(BIO 120) Chp 4 Slides Prokaryotic Cells

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Prokaryotes are mainly divided into 2 domains:

1. Bacteria

2. Archaea

Bacteria v.s. Archaea

Similarities

They both have…

• Unicellular

• Circular DNA in a nucleoid (DNA is not enclosed in a nucelus)

• 70S ribosomes

• Reproduce by binary fission

• May have flagella, plasmids, and cell walls

Differences

Feature	Bacteria	Archaea
Cell Wall	Most have peptidoglycan (murein).	No peptidoglycan; may have pseudopeptidoglycan, proteins, or polysaccharides.
Membrane Lipids	Fatty acids linked to glycerol by ester bonds.	Ether bonds link branched isoprenoid chains to glycerol → more stable in extremes.
Ribosomes	70S, sensitive to antibiotics like streptomycin and chloramphenicol.	70S, but proteins and rRNA more similar to eukaryotes. Not affected by many bacterial antibiotics.
RNA Polymerase	One simple type.	Multiple complex types (similar to eukaryotic RNA polymerases).
Genetic Organization	No introns (mostly).	Some genes have introns (like eukaryotes).
Environment	Found almost everywhere (soil, water, inside hosts).	Often extremophiles: halophiles (salt), thermophiles (heat), acidophiles (acid), methanogens (anaerobic).
Pathogenicity	Many pathogenic species (e.g., E. coli, Salmonella, S. aureus).	No known human pathogens.
Examples	Escherichia coli, Staphylococcus aureus, Mycobacterium tuberculosis.	Halobacterium (salt-loving), Methanobrevibacter (methane-producing), Sulfolobus (acid-thermophile).

T or F: Prokaryotic cells ALWAYS have a cell wall.

False. 

Most prokaryotic cells have cell wall, but some don’t (e.g. mycoplasmas).

(a) What are ribosomes? 

(b) Compare ribosomes in prokaryotic cells v.s. eukaryotic cells.

(a) Ribosomes: 

• non-membrane-bound organelles responsible for protein synthesis

• found in all cells (but structurally diff b/w prokaryotes & eukaryotes)

(b)  prokaryotic cells v.s. eukaryotic cells

Feature	Prokaryotic Ribosomes	Eukaryotic Ribosomes
Size	70S (made of 50S + 30S subunits)	80S (made of 60S + 40S subunits)
Location	Free-floating in cytoplasm	Free in cytoplasm or attached to rough ER
Complexity	Smaller, simpler	Larger, more complex
Function	Protein synthesis	Protein synthesis
Antibiotic Sensitivity	Targeted by antibiotics like erythromycin	Not affected by these antibiotics

Q: Why can antibiotics target prokaryotic ribosomes without harming human cells?

A: Because prokaryotic ribosomes are smaller (70S) and structurally different from eukaryotic ribosomes, making them a selective target for antibiotics.

Genetically, which prokaryote — archaea or bacteria — is close to eukaryotes than the other prokaryote.

Genetically, archaea are closer to eukaryotes than to bacteria, even though both are prokaryotic in structure.

Q: What is the role of prokaryotic ribosomes in treating bacterial infections?

A: Antibiotics can bind to prokaryotic ribosomes and inhibit protein synthesis, helping eliminate bacterial infections without affecting human cells.

Q: Where are eukaryotic ribosomes located, and how does this affect protein production?

A: Eukaryotic ribosomes may be free in the cytoplasm or bound to the rough endoplasmic reticulum, allowing for compartmentalized and specialized protein production.

________ are highly diverse and medically important because many are pathogens.

Bacteria are highly diverse and medically important because many are pathogens.

________ are unique biochemically, adapted to extreme environments, and provide clues about early life on Earth.

Archaea are unique biochemically, adapted to extreme environments, and provide clues about early life on Earth.

Prokaryotes reproduced by ______________.

Prokaryotes reproduced by binary fission.

Another term for “binary fission” is “__________________” or “__________________”.

Another term for “binary fission” is “asexual reproduction” or “cell division”.

Pleomorphism

• describes bacterial species that has variability in shape

  • these bacteria can adapt shape to survive environmental stressors

Name & describe the various arrangements on coccus-shaped prokaryotes.

Name & describe the arrangements on bacillus-shaped prokaryotes.

Bacilli (rods) divide in one plane and then can separate.

