Block E - Microbial Structure & Function

Question 1

Why are bacterial cells small? (4 marks)

Answer 1

-smaller cells have a larger surface area relative to their volume compared to larger cells, this allows them more efficient and faster transport across their membrane
-faster division
-reduced energy demand
-maximises resource utilization

Question 2

Describe the cell envelope of gram negative bacteria

Answer 2

-it has two membranes, a lipopolysaccharide and peptidoglycan

Question 3

Describe the cell envelope of gram positive bacteria

Answer 3

-it has one membrane of peptidoglycan

Question 4

How would you gram stain to identify gram positive and gram negative bacteria? (5 marks)

Answer 4

-stain cells with crystal violet
-iodine is added which binds to CV and forms a CVI complex
-decolourise cells with ethanol and Gram + remain purple and Gram - loses colour
-add safranin which stains Gram - bacteria
-Gram + bacteria stains purple and Gram - bacteria stains pink

Question 5

Explain the Sec and Tac system limitations that bacteria have?

Answer 5

-the sec system translocates unfolded proteins across the inner membrane and requires ATP. however it cannot transport folded proteins and can be slow and inefficient
-the tat system is responsible for exporting folded proteins, but it requires the presence of a proton motive force. his system has limitations in the type of proteins it can export
-overloading of these systems can lead to bottlenecks, where proteins cannot be efficiently secreted

Question 6

What does SecYEG do?

Answer 6

forms the core protein conducting channel

Question 7

What does SecA do?

Answer 7

its an ATPase that drives protein translocation

Question 8

What is the role of SecD, SecF and YajC?

Answer 8

these are accessory proteins that enhance efficiency by coupling the proton motive force to translocation and prevents backwards movement

Question 9

What is the role of SecB?

Answer 9

its a chaperone

Question 10

Whats the role of YidC?

Answer 10

it inserts integral membrane proteins

Question 11

Whats the role of TatA?

Answer 11

forms the translocation protein channel

Question 12

Whats the role of TatB?

Answer 12

interacts with the signal peptide and is involved in protein recognition

Question 13

Whats the role of TatC?

Answer 13

recognizes the signal sequences and recruits TatB and TatA

Question 14

In the Tat pathway, protein translocation is driven by ____

Answer 14

PMF

Question 15

Compare the flagellum of bacteria to archaea?

Answer 15

-in bacteria, the flagellum is powered by a proton motive force while the archaeal flagellum uses ATP hydrolysis as its energy source

Question 16

How are flagellums assembled? (3 marks)

Answer 16

-the proteins, MS ring, C ring, P and L rings assemble spontaneously based on their intrinsic affinities
-a specialized secretion system transports flagellar components through the hollow rod and filament.
-components are assembled in a specific order, ensuring that the flagellum functions correctly
-the basal body motor proteins (MotA and MotB) are integrated to power the rotation of the flagellum, these harnedd energy from the PMF

Question 17

What is gliding motility? (3 marks)

Answer 17

-a form of movement used to move smoothly across solid surfaces without the use of flagella.
-this only occurs on solid surfaces, such as agar or host tissue
-the movement is powered by PMF or ATP.

Question 18

Name 2 mechanisms of gliding motility (2 marks)

Answer 18

-adhesion and propulsion via surface proteins
-slime secretion to propel the bacterium forward