Basic Bacteria Structure & Metabolism

Question 1

Acid Fast Stain

Answer 1

Question 2

Spirochetes

Answer 2

• Stain poorly or too thin
• Darkfield microscopy

Question 3

Mycoplasma

Answer 3

•no cell wall

Question 4

Chlamydia & Rickettsia

Answer 4

• Obligate intracellular
• Cell walls minimized

Question 5

Answer 5

Question 6

Answer 6

Question 7

Answer 7

Question 8

Answer 8

Question 9

Answer 9

Question 10

Answer 10

• LPS consists of a toxic lipid A, a core polysaccharide, and polysaccharide side chains called O antigens in some bacteria.

Question 11

Cell Membrane

Answer 11

The bacterial cell (plasma) membrane is exceptionally rich in proteins and does not contain sterols. It plays a role in segregation of daughter chromosomes at cell division, analogous to the role of the mitotic apparatus of eukaryotes. The membrane is the site of synthesis of DNA, cell wall polymers, and membrane lipids and contains the entire electron transport system of the cell. Like cell membranes of eukaryotes, it is a permeability barrier and contains proteins involved in selective and active transport of solutes. It is also involved in secretion to the exterior of proteins, including exotoxins and hydrolytic enzymes involved in the pathogenesis of disease.

Question 12

Flagella

Answer 12

Flagella are molecular organelles of motility found in many species of bacteria, both Gram positive and Gram negative. They may be distributed around the cell (peritrichous), at one or at both ends of the cell (polar). In all cases, they made of proteins, are long (up to 20 µm) individually helical in shape and propel the cell by rotating at the point of insertion in the cell envelope. The presence or absence of flagella and their position are important taxonomic characteristics.

Question 13

Pili

Answer 13

Pili (fimbriae) are hair-like projections up to a thousand of which are found on the surface of cells of many Gram-positive and Gram-negative species. They are composed of molecules of a protein called pilin arranged to form a tube with a minute, hollow core. They are, in many cases, adhesins, responsible for the ability of bacteria to colonize surfaces and cells.

Question 14

Capsule

Answer 14

Many bacterial cells surround themselves with one or another kind of hydrophilic gel. This layer is often quite thick; even thicker than the diameter of the cell itself. Because it is transparent, this layer is usually not seen microscopically unless special stains are used or it is made visible by its ability to exclude particulate material, such as India ink. If the material forms a reasonably discrete layer, it is called a capsule; if it is amorphous in appearance, it is referred to as a slime layer. Most capsules or slime layers are polysaccharides made of single or multiple types of sugar residues.

Question 15

Core

Answer 15

In contrast to the structural richness of the layers and appendages of the cell envelope, the interior seems relatively simple. There are two clearly visible regions, one granular (the cytoplasm) and one fibrous (the nucleoid).

Question 16

Cytoplasm

Answer 16

The dense cytoplasm is bounded by the cell membrane. It appears granular because it is densely packed with ribosomes, which are much more abundant than in the cytoplasm of eukaryotic cells. This reflects the higher growth rate of bacteria. The overall subunit structure of the bacterial ribosome resembles that of eukaryotic ribosomes, but is smaller. It differs enough in function that a large number of antimicrobial agents have the prokaryotic ribosome as their target (i.e. aminoglycosides, tetracyclines, macrolides). Except for the functions associated with the cell membrane, all of the metabolic reactions of the cell take place in the cytoplasm. The cytoplasm has a cytoskeleton composed of actin and tubulin filaments which serves to localize proteins and along with the cell wall, give shape to the cell.

Question 17

Nucleoid

Answer 17

The bacterial genome resides on a single chromosome (there are rare exceptions) which includes 600 to 64,000 genes encoded in one, large, circular molecule of double-stranded DNA. In contrast to eukaryotes, most bacterial genes have no introns. Tightly packed by supercoiling, the chromosome together with related proteins is localized in the area of the cell interior called the nucleoid. This lack of compartmentalization makes metabolic processes more efficient than in eukaryotic cells because there is no need to transport mRNA from where it is made to where it functions.

Question 18

Plasmids

Answer 18

Many bacteria contain small, usually circular, double-stranded DNA molecules called plasmids. Plasmids are physically separate from the chromosome and replicate independently. They typically contain up to 30 genes. More than one type of plasmid or several copies of a single plasmid may be present in the cell. Plasmid genes involved in virulence and antimicrobial resistance are of particular importance in medical bacteriology. The mechanisms involved will be discussed under bacterial genetics.

Question 19

Spores

Answer 19

Question 20

Bacterial Metabolism

Answer 20

• Rapid pace – up to 100X vs human
• Highly diverse Highly efficient

Question 21

Bacterial Metabolism ATP Generation

Answer 21

Question 22

Aerobes

Answer 22

require O2, respiration

Question 23

Anaerobes

Answer 23

require absence of O2, fermentation

Question 24

Facultative

Answer 24

grows either way, respiration or fermentation (usually referred to as facultative anaerobic and rarely facultative aerobic)

Question 25

Microaerophilic

Answer 25

reduced O2 (8-10% vs ~21%)

Question 26

Replication

Answer 26

DNA Synthesis

Question 27

Transcription

Answer 27

RNA Synthesis \*Trancription and Translation occur concurrently

Question 28

Translation

Answer 28

protein synthesis \*Trancription and Translation occur concurrently

Question 29

Enzymatic Systems Respond to Stimuli

Answer 29

* Activation * Suppression * Feedback

Question 30

ADP-ribosylation (ADPR)

Answer 30

Relatively few biosynthetic pathways are unique to bacteria, but some of them form a basis for bacterial vulnerability or bacterial pathogenicity. One of the most powerful called ADP-ribosylation (ADPR) is the mechanism for the action of multiple bacterial toxins (i.e. pertussis toxin, diphtheria toxin, exotoxin A). * Toxin active unit binds both nicotinamide adenine dinucleotide (NAD) from body fluids and its target protein typically a human enzyme * This catalyzes the transfer of an ADP-ribose group to the target protein * The ADP-ribosylated protein is rendered inactive by this action. * The biologic outcome of ADPR depends on the normal function of the now ADPribosylated target protein. If it is crucial to an essential process like protein synthesis the result is cell death. If it is a regulatory protein, the pathway it regulates may be either suppressed or stimulated.

Question 31

Protein Secretion

Answer 31

Proteins destined for the wall, membranes, or periplasm are translocated by a general secretory pathway (GSP), which consists of cytosolic chaperones and an integral membrane enzyme (translocase) consisting of several proteins operating cooperatively. For pathogenic bacteria the mechanisms by which proteins are secreted is particularly important because it includes the exotoxins which play a prominent role in virulence. In Gram-negative species multiple pathways have been discovered that accomplish export of proteins across the outer membrane into the environment. Two of these (types III and IV) play a prominent role in the secretion of virulence factors.

Question 32

Type III

Answer 32

Type III systems involve as many as 20 protein components. They cause syringe-like injection of these proteins activated by contact of the bacterial surface syringe with mammalian host cells. This leads to the direct secretion of bacterial proteins into the cytoplasm of the mammalian cell.

Question 33

Type IV

Answer 33

Type IV systems are like type III but are also able to transfer DNA between bacterial cells or between a bacterial and a eukaryotic cell.