Sinle bacci

Diplobacci — two bacilli

Streptobacci — chain of bacilli

Palisades (less common) — rods lined up parallel or at sharp angles due to snapping division of the bacilli

Coccobacillus — A very short, oval rod that looks like a “fat bacillus” or an elongated coccus.

• Appears intermediate between cocci and bacilli under the microscope.

• Shape: plump, oval rods.

• Arrangement: Usually occur singly, sometimes in pairs.

• Size: Shorter than typical bacilli, but not perfectly round like cocci.

“coccobacillus” literally means coccus-like bacillus.

🔹 Examples of Coccobacilli

• Haemophilus influenzae → causes meningitis, pneumonia.

• Bordetella pertussis → causes whooping cough.

• Brucella species → cause brucellosis (zoonotic infection).

• Chlamydia trachomatis → obligate intracellular coccobacillus.

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🔹 Clinical Relevance

• Many pathogenic bacteria are coccobacilli.

• Because they are hard to classify at first glance (not purely cocci or bacilli), lab tests like Gram stain, culture, and molecular methods are important for identification.

Name & describe the irregular prokaryotic shapes.

Q: Which Gram-positive cocci appear lancet-shaped and in pairs, and are commonly associated with pneumonia?

A: Streptococcus pneumoniae — Gram-positive, lancet-shaped cocci in pairs, often seen in respiratory infections like pneumonia.

Q: What Gram-negative diplococci are typically found within white blood cells in urethral discharge and are linked to sexually transmitted infections?

A: Neisseria gonorrhoeae — Gram-negative diplococci, often located inside or near white blood cells, associated with gonorrhea.

What type of shape & arrangement is this?

Streptococci

What type of shape & arrangement is this?

Streptococci

Streptococcus pyogenes is also called “____________”.

Streptococcus pyogenes is also called “Step Group A”.

Name 2 examples bacterial species that are cocci.

• Streptococcus pyogenes (Strep group A)

• Staphylococcus aureus

• Neisseria gonorrhoeae

Streptococcus pyogenes

• also called “Step Group A”

• gram-positive bacteria

• appears as cocci arranged in chains

• causes —> pharyngitis (strep throat)

• major symptom: “strawberry throat” — sore throat w/ red & swollen tonsils

• can progress into scarlet fever if bacteria produces erythrogenic toxin

  • these toxins produce immune reaction that presents as red cheeks & rash

Streptococcus pyogenes

• Description (shape, arrangement, gram+/-) 

• Diseases & symptoms

• Significance

Also called “Step Group A”

Description

• Shape: Cocci (spherical)

• Arrangement: Chains

• Gram-positive

Diseases it causes & symptoms

• pharyngitis (strep throat)

• can progress into —> scarlet fever if bacteria produces erythrogenic toxin

  • these toxins produce immune reaction that presents as red cheeks, red tongue, rash

• if untreated —> rheumatic heart fever (RHF) which is leading cause of heart disease in children worldwide

Significance

• Can lead to systemic complications if untreated.

Streptococcus aureus folliculitis 

• Description (shape, arrangement, gram+/-) 

• Diseases, symptoms, treatment, prevention

• Significance

Description

• Shape: Cocci (spherical)

• Arrangement: Chains

• Gram-positive

Diseases it causes & symptoms

• Bacterial infection of hair follicles 

• Symptoms:

  • small red bumps

  • pustules/bumps

  • shaving bumps

• Treatment:

  • mild cases —> warm compresses

  • severe cases —> topical & oral antibiotics/ointments

• Prevention: 

  • good hygiene

  • handwashing

Significance

• Opportunistic pathogen

• resistant strains (MRSA) cause healthcare-associated infections.

Stye

• Cause

• Symptoms

• Treatment

• Cause: Staphylococcus aureus on eyelid

• What: infected/inflamed skin gland or hair follicle

• Symptoms: 

  • small painful bump on eye

  • redenss

  • swelling

  • tenderness

• Treatment:

  • most cases —> condition resolves on its own w/ warm compression

  • severe cases —> antibiotics

Neisseria gonorrhoeae

• Description (shape, arrangement, gram+/-) 

• Diseases, symptoms, treatment, prevention

• Significance

Description

• Shape: Cocci (spherical)

• Arrangement: Chains

• Gram-positive

Diseases it causes & symptoms

• Bacterial infection of hair follicles 

• Symptoms:

  • small red bumps

  • pustules/bumps

  • shaving bumps

• Treatment:

  • mild cases —> warm compresses

  • severe cases —> topical & oral antibiotics/ointments

• Prevention: 

  • good hygiene

  • handwashing

_______ divide in one plane, then can separate.

Bacilli divide in one plane, then can separate.

