Download MBBS (Bachelor of Medicine, Bachelor of Surgery) 1st year (First Year) Biochemistry ppt lectures Topic 41 Catabolism Of Carbon Skeletons Notes. - biochemistry notes pdf, biochemistry mbbs 1st year notes pdf, biochemistry mbbs notes pdf, biochemistry lecture notes, paramedical biochemistry notes, medical biochemistry pdf, biochemistry lecture notes 2022 ppt, biochemistry pdf.
Catabolism of Carbon Skeletons of aa and
related disorders-I
Department of Biochemistry
Specific Learning Objectives
Catabolism of Carbon Skeletons of aa and related disorders:
Distinguish following disease states associated with Inborn Errors of Metabolism, including
deficient enzyme, relation of deficiency to build-up of secondary metabolites, and clinically relevant
information related to disease state (vitamin deficiencies, symptoms, diagnosis, pathology and
treatