BIOL 251 Exam 2 Study Guide

Binary Fission

1. DNA replication (circular chromosome copied)

2. Cell elongation (chromosomes move apart)

3. Septum formation (membrane + wall grow inward)

4. Division → 2 identical daughter cells

Microbial Growth Phase

1) Lag Phase

2) Log Phase

3) Stationary Phase

4) Death Phase

Lag Phase

• No division yet

• Cells adapting, making enzymes

• High metabolic activity

Log Phase

• Rapid cell division

• Population doubling at constant rate

• Cells most metabolically active & sensitive to antibiotics

Stationary Phase

• Growth = death

• Nutrients depleted, waste accumulates

• Stress responses/sporulation may occur

Death Phase

• Cells dying faster than dividing

• Population declines

Superoxide dismutase (SOD)

Converts superoxide into H2O2

Catalase

Converts H2O2 into H2O and O2

Peroxidase

Converts H2O2 into H2O

Difference between aerobes and anaerobes?

Aerobes have SOD and catalase. Anaerobes don’t have these.

Lytic Cycle vs. Lysogenic Cell

Lytic destroys host cell. Lysogenic cells survive initially.

Lytic Cycle

1. Attachment

2. Entry

3. Biosynthesis (viral parts made)

4. Assembly

5. Release (lysis → cell bursts)

Lysogenic Cycle

1. Attachment & entry

2. Viral DNA integrates into host DNA → prophage

3. Replicated with host cell

4. Can switch to lytic later

Lysogenic Conversion

When a bacterium gains new traits from prophage DNA

Examples:

• Toxin production

• Increased virulence

Acute Infection

• Rapid onset

• Short duration

• Symptoms appear quickly

• Virus is cleared or host dies

Acute Infection Steps

1. Entry into host

2. Primary replication

3. Spread to target tissue

4. Secondary replication

5. Symptoms appear

6. Immune response clears virus

Persistent Infections

1) Chronic

2) Latent

3) Slow

Chronic Infection

• Continuous virus production

• Symptoms may be mild or ongoing

Latent Infection

Virus remains dormant until it reactivates later.

Slow Infection

• Gradual disease over long time

• Damage builds slowly

Goal of Antimicrobials

• Target prokaryote-specific structures

Why don’t antimicrobials effect humans?

• Humans don’t have:

  • DNA gyrase

  • Same RNA polymerase structure

  • Folic acid synthesis pathway

Folic Acid Synthesis Inhibitors

Block nucleotide production, which stops production of DNA/RNA

What does DNA gyrase do?

Supercoils DNA for replication

How does metronidazole work?

Produces toxic radicals that damage DNA in anaerobes

Folic Acid

Makes the building blocks of DNA and RNA

RNA Polymerase Inhibitors

Block transcription and protein synthesis

DNA Gyrase Inhibitors

Prevents DNA supercoiling, stopping replication

Sulfonamides

Trimethoprim

Folic Acid Inhibitors

Fluoroquinolone

DNA Gyrase Inhibitor

Rifampin

RNA Polymerase Inhibitor

Griseofulvin

• Targets fungi

• Disrupts mitotic spindle (microtubules)

• Stops cell division

Metronidazole

• Activated in anaerobic organisms

• Produces toxic radicals → DNA damage

• Only works in low-oxygen environments

Biofilm Formation Steps

1. Attachment to surface

2. Colonization (cells multiply)

3. Extracellular matrix production

4. Maturation

5. Dispersion

Quorum Sensing

• Cell-to-cell communication using signaling molecules

• When population is large → genes activated

What does quorum sensing control?

1) Biofilm production

2) Virulence factor production

Risk Factors for Biofilm Diseases

• Medical devices (catheters, implants)

• Chronic wounds

• Poor hygiene

• Immunocompromised patients

Biofilms and Virulence

Protect bacteria from:

• Antibiotics

• Immune system

• Hard to treat → chronic infections

Endospores

Dormant, highly resistant structures that can survive heat, radiation, and chemicals

Endospore Formation

1. DNA copied

2. Spore forms inside cell

3. Protective layers develop

4. Cell lyses → spore released

Sterilization

ALL microbes destroyed.