Cocci can divide in different planes (meaning _________) and how they divide determines their _________.

Cocci can divide in different planes (meaning directions) and how they divide determines their arrangement.

_____ is spherical bacteria.

Cocci is spherical bacteria.

If cocci divide in one plane —> they line up in a ______, called __________.

If cocci divide in one plane —> they line up in a chain, called streptococcus.

If cocci divide in two planes —> they form __________, called ________.

If cocci divide in two planes —> they form groups of 4, called tetrads.

If cocci divide in three planes —> they form _________________, called ________.

If cocci divide in three planes —> they form cube-like packets of 8, called sarcinae.

If cocci divide in many random planes —> they form _________________, called ____________.

If cocci divide in many random planes —> they form grape-like clusters, called staphylococcus.

(“staphylo” = cluster).

T or F: Streptococcus pyogenes are cocci in chains.

True.

Staphylococcus aureus → cocci in _________ (____ plane division).

Staphylococcus aureus → cocci in clusters (many plane division).

T or F: Unlike cocci, bacilli usually divide in one plane.

True. Results in arrangements of singles, pairs, or chains.

Coccobacilli belongs to which group of bacterial shapes?

Coccobacilli is considered part of bacilli group.

___________ is the leading cause of food-borne illnesses, hospitalizations, and deaths.

Salmonella is the leading cause of food-borne illnesses, hospitalizations, and deaths.

Salmonella

• Pathogen

• Transmission

• Symptoms

• Significance

Pathogen

• Salmonella enterica

• Gram-negative

Transmission

• Contaminated food or water

• Contact with fecal matter

• Commonly associated w/ poultry & eggs

• Reptiles, especially pet turtles

Symptoms

• Moderate fever

• Abdominal cramps

• Diarrhea

• Nausea

• Possible septicemia (blood poisoning) —> when the bacteria enters the bloodstream

Significance

Leading cause of foodborne illness → important in food safety.

What is the normal habitat of Salmonella? 

GI tract in animals/humans, but is always pathogenic to humans

What is the incubation time for Salmonella? Why is this significant?

• Incubation time ~12-35 hours —> long bc bacteria needs to invade intestinal mucosa before multiplying there

T or F: Salmonella is an opportunistic pathogen. 

• Not classified as opportunistic, but some strains cause disease more severely and more frequently in vulnerable hosts 

  • Can also invade bloodstream, especially in immunocompromised, very young, or elderly individuals 

What foods should especially avoided in order to prevent Salmonella infection? Explain why.

Poultry & raw eggs

• Even whole eggs can be infected bc Salmonella can be transmitted into them by chickens before they are laid (transovarian transmission) 

• So foods like mayonnaise or egg nog that contain raw eggs are risky to eat 

Incubation Time

Refers to period b/w ingestion of pathogen & onset of symptoms

Curved bacilli are called _____.

Curved bacilli are called vibrio.

Name & briefly describe the main bacterial shapes. 

Provide example of bacteria for each.

(1) Cocci

• spherical

• e.g. Streptococcus pyogenes (strep throat)

(2) Bacilli 

• includes cocobacilli

• elongated rod-shape 

• Example —> Escherichia coli (normal gut flora, but also a pathogen)

(3) Spirillum/Spirochete (spiral-shaped)

• Description: Curved, helical, or corkscrew-like; motile with flagella or axial filaments.

• Example —> Treponema pallidum (causes syphilis)

(4) Vibrio: curved bacilli-shape

e.g. Vibrio (curved rod, comma-shaped): Vibrio cholerae – causes cholera.

(5) Coccobacilli

• short, oval-shaped rod, between cocci and bacilli

• Example—> Haemophilus influenzae – can cause respiratory infections and meningitis.

Sometimes bacilli and curved (i.e. spiral shapes like vibrio). Their ______ and _____________ determines what they are called. 

Sometimes bacilli and curved (i.e. spiral shapes like vibrio). Their length and stiffness determines what they are called. 

