Biochemistry Lecture 12: Amino Acids Conversion

Questions and Answers

What is the function of glucuronyl transferase enzyme in the hepatocyte?

To break down hydrogen peroxide in the RBCs

To synthesize creatine phosphate in muscles

To convert conjugated bilirubin to urobilinogen

To attach glucuronic acid to bilirubin, forming conjugated bilirubin (correct)

What is the main function of glutathione in the body?

To provide defense mechanism against certain toxic compounds (correct)

To activate some enzymes and inactivate insulin hormone

To absorb amino acids in the gut

To synthesize creatine phosphate in muscles

What is the product of glucuronic acid attachment to bilirubin?

Urobilin

Urobilinogen

Stercobilin

Conjugated Bilirubin (correct)

What is the main site of creatine synthesis?

Kidney, liver, and pancreas Signup and view all the answers

What is the function of glutathione in RBCs?

To break down hydrogen peroxide and prevent hemolysis Signup and view all the answers

What is the fate of majority of urobilinogen?

Excreted with the feces Signup and view all the answers

What is the structure of glutathione?

A tripeptide formed of three amino acids Signup and view all the answers

What is the role of creatine phosphate in muscles?

To store high energy phosphate and provide phosphate to ADP to form ATP during muscle exercise Signup and view all the answers

What is the function of creatine phosphate in muscles?

Not mentioned in the content Signup and view all the answers

What is the function of creatine kinase enzyme?

To catalyze the formation of creatine phosphate Signup and view all the answers

Which isoenzyme of creatine kinase is mainly found in heart muscle?

CK-MB Signup and view all the answers

What is the end product of creatine metabolism?

Creatinine Signup and view all the answers

What is the normal range of plasma creatinine?

0.6 - 1.4 mg/dl Signup and view all the answers

What is the precursor for Tyrosine in the liver?

Phenylalanine Signup and view all the answers

What is the deficiency of phenylalanine hydroxylase enzyme?

Phenylketonuria Signup and view all the answers

What is the characteristic sign of Phenylketonuria?

Mental retardation Signup and view all the answers

What is the primary method for diagnosing phenylketonuria in infants?

Measuring blood phenylalanine levels using a Guthrie test Signup and view all the answers

Which of the following conditions is characterized by a deficiency of homogentisate oxidase enzyme?

Alkaptonuria Signup and view all the answers

What is the primary treatment for hereditary tyrosinemia?

Feeding a diet low in tyrosine and phenylalanine Signup and view all the answers

Which of the following is a common consequence of alkaptonuria?

Generalized pigmentation of connective tissues Signup and view all the answers

What is the approximate frequency of phenylketonuria in live births?

1 in 10,000 Signup and view all the answers

What is the recommended duration for dietary restrictions in individuals diagnosed with phenylketonuria?

Until the age of 6 years Signup and view all the answers

Which of the following enzymes is deficient in albinism?

Tyrosine hydroxylase Signup and view all the answers

What is the primary characteristic of acute hereditary tyrosinemia?

Failure to thrive and liver failure Signup and view all the answers

What physiological function is associated with glycine?

Precursor for collagen and bile salts Signup and view all the answers

What is the first product formed when glycine reacts with Succinyl CoA?

Amino levulonic acid (ALA) Signup and view all the answers

How much bilirubin is produced daily from the degradation of hemoglobin in adults?

250–400 mg Signup and view all the answers

What percentage of bilirubin is derived from hepatic turnover of hem proteins?

20-25% Signup and view all the answers

What is biliverdin converted to during the degradation of heme?

Bilirubin Signup and view all the answers

Which of the following proteins bind unconjugated bilirubin in the liver?

Cytosolic Y protein and cytosolic Z protein Signup and view all the answers

What happens to released iron after the oxidation of heme?

It's recycled Signup and view all the answers

What is the lifespan of red blood cells in the human body?

120 days Signup and view all the answers

Study Notes

Conversion of Amino Acids to Specialized Products

Glycine is a non-essential glucogenic amino acid that serves as a precursor for various nitrogen-containing compounds.
Glycine is converted to:
Haeme (combines with globin protein to form hemoglobin)
Hippuric acid
Glutathione
Glyoxylic acid
Purine bases
Bile salts
Collagen
Creatine
Serine
Neurotransmitter

Haeme Metabolism

Haeme is degraded to bilirubin, which is produced daily in adults (250-400 mg).
70-80% of bilirubin comes from degradation of haemoglobin, while 20-25% comes from hepatic turnover of haem proteins.
The life span of red blood cells is approximately 120 days.
Senescent red blood cells are phagocytosed by cells of the reticuloendothelial system (spleen and liver).
Haem is oxidized by the haem oxygenase system, releasing ferric iron (Fe3+) and carbon monoxide (CO).
Biliverdin is reduced to bilirubin by biliverdin reductase.
Unconjugated bilirubin is transported to the liver, where it is bound to albumin and then conjugated with glucuronic acid.
Conjugated bilirubin is water-soluble and travels down the GI tract.

Glutathione

Glutathione is a tripeptide formed from glutamate, cysteine, and glycine.
It exists in two forms: reduced (G-SH) and oxidized (G-SS-G).
Functions of glutathione include:
Defense against toxic compounds (detoxification)
Absorption of amino acids
Protection against cell damage and hemolysis of RBCs
Activation of some enzymes
Inactivation of insulin hormone

Creatine

Creatine is synthesized from glycine, arginine, and methionine in the kidney, liver, and pancreas.
Functions of creatine:
Creatine is phosphorylated to creatine phosphate in muscles.
Creatine phosphate acts as a store of high-energy phosphate in muscles and is used during muscle exercise.
Creatine kinase enzyme (CK) catalyzes the formation of creatine phosphate.
There are three isoenzymes of CK: CK-MM (skeletal muscles), CK-MB (heart muscle), and CK-BB (brain).
Creatine phosphate is degraded to creatinine, which is excreted by the kidney in urine.
Diagnostic importance of creatinine:
Estimation of plasma creatinine is used as a kidney function test.
High blood creatinine and urea levels are sensitive indicators of renal failure.

Phenylalanine Metabolism

Phenylalanine is a ketogenic and glucogenic essential amino acid.
Functions of phenylalanine:
Precursor for tyrosine in the liver
Deficiency of phenylalanine hydroxylase enzyme or dihydrobiopterin reductase results in phenylketonuria (PKU).
Effects of PKU:
Mental retardation
Increased blood phenylalanine
Failure to walk and talk
Hyperactivity and tremors
Failure to grow
Skin lesions (eczema)
Frequency of PKU: 1 in 10,000 live births
Diagnosis of PKU: measurement of blood phenylalanine by the Guthrie test in infants at 4 days old
Prevention of PKU: feeding infants with PKU a diet containing very low levels of phenylalanine

Hereditary Tyrosinemia (Tyrosinosis)

Definition: inability to metabolize tyrosine and p-hydroxyphenylpyruvate
Cause: deficiency of tyrosine α-Ketoglutarate transaminase and p-hydroxyphenylpyruvate oxidase enzymes
Forms of tyrosinemia: acute (death from liver failure within 7 months) and chronic (liver cirrhosis and hepatic carcinoma, mild mental retardation)
Prevention and treatment: feeding a diet containing very low levels of tyrosine and phenylalanine

Alkaptonuria

Definition: benign disease resulting from deficiency of homogentisate oxidase enzyme
Effects:
Deposition in joints causing arthritis
Deposition in connective tissue causing generalized pigmentation
Excretion in large amounts in urine, which is oxidized in the air giving dark urine

Albinism

Definition: hereditary deficiency of tyrosine hydroxylase enzyme in melanocytes
Effects: defective synthesis of melanin pigments, affecting the eyes, skin, and hair
Types of albinism:
Ocular albinism
Cutaneous albinism

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Description

This quiz covers the conversion of amino acids to specialized products, including glycine's role in producing haeme, hippuric acid, and other compounds with physiological functions.