Harper's Biochemistry Chapter 27 - Biosynthesis of the Nutritionally Nonessential Amino Acids

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Questions and Answers

Which amino acid is primarily synthesized from homocysteine and is not considered nutritionally essential?

L-Serine

L-Tyrosine

L-Cysteine (correct)

L-Proline

What is the main precursor for the synthesis of glycine in mammals?

Serine (correct)

Choline

Alanine

Glutamate

Why is dietary tyrosine not able to replace phenylalanine in the diet?

Phenylalanine is nonessential and can be synthesized from other amino acids.

Tyrosine has no dietary significance.

The conversion of phenylalanine to tyrosine is irreversible. (correct)

Tyrosine can be converted to phenylalanine.

Which pathway accurately describes the initial step in proline biosynthesis?

Glutamate's γ-carboxy group is converted to an anhydride. Signup and view all the answers

Which reaction results in the formation of alanine through transamination?

Pyruvate to Alanine Signup and view all the answers

What additional routes exist for glycine formation in mammals?

From serine and choline Signup and view all the answers

In collagen biosynthesis, hydroxyproline and hydroxylysine are important. What is a key characteristic of these amino acids?

They are formed post-translationally. Signup and view all the answers

Which enzyme catalyzes the synthesis of asparagine from aspartate?

Asparagine synthetase Signup and view all the answers

What role does tetrahydrobiopterin play in the metabolism of phenylalanine?

It provides reducing power derived from NADPH. Signup and view all the answers

Which metabolic pathway is involved in producing glycine aside from transamination?

Serine biosynthesis Signup and view all the answers

The reaction dependent on Mg-ATP is characteristic of which amino acid synthesizing enzyme?

Asparagine synthetase Signup and view all the answers

Which of these amino acids is considered a nonessential amino acid due to its synthesis in the body?

Aspartate Signup and view all the answers

What is a significant feature of the transamination reaction between pyruvate and glutamate?

It results in alpha-ketoglutarate. Signup and view all the answers

What is the primary role of asparagine in amino acid metabolism?

To serve as a precursor for glutamate synthesis Signup and view all the answers

What is the intermediate formed during the conversion of glutamate to glutamine?

γ-glutamyl phosphate Signup and view all the answers

Which enzyme is responsible for the conversion of 3-phosphoglycerate to serine?

3-phosphoglycerate dehydrogenase Signup and view all the answers

Which amino acid conversion process is characterized by the use of both ammonium ion and glutamine as nitrogen sources?

Aspartate to asparagine Signup and view all the answers

What is the consequence of the coupled hydrolysis of PPi to Pi in the asparagine synthesis reaction?

It strongly favors the synthesis of asparagine Signup and view all the answers

Which compound provides the nitrogen in the enzyme-catalyzed reaction converting aspartate to asparagine?

Glutamine Signup and view all the answers

Which factor directly influences the cytotoxic ammonium ion concentration during the synthesis of glutamate?

The reductive amidation of α-ketoglutarate Signup and view all the answers

What type of reaction is the conversion of glutamate to glutamine primarily categorized as?

Amidation Signup and view all the answers

In what metabolic pathway is the 3-phosphoglycerate dehydrogenase involved?

Glycolysis Signup and view all the answers

What is the fate of the γ-amino group of the tetrahedral intermediate during the glutamine synthesis process?

It is released as a proton Signup and view all the answers

Which statement about the synthesis of tyrosine is true?

Tyrosine is classified as nutritionally semiessential. Signup and view all the answers

What role do glutamate dehydrogenase and glutamine synthetase play in amino acid biosynthesis?

They help incorporate the ammonium ion into amino acids. Signup and view all the answers

In individuals suffering from Marasmus, which amino acid synthesis deficiency could contribute to their condition?

Inadequate synthesis of tyrosine. Signup and view all the answers

Which amino acid is derived from the posttranslational modifications seen in collagen biosynthesis?

Proline Signup and view all the answers

What distinguishes nonessential amino acids from essential amino acids?

Nonessential amino acids can be synthesized by the body, though not always efficiently. Signup and view all the answers

Which pathway is involved in the biosynthesis of amino acids that include potentially toxic ammonium ions?

Combined enzymatic actions of multiple amino acid biosynthesis pathways. Signup and view all the answers

What is a significant consequence of Menkes Syndrome on amino acid metabolism?