Vibrio cholerae

• Shape

• Transmission

• Symptoms

• Significance

• Describe its shape.

• What symptoms does it cause?

• Mortality rate?

• Treatment?

Pathogen 

• comma-shaped rod w/ single flagellum

Symptoms

• vomiting

• copious watery feces, “rice-water stool”

• severe cases —> fluid loss of 1 litre/hr (severe dehydration) 

Mortality Rate: 55% to 70%

Treatment

• Oral-rehydration therapy

Significance: Flagella + toxin enable rapid colonization and fluid loss; oral rehydration therapy critical.

What is in this image? 

Vibrio cholerae

The Two Major Groups of Appendages

Major Groups

Flagella & Axial Filaments —> Provide Motility

Fimbriae, pili, nanowires —> Provide attachment points or channels

Classification of Prokaryotic Cells

• Unicellular → each organism is a single cell.

• Peptidoglycan cell wall → provides strength and prevents osmotic lysis.

• No membrane-bound organelles → DNA is free in cytoplasm (nucleoid).

• Morphological diversity → shapes and arrangements aid in identification.

• Divide by binary fission → rapid population growth.

Significance: Simple structure allows adaptability, rapid evolution, and survival in diverse environments.

T or F: Shape and arrangement of bacteria may relate to pathogenic mechanisms. 

True. 

For example, clusters are able to resist phagocytosis.

Pleomorphic translated means “____________”. It’s used to describe prokaryotes without a ________.

Pleomorphic translated means “many-formed”. It’s used to describe prokaryotes without a cell wall.

Flagella

• Function

• Structure

• Arrangement Types

• Movement Types

• Example

• Significance

Function: motility (movement); can also aid in attachment.

Arrangement Types:

Polar —> flagella attached at one or both ends of cell

The following 3 are all considered polar arrangements:

• monotrichous —> single flagellum at one end

• amphitrichous —> single flagella at both ends

• lophotrichous —> tuft of multiple flagella at one end

Peritrichous —> flagella dispersed randomly over surface of cell

Movement Types:

• Runs: Smooth forward motion

• Tumbles: Random changes in direction

Example: Campylobacter jejuni uses flagella to burrow into intestinal mucus.

Significance: Motility enhances invasion and colonization.

Chemotaxis

Movement of flagella in response to chemical signals (toward nutrients or away from toxins)

Fimbriae

• Function

• Structure

• Example

• Significance

Structure: Short, numerous, hair-like structures (protein-based)

Function: Attachment/adhesion

• Help bacteria stick to surfaces, host cells, and each other

• Crucial for forming biofilms (communities of bacteria on surfaces)

• Contribute to pathogenicity by allowing bacteria to colonize host tissues

Example: E. coli and Neisseria gonorrhoeae require fimbriae to infect.

Significance: Essential for colonization; without them → reduced pathogenicity.

Pili

• Structure

• Function

• Significance

Pili (Sex Pili)

• Structure:

  • Long, rigid, tubular projections.

  • Fewer in number (1–2 per cell).

  • Longer than fimbriae.

• Functions:

  • Attachment (limited role, minor surface adhesion).

  • Conjugation (horizontal gene transfer / bacterial sex):

    • Form a bridge between two bacteria.

    • Transfer plasmids (small circular DNA).

    • Spread genetic traits such as antibiotic resistance and virulence factors.

• Significance:

  • Critical for bacterial evolution and adaptation.

  • Major mechanism by which resistance genes spread through bacterial populations.

How is flagella related to pathogenicity? 

• Allow bacteria to invade tissues by moving through mucus or fluids

• Help bacteria escape immune responses by changing direction

• Some pathogens use flagella to reach target cells (e.g., Helicobacter pylori uses flagella to burrow into stomach lining)

How is fimbriae related to pathogenicity?

• Essential for initial attachment to host cells

• Without fimbriae, many bacteria can't colonize or cause infection

• Example: Neisseria gonorrhoeae uses fimbriae to attach to urogenital tract cells

How is pili related to pathogenicity?

• Conjugation pili allow bacteria to share virulence genes

• This can increase a population’s ability to cause disease

• Also play a role in adhesion, though less than fimbriae

Surface Coatings: Glycocalyx

1. Slime layer – loose, protects from drying and nutrient loss.

2. Capsule – dense, thick layer; prevents phagocytosis and aids in adhesion.

   • Example: Streptococcus pneumoniae → capsule is its main virulence factor.

