Structures External to the Prokaryotic Cell Wall

What is the glycocalyx?

A viscous, gelatinous layer external to the cell wall.

What is the glycocalyx made of?

Polysaccharide and/or polypeptide.

What are the two types of glycocalyx?

Capsule and slime layer

What characterizes a capsule?

Neatly organized and firmly attached

What characterizes a slime layer?

Unorganized and loosely attached.

How does the glycocalyx contribute to virulence?

Capsules prevent phagocytosis and help microbes adhere to surfaces.

Examples of capsule-forming bacteria?

Bacillus anthracis, Klebsiella pneumoniae, Streptococcus pneumoniae.

What helps form biofilms

Extracellular polymeric substance (EPS) from the glycocalyx.

Functions of EPS in biofilms

Protects cells and helps microbes attach to surfaces.

Examples of biofilm-forming bacteria?

Streptococcus mutans, Vibrio cholerae.

What are flagella

Filamentous appendages that propel bacteria.

What protein are flagella made of?

Flagellin

Where do flagella originate from?

The cell membrane (not the cell wall).

What are the three parts of a flagellum

What are the three parts of a flagellum

What is an atrichous bacterium?

One that lacks flagella

What is a peritrichous arrangement?

Flagella distributed over the entire cell.

What is a monotrichous arrangement?

A single flagellum at one pole

What is a lophotrichous arrangement?

A tuft of flagella from one pole

What is an amphitrichous arrangement?

Flagella at both poles of the cel

What is taxis?

Movement of bacteria toward or away from a stimulus.

What is chemotaxis?

Movement in response to chemicals.

What is phototaxis?

What is phototaxis?

How do flagella move bacteria?

By rotating to “run” or “tumble.”

What happens during positive chemotaxis?

More runs, fewer tumbles—bacteria move toward the attractant.

What happens during negative chemotaxis?

More tumbles—bacteria move away from the repellent.

What are flagella proteins called?

H antigens—used to distinguish bacterial serovars (e.g., E. coli O157:H7).

H antigens—used to distinguish bacterial serovars (e.g., E. coli O157:H7).

Glycoproteins called archaellins.

How do archaella move?

They rotate like flagella

What energy source do archaella use?

ATP

Where are archaella anchored?

To the cell surface.

What are axial filaments also called?

Endoflagella

Where are axial filaments found?

In spirochetes.

How do axial filaments move the cell?

Rotation causes corkscrew-like movement.

What are fimbriae

Hairlike appendages that allow for attachment.

What role do fimbriae play in biofilms

They help bacteria adhere to surfaces and form biofilms

Examples of bacteria with fimbriae

Neisseria gonorrhoeae, E. coli O157.

What are pili involved in?

Motility (gliding and twitching) and DNA transfer.

What is a conjugation pilus?

What is a conjugation pilus?

What is the bacterial cell wall?

A complex, semirigid structure that gives shape and protects the cell.

What does the cell wall protect against?

Adverse environmental changes and osmotic pressure.

Is the cell wall found in all prokaryotes?

Present in most; also found in some eukaryotes.

What roles does the cell wall play in bacteria?

Attachment, pathogenicity, and antibiotic targeting.

What is the main component of bacterial cell walls?

Peptidoglycan.

What are the repeating units in peptidoglycan?

N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).

How are NAG-NAM rows linked?

By polypeptides forming a lattice structure.

What does penicillin target?

The peptide cross-bridges in peptidoglycan, weakening the cell wall.

How can cell wall composition be used?

To differentiate major groups of bacteria.