Impaired copper transport affecting collagen formation. Signup and view all the answers

Which amino acid is not derived from the amino acids typically classified as nutritionally semiessential?

Cysteine Signup and view all the answers

Which statement is true regarding posttranslational modifications in amino acids?

They may lead to the formation of unique structural features in proteins. Signup and view all the answers

In the context of amino acid synthesis, what is a key reason why young children might experience growth issues?

Insufficient production of nutritionally semiessential amino acids. Signup and view all the answers

Which amino acids are classified as nutritionally essential according to their roles in tissue aminotransferase reactions?

Valine, Leucine, Isoleucine Signup and view all the answers

What is the enzymatic activity associated with the conversion of phenylalanine to tyrosine?

Hydroxylation that involves a co-factor deficiency Signup and view all the answers

Which of the following elements is NOT necessary for the hydroxylation of proline and lysine during collagen synthesis?

Calcium Signup and view all the answers

In Menkes Syndrome, which bioelement is particularly deficient, impacting copper utilization?

Copper Signup and view all the answers

Which term describes amino acids that must be obtained from the diet due to the body's inability to synthesize them?

Nutritionally essential amino acids Signup and view all the answers

What is the outcome when there is a deficiency of vitamin C in collagen biosynthesis?

Impaired stability of collagen and scurvy development Signup and view all the answers

Which amino acid is derived from the decarboxylation of α-ketoglutarate during metabolism?

Proline Signup and view all the answers

In the context of metabolic pathways, what is the primary role of aminotransferases regarding essential amino acids?

Interconverting amino acids and their corresponding α-keto acids Signup and view all the answers

Which of the following conditions is NOT associated with a deficiency in protein energy intake?

Diabetes mellitus Signup and view all the answers

Which of the following vitamins is essential for the reduction of dihydrobiopterin during amino acid metabolism?

Vitamin C Signup and view all the answers

What condition is characterized by a dietary deficiency of vitamin C leading to bleeding gums and poor wound healing?

Scurvy Signup and view all the answers

Which disorder results from a lack of copper, affecting collagen biosynthesis and leading to symptoms like kinky hair and growth retardation?

Menkes syndrome Signup and view all the answers

Which disorder is caused by an impaired ability of connective tissue to form peptidy 4-hydroxyproline and 5-hydroxylysine due to nutritional deficiencies?

Ehlers-Danlos syndrome Signup and view all the answers

What condition might develop in a child weaned onto a starchy diet that lacks sufficient protein and calories?

Kwashiorkor Signup and view all the answers

Which amino acid deficiencies can result in unstable collagen structure and lead to connective tissue disorders?

Proline and hydroxyproline Signup and view all the answers

Which genetic disorder is characterized by fragile bones and a deficiency in collagen synthesis?

Osteogenesis imperfecta Signup and view all the answers

What is a potential outcome of both caloric intake and specific amino acid deficiencies in patients with short bowel syndrome?

Marasmus Signup and view all the answers

What is the condition that results from a child being weaned onto a starchy diet lacking in protein?

Kwashiorkor Signup and view all the answers

Which amino acid requires the most enzymatic steps for its synthesis according to the provided data?

Arginine Signup and view all the answers

What type of dietary deficiency is predominantly associated with both kwashiorkor and marasmus?

Protein deficiency Signup and view all the answers

How many total enzymes are required for the synthesis of nutritionally nonessential amino acids as listed?

17 Signup and view all the answers

Which of the following amino acids is NOT classified as nutritionally essential?

Glycine Signup and view all the answers

In the context of amino acid metabolism, what is a significant characteristic of marasmus?

Overall caloric deficiency Signup and view all the answers

Which nutritionally essential amino acid requires both shared and non-shared enzymatic steps for its synthesis?

Isoleucine Signup and view all the answers

Which of the following disorders is linked to specific amino acid metabolism due to deficiency?

Kwashiorkor Signup and view all the answers

What dietary component is specifically mentioned as poor sources leading to amino acid deficiency in certain regions?

Grains Signup and view all the answers

Which specific elongation factor is involved in recognizing selenocysteyl-tRNASec for incorporation into proteins?

Selenocysteine insertion sequence binding protein Signup and view all the answers

What role do both procollagen-proline 4-hydroxylase and procollagen-lysine 5-hydroxylase play in collagen biosynthesis?

They catalyze mixed-function oxidase reactions that incorporate molecular oxygen. Signup and view all the answers

Which compound serves as a substrate for the production of cysteine in the body?