   • Significance: Encapsulation makes bacteria more virulent and harder to clear.

3. Biofilms – communities attached to surfaces, encased in glycocalyx.

   • Found on teeth (plaque), catheters, implants.

   • Significance: Protect bacteria from immune system & antibiotics.

Function of Cell Wall & Envelope

• Functions:

  • Maintains shape, prevents osmotic lysis, protects from host defenses.

  • Determines Gram reaction → critical for identification and treatment.

Gram+ bacteria

• Thick peptidoglycan, teichoic acids, exotoxin production.

• Sensitive to penicillin and lysozyme.

• Significance: Simpler structure makes them more vulnerable to certain antibiotics.

Gram– bacteria:

• Thin peptidoglycan, outer membrane with LPS (endotoxin).

• Barrier to antibiotics and detergents.

• Significance: Outer membrane contributes to antibiotic resistance and immune evasion.

Plasma Membrane

• selective barrier

• site of transport

• enzyme activity

• ATP production

Cytoplasm

• site of metabolism

• contains enzymes

• cytoskeleton for shape

Nucleoid

• houses DNA

• controls cell function & growth

Plasmids

• extra DNA

• carry virulence or resistance genes

• ribosomes (70S)

  • perform protein synthesis by translating genetic instructions provided by plasmids into proteins

  • target for some antibiotics (e.g. tetracyclines)

Endospores

• Produced by Gram+ Bacillus & Clostridium.

• Trigger: nutrient depletion (C, N).

• Extremely resistant to heat, freezing, radiation, disinfectants.

• Sporulation → dormancy; Germination → return to vegetative state.

• Example: Clostridium difficile → healthcare-associated diarrhea.

• Significance: Hard to eradicate; important in hospital infection control & food sterilization.

Q: What is bacterial conjugation and why is it important?

• Conjugation = DNA transfer between bacteria via pili (sex pilus).

• Transfers plasmids (extra-chromosomal DNA).

• Often carries genes for antibiotic resistance or virulence.

• A form of horizontal gene transfer (not reproduction).

• Significance: Major contributor to rapid bacterial evolution and spread of resistance.

What is the structure and function of the prokaryotic plasma membrane?

• Structure: Phospholipid bilayer (fluid mosaic), proteins (enzymes, transporters, receptors).

• Functions:

  • Selective barrier → regulates nutrient/waste/gas exchange.

  • Site of ATP production (no mitochondria in prokaryotes).

  • Houses enzymes for metabolism.

• Damage: Alcohols, disinfectants, and antibiotics can disrupt it → leakage and cell death.

• Significance: Essential for survival; key antibiotic target.

Q: What is the prokaryotic cell envelope and why is it important?

• Layers:

  • Cell wall (peptidoglycan).

  • Cytoplasmic membrane.

  • Outer membrane (Gram– only).

• Gram+ bacteria:

  • Thick peptidoglycan, teichoic acids, exotoxin producers, penicillin-sensitive.

• Gram– bacteria:

  • Thin peptidoglycan, outer membrane with LPS (endotoxin), resistant to many antibiotics.

• Significance:

  • Protects cell from osmotic lysis.

  • Determines Gram stain reaction (diagnosis/antibiotic choice).

  • Virulence factor (LPS/endotoxin in Gram– bacteria).

Q: What is a PPD test and what does it indicate?

• PPD (purified protein derivative) test = tuberculin skin test.

• Small injection under skin → read 48–72 hours later.

• Positive test = person exposed to Mycobacterium tuberculosis.

• Indicates either latent TB infection or active TB disease (requires further testing).

• Significance: Screening tool for TB; identifies infected individuals before symptoms progress.

Q: What is a biofilm and why is it clinically significant?

• Biofilm = community of bacteria attached to a surface, embedded in glycocalyx (slime/capsule).

• Formation: Attachment → growth → secretion of protective extracellular matrix.

• Examples: Dental plaque, catheter/implant infections.

• Advantages for bacteria:

  • Protection from antibiotics, disinfectants, and immune cells.

  • Allows communication & genetic exchange between cells.

• Significance:

  • Major source of chronic, hard-to-treat infections.

  • Common cause of healthcare-associated infections.