Block C - Microbial Physiology

Question 1

What is the process of nitrogen assimilation in terms of microbes?

Answer 1

it refers to the process by which microorganisms take up inorganic nitrogen compounds like ammonia, nitrate or nitrite and incorporate them into organic molecules such as amino acids, nucleotides and proteins.

Question 2

__ is the most stable form of nitrogen and is a major reservoir.

Answer 2

N2

Question 3

Nitrogen must be _____ from the relatively inert N2 to biologically accessible ____

Answer 3

reduced
NH3

Question 4

What is nitrogen fixation?

Answer 4

conversion of atmospheric nitrogen into ammonia.

Question 5

What is anammox?

Answer 5

direct conversion of ammonium and nitrite into nitrogen gas under anaerobic conditions

Question 6

What is the Haber-Bosch process?

Answer 6

an industrial method for synthesizing ammonia from atmospheric nitrogen gas and hydrogen gas.

Question 7

What enzyme catalyses nitrogen fixation?

Answer 7

nitrogenase

Question 8

Describe the makeup of the nitrogenase complex (2 marks)

Answer 8

-dinitrogenase reductase (Fe protein), it brings the reducing power and energy for the reaction
-dinitrogenase (MoFe protein) performs the actual reduction of N2 at its FeMo cofactor active site

Question 9

Why is nitrogen fixation energetically demanding?

Answer 9

because breaking the triple bond in N2 requires a high energy input

Question 10

What is the ecological importance of anammox? (2 marks)

Answer 10

it helps reduce eutrophication by mitigating nutrient overloading in water bodies. this prevents excessive algal blooms, which can lead to oxygen depletion and the death of aquatic organisms.

Question 11

Detail the GS pathway of ammonium assimilation

Answer 11

this uses the substrates, ammonium and glutamate and is catalysed by the glutamine synthetase enzyme.

Question 12

Detail the GOGAT pathway of ammonium assimilation

Answer 12

this uses the substrates, glutamine and 2-oxoglutarate and is catalysed by the enzyme glutamate synthase.

Question 13

Detail the GDH pathway of ammonium assimilation

Answer 13

this uses the substrates ammonium and 2-oxoglutarate and is catalysed by glutamate dehydrogenase.

Question 14

Which ammonium assimilation pathway would we use in high ammonium levels and why?

Answer 14

the GDH pathway would be used as it is simpler and more energy efficient

Question 15

Which ammonium assimilation pathway would we use in low ammonium levels and why?

Answer 15

GS-GOGAT pathway is preferred because it has a higher affinity for ammonium, although it requires more energy

Question 16

What is glutamate used for?

Answer 16

it is a key amino acid and precursor for other amino acids

Question 17

What is glutamine used for?

Answer 17

its a major nitrogen donor for biosynthetic processes, including synthesis of nucleotides, nucleic acids and other amino acids.

Question 18

What is glutamine syntetase regulated by?

Answer 18

its regulated by adenylylation

Question 19

What is the composition of phospholipids in a membrane?

Answer 19

-the general structure is a phospholipid bilayer
-it has amphipathic molecules with a hydrophilic head and two hydrophobic tails.

Question 20

What are porins?

Answer 20

porins are a class of proteins that form large, water filled channels in the outer membrane of gram negative bacteria and mitochondria

Question 21

What function do porins perform?

Answer 21

-the interior of the channel is hydrophilic, allowing water and small hydrophilic molecules to pass through
-it facilitates passive diffusion, which does not require ATP

Question 22

What’s the difference between general porins and specific porins with examples?

Answer 22

general porins allow the non-specific passage of small hydrophilic molecules e.g OmpF in E. coli allows diffusion of sugars, ions and nutrients.
specific porins transport selective molecules or classes of molecules based on certain properties. e.g LamB in e. coli facilitates the uptake of maltose

Question 23

What is the function of the cytoplasmic membrane i bacteria? (3 marks)

Answer 23

-it has selective permeability, small non polar molecules diffuse freely
-transport proteins facilitate the movement of ions, nutrients and waste products
-in bacteria the cytoplasmic membrane house proteins involved in the electron transport chain for respiration

Question 24

Compare channel and carrier proteins? (3 marks)

Answer 24

-channel proteins form a continuous hydrophilic pore for direct diffusion which leads to a fast transport rate.
-carrier proteins bind and transport molecules via conformational change which can be much slower than channel proteins.
-channel proteins always transport down the gradient, though passive diffusion which requires no energy while carrier proteins can be passive or active, active transport requires ATP

Question 25

In the context of carrier proteins, what is a porter?

Answer 25

a porter is a specific type of transporter that facilitates the movement of molecules

Question 26

How does secondary active transport work?

Answer 26

-secondary active transporters couple the downhill movement of ions along their gradient to the uphill transport of another molecule, such as glucose, amino acids or ions
-the potential energy stored in the ion gradient powers the transport of he second molecule

Question 27

What are symporters?

Answer 27

They move two substances in the same direction across the membrane

Question 28

What are antiporters?

Answer 28

Move two substances in opposite directions across the membrane

Question 29

Do pumps rely on primary of secondary active transport? Define the answer you choose

Answer 29

they rely on primary active transport, which means they use energy from ATP or other sources.

Question 30

What are ABC transporters?

Answer 30

a family of carrier proteins which use the energy derived from ATP hydrolysis to transport various molecules across cellular membranes

Question 31

What is the difference between importers and exporters?

Answer 31

-importers are only present in prokaryotes ad facilitate the uptake of essential nutrients
-exporters are in all organisms are remove toxins, drugs and metabolic by-products

Question 32

What is the mechanism of action for ABC transporters (4 marks)

Answer 32

-the substrate binds to the transporter at a specific site
-the NBDs bind ATP, causing a conformational change in the transporter
-this shifts the substrate binding pocket, moving the substrate across the membrane
-ATP is hydrolysed to ADP, resetting the transporter to its original conformation

Question 33

What are group translocators?

Answer 33

they are a specialized type of transport system in which a molecule is chemically modified as it is transported across the membrane. this is unique to prokaryotes and often seen in bacteria.

Question 34

Where does the energy for group translocators come from?

Answer 34

they come from phosphoenolpyruvate (PEP), which is a high energy intermediate in bacteria glycolysis.

Question 35

Describe briefly how microbes assimilate sulphur.

Answer 35

Microbes absorb sulphur primarily as sulphate from the soil or water. sulphate is converted into organic sulphur compounds, like two most important amino acids, cysteine and methionine.