Homocysteine Signup and view all the answers

Which enzyme is crucial for the redox reactions involving selenocysteine in the human body?

Thioredoxin reductase Signup and view all the answers

What is the likely impact of a deficiency in vitamin C on collagen synthesis?

It would lead to improper cross-linking of collagen fibers. Signup and view all the answers

What is the primary reaction that converts glutamate to proline in biosynthesis?

Reduction following cyclization of glutamate γ-semialdehyde Signup and view all the answers

Which enzyme is responsible for the hydrolytic removal of the phosphoryl group from phosphoserine?

Phosphoserine hydrolase Signup and view all the answers

What is a significant characteristic of the reaction converting phenylalanine to tyrosine?

It requires tetrahydrobiopterin as a cofactor. Signup and view all the answers

What is the ultimate precursor for cysteine synthesis in terms of nutritional importance?

Methionine Signup and view all the answers

Which of the following statements about hydroxylated amino acids is true?

They do not have specific tRNAs for incorporation during translation. Signup and view all the answers

In the metabolic pathway of phenylalanine to tyrosine, what is the fate of the oxygen atoms involved in the reaction?

Both atoms are reduced to form water. Signup and view all the answers

What distinguishes the transformation of 3-phosphoglycerate to serine in amino acid metabolism?

It requires the action of a dehydrogenase enzyme. Signup and view all the answers

Which amino acid is derived from the hydrolysis of cystathionine?

Cysteine Signup and view all the answers

In collagen biosynthesis, what role do hydroxyproline and hydroxylysine play?

They enhance protein stability through cross-linking. Signup and view all the answers

What is the significance of the reaction catalyzed by cystathionine β-synthase in amino acid metabolism?

It links homocysteine and serine to form cystathionine. Signup and view all the answers

What is the key product formed from the amidation of glutamate catalyzed by glutamine synthetase?

Glutamine Signup and view all the answers

Which intermediate is formed during the conversion of glutamate to glutamine?

γ-Glutamyl phosphate Signup and view all the answers

What role does the hydrolysis of PPi to Pi play in the synthesis of asparagine?

It strongly favors the reaction. Signup and view all the answers

Which enzyme catalyzes the reaction that produces serine from 3-phosphoglycerate?

3-Phosphoglycerate dehydrogenase Signup and view all the answers

Which amino acid synthesis utilizes both ammonium ion and glutamine as nitrogen sources?

Asparagine Signup and view all the answers

During the synthesis of glutamate, what is the primary effect of reducing ammonium ion concentration?

It promotes more glutamate synthesis. Signup and view all the answers

What is the function of NH4+ in bacterial asparagine synthetases?

It provides a nitrogen source. Signup and view all the answers

Which reaction type does the conversion of aspartate to asparagine primarily represent?

Amidation Signup and view all the answers

In terms of enzymatic activity, what initiates the reaction for the formation of γ-glutamyl phosphate during glutamine synthesis?

Binding of glutamate Signup and view all the answers

What is the final product released after the dephosphorylation step in the formation of serine from 3-phosphoglycerate?

Serine Signup and view all the answers

Match the following terms related to amino acids with their correct definitions:

Essential amino acids = Must be obtained from the diet Nutritionally nonessential amino acids = Can be synthesized by the body Transaminases = Enzymes that facilitate amino acid metabolism Scurvy = Disorder caused by vitamin C deficiency Signup and view all the answers

Match the following amino acids with their associated biosynthesis precursors:

Aspartate = Oxaloacetate Glutamate = α-Ketoglutarate Serine = 3-Phosphoglycerate Glycine = Threonine Signup and view all the answers

Match the vitamin with its role in amino acid metabolism:

Vitamin C = Prevents scurvy by aiding collagen synthesis Folate = Involved in amino acid metabolism Vitamin B6 = Coenzyme in transamination reactions Vitamin E = Antioxidant that protects cellular membranes Signup and view all the answers

Match the following amino acids with their nutritional classification:

Phenylalanine = Essential Glycine = Nutritionally nonessential Valine = Essential Glutamine = Nutritionally nonessential Signup and view all the answers

Match the following amino acids with their role in collagen biosynthesis:

Hydroxyproline = Stabilizes collagen structure Hydroxylysine = Involved in cross-linking of collagen Proline = Precursor for hydroxyproline Lysine = Precursor for hydroxylysine Signup and view all the answers

