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Overview of Nitrogen Metabolism 2


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How many electrons and ATP molecules are needed to reduce atmospheric nitrogen?
8 electrons and 16 ATP
Name the enzyme that catalyzes the reductive amination reaction of ∂-ketoglutamate to glutamate (and its reverse rxn)? Besides the enzyme, what else is required for this reaction?
a) Glutamate dehydrogenase⬦ b) NH4 + NADH or NADPH
a) Name the enzyme that catalyzes the reductive amidation reaction of the carboxylate group of glutamate to produce glutamine (and its reverse rxn)?

b) What else is required for this rxn?

c) Why is glutamate considered a "gate
a) glutamine synthetase…

b) NH4 + ATP

c) Glutamate's ∂-amino can be tranfered to become the ∂-amino of another amino acid.


e) these rxns show how nitrogen (in the form of amonia/amonium) can enter biologic systems
Is glutamine found in great or small concentration in the blood?
Main Scheme of AA metabolism:

a) what are the three fates of amino acids taken into a cell from the blood stream?

b) What is the first step in catabolism of amino acids?
a) AA -->
1) Proteins,
2) N- containing molecules (nucleotides),
3) catabolism.

b) removal of the nitrogen
Name the essential amino acids. (hint: TV PHaT MILL)
threonine, valine, phenylalanine, histadine, arginine (in young), tryptophan, methionine, isoleucine, leucine, lysine
What are the 3 amino acids generally lacking in plants?
Lys, Met, Trp
(a) what is the problem of having a narrow protein source?

b) Why does a high gelatin diet deplete Met?
(a) Because each source offers its own set of amino acid, and having multiple sources guarantees that you will get a variety of amino acids.

b) Gelatin lacks cysteine, so the body will synthesize it... the problem is that cysteine synthesis requires Met, thus a high gelatin diet will deplete Met
Give 3 advantages to amino acid turnover.
1) quality control of proteins⬦ 2) provides continuous supply of amino acids that may be in more demand⬦ 3) metabolic control.
a) Where does most protein turnover occur?

b) do most amino acids come from dietary sources or protein turnover?
a) digestive enzymes, sloughed off intestinal cells, skeletal muscle

b) protein turnover
a) How does turnover play an important role in metabolic control?

b) Should a highly controlled metabolic process have enzymes with a long or short half life?
a) Turnover plays a regulatory role by adjusting the amounts of key enzymes by altering their synthesis and degradation rates

b) short - the half-life length is a tighter regulation of the enzyme
Assign values to the following?

- Dietary protein
- Amino acids released from protein turnover

- Amino acids used for protein synthesis
- Amino acids catabolized/excreted

Assign values to the following?

- Dietary protein = 100g
- Amino acids released from protein turnover = 300g

- Amino acids used for protein synthesis = 300g
- Amino acids catabolized/excreted = 100g

Total amino acid mass gained/lost = 0g

Total body amino acid pool= 100g

Body mass of protein = 12,000g
Describe Positive Nitrogen Balance
a scenario where amino acid dietary input (to tissue protein) exceeds the sum of excretion and production of nitrogen containing molecules (purines, hemes, etc.)
a) what can have the biggest effect on the body's total amino acid pool, dietary intake or the percentage or the changes in the percent change of body mass protein?

b) What is the average body mass of protein in grams?
a) percent change of body mass protein.

b) 12000 g
What kind nitrogen balance will a person who is undergoing growth, pregnancy, lactation, recovery from physiologic stress? Describe this state.
Positive Nitrogen Balance: greater dietary protein input than excretion.
What kind nitrogen balance will a person who is undergoing surgery, trauma, burns, physiologic stress? Describe this state.
Negative Nitrogen Balance: greater tissue breakdown and excretion than than dietary input.
a) What kind nitrogen balance will a person who is receiving inadequate dietary input? (Kwashiorkor) Describe this state.

b) When is Kwashiorkor seen and

c) What causes Kwashiorkor effects?

d) what precipitates the negat
Negative Nitrogen Balance: inadequate input, with tissue protein being used to supply amino acid pool and basic production N-containing molecules, where excretion is larger than dietary input.

b) it's seen in children in developing countries as they wean from breast milk to diets high in carbohydrates

c) Muscle wasting and distended abdomen may be due to a lack of serum proteins that cause edema

d) infection or starvation: "Maramus" = low protein, high carbohydrates.
What kind nitrogen balance will a person who is lacking in one amino acid? Describe this state.
Negative Nitrogen Balance: tissue breakdown results to synthesize the needed amino acid... and the input is equal to the excretion... but the tissue proteins are being slowly depleted to produce the deficient amino acid.
1. Describe the gamma-glutamyl cycle that allow amino acid membrane transport.

2. Which enzyme is needed to release the amino acid from gamma-glu?

2. Does a deficiency in a major proteolytic enzyme have a general effect, or specific
1. Amino acid is transported across the membrane by glutathione > then cysteinylglycine is removed leaving a glutamyl-AA > the amino acid leaves, leaving 5-oxoproline, while cysteinylglycine converts to cystein and glycine > (add ATP converts 5-oxyproline to...) > glutamate (add ATP to add cystein to glutamate) > gamma-glutamylcysteine (add ATP to add glycine) > glutathionine is now recycled.

