Amino Acids Overview

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Questions and Answers

What concentration range of phenylalanine indicates mild PKU?

1,200-1,800 μmol/L

180-600 μmol/L

600-1,200 μmol/L (correct)

Over 1,800 μmol/L

Which procedure requires pretreatment of dried blood filter disks with trichloroacetic acid (TCA)?

Gas chromatography-mass spectrometry (GS/MS)

Microwave-assisted silylation

Microfluorometric assay (correct)

Direct measurement of phenylalanine

What is the main characteristic of hydroxyphenylalaninemia?

Low concentrations of phenylalanine

Excess accumulation of phenylketones

Elevated neurotransmitter production

Deficiency in BH4 enzyme regeneration (correct)

What does BH4 deficiency primarily lead to?

Elevated blood concentrations of phenylalanine Signup and view all the answers

Which screening method is considered rapid for diagnosing neonatal PKU?

Microwave-assisted silylation Signup and view all the answers

What distinguishes selenocysteine from other amino acids?

It replaces sulfur with a selenium atom. Signup and view all the answers

Which of the following statements about pyrrolysine is true?

It is encoded by the UAG codon. Signup and view all the answers

In what processes is glycine essential?

The synthesis of nucleic acids, bile acids, and more. Signup and view all the answers

Why is proline important for the body?

It aids in wound healing and strengthening tissues. Signup and view all the answers

Which amino acid acts as an inhibitory neurotransmitter in the central nervous system?

Glycine Signup and view all the answers

What is a characteristic of aminoacidopathies?

They result from inherited errors of metabolism. Signup and view all the answers

Which amino acid is crucial for the synthesis of hydroxyproline?

Proline Signup and view all the answers

What role does glycine play in glycogen storage?

It enhances glycogen storage. Signup and view all the answers

What is the primary characteristic of argininosuccinic aciduria?

It involves a mutation in the ASL gene. Signup and view all the answers

Which of the following is NOT a clinical symptom associated with argininosuccinic aciduria?

Vision loss Signup and view all the answers

Which treatment option is specifically indicated for managing argininosuccinic aciduria?

Administration of sodium benzoate and sodium phenylacetate Signup and view all the answers

What compound is specifically tested for using the cyanide-nitroprusside test?

Cystine Signup and view all the answers

Which method is utilized for quantitative analysis of amino acids in urine?

Ion exchange chromatography Signup and view all the answers

What is the primary structure of a protein defined by?

The sequence of amino acids Signup and view all the answers

Which of these amino acids is NOT commonly elevated in argininosuccinic aciduria?

Cystine Signup and view all the answers

How often does argininosuccinic aciduria occur in births worldwide?

1 in 70,000 births Signup and view all the answers

What type of cells are responsible for synthesizing immunoglobulins?

B cells Signup and view all the answers

Which of the following is NOT commonly tested as a transport protein?

Insulin Signup and view all the answers

What is the main purpose of enzymes in the body?

To catalyze biochemical reactions Signup and view all the answers

What process involves the formation of mRNA from a DNA template?

Transcription Signup and view all the answers

Which of the following hormones is synthesized in the liver and released into circulation?

Cortisol Signup and view all the answers

What role do structural proteins serve in the body?

Providing structure to cells and tissues Signup and view all the answers

What is the relationship between amino acids and codons?

One codon codes for one amino acid Signup and view all the answers

Which of the following groups includes enzymes that are clinically important for evaluating tissue damage?

Transaminases, dehydrogenases, and phosphatases Signup and view all the answers

What percentage of carbohydrate composition defines glycoproteins?

10% to 40% Signup and view all the answers

Which of the following is an example of a glycoprotein?

Haptoglobin Signup and view all the answers

What defines a mucoprotein in terms of carbohydrate percentage?

Greater than 40% Signup and view all the answers

What is the primary function of mucin?

To lubricate and protect body surfaces Signup and view all the answers

Which of the following substances does albumin NOT transport?

Nutrients like glucose Signup and view all the answers

Which condition is NOT associated with decreased albumin levels?