Match the following terms with their correct definitions:

Nutritionally essential amino acids = Amino acids that must be present in the human diet Nutritionally nonessential amino acids = Amino acids that do not need to be present in the diet Biosynthesis = The process of producing complex molecules from simpler ones ATP = A molecule that provides energy for biological processes Signup and view all the answers

Match the following classes of amino acids with their numbers:

Essential amino acids = 8 Nonessential amino acids = 12 Total common amino acids = 20 Enzymes for essential amino acids synthesis = Large relative to nonessential Signup and view all the answers

Match the following descriptions with the appropriate terms:

Plants and bacteria = Organisms that can synthesize certain amino acids Humans = Organisms that must obtain certain amino acids through diet Metabolically essential amino acids = Amino acids important for metabolism Reactions in biosynthesis = Chemical processes that produce amino acids Signup and view all the answers

Match the following historical aspects with their significance:

1930s = Period when the distinction of essential and nonessential amino acids was established Purified amino acids diet = Used to investigate amino acid requirements Neglect of certain biosynthesis pathways = Not discussed for humans in the context of amino acid Survival advantage = Benefit for retaining the ability to biosynthesize certain amino acids Signup and view all the answers

Match the following features to their correct descriptions:

Nutritionally essential = Must be ingested from food Nutritionally nonessential = Can be synthesized in the body Chemical reactions = Processes determining amino acid formation Dietary implications = Impact on amino acid availability for health Signup and view all the answers

Study Notes

Amino Acid Metabolism

Certain amino acids are not essential for human health.
Essential vs Nutritionally essential amino acids are different.
- 8 amino acids are nutritionally essential for humans.
- 12 nutritionally non-essential amino acids can be synthesized metabolically.
The citric acid cycle and glycolysis intermediates are precursors for some amino acids (aspartate, asparagine, glutamate, glutamine, glycine, and serine).
Transaminases play a key role in amino acid metabolism.
4-hydroxyproline and 5-hydroxylysine are formed in proteins like collagen.
Vitamin C deficiency (scurvy) impacts collagen formation.
Selenium, despite being toxic, is essential for selenocysteine, a component of some proteins.
A mixed-function oxidase is defined and its role in some reactions is outlined.
Tetrahydrobiopterin is a crucial component in tyrosine biosynthesis.
Modified tRNA is involved in selenocysteine insertion during protein synthesis.

Biomedical Importance of Amino Acids

Amino acid deficiencies can arise from inadequate intake or absorption.
Kwashiorkor and marasmus are nutritional disorders caused by deficiencies.
Short bowel syndrome can lead to nutritional issues for patients.
Genetic disorders affect the formation of hydroxyproline and hydroxylysine in collagen.
Menkes syndrome, linked to a copper deficiency, affects collagen structure.

Biosynthesis of Nonessential Amino Acids

Glutamate is derived from a-ketoglutarate via glutamate dehydrogenase.
Glutamine synthesis involves glutamine synthetase and y-glutamyl phosphate as intermediates.
Alanine and aspartate biosynthesis are via transamination of pyruvate and oxaloacetate, respectively.
Asparagine synthesizes via glutamines production.
Serine is formed by oxidation of 3-phosphoglycerate, via transamination and dephosphorylation
Glycine synthesis uses glyoxylate, glutamate, or alanine via aminotransferases.
Proline synthesis follows a pathway with glutamate y-semialdehyde as a crucial intermediate.
Cysteine is synthesized from methionine, with homocysteine and serine as intermediates.
Tyrosine production from phenylalanine requires phenylalanine hydroxylase.
Hydroxyproline and hydroxylysine's biosynthesis are specific to collagen.
The hydroxylases require vitamin C and molecular oxygen.
Valine, leucine, and isoleucine are interconverted by tissue aminotransferases.

Selenocysteine

Selenocysteine (21st nonessential amino acid) is found in some proteins.
It's a crucial part of some enzymes involved in redox reactions.
Selenocysteine biosynthesis involves serine, selenate, ATP, specific tRNA (tRNASec), and multiple enzymes.
The selenocysteine insertion element (stem-loop in mRNA) guides correct incorporation.

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Explore the intricacies of amino acid metabolism, including essential and non-essential types, and their synthesis pathways. Understand the roles of transaminases, vitamins, and the importance of modified tRNA in protein synthesis. This quiz will test your knowledge on metabolic functions and biochemical processes related to amino acids.