Chapter 4: Survey of Prokaryotic Cells

What are the three domains of life?

Bacteria, Archaea, and Eukarya

Bacteria & Archaea vs. Eukarya

Bacteria & Archaea both are prokaryotic (lack a nucleus and membrane-bound organelles), while Eukarya are eukaryotic

Bacteria vs. Archaea

Bacteria have peptidoglycan cell walls

Archaea have unique lipids in membranes, no peptidoglycan, and can survive in extreme environments

Three main bacterial shapes?

1. Coccus (spherical)

2. Bacillus (rod-shaped)

3. Spirillum/Spirochete (spiral)

Common bacterial arrangements:

• Diplo- (pairs)

• Strepto- (chains)

• Staphylo- (clusters)

• Tetrads (groups of four)

• Sarcinae (cubical packets)

Gram-positive Bacteria

thick peptidoglycan, teichoic acids, no outer membrane, stains PURPLE

Gram-negative Bacteria

thin peptidoglycan, outer membrane with LPS, stains PINK

Why are gram-negative bacteria harder to treat with antibiotics?

their outer membrane protects against many antibiotics and immune responses

Structure of LPS (lipopolysaccharides)

1. Lipid A (toxic component)

2. Core polysaccharide

3. O-antigen (varies among species)

Why is LPS medically significant?

it triggers strong immune responses and can cause septic shock

What are inclusion bodies?

storage structures in bacteria for nutrients like glycogen, sulfur, or phosphate

Why do bacteria have inclusion bodies?

to store nutrients for when resources are scarce

What bacteria have mycolic acids in their cell walls?

Mycobacterium and Nocardia (e.g., tuberculosis and leprosy-causing bacteria).

Why are mycolic acids important?

They make bacteria resistant to desiccation and many antibiotics

Fluid Mosaic Model

a model of the cell membrane where lipids and proteins move fluidly within a flexible bilayer

Key components of the cell membrane

phospholipids, proteins, and cholesterol (in eukaryotes)

Biofilm

a community of bacteria living within a protective slime layer

How do biofilms form?

bacteria attach to a surface, multiply, and produce an extracellular matrix

Why are biofilms significant in medical microbiology?

they make infections harder to treat and resist antibiotics (e.g., in catheters, teeth, and lungs)

Flagellar Arrangements: MONOTRICHOUS

one flagellum

Flagellar Arrangements: LOHOTRICHOUS

multiple flagella at one end

Flagellar Arrangements: AMPHITRICOUS

flagella at both ends

Flagellar Arrangements: PERITRICHOUS

flagella all over the surface

Components of peptidoglycan?

• glycan chains (NAM and NAG sugars)

• peptide cross-links (hold the layers together)

Sizes of prokaryotic ribosomes?

70S (made of 50S + 30S subunits)

Sizes of eukaryotic ribosomes?

80S (made of 60S + 40S subunits)

Cyanobacteria

perform oxygenic photosynthesis (release oxygen)

Green/Purple Sulfur Bacteria

perform anoxygenic photosynthesis (do not release oxygen)

Methanogen

a type of archaea that produces methane (CH₄) as a metabolic byproduct

Where are methanogens found?

in anaerobic environments like swamps, cows’ stomachs, and sewage

Periplasmic flagella

internal flagella found in Spirochetes, helping them move in a corkscrew motion

Mycoplasmas

bacteria that lack a cell wall; they are flexible and resistant to antibiotics targeting peptidoglycan

What disease is caused by Mycoplasma pneumoniae?

atypical (walking) pneumonia

Endospore

a dormant, highly resistant bacterial structure that survives harsh conditions

What genera of bacteria form endospores?

Bacillus and Clostridium (e.g., anthrax, tetanus, botulism)

Plasmid

a small, circular piece of DNA in bacteria that can carry antibiotic resistance genes

Characteristics of living things?

• growth

• reproduction

• metabolism

• response to stimuli

• homeostasis

Chemotaxis

the movement of bacteria in response to chemical signals (toward nutrients, away from toxins)

Spirilla

rigid, external flagella, move in a twisting motion

Spirochetes

flexible, have internal periplasmic flagella, move in a corkscrew motion