Problem Set #8

Question 1

What chemical form does nitrogen need to be in before it can be incorporated by plants into organic compounds?

Answer 1

NH4+ or NH3

Question 2

Nitrogen can be obtained from the environment in 2 main forms: one from air and one from soil. What are they?

Answer 2

Air: N2
Soil: NH3 or NO3-

Question 3

What is the enzyme responsible for fixing nitrogen?

Answer 3

Nitrogenase

Question 4

In nitrogenase, N2 is thought to bind to a metal cluster where it is reduced. What is the metal cluster called?

Answer 4

Iron molybdenum cofactor (FeMoCo)

Question 5

How many equivalents of ATP are needed to reduce N2 to 2 NH3?

Answer 5

16

Question 6

How many reducing equivalents are consumed?

Answer 6

8

Question 7

What is the dominant form of oxidized nitrogen found in the soil and utilized by plants?

Answer 7

NO3

Question 8

Glyphosate inhibits an enzymes called EPSP synthase that is required for the synthesis of which amino acids? Why is this fatal to the plant?

Answer 8

Tryptophan, tyrosine, phenylalanine

Question 9

Where each reaction occur (cytosol or plastids)
NO3-->NO2
SO4-->SO3
NO2-->NH3
SO3-->H2S

Answer 9

cytosol
plastid
plastid
plastid

Question 10

Nitrogen is stored in seeds as what kind of molecule?

Answer 10

Protein

Question 11

What amino acids is the precursor for chlorophyll biosynthesis?

Answer 11

Glutamate

Question 12

The first enzymatic step in the leucine and valine synthetic pathway is inhibited by either valine or leucine. This is very common in synthetic metabolic pathways and prevents excessive production by the pathway. What is this type of metabolic regulation called?

Answer 12

feedback regulation

Question 13

What is glutathione? list 3 functions

Answer 13

Glutathione is an important sulfur containing reducing agent in plants

1) signaling
2) conjugate hormones
3) deactivating xeobiotics