Chapter 14 Amino Acid Biosynthesis

Question 1

What is the importance of nitrogen?

Answer 1

• An essential element found in amino acids, nitrogenous bases, & many other molecules
• It is assimilated by conversion into a amide group of glutamine, which can be used for other carbon-containing compounds like amino acids
• They are one of the four atoms involved in biological systems (Carbon, Hydrogen, Oxygen & Nitrogen)

Question 2

What are the classification of amino acids?

Answer 2

1) Essential (“TTV PILLM”, they are the amino acids that our body cannot synthesize and we must obtain them from our diet, TTV PILLM is a mnemonic to remember then Tryptophan, Threonine, Valine, Phenylalanine, Isoleucine, Leucine, Lysine & Methionine)

2) Nonessential (contains the other amino acids which the body can synthesize on its own)

• FYI: histidine is semi-essential amino acid where in some situation like rapid growth or infancy it is considered to be essential but other than that the body can produce its own along with arginine, cysteine, & tyrosine which are also considered essential during childhood

Question 3

What is meant by complete protein?

Answer 3

Usually animal protein which contains all of the essential amino acids

Question 4

Can we store amino acids?

Answer 4

No, and that’s why we have an “amino acid pool” usually around 300 grams which are maintained by the process of amino acid biosynthesis and amino acid degradation

Question 5

What are the functions served by the amino acids?

Answer 5

1) Synthesis of proteins

2) Source of nitrogen atoms which is required by various synthetic reaction pathway

3) The carbon-skeleton (non-nitrogen components of amino acid) are a source of energy and a precursor of various reaction pathway

Question 6

What can negative nitrogen balance cause?

Answer 6

When an individual cannot replace lost nitrogen from dietary sources he is said to have a negative nitrogen balance which can lead to kwashiorkor malnutrition (growth failure, liver enlargement, decrease in mass, function of the heart and kidney)

Question 7

How is nitrogen transported into the cells?

Answer 7

1) mainly Na+ dependent pump

2) y-glutamyl cycle

Question 8

What are the reactions of amino acids?

Answer 8

1) Transamination reactions (“requires pyridoxal-phosphate “derivative of vitamin B6”” dominates amino acid metabolism transferring a-amino group from an a-amino acid to an a-keto acid, catalyzed by aminotransferases or transaminases “usually from the amide nitrogen of glutamine or asparagine), where the enzyme transaminases work, this reaction can synthesize amino acids from glycolysis intermediates which cannot be aminated directly (unlike glutamate “which we have the enzyme that can aminate it directly), like the synthesis of aspartate from oxaloacetate where the enzyme aspartate transaminase (AST) take an amine group from glutamate and transfers it to oxaloacetate to produce aspartate, this reaction occurs mostly in the liver

2) direct reductive amination (direct incorporation of ammonium ions) there are two ways:

A) direct amination of a-ketoglutarate to glutamate (catalyzed by glutamate dehydrogenase)
B) formation of amides by the direct amination of aspartate to asparagine and glutamate to glutamine (catalyzed by glutamine synthytase)

Question 9

What is meant by an a-keto acid?

Answer 9

It is when we remove the amine group in the amino acids (amino acid - amine group)

Question 10

What is some of the common name of a-keto acids?

Answer 10

1) pyruvate (a-keto acid of alanine “ALT”)

2) oxaloacetate (a-keto acid of aspartate “AST”)

3) a-keto glutarate (a-keto acid of glutamate “we have the enzyme that can cooperate free ammonia to convert a-ketoglutarate into glutamate” without a transamination reaction)

Question 11

Which medical report uses AST & ALT as a marker?

Answer 11

Liver function reports

Question 12

How are the aminotransferases enzymes specific?

Answer 12

They are found in the cytoplasm and the mitochondria having two specifities:

1) the type of a-amino acid that donates the a-amino group

2) the a-keto acid that accepts the a-amino group

Question 13

Which coenzyme is required by the aminotransferases?

Answer 13

Pyridoxal-5’-phosphate (PLP) derived from pyridoxine (vitamin B6), it also plays an important role in decarboxylations, racemization and other side chain reactions

Question 14

What are some examples of importance amino acid/a-keto acid pairs?

Answer 14

1) glutamate/a-ketoglutarate: as a-ketoglutarate is an intermediate in the citric acid cycle, glutamate can be synthesized directly

2) OAA/Aspartate pair: as it is involved in the disposal of nitrogen in the urea cycle

3) pyruvate/alanine pair: it has an important function in the glucose-alanine cycle

Question 15

How can we transfer the ammonium (NH4+) ions to other molecules?

Answer 15

1) Direct amination of a-keto acid

2) Adding the ammonia into the R group of the amino acid (1) converting aspartate to asparagine & 2)converting glutamate to glutamine only)

Question 16

What is the main amino acid used to transport free ammonia?

Answer 16

Glutamine, where free ammonia gets cooperated into glutamate forming glutamine and then it is released into the blood to the liver where it is deaminated and the ammonia is secreted in the urea

Question 17

What is hyperammonimia?

Answer 17

Common in patients with liver diseases, it is the Increase of ammonia levels in the blood which is very dangerous, one of the consequences is that our body will start producing excess glutamine & glutamate which will deplete us from a-ketoglutarate causing a dysfunction in the TCA cycle (no more enough energy)

Question 18

How many families are the amino acids classified into, and what are there precursors and examples of there products?

Answer 18

1) serine family (Glycerate-3-phosphate produces serine)

2) glutamate family (a-ketoglutarate - produces glutamate which produces glutamine)

3) aromatic family (phosphoenolpyruvate + erythrose-4-phosphate)

4) aspartate family (oxaloacetate produces aspartate)

5) pyruvate family (pyruvate produces alanine)

6) histidine family (ribose-5-phosphate produces histidine)

• FYI each of these families are synthesized from TCA cycle or Glycolysis intermediates

Question 19

What catalyzes the conversion of glutamate into glutamine?

Answer 19

Glutamine synthetase (requires ATP) occurs in the liver, brain, kidney, muscles & intestine (glutamine is involved in protein synthesis and ammonia transport, and the kidneys and small intestine uses it as a energy source)

Question 20

Overview of the aspartate family

Answer 20

• Derived from oxaloacetate in a transamination reaction (AST)
• it influences the flow of carbon and nitrogen within the cell, Asparatate is also a source of nitrogen in the urea formation & the citric acid cycle OAA and an important precursor for nucleotide synthesis
• Aspargine, threonine, lysine & methionine are its other members
• Threonine contributes to the synthesis of isoleucine

Question 21

Overview of the pyruvate family

Answer 21

• Consists of alanine, valine, leucine & isoleucine
• Alanine is synthesized from pyruvate by the alanine aminotransferases (ALT) its cycle contributes to the maintenance of the blood glucose

Question 22

Overview of the aromatic family

Answer 22

• Consists of phenylalanine, tyrosine, & tryptophan
• Tryptophan is a precursors of (NAD+, NADP+ & serotonin)
• Phenylalanine or tyrosine are precursors of (dopamine, epinephrine & norepinephrine)

Question 23

Overview of the glutamate family

Answer 23

• Contains proline, arginine, & glutamine
• a-Ketoglutarate gets converted into glutamate by reductive amination and transamination

Question 24

What is meant by the carbon skeleton?

Answer 24

The non-nitrogen components of amino acids

Question 25

Which amino acid represents the major transport from of amino nitrogen?

Answer 25

The branched-chain amino acids (BCAA):

1) valine
2) leucine
3) isoleucine