Bacterial Structure Flashcards by Joel Glotfelty

Lack a nuclear membrane

Prokaryotes

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Bacteria divide by

Transverse fission

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Bacterial multiplication is fast. Each division cycle can be as short as

20 minutes

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Rod-shaped bacteria are the

Bacilli

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Spherical shaped bacteria are the

Cocci

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What are the two actin homologues that are required for chromosome/plasmid segregation?

mreB and parM

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mreB and parM form which types of filaments?

Helical or double-helical

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A major target for anti-bacterial drugs

-has three layers

Bacterial envelope

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What are the three layers of the bacterial envelope?

) Plasma membrane
) Cell wall
) Structures outside wall

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The bacterial plasma membrane is made up of a

Lipid bilayer with proteins

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Functions in the import and export of solutes

Bacterial plasma membrane

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The bacterial plasma membrane has complexes of respiratory chain that are the equivalent of the

Inner mitochondrial membrane

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The bacterial cell wall is made up of a long-chain or polysaccharide with peptide cross-links. This material is called

Peptidoglycan

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The bacterial cell wall is essential to the integrity of the bacterial envelope. Damage to the cell was leads to

Osmotic lysis

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Has no equivalent in mammalian cells, so antibiotics that target it have excellent selective toxicity

Bacterial cell wall

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What type of receptors are commonly found in the bacterial cell wall?

Toll-like receptors

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Disaccharide + peptide units assembled in cytosol on lipid carrier

Peptidoglycan

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Peptidoglycan is assembled in the

-on a lipid carrier

Cytosol

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The disaccharide/peptide units of peptidoglycan that had been assembled in the cytosol are transported across the

Plasma membrane

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Here we see the disaccharides assembled into long chains and the chains are then cross-linked by

-essential for strength of wall

Peptide bonds

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A structural analogue of the D-ala-D-ala of peptidoglycan side chains

Penicillin

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Binds active site of cross-linking enzyme and forms irreversible covalent bond, inactivating the enzyme

Penicillin

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Penicillin results in new peptidoglycan being formed without

Cross-links

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Penicillin action requires new peptidoglycan formation so it acts best on

Growing cells

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Differences in peptidoglycan thickness cause bacterial cells to stain differently. We call this the

Gram stain

The first step in identifying the bacteria is the

Gram stain

Thick peptidoglycan, i.e. 20-50 layers

Gram-positive (blue/purple)

Thin peptidoglycan, i.e. 1-3 layers

Gram negative (red/pink)

Retains more dye

Thick peptidoglycan

What are the 4 characteristics of the envelopes of gram-positive bacteria?

Thick peptidoglycan, protein fibrillae, teichoic acids, and group carbohydrates

Adhere to mammalian cells and extracellular matrix; -many types per cell

Protein fibrillae

Polymers of sugar alcohols linked by phosphate groups

Teichoic acids

Teichoic acids are unique to

Gram-positive bacteria

Linked to peptidoglycan –in some groups, important in identification

Group Carbohydrates

Bind membrane proteins of mammalian cells

Protein Fibrillae

In EM, protein fibrillae appear as?

Fuzz on cell surface

Protein fibrillae are covalently linked to

Peptidoglycan

Essential to virulence and serve as a potential target of anti-biotics

Protein fibrillae

What are the four components of the bacterial envelopes of gram-negative bacteria?

Plasma membrane, thin peptidoglycan, outer membrane, and periplasm

Serves as a second membrane (lipid bilayer/protein) that is outside of the peptidoglycan

Outer membrane of gram-negatives

Space between outer and inner (plasma) membranes

Periplasm

Filled with enzymes, solute carrier proteins, polysaccharides -Not an empty space

Periplasm

Protein assemblies traverse the periplasm and link

Inner and outer membranes

The inner leaflet of the outer membrane of gram negative bacteria has typical

Phospholipids

The outer leaflet of the outer membrane of gram negative bacteria on the other hand is composed lost entirely of

Lipopolysccharide (LPS)

The fatty acids in the outer membrane are tightly packed and are

Saturated FAs

The outer membrane is HIGHLY -major defense against toxic small molecules

Impermeable

Allow solutes to traverse the outer membrane

Porin proteins

A trimer

Porin protein

Each monomer of this protein is a cylinder made up of walls of beta sheet

Porin protein

The exterior of a porin cylinder is covered with

Hydrophobic amino acids

This allows porin to be embedded in the lipid bilayer of the

Outer membrane

The interior of the porin cylinder is lined with -serves as the "pore" for diffusion of solutes

Hydrophilic amino acids

Determines the ability of antibiotics to enter the cell

The pore diameter

LPS is on the outer leaflet of the outer membrane and is composed of which three parts?

1. ) O-antigen 2. ) Core 3. ) Lipid A

A polymer made up of repeating units of 3-5 sugars

O-antigen

A phosphorylated, complex oligosaccharide

LPS core

A disaccharide + 6-8 saturated fatty acids

Lipid A

Te length of the O-antigen varies with

Species

Helps bacteria to evade the immune system -some species change the antigenic structure

O-antigen

The length of the O-antigen diverts the

MAC of complement

Lipid A is a disaccharide with 6-8 saturated fatty acids. It has a toxic portion that is called the

Endotoxin

Integral portion of the cell wall of gram-negative bacteria that is released only when the cell lyses -The toxic poriton

Lipid A

The LPS receptors on monocytes are

Toll-like receptors

LPS binding to TLR leads to the synthesis and release of

Inflammatory cytokines

Can cause septicemia and produce septic shock -can also result in DIC

Lipid A (toxic to body)

Bacteria in the bloodstream

Septicemia

Present in both living and dead bacteria, and is not removed by sterilization

Lipid A (Endotoxin)

Must be removed from materials before parenteral use

Endotoxin

Kills bacteria, but can result in release of endotoxin and other inflammatory components

Antibiotic treatment

The release of endotoxin and other inflammatory components can then create

Fever and hypotension

What are the three types of bacterial appendages?

Flagella, Pili, and conjugated pili

Function in locomotion (H antigen)

Flagella

Function in adhesion

Pili (fimbrae)

Function in the transfer of DNA between cells

Conjugation Pili

Bacteria is propelled through medium by

Rotation of flagella

The basal body of the flagella rotates in the bacterial envelope. This is driven by

H+ Inflow

The H+ inflow causes rotation of the flagellum, which then

Propels the cell

Enable bacteria to adhere to mammalian cells or to eachother

Pili

Special organelles for DNA transfer

Conjugation pili

Protect bacteria from phagocytes

Capsules

Made up of K antigen, which is mostly high MW polysaccharides

Capsules

Not visible in Gram-stain, and requires a special stain or EM?

Bacterial capsules

Specialized cells for dispersal, resisting unfavorable environments

Bacterial spores

Made up of thick walls and are metabolically inert -omnipresent in soil and plant material

Bacterial spores

Bacterial spores are resistant to -require autoclave for sterilization

Boiling

Bacterial spores are formed in response to starvation, and are made by only some

Gram-positive Rods

Are highly refractile, but do not Gram-stain because of the thickness of their walls

Spores

Bacteria change the direction of their swimming by reversing direction in which their

Flagella Rotate

Smooth swimming is the result of

Counter-clockwise rotation

Random tumbling is the result of

Clockwise rotation

When swimming up a concentration gradient of attractant, we see the suppression of

Tumbling

When swimming down the concentration gradient we see promotion of

Tumbling and re-orientation