Bacterial Toxins and Gram-Negative Cell Wall

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Questions and Answers

Which statement about endotoxins is true?

Endotoxins are part of the outer membrane of Gram-negative bacteria. (correct)

Endotoxins are produced by both Gram-positive and Gram-negative bacteria.

Endotoxins are less heat stable than exotoxins.

Endotoxins can act as enzymes.

What is a key difference between endotoxins and exotoxins?

Exotoxins are heat stable, whereas endotoxins are not.

Exotoxins can act as enzymes, while endotoxins cannot. (correct)

Endotoxins are produced by both Gram-positive and Gram-negative bacteria.

Endotoxins can be heat destroyed easily while exotoxins cannot.

Which of the following contributes to symptoms such as fever and septic shock?

Exotoxins.

All bacterial toxins.

Only Gram-positive bacteria.

Endotoxins. (correct)

Which characteristic is true for endotoxins?

They are poor antigens. Signup and view all the answers

Which statement about exotoxins is accurate?

Exotoxins have a specific effect based on bacterial strain. Signup and view all the answers

What is the primary function of magnetosomes in bacteria?

To aid in magnetotaxis Signup and view all the answers

What is the role of gas vacuoles in cyanobacteria?

Confer buoyancy Signup and view all the answers

Which structure is specifically responsible for survival in unfavorable conditions among bacteria?

Endospore Signup and view all the answers

What does the cortex of an endospore consist of?

Loosely cross-linked peptidoglycan Signup and view all the answers

Which of the following describes the endospore's exosporium?

Outer protein covering Signup and view all the answers

What are the two subunits of ribosomes in bacteria?

Small and large subunits Signup and view all the answers

Which type of bacteria commonly forms endospores?

Bacillus spp. Signup and view all the answers

What mineral do Gleomargarita cyanobacteria specifically form within their cells?

Benstonite Signup and view all the answers

What is the shape of the genetic material in prokaryotes?

Circular Signup and view all the answers

What type of ribosome is found in eukaryotes?

80S Signup and view all the answers

Which option correctly states the number of chromosomes typically found in prokaryotes?

Usually only one Signup and view all the answers

Which of the following is a characteristic of eukaryotic chromosomes?

Generally linear Signup and view all the answers

Where does transcription occur in eukaryotic cells?

In the nucleus Signup and view all the answers

Which of the following is true about plasmids in prokaryotes?

They are usually present Signup and view all the answers

What type of RNA is part of the 60S subunit in eukaryotes?

5.8S RNA Signup and view all the answers

Which of the following is NOT a typical characteristic of introns?

Coding sequences Signup and view all the answers

What is the primary function of hydrogenosomes in some eukaryotic microorganisms?

Oxidation of pyruvate to H2, CO2, and acetate Signup and view all the answers

Which enzyme is considered the key enzyme of the Calvin cycle found in the stroma of chloroplasts?

Ribulose bisphosphate carboxylase (RubisCO) Signup and view all the answers

What distinguishes rough endoplasmic reticulum (ER) from smooth ER?

Presence of ribosomes on its surface Signup and view all the answers

What is the primary role of the Golgi complex in eukaryotic cells?

Chemical modification and sorting of ER products Signup and view all the answers

What is the main function of lysosomes in eukaryotic cells?

Digesting macromolecules and recycling cellular components Signup and view all the answers

What structural feature is characteristic of thylakoids within chloroplasts?

Flattened membrane discs containing chlorophyll Signup and view all the answers

Which component of eukaryotic cells is responsible for providing structural support and maintaining cell shape?

Cytoskeleton Signup and view all the answers

What type of metabolism do hydrogenosomes utilize?

Strictly fermentative metabolism Signup and view all the answers

What is the primary component of the archaeal cell wall?

Pseudomurein Signup and view all the answers

Which statement about S-layers in Archaea is correct?

S-layers can form different symmetries. Signup and view all the answers

How does the alcohol treatment affect Gram-positive bacteria during Gram staining?

It dehydrates the peptidoglycan. Signup and view all the answers

What is the role of glycocalyx in bacterial cells?

It protects from phagocytosis. Signup and view all the answers

Which statement differentiates between a capsule and a slime layer?

Capsules adhere more firmly compared to slime layers. Signup and view all the answers

What is the function of flagella in bacteria?

Movement through liquid Signup and view all the answers

What component anchors the flagellum motor in Gram-negative bacteria?

