Learn: Bacterial Cell Structure, Peptidoglycan, and Antibiotic Targets

Why can breaking peptidoglycan cause a bacterium to explode?

Water tends to enter because solute concentration is high inside the bacterium.

What does lysozyme do to bacteria?

It destroys/breaks peptidoglycan.

Which is more sensitive to lysozyme, Gram-positive or Gram-negative bacteria?

Gram-positive bacteria.

What does penicillin target?

Peptidoglycan synthesis.

During which growth phase is penicillin more effective?

Log phase.

Can an antibiotic targeting peptidoglycan affect both Gram-positive and Gram-negative bacteria?

Yes.

Approximately what percentage of bacterial mass is water?

70%.

What is a hydrophilic molecule?

A molecule that interacts with water and is soluble in water.

What is a hydrophobic molecule?

A molecule that does not interact with water and is insoluble in water.

What is an amphipathic molecule?

A molecule containing both a hydrophilic region and a hydrophobic region.

How do amphipathic molecules orient in water?

Hydrophobic portions associate away from water, while hydrophilic portions interact with water.

Why do phospholipids spontaneously form bilayers in water?

They are amphipathic.

Can hydrophilic molecules freely cross a membrane made only of phospholipids?

No.

How can hydrophilic substances cross the cell membrane?

Through membrane proteins that form hydrophilic pathways.

True or false: Hydrophilic substances always enter by simple diffusion.

False.

True or false: The presence of the outer membrane determines Gram staining.

False.

What are pili?

Multiprotein bacterial surface complexes.

What are the major functions of pili?

Adhesion, locomotion, and lateral gene transfer.

How can antibodies against pili help prevent infection?

By blocking bacterial attachment.

How do pili contribute to biofilms?

They help bacteria adhere to surfaces.

What is a biofilm?

A polysaccharide-encased community of microorganisms.

What is an example of a biofilm?

Dental plaque.

What is conjugation in bacteria?

Lateral gene transfer through a connecting pilus.

Which structure is directly involved in conjugation?

A pilus.

Why is lateral gene transfer important for antibiotic resistance?

It spreads antibiotic-resistance genes among bacteria.

What functions can plasmid lateral gene flow transmit?

Traits such as enterotoxin production and antibiotic resistance.

What is the flagellum?

A multiprotein complex that mediates microbial locomotion.

What are the two important flagellar functions for pathogenicity?

Locomotion and adhesion.

What stabilizes a folded protein thermodynamically?

Non-covalent interactions between amino-acid R groups.

What energetic factor works against protein folding?

Loss of entropy.

Why are folded proteins described as only marginally stable?

Favorable interactions promote folding, but entropy loss opposes it.

About how much energy is needed to unfold an average 40-kDa protein?

About 170 kJ/mol.

What two 'tricks' keep metabolism from releasing destructive amounts of energy at once?

Energy is released in small quantities and coupled to energy-consuming reactions.

What is a protein made of?

An array of amino acids connected by covalent bonds.

What part of an amino acid differs among the 20 amino acids?

The R group.

What kinds of R groups are emphasized?

Hydrophilic (polar/charged) and hydrophobic (nonpolar) R groups.

How do soluble proteins arrange hydrophobic and hydrophilic amino acids in water?

Hydrophobic amino acids cluster toward the center; hydrophilic amino acids are on the surface.

If a cytoplasmic protein has a solvent-exposed hydrophobic region, what would you predict?

That the hydrophobic region is interacting with a hydrophobic molecule.

What amino acids would you predict in a protein region that binds a negatively charged molecule?

Hydrophilic, positively charged amino acids.

How are membrane proteins able to sit in the hydrophobic membrane interior?

Regions contacting the membrane's hydrophobic core expose hydrophobic amino acids.

Which bacteria have an outer membrane?

Gram-negative bacteria.

What are amino acids that are hydrophilic and positively charged?

Hydrophilic, positively charged amino acids.

What are the major components of the Gram-negative outer membrane?

Proteins, phospholipids, and lipopolysaccharides (LPS).

Where are phospholipids and LPS located in the Gram-negative outer membrane?

The inner layer contains phospholipids; the outer layer contains lipopolysaccharides.

What is the main bacterial function of the outer membrane?

