Nitrogen Metabolism

Question 1

What are the pairs to know?

Answer 1

Glutamate and alpha ketoglutarate
Alanine and pyruvate
Aspartate and oxaloacetate

Question 2

How is ammonium transported to the liver from muscle cells?

Answer 2

Through the glutamate-alanine cycle

Question 3

What is the rate-limiting step of urea synthesis?

Answer 3

Carbamoyl Phosphate Synthetase I (converted of bicarbonate and ammonium to carbamoyl phosphate)

Question 4

Regulators of CPS I

Answer 4

N-acetylglutamate is an allosteric activator

it is required for CPS I activity, therefore it is an obligate activator

Question 5

How is N-acetylglutamate formed?

Answer 5

from Acetyl CoA and glutamate by N-acetylglutamate synthase, which is a reaction stimulated by Arginine

Question 6

Function of Arginase

Answer 6

Cleaves arginine, using water, to create urea and ornithine (to be recycled)

Question 7

What link the urea cycle and CAC?

Answer 7

Aspartate and Fumarate

Question 8

Where does the urea cycle occur?

Answer 8

Almost exclusively in the liver, in both the cytosol and mitochondria

Question 9

What are the precursors of urea?

Answer 9

NH4+, CO2, and aspartate (which donates an amino group)

Question 10

What are poryphyrins?

Answer 10

Cyclic compounds that bind primarily Fe2+ or Fe3+; the most common is heme which binds a single Fe2+ and it is a prosthetic group for hemoglobin, cytochromes, and some enzymes; all carbon and nitrogen atoms in the structure are derived from glycine and succinyl CoA

Question 11

What is acute intermittent porphyria?

Answer 11

a heterozygous genetic disease which includes abdominal pain, neuropsychiatric problems, motor weakness; occurs because of starvation or insufficient carbohydrate

Question 12

What is porphyria cutanea tarda?

Answer 12

disease which causes red urine, strong teeth fluorescence under UV light, skin sensitivity towards light, anemia due to insufficient heme

Question 13

Name the catelcholamines and what they’re synthesized from

Answer 13

dopamine, norepinephrine, and epinephrine, all synthesized from tyrosine; they all occur in the same pathway, so to synthesize a singular product you will need to inhibit the succeeding steps

Question 14

What is histamine?

Answer 14

A molecule that mediates the allergic response and is a strong vasodilator; it is synthesized by decarboxylating histidine; also used in gastric acid secretion (allows cAMP to move H pump to the sruface

Question 15

What is seratonin?

Answer 15

A molecule that mediates pain perception, sleep, temperature, blood pressure, appetite, sense of well-being (converted to melatonin in the brain); melatonin maintains circadian rhythm; it is found in abudnance in intestinal mucosa, and a little in CNS where it is a neurotransmitter; seratonin is synthesized from tryptophan

Question 16

What is creatine?

Answer 16

A high-energy compound found in muscle; it’s its phosphorylated form (phosphocreatine or creatine phosphate) can be used to replenish ATP levels for a few minutes; it is synthesized from glycine, guanidino group of arginine, and methionine

Question 17

What are the coenzymes of Glu DH?

Answer 17

NAD or NADP

Question 18

How do plants and microoranisms assimilate nitrogen?

Answer 18

They combined ammonium to a-KG to make glutamate via glutamate dehydrogenase (and NADPH+H); then, ammonium and glutamate are combined to make glutamine via glutamine synthetase; glutamate synthase replenishes glutamate by transferring an ammonia from glutamine to a-KG as well as reducing a-KG

Question 19

What do we need to know about glutamine synthetase??

Answer 19

1. It is ubiquitous in nature–found in every organism
2. It is the primary regulation point in nitrogen metabolism; glutamine is the source of amino in many biosynthetic reactions
3. Regulated by 8 allosteric effectors; combined effect of inhibitors AMP, tryptophan, carbamoyl phosphate, CTP, histidine, and glucosamine 6-phosphate are more than additive (synergistic); Gln Synthetase is also regulated by the covalent modification of adenylylation (addition of an AMP)–this inhibits the enzyme and makes it more sensitive to inhibitors; glycine and alanine can also act upon Gln Synthetase to inhibit it

Question 20

Where does adenylation occur on Gln Synthetase?

Answer 20

Tyrosine residue; ATP is added, and a pyrophosphate is removed

Question 21

What is the structure of Gln Synthetase?

Answer 21

12 identical subunits, each with a tyrosine for possible adneylylation; the more sites adenylylated means the more sensitive the enzyme is to inhibition

Question 22

What are the important reactions in amino acid and nucleotide synthesis?

Answer 22

1. Transamination reaction via aminotransferase (with coenzyme pyridoxal phosphate, or vitamin b6);
2. 1-carbon transfer reactions–enzyme cofactors S-adenosyl methionine (SAM) or tetrahydrofolate aka folic acid vitamin B9);
3. transfer of an amino or amide group from glutamine via enzyme glutamine amidotransferase

Question 23

What does SAM transfer?

Answer 23

One methyl group from methionine

Question 24

What pathways are all amino acids synthesized from?

Answer 24

Glycolytic, pentose phosphate pathway, and TCA cycle

Question 25

Remember that amino acids are not always present in equal amounts; they must be synthesized in the correct amounts and the right time for protein synthesis

Answer 25

ye

Question 26

What are the non-essential amino acids we need to know?

Answer 26

alanine, aspartate, and asparagine

Question 27

What are the essential amino acids we need to know?

Answer 27

isoleucine, valine, leucine

Question 28

What are the types of feedback inhibition?

Answer 28

Product inhibition; sequential inhibition; concerted; and enzyme multiplicity