L ring Signup and view all the answers

Which part of the flagellum is associated with movement?

Basal body Signup and view all the answers

Which characteristic is true regarding Gram-negative bacteria compared to Gram-positive bacteria?

They have a more complex cell wall structure. Signup and view all the answers

After the alcohol wash in the Gram staining process, what typically happens to Gram-negative bacteria?

They lose the crystal violet-iodine complex. Signup and view all the answers

Study Notes

Gram-Negative Cell Wall

Contains Lipopolysaccharide (LPS) as endotoxin, known to elicit strong immune responses.
Endotoxins are heat stable, making them difficult to destroy under regular sterilization conditions.
Endotoxins contribute to symptoms like fever, hemorrhaging, and septic shock during infections.

Bacterial Endotoxin vs Exotoxin

Endotoxins are lipopolysaccharides, while exotoxins are soluble proteins that can act as enzymes.
Both are produced by pathogenic bacteria.
Gram-negative bacteria produce both endotoxins and exotoxins, while Gram-positive bacteria only produce exotoxins.
Endotoxins are a part of the outer membrane of the cell wall in Gram-negative bacteria, while exotoxins are extracellular (secreted).
Exotoxins are more toxic than endotoxins.
Exotoxins are specific to particular bacterial strains, while endotoxins are not.
Endotoxins are heat stable, while exotoxins are not.
Endotoxins are poor antigens, while exotoxins are highly antigenic.
Exotoxins stimulate the immune system to produce antitoxins that neutralize the toxin.

Archaeal Cell Wall

Contains PSEUDOMUREIN, a polysaccharide similar to peptidoglycan.
Contains S-LAYERS, the most common type of cell wall in Archaea, which are paracrystalline surface layers.
S-layers can form various symmetries: hexagonal, tetragonal, or trimeric.
S-layers are strong enough to withstand osmotic pressure and are always the outermost wall layer, in direct contact with the environment.

Gram Staining

Crystal violet-iodine complex forms in the cell.
In Gram-positive bacteria, alcohol dehydrates the peptidoglycan, preventing the complex from leaving.
In Gram-negative bacteria, alcohol dissolves the outer membrane, leaving holes in the peptidoglycan, allowing the crystal violet-iodine complex to wash out.

Bacterial Cell Surface Structure

Glycocalyx: an extracellular layer composed of polysaccharide, polypeptide, or a combination of both.
Protects pathogenic species from phagocytosis by macrophages.
Capsule: Glycocalyx layer that adheres firmly to the cell wall.
Slime Layer: Glycocalyx that is loosely attached to the cell wall.

Flagella

Tiny rotating machines that function to push or pull the cell through a liquid.
Gram-negative bacteria have a basal body with two pairs of rings.
Gram-positive bacteria have a basal body with only one pair of rings.
Motility test: a needle with cells stabbed in tubes with motility test medium (gelatin). Non-motile bacteria remain in a localized region, while motile bacteria disperse throughout the medium.

Flagellum Components

Flagellin: protein found in the filament of a bacterial flagellum.
Hook: wider region at the base of the filament.
Flagellum motor: anchored in the cytoplasm membrane and cell wall, consisting of a central rod passing through a series of rings:
- L ring: outer ring anchored in the LPS layer of Gram-negative bacteria.
- P ring: second ring anchored in the peptidoglycan layer of the cell wall.
- MS and C rings: located within the cytoplasm membrane and cytoplasm, respectively.

Inclusion Bodies: Magnetosomes

Some bacteria can orient themselves within a magnetic field due to the presence of magnetosomes.
Magnetosomes impart a magnetic dipole on a cell, enabling it to orient itself in a magnetic field.
Magnetotaxis: process of migrating along Earth's magnetic field lines.
Magnetosomes are enclosed by a thin membrane that catalyzes iron precipitation during magnetosome synthesis.

Inclusion Bodies: Gas Vacuoles

Confer buoyancy.
Conical-shaped structures, hollow yet rigid.
Variable in length and diameter.
Cyanobacteria and algae can form massive accumulations of gas vacuoles called blooms in lakes and other bodies of water.

Inclusion Bodies: Endospores

Highly differentiated cells extremely resistant to heat, harsh chemicals, and radiation.
Function as survival structures to endure unfavorable growth conditions.
Represent a dormant stage of a bacterial life cycle: vegetative cell – endospore – vegetative cell.
Endospore-forming bacteria (Bacillus spp.) are commonly found in soil.
Malachite green is used to stain endospores.