Disinfection

Most microbes killed (not spores)

Sanitization

Reduce to safe levels

Degerming

Remove microbes from surface (e.g., handwashing)

BSL-1

Harmless microbes

BSL-2

Moderate risk(lab precautions)

BSL-3

Serious airborne pathogens

BSL-4

Deadly, no treatment (e.g., Ebola)

Critical Objects

Enter body and require sterilization

Semi-Critical Objects

Touch mucous membranes or non-intact skin and require high-level disinfection

Noncritical Objects

Touch intact skin, require low-level disinfection

How Antimicrobials Kill

Mechanisms:

• Damage cell wall/membrane

• Denature proteins

• Damage DNA

• Inhibit enzymes

Factors Affecting Antimicrobial Effectiveness

• Number of microbes

• Environment (temp, pH)

• Presence of organic matter

• Exposure time

• Microbe type (spores harder to kill)

Alcohol

Denatures proteins by disrupting the intramolecular hydrogen bonding between the side chains, used as antiseptic

Halogens

Oxidizes amino acids

Chlorine

Halogen that purifies water

Iodine

Halogen that kills bacteria on skin

Phenolics

Disrupt membranes by making them more permeable, used in disinfectants

Alkylating agents

Damages DNA/proteins by covalently attaching alkyl groups to them, used in sterilization

Heavy Metals

Inactivate proteins by interfering with the folding of nascent or non-native proteins, used in antiseptics(limited)

Surfactants

Disrupt membranes by acting as amphipathic agents that insert their hydrophobic tails into the lipid bilayer, used in soaps

Heat

Sterilization

Radiation

DNA damage

Filtration

Removes microbes

Cold

Slows growth

How do microbes acquire resistance?

• Mutation

• Horizontal gene transfer:

  • Conjugation

  • Transformation

  • Transduction

Enzyme Production

Destroy drug

Efflux Pumps

Pump drug out

Target Modification

Drug can’t bind

Reduced permeability

Drug can’t enter

Microbial Antagonism

• Compete for nutrients

• Produce antimicrobial substances

• Prevent pathogen attachment

Portals of Entry

How pathogens got in

Mucous Membranes

• Respiratory (inhalation)

• GI tract (ingestion)

• Genitourinary (sexual contact)

Skin

• Cuts, abrasions, injections

Parenteral route

Direct deposition (needles, bites, surgery)

Placenta

Mother to fetus

Portals of Exit

• Respiratory droplets (coughing, sneezing)

• Feces (GI infections)

• Urine (UTIs)

• Blood (insects, needles)

• Skin (lesions)

• Genital secretions

First Line of Defense

Skin and Mucous Membranes

Skin

• Physical barrier (tight cells, keratin)

• Dry, acidic → inhibits growth

• Shedding removes microbes

Mucous Membranes

• Mucus traps microbes

• Cilia move them out (mucociliary escalator)

Lysozyme

Breaks bacterial cell walls

Sebum

Acidic, antimirobial

Gastric Acid

Kills ingested microbes

Defensins

Damage membranes

Lactoferrin

Binds to iron and starves bacteria

3 Activation Pathways

1) Classical

2) Lectin

3) Alternative

Classical Pathway

Trigger: antigen-antibody complex
Adaptive + innate link

Lectin Pathway

Trigger: mannose on microbial surfaces

Alternative Pathway

Trigger: direct contact with pathogen surface

C3b

Opsonization (tags for phagocytosis)

C3a, C5a

Inflammation (recruit immune cells)

C5b–C9

Membrane Attack Complex (MAC) —> lysis

Neutrophils

• First responders

• Short-lived

• Targets bacteria

Macrophage

• Long-term, tissue-resident

• Antigen presentation

Lymphocytes

B-cells and T-cells

B-Cells

Produce antibodies

T-cells

• Helper (CD4): coordinate

• Cytotoxic (CD8): kill infected cells

Dendritic Cells

Best antigen-presenting cells

Natural Killer(NK) Cells

Kill virus-infected & cancer cells

Virulence

Structures/mechanisms that allow pathogens to enter host cells