Obesity Signup and view all the answers

What can be measured to assess the capillary efflux of albumin?

Transcapillary escape rate Signup and view all the answers

Which of the following can lead to a decrease in albumin levels?

Excessive hydration Signup and view all the answers

Study Notes

Amino Acids

Selenocysteine (Sec) is the 21st amino acid
- It is synthesized from serine
- It is not directly coded for in the genetic code
- It is encoded by a UGA codon, which is normally a stop codon
- It is a selenium analogue of cysteine
- It is essential for the synthesis of nucleic acids, bile acids, proteins, peptides, purines, ATP, porphyrins, hemoglobin, glutathione, creatine, bile salts, glucose, and glycogen
Glycine (Gly) is an inhibitory neurotransmitter in the CNS
- It improves glycogen storage and promotes healing
Proline (Pro) is produced from glutamine
- It is a precursor for hydroxyproline
- It is involved in wound healing, strengthening of joints, tendons, and cardiac tissue
- It works in tandem with Vitamin C to promote healthy connective tissues
Pyrrolysine (Pyl) is not present in humans
- It is the 22nd amino acid
- It is used by prokaryotes and single-celled microorganisms as part of their methane-producing metabolism
- A lysine derivative is encoded by the UAG codon

Aminoacidopathies

A class of inherited errors of metabolism
There are partial deficiencies, such as mild PKU, which result in phenylalanine concentrations between 600 to 1,200 μmol/L

Phenylketonuria (PKU)

Patients with phenylalanine concentrations ranging from 180-600 μmol/L with no accumulation of phenylketones are considered to have non-PKU mild hyperphenylalaninemia.
There are several screening tests used to diagnose PKU:
- Microfluorometric assay:
  - Used for the direct measurement of phenylalanine in dried blood filter disks
  - It yields quantitative results
  - It is more adaptable to automation
  - It is not affected by the presence of antibiotics
  - Procedure is based on the fluorescence of a complex formed by phenylalanine, ninhydrin, and copper in the presence of a dipeptide
  - Requires pretreatment of the dried blood filter disk with trichloroacetic acid (TCA)
- Microwave-assisted silylation:
  - A rapid diagnostic procedure for neonatal PKU
  - Positive screening results need to be differentiated from PKU so that treatment can be initiated
- **Gas chromatography-mass spectrometry (GS/MS): **
  - Can be used to screen for PKU

Hydroxyphenylalanemia

A deficiency in enzymes needed for the regeneration and synthesis of tetrahydrobiopterin (BH4)
- BH4 is a cofactor for enzymatic hydroxylation of phenylalanine, tyrosine, and tryptophan
BH4 deficiency results in elevated blood concentrations of phenylalanine and deficient production of neurotransmitters from tyrosine and tryptophan.
Treatment includes:
- High-caloric, protein-restrictive diet
- Arginine supplementation
- Administration of sodium benzoate and sodium phenylacetate
Symptoms include:
- Restlessness
- Memory loss
- Personality changes
- Seizures
- Coma

Argininosuccinic Aciduria

An urea cycle disorder that is inherited in an autosomal recessive pattern
Result of a mutation in the ASL gene
Occurs about 1 in 70,000 births worldwide

Clinical Symptoms of Argininosuccinic Aciduria

Symptoms include:
- Vomiting
- Lethargy
- Seizures
- Coma
- Delayed development
- Failure to thrive
- Hyperammonemia
- Hepatomegaly
Patients may have a characteristic odor of ammonia in their breath.

Treatment For Argininosuccinic Aciduria

Treatment for argininosuccinic aciduria depends on the severity of the disorder and the specific mutations involved, The goal of treatment is to lower ammonia levels in the blood.