Endospore Layers

Exosporium: thin protein covering on the outermost layer of the endospore.
Spore coats: composed of spore-specific proteins (second layer).
Cortex: next to the spore coat, consisting of loosely cross-linked peptidoglycan.
Core: inside the cortex, containing the core wall, cytoplasm membrane, cytoplasm, nucleoid, ribosomes, and other cellular essentials.

Ribosomes

Two subunits:
- Smaller subunit (SSU) binds to mRNA.
- Larger subunit (LSU) binds to the tRNA and amino acids.
Prokaryotes have 70S ribosomes:
- 50S (LSU) contains 23S RNA, 5S RNA, and 34 proteins.
- 30S (SSU) contains 16S RNA and 21 proteins.
Eukaryotes have 80S ribosomes:
- 60S (LSU) contains 28S RNA, 5.8S RNA, 5S RNA, and 46 proteins.
- 40S (SSU) contains 18S RNA and 33 proteins.

Genetic Material of Bacteria: DNA

Essential functions of genetic material: replication and expression.
Contained in a single circular molecule called the "Bacterial chromosome".
NUCLEOID: irregular shape of chromosomes located in the cytoplasm, without an envelope.

Prokaryotes vs. Eukaryotes: DNA Comparison

Characteristic	Prokaryotes	Eukaryotes
Number (ploidy)	Usually only one, haploid	Generally in multiples of two, diploid
Shape	Generally circular with no free ends	Generally linear
Extrachromosomal	Usually present (plasmids)	Generally absent
Introns	Generally absent	Present
Number of genes in chromosome	One	Two
Gene action	Replication, transcription, and translation in the cytoplasm	Replication in the nucleus, transcription in the nucleus, translation in the cytoplasm

Matrix

Innermost compartment of the mitochondria.
Contains enzymes for the oxidation of organic compounds (citric acid cycle).

Eukaryotic Microorganisms: Hydrogenosomes

Some eukaryotic microorganisms live an anaerobic lifestyle.
They lack mitochondria and may contain HYDROGENOSOMES.
Hydrogenosomes lack citric acid cycle enzymes and cristae.
Carry out a strictly fermentative metabolism.
The major biochemical reaction is the oxidation of pyruvate to H2, CO2, and acetate.

Eukaryotic Microorganisms: Chloroplast

Chlorophyll-containing organelles found in phototrophic microbial eukaryotes (algae).
Function to carry out photosynthesis.
Have a permeable outer membrane and a much less-permeable inner membrane.
Innermost membrane surrounds the STROMA, which contains the enzyme ribulose bisphosphate carboxylase (RubisCO) - the key enzyme of the Calvin cycle.
THYLAKOIDS: flattened membrane discs where chlorophyll and other components needed for ATP synthesis are located.

Eukaryotic Microorganisms: Endoplasmic Reticulum

Network of membranes continuous with the nuclear membrane.
Two types:
- ROUGH ER: contains attached ribosomes - produces glycoproteins and new membrane material.
- SMOOTH ER: does not contain attached ribosomes - participates in the synthesis of lipids and facilitates some aspects of carbohydrate metabolism.

Eukaryotic Microorganisms: Golgi Complex

Stack of membrane-bound sacs called cisternae.
Products of the ER are chemically modified and sorted - destined for secretion or for function in other membranous structures in the cell.
Modifications: glycosylations (addition of sugar residues) that convert proteins into glycoproteins, targeting them to specific locations in the cell.

Eukaryotic Microorganisms: Lysosomes

Membrane-enclosed compartments containing digestive enzymes that hydrolyze proteins, fats, and polysaccharides.
Functions:
- Fuse with food that enters the cell in vacuoles.
- Release digestive enzymes that break down food for biosynthesis and energy generation.
- Degrade damaged cellular components and recycle them for new biosynthesis.

Eukaryotic Microorganisms: Cytoskeleton

Internal support network consisting of:

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Description

This quiz explores the differences between bacterial endotoxins and exotoxins, with a focus on the unique characteristics of Gram-negative bacteria. Understand the implications of lipopolysaccharides (LPS) in immune response and how they contribute to disease symptoms. Test your knowledge on the stability and toxicity of these bacterial toxins.