2. 5-oxyprolinase

3. Somwhat specific, since the enzymes will have lytic activities only on certain residues.
1. What is the major enzyme involved in the activation of other proteolytic enzymes (zymogens)?

2. Why are proteins digested in the gut?

3. How do amino acid membrane transporter found in the gut differ from those in the kidneys?
1. Trypsin

2. They are too large to be absorbed and must be digested to amino acid or small peptides (di or tripeptides) first

3. They don't

4. L and cationic

a) Cationic = basic amino acids, cystein
b) Anionic = gluatamate, aspartate
c) L = neutral amino acids, especially branched chain and phenylalanine
d) ASC = neutral amino acids, especially serine, alanine and cysteine
e) Gly = glycine, proline, hyroxyproline
f) N = Histidine, asparagine, glutamine
1. How many ATP are needed to transport amino acids across the intestinal border?

2. How many ATP are needed to transport amino acids across the seosal side of the epithelial cell border?

3. Where else are amino acid transporters fo
1. 1/3 ATP/amino acid

2. None, it follows its concentration gradient all the way to the portal vein to the liver. (this [gradient] can be reversed to send AA to epithelial cells during starvation)

3. Liver, muscle kidney (where amino acids are saved from excretion)

4. Blood urea nitrogen (mg/100 ml urea) it measures the concentration of nitrogen in the blood in the form of urea.

5. A high BUN implies tissue damage or poor kidney function

6. multiply by 0.5
1. What is the source of the nitrogen found in uric acid?

2. ammonia is toxic in the blood, but what purpose does it serve in the urine?
1. the breakdown of nucleic acids (adenine and guanine)

2. balance pH
1. What is the major high energy phosphate donor in skeletal muscle?

2. what is its fate?
1. creatine

2. creatine phosphate is cyclized to creatinine and excreted in the urine.
1. What is the importance of creatinine?

2. why isn't creatinine reabsorbed?
1. No physiologic usefulness, but it is used to normalize clearance of urinary solutes (an accurate measure of time during which urine was formed)

Note: creatine phosphate is a high energy phosphorylated moiety.

2. no transporters
what does a high "absolute" value of creatinine blood level suggest?
kidney filtration problems
What is cystinuria?
A urinary tract disease⬦ an autosomal recessive disorder that results in the rise in cysteine (arginine, lysine and ornithine) in the urine due to a defective transporter⬦ causes cystine stones
What are 3 thing you can do to treat for cystinuria?
a) hydration, b) increase urine alkalinity, c) thiol compounds which forms more soluble mixed disulfides.
Name the 7 metabolites that amino acids are metabolized into.
pyrvate, acetyl CoA, ∂-ketoglutamate, succinyl CoA, Fumarate, oxaloacetate, acetoacetate
1. Which amino acids can be oxidized to produce energy or energy storage molecules?

2. Where do ketogenic amino acids funnel through?

3. where do glucogenic amino acids funnel through?

4. which 2 amino acids are strictl
1. all 20 AA

2. Acetyl CoA, (--> acetoacetyl CoA-->) HMG-CoA --> Acetoacetyl CoA

3. Pyruvate to form glucose
Give the pathway of pyruvate to glucogenesis.

a) intermediates
b) enzymes
a) Pyruvate -(1)-> oxaloacetate -(2)-> PEP --> glucogenesis

b) 1= pyruvate carboxylase, 2= PEPCK

Which amino acids funnel into ∂-KG? (hint: PHAG)
proline, histadine, arginine, glutamine
What do proline, histadine, arginine, and glutamine funnel into before entering into ∂-KG?
Which amino acids funnel into succinyl CoA? [hint: I (want my) MTV... and "T" rhymes w/3]
Isoleucine, methionine, threonine, valine
Which intemediate must (Isoleucine, methionine, threonine, valine) funnel through before succinyl CoA?
Propionyl CoA --> Methylmalonyl CoA --> Succinyl CoA
Which amino acids funnel into fumarte? (hint: When you are "tired" you could use more ATP)
Aspartate, tyrosine and phenylalanine

(explanation of hint: tired sounds like tyrosine)
Which amino acids funnel into oxaloacetate? (hint: AA)
aspartate and asparagine
Which amino acids funnel into acetyl CoA? (hint: LITT)
Lysine, Isoleusine, threonine, tryptophan
What is the pathway for acetyl CoA to reach acetoacetate?
Acetyl CoA --> Acetoacetyl CoA --> HMG CoA --> Acetoacetate (ketone Bodies)
What is significant about acetoacetate?
Ketone bodies
Besides (Lysine, Isoleusine, threonine, tryptophan) what 3 other amino acids can funnel into the acetoacetate (ketone body)? (Think ringed AA for two of them)
Leucine and phenylalanine, tryosine.
(a) Which two amino acids are considered ketogenic amino acids?

(b) What are the other amino acids considered?

(Hint:Lucy Lu KiLLed biLL w/ Keto)
(a) leucine and lysine⬦

b) the others are considered glucogenic amino acids.

(Eplanatin of hint: LL = keto)
What is the pathway for pyruvate or oxaloacetate to enter the glucogenic pathway?
Pyruvate (with pyrvuate carboxylase) --> oxaloacetae (with PEPCK) --> PEP --> glucogenesis

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