9-12 Nitrogen Incorporation, Amino Acids, Urea Cycle Douglas RR

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1

Lecture 41

Objectives

2

Some amino acids are ______ and derived from exogenous sources.

essential

3

Amino acid catabolism will generate _______, a nontoxic carrier of nitrogen atoms.

urea

4

Urea synthesis occurs in the ______.

liver

5

The amino acids _______ and ______ will carry amino acid nitrogen from peripheral tissues to the liver.

alanine and glutamate

6

_______ recovered from deamination of alanine in the liver is a source of glucose via gluconeogenesis.

pyruvate

7

The key enzymes involved in nitrogen disposal are a class of ________.

transaminases.

8

The transaminases of interest here are ________ and _______.

glutamate dehydrogenase and glutaminase

9

Humans make 11 amino acids de novo. These are considered ________.

non-essential

10

Humans take 10 amino acids from their diet. These are considered _______.

essential

11

The Urea Cycle consists of four steps and incorporates a nitrogen from ______ and one from ______ into urea.

ammonia and aspartate

12

Disorders of the Urea Cycle lead to ________, a condition that is toxic to the nervous system, to health, and to development.

hyperammonemia

13

Lecture 41

Slide Notes

14

Amino acids are this type of compound.

alpha amino carboxilic acids

15

All non-essential amino acids are derived from their corresponding _________.

alpha-keto acids; this makes most of the amino acids; via transamination or direct amination in activation

16

Naturally occuring amino acids are in the ______ configuration.

L-configuration

17

Most amino acids, when they are metabolized, can feed into carbohydrate metabolism. These are called _______ amino acids.

glucogenic

18

There are only two "ketogenic" amino acids that are precursors to fatty acyls and keto acids. These don't lead to glucose. They are _____ and ______.

lysine and leucine

19

List the ten essential amino acids.

Phenylalanine, Valine, Threonine, Tryptophan, Isoleucine, Methionine, Histidine, Arginine, Leucine, Lysine

20

Which of the amino acids is listed both as an essential and non-essential amino acid?

arginine

21

Modifications to form non-essential amino acids include transfer of ______ and _____.

amino groups and sulfur

22

Atmospheric nitrogen is converted to _____ and ______ by nitrogen fixing bacteria, which are fixed to amino acids and proteins by plants that become included in our diet.

nitrate and ammonia

23

Muscle _____ is a source of amino acids during malnutrition, starvation, and essential amino acid deficiency.

protein

24

Nitrogen is removed from amino acids by three different enzymes to yield carbon backbones used for energy. These reactions are classified _______, _______, and _______.

Transamination, Oxidative Deamination, and removal of water by Dehydratase

25

What is the nitrogen balance of a child in rapid growth or in a recovering trauma victim?

Positive nitrogen balance; consumption > excretion

26

What is the nitrogen balance of a person experiencing protein malnutrition, fasting, starvation, or deficient in an essential amino acid?

Negative Nitrogen Balance; consumption < excretion

27

This test is done to assess kidney function and measures the amount of nitrogen in blood that is associated with urea.

Blood Urea Nitrogen (BUN)

28

The source of normal nitrogen excretion is excess nitrogen from _______.

protein

29

Supplementation of these three amino acids is required in premature infants or in those with liver disease.

Cystein, Tyrosine, and Arginine

30

_______ is the toxic nitrogen containing substance that is produced first and later converted to urea.

Ammonia (NH3/NH4+)

31

80% of nitrogen is excreted as urea. This amount to ____ grams per day.

20 to 30 grams per day

32

The major process of moving nitrogen among amino acids is called _________.

transamination

33

________ is the major participant in transaminations. The gateway between amino groups and free ammonia.

glutamate

34

All amino acids except ______ and ______ undergo transaminations.

lysine and threonine

35

The major cofactor for amino transfers by transaminase (aminotransferase) is ______.

pyridoxyl phosphate

36

In the liver, free ammonia is incorporated into glutamate by ________.

glutamate dehydrogenase

37

_______ is involved in the amination of alpha-ketoglutarate; whereas, ______ is used in oxidative deamination that frees ammonia and alpha-ketoglutarate.

NADPH amination; NAD+ deamination

38

Pyridoxal phosphate is an enzyme bound form of vitamin _____.

vitamin B6

39

The NH2 of amino acids _____ or _____ displace the linkage between pyridoxal phosphate and a lysine residue of the aminotransferase.

glutamate or aspartate

40

As a treatment for tuberculosis, the drug _______ functions to decrease available vitamin B6 by assoicating it with pyridoxal.

isoniazid

41

High levels of aminotransferases in serum indicate _____ damage.

liver

42

The three key intermediary metabolites of transamination are _____, _____, and _____.

pyruvate, alpha-ketoglutarate, and oxaloacetate

43

________ is the transfer of an amino group to a keto acid.

transamination

44

________ is the replacement of an amino group with oxygen with the resulting release of free ammonia.

oxidative deamination

45

_________ is the removal of water to form an imine. If water is added back a keto acid and ammonia is formed.

dehydratase

46

Both oxidative deamination and dehydratase reactions require oxidation by invovling a ________ as a cofactor.

Flavin mononucleotide (FMN)

47

Dehydratase reactions remove water and work exclusively with hydroxyamino acids ________ and ________.

serine and threonine

48

Intestinal ______ are the major source of ammonia.

bacteria

49

________ is involved in a reversible reaction and can catalyze release or incorporation of ammonium to or from glutamate.

