Lecture 4 Cell structure

Question 1

Explain the major differences between gram positive and gram negative bacteria

Answer 1

In gram positive bacteria there is no outer membrane, it has a thick peptidoglycan wall, technoic acid is present and it has a low lipid content. Gram staining binds and turns positive bacteria purple
In gram negative bacteria there is an outer membrane rich with lipids, there is a thin peptidoglycan wall and no technoic acid is present. Gram staining doesnt bind to negative bacteria and turns it pink

Question 2

Define peptidoglycan

Answer 2

Unique to bacteria, permeable to small molecules and is a common target for antibiotics

Question 3

Define the outer membrane of bacteria

Answer 3

The outer membrane of bacteria is only in gram -ve bacteria, is hydrophobic so is impermeable and promotes resistance to bile salts, detergents and some antibiotics

Question 4

Desribe the signal transduction and two component regulatory system

Answer 4

The sensor kinase detects the environmental signal (increased temp or pressure) and autophosphorylates which activates the sensor kinase. The SK then phosphorylates the response regulator (OmpR). The phosphorylated response regulater binds to the operator and blocks/stimulates transcription.

Question 5

Define flagella

Answer 5

Flagella are made of flaggilin and are surface appendages that assist in swimming motility of bacteria, allowing them to move. Movement driven by proton motive force

Question 6

What are antigenic variants

Answer 6

Antigenic variation refers to the mechanism by which an infectious agent such as a protozoan, bacterium or virus alters its surface proteins in order to evade a host immune response.

Question 7

Define pili

Answer 7

Pili are surface appendages that attach a bacterial cell to specific surfaces or to other cells. It can also attach two bacterial cells

Question 8

Define endospores

Answer 8

Endospores are highly differentiated cells resistant to harsh environments like heat, chemicals and radiation. Endospores are in the dormant stage of the bacterial cycle and are present only in some gram positive bacteria. Bacteria differentiate into endospores to ensure survival of bacterium through environmental stress

Question 9

What are capsules and slime layers

Answer 9

Polysaccharide layers that assist in attachment to surfaces and protect against phagocytosis

Question 10

What are biofilms

Answer 10

Group of bacterial cells connected to surface and enclosed in a matrix excreted by the cells. Biofilms protect the cells from detachment and phagocytosis and keep nutrients inside.

Question 11

What are biofilms general role in infection

Answer 11

Found as dental plaque, lungs of patients with cystic fibrosis, middle ear infections and on catheters.

Question 12

What and where are K antigens

Answer 12

Pili antigenic variations called K antigens among enterobacteriaceae

Question 13

What and where are H antigens

Answer 13

Flagella antigenic variants called H antigens among enterobacteriaceae