Cystinuria

A genetic disorder characterized by the inability to reabsorb cystine and other dibasic amino acids in the kidneys
The most common treatment for cystinuria is to:
- Increase fluid intake
- Minimize excessive protein intake
- Control urine pH
Screening test:
- Cyanide-nitroprusside test:
  - Produces a red-purple color with sulfhydryl groups
  - False positives must be ruled out
  - A large amount of urinary levels of three amino acids with a similar structure to cystine — Ornithine, Lysine, Arginine
- Ion exchange chromatography:
  - Used for quantitative analysis for amino acids in urine or plasma

Protein Basic Structure

There are 4 distinct levels of a protein’s structure:
- Primary, Secondary, Tertiary, and Quaternary

Primary Structure

The number & types of amino acids in a specific amino acid sequence
- Ex. Primary structure of a protein is the sequence of amino acids.

Protein Synthesis

Proteins are synthesized in the ribosomes of cells.
The process involves:
- Transcription: The process where double-stranded DNA unfolds in the nucleus, and one strand is used as a template for the formation of a complementary strand of mRNA
- Translation: The process in which the mRNA travels to the ribosomes in the cytoplasm and is translated into a protein.

Hormones

Hormones are chemicals produced by endocrine glands that are secreted into the bloodstream and travel to organs and tissues throughout the body.
Hormones regulate a wide range of bodily functions.
Commonly tested hormones: insulin, testosterone, growth hormone, follicle-stimulating hormone, and cortisol

Transport Proteins

Proteins involved in the transport of ions, small molecules, or macromolecules
The protein’s structure allows it to bind to the molecule being transported.
Commonly measured transport proteins: hemoglobin, albumin, ceruloplasmin, haptoglobin, and transferrin

Enzymes

Protein catalysts that mediate biochemical reactions.
Normally found intracellularly, but are found in the bloodstream if there is tissue damage.
Transaminases,dehydrogenases, and phosphatases are examples of enzyme groups that are routinely tested in the clinical laboratory.

Structural Proteins

Provide structure to many cells and tissues throughout the body, such as muscle, tendons, and bone matrix.
Often exist in long fibers.

Immunoglobulins

Proteins produced by B cells (lymphocytes) in the bone marrow
They mediate the humoral immune response to identify and neutralize foreign antigens.
Clinically important immunoglobulins are IgG, IgM, IgE, and IgA.

Glycoproteins

Contain a composition of 10% to 40% carbohydrate.
Examples of glycoproteins are haptoglobin and α1 – antitrypsin.

Mucoproteins/Proteoglycans

Contain a conjugate percentage of carbohydrate greater than 40%.
An example of a mucoprotein is mucin, which is a lubricant that protects body surfaces from friction or damage.

Albumin

The most abundant protein in human plasma.
Synthesized in the liver.
Exists in the interstitial space.
Has a transcapillary escape rate, which measures the capillary efflux of albumin.
Transports:
- Thyroid hormones
- Iron
- Fatty acids
- Unconjugated bilirubin
Dye quantification of albumin is used to measure levels.
Decreased albumin can indicate:
- Malnutrition & malabsorption
- Liver disease
- Protein losing enteropathy
- Kidney loss
- Skin loss (exfoliative dermatitis)
- Hypothyroidism
- Dilution by excess: Polydipsia
- Acute disease states
- Mutation (autosomal recessive state)
- Hemodilution

Globulin

A group of proteins found in blood plasma
Can be divided into several subclasses:
- Alpha-globulins: Transport lipids and hormones, form clotting factors, and help in immune response.
- Beta-globulins: Transport iron and lipids, activate complement, and act as enzymes.
- Gamma-globulins: Consist mainly of antibodies (immunoglobulins) that help fight infections.

Prealbumin (Transthyretin)

A protein that is synthesized in the liver.
Carries thyroid hormones and retinol (vitamin A) in the blood.
Useful marker for nutritional status and overall health
Levels are lower in cases of malnutrition, inflammation, and some liver diseases.
Levels are higher in cases of some types of tumors.

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Description

This quiz covers key information about amino acids including their synthesis, functions, and unique characteristics. Topics include Selenocysteine, Glycine, Proline, and Pyrrolysine, highlighting their roles in human health and biology. Test your knowledge on these crucial building blocks of life!