It acts as a semipermeability barrier to diffusion of molecules into and out of the cell.

Why are Gram-negative infections associated with higher mortality?

Because lipopolysaccharide (LPS) is very toxic to mammals.

Is causing toxicity the bacterial biological role of the outer membrane?

No, its role is as a semipermeability barrier.

Which group is susceptible to polymyxin B?

Gram-negative bacteria.

If polymyxin B destroys outer-membrane integrity, which function is primarily affected?

The semipermeability-barrier function.

Does peptidoglycan block polymyxin B from reaching LPS in Gram-negative bacteria?

No, LPS is on the outer surface of the outer membrane.

How does the lecture contrast cellulose combustion with glucose metabolism?

Cellulose combustion releases heat and light; glucose oxidation releases usable energy captured in ATP.

What is metabolism?

Chemical reactions in which energy released in small quantities is coupled to reactions that consume that energy.

What is catabolism?

Degradation reactions associated with energy production.

What is anabolism?

Synthesis reactions associated with energy consumption.

What is ATP's role in metabolism?

It captures/transfers usable chemical energy to couple energy-producing and energy-consuming reactions.

How much energy is required to synthesize each energy-rich covalent bond in ATP?

About 45-65 kJ/mol.

What happens to H during electron transport?

H is sent out of the cell.

What happens to OH during electron transport?

OH is kept inside the cell.

What charge and pH conditions result outside the cell during electron transport?

The outside becomes positively charged and acidic.

What charge and pH conditions result inside the cell during electron transport?

The inside becomes negatively charged and alkaline.

What is the proton motive force?

The pH gradient plus the electrochemical potential.

What does the proton motive force ultimately help drive?

ATP production.

What major pathway converts glucose into two pyruvate molecules?

Glycolysis.

What major pathway follows pyruvate processing?

The citric acid (Krebs/TCA) cycle.

What is the overall sequence of metabolism emphasized in the slides?

Glucose → pyruvate → citric acid cycle → electron transport chain → ATP + water.

What electron carriers feed the electron transport chain?

NADH and FADH2.

What molecule serves as the final electron acceptor in the electron transport chain?

Oxygen, which contributes to formation of water.

What enzyme complex uses the proton gradient to make ATP?

ATP synthase.

What is pathogenicity?

The ability to cause disease.

What are the 3 Koch's postulates?

1) Isolate the microorganism as a pure culture from disease lesions. 2) Inoculating the pure culture into a susceptible host should cause the disease. 3) Recover the microorganism again from the lesions of the infected host.

What observation would conflict with Koch's postulates?

Finding the suspected microorganism colonizing healthy individuals without symptoms.

Which infections are associated with higher mortality?

Gram-negative infections.

What is the major bacterial-envelope difference between Gram-positive and Gram-negative bacteria?

Gram-positive: thick peptidoglycan; Gram-negative: thin peptidoglycan plus an outer membrane.

Is the cell membrane part of the bacterial envelope?

No, the bacterial envelope does not include the cell membrane.

What determines the Gram-staining result?

The thickness of the peptidoglycan layer.

Why do Gram-positive bacteria remain purple after alcohol treatment?

Their thick peptidoglycan collapses and traps the crystal violet-iodine product, resisting decolorization.

Why do Gram-negative bacteria become decolorized during the alcohol step?

Their thinner peptidoglycan retains the crystal violet-iodine product less efficiently, so alcohol removes it.

Do Gram-negative bacteria have thicker peptidoglycan than Gram-positive bacteria?

No, Gram-negative bacteria have thin peptidoglycan; Gram-positive bacteria have thick peptidoglycan.

How is peptidoglycan organized?

As a multilayer, net-like structure around the bacterium.

What are the two polymer components of peptidoglycan?

A polysaccharide polymer and a peptide polymer.

What sugar derivatives form the polysaccharide portion of peptidoglycan?

N-acetylglucosamine and N-acetylmuramic acid.

What is the main biological function of peptidoglycan?

It gives the bacterium shape and rigidity and prevents swelling/explosion from internal pressure.

Is peptidoglycan the selective semipermeability barrier?

No, it is permeable to water and small molecules; the cell membrane and outer membrane act as semipermeability barriers.