram-positive bacteria have a thick peptidoglycan layer, while Gram-negative bacteria have a thin peptidoglycan layer, an outer membrane, and a periplasm.

What enzyme found in human secretions can destroy peptidoglycan?

Lysozyme.

What is the purpose of a differential staining technique like the Gram stain?

It renders different kinds of cells different colors, allowing for differentiation between bacterial groups.

What color do Gram-positive bacteria appear after a Gram stain?

Purple-violet.

What color do Gram-negative bacteria appear after a Gram stain?

Pink.

Why is the Gram stain clinically significant?

It provides rapid results (around 10 minutes) to help distinguish bacterial groups and determine the appropriate antibiotic treatment.

What is the most common type of Archaea cell wall?

The S-layer (protein shell).

What unique component may be found in some Archaea cell walls that is similar to peptidoglycan?

Pseudomurein.

Where is the outer membrane found in bacterial cells?

Only in Gram-negative bacteria, external to the cell wall.

What is a major component of the outer membrane in Gram-negative bacteria, besides phospholipids?

Lipopolysaccharide (LPS).

What is Lipid A, and what are its effects?

Lipid A is an endotoxin component of LPS that, when released from dying Gram-negative cells, can cause fever, rapid blood vessel dilation, and decreased blood pressure.

What is the periplasmic space?

The gap between the outer membrane and the peptidoglycan in Gram-negative bacteria, housing many extracellular proteins, digestive enzymes, and transport proteins.

What is the difference between a slime layer and a capsule?

A slime layer is a loosely attached, easily deformed polysaccharide coat, while a capsule is a thick, tightly attached protective layer that aids in pathogenicity and protects against phagocytosis.

What are pili (fimbriae) used for in bacteria?

They are short filamentous projections that help bacteria adhere to surfaces, enhancing colonization and pathogenicity.

What are flagella (archaella) used for by prokaryotes?

They are long, helical appendages used for movement (locomotion).

What powers bacterial flagella?

Proton motive force (PMF).

What powers archaeal archaella?

ATP hydrolysis.

Describe the two phases of flagellar movement in prokaryotes.

RUN (flagella bundle, rotate counterclockwise for smooth forward motion) and TUMBLE (flagella rotate clockwise, bundle disaggregates for random reorientation).

What is taxis?

Directed movement in response to a stimulus, such as chemotaxis (chemical), phototaxis (light), or aerotaxis (oxygen).

What are the main functions of the cytoplasmic membrane in prokaryotes?

Regulating substance movement (selective permeability), serving as a protein anchor, and energy conservation (generating PMF and site of cellular respiration).

What is the fluid-mosaic model of the cell membrane?

It describes the membrane as a gel-like, dynamic structure with proteins embedded within it, not necessarily fixed in one spot.

What are ribosomes?

Sites of protein synthesis in all cells, composed of protein and RNA.

What are granules in prokaryotic cells?

Densely packed materials that serve as storage sites for important molecules like glycogen, polyphosphate, or sulfur.

What are endospores?

Highly differentiated, dormant cells formed by some bacteria in response to declining environmental conditions, serving as a survival mechanism resistant to harsh conditions.

Why is it important clinically to know if a patient has a spore-forming bacterial infection?

Endospores are highly resistant to heat, desiccation, radiation, and many disinfectants, making them difficult to eliminate and posing challenges for sterilization and treatment.