Glutamate Dehydrogenase (GDH); allows uptake of ammonia in muscle and release in liver and kidneys

50

The enzymes _______, ______, and _______ are all involved in fixing nitrogen into biomolecules.

GDH, glutamine synthetase, and carbamoyl phosphate synthetase

51

The amino acids ______ and _____ feed nitrogen into urea and link amino acid catabolism and energy metabolism.

glutamine and asparargine; cleaved by glutaminase and asparaginase to glutamate and aspartate

52

During metabolic interconversions of amino acids, the amino group of ______ is transferred to alpha keto glutarate to yield _______ and _______.

alanine amino group transferred to alpha keto glutarate to yield pyruvate and glutamate

53

Transamination involving essential amino acids is unidirectional because the body cannot synthesize the equivalent ________.

alpha keto acid; alpha keto acid analogs can be provided in the diet in liver failure and resulting hyperammonemia

54

All transamination reactions involve ______ and ______.

glutamate and alpha ketoglutarate

55

______ and ______ from muscle make up 50% of muscle released amino acids.

Alanine and Glutamine; alanine recycled from the muscles to liver yields ammonia for urea and pyruvate for glucose.

56

Glutamine is synthesized via _______ to fix nitrogen in muscle for transport to the liver, where it yields urea in tranformations to glutamate and alpha-keto-glutarate.

glutamine synthetase

57

Nitrogen atoms in urea come from _______ and _______.

ammonia and aspartate

58

_______ is an enzyme that fixes ammonia release from glutamine and other amino acids.

Carbamoyl phosphate synthetase (CPS I); located in mitochondria, not part of urea cycle

59

Mitochondrial CPS I requires _______ as a cofactor for activity.

N-acetylglutamate

60

CPSII is used in the cytosol for ______ synthesis.

pyrimidine

61

________ is an enzyme of the urea cycle that catalyzes formation of citrulline from ornithine and carbamoyl phosphate. Deficiency leads to high blood concentrations of ammonia and orotic acid.

ornithine transcarbamoylase; deficiency symptoms result from shunting of carbamoyl phosphate to pyrimidine synthesis

62

________ is an enzyme of the urea cycle that catalyzes formation of argininosuccinate from citrulline and aspartate. Its deficiency leads to high blood concentrations of ammonia and citrulline.

argininosuccinate synthetase

63

_______ is an enzyme of the urea cycle that catalyzes cleavage of argininosuccinate to arginine and fumarate. Its deficiency leads to high blood concentrations of ammonia and citrulline.

argininosuccinase

64

_______ is an enzyme involved in the cleavage of arginine to ornithine and urea. Its deficiency leads to moderately increased blood ammonia and high blood concentrations of arginine.

arginase

65

The indicator that CPS I is limited due to defects in mitochondrial ornathine transcarbamoylase is elevated levels of ________ in blood and urine.

orotic acid

66

The urea cycle is up-regulated in the presence of high dietary ______ and during _______.

high dietary protein and during starvation

67

The urea cycle is down-regulated in the presence of high dietary ______.

carbohydrate

68

The short term regulation of the urea cycle includes activation of CPS I, which is the enzyme just prior to the urea cycle. This activation is accomplished by its allosteric activator _________.

N-acetylglutamate; this is stimulated by high levels of arginine

69

__________ results in diffusion of ammonia across the the blood/brain barrier and resulting cerebral edema.

ammonia toxicity

70

Ammonia toxicity is treated with _______ or _______, which condense with glycine and glutamine, which are then excreted.

benzoate or phenylacetate; nitrogen intake is also controlled along with avoidance of endogenous protein breakdown. The patient is fed Alpha keto-acids

71

Deficiency of _______ or ______ results in hyperammonemia, encephalopathy, and respiratory alkalosis. It is fatal in infants. It is autosomal recessive.

CPS I or N-acetylglutamate

72

Deficiency of ________ is the most common urea cycle defect. It leads to MR and death from ammonia accumulation. It mostly affects males because it is X-linked.

Ornithine transcarbamoylase

73

Deficiency of ______ leads to accumulation of citrulline in blood and urine. It is an autosomal recessive disease that causes severe hyperammonemia.

argininsuccinate synthetase; treatment involves low protein and arginine supplements

74

Treatments for urea cycle enzyme deficiencies include...

1. limit protein intake
2. remove excessive NH3 (benzoate or phenylacetate)
3. replace missing intermediates
4. liver transplant

75

Free ammonia is incorporated into ________ by its synthetase. This is the most abundant circulating amino acid. ATP is required to fix nitrogen to this amino acid (thus the synthetase).

glutamine

76

Ammonia, glutamate, and urea are excreted in the ______.

kidney

77

Two-thirds of _______ produced in the urea cycle is used for glucose or ATP formation.

fumarate

78

The primary nitrogenous excretion product in human urine is _______.

urea

79

A compound common to the urea cycle and the tricarboxylica cid cycle is _______.

fumarate

80

Which of the following amino acids has an important role in the transport of amino groups from peripheral tissues to the liver?
A. Serine
B. Methionine
C. Glutamine
D. Arginine
E. Pyruvate

C. Glutamine

81

Which of the following Enzymes will can directly fix NH4 into biomolecules?
A. Glutamine synthetase
B. Arginase
C. Glutaminase
D. Argininosuccinate synthetase
E. N-acetyl glutamate synthetase

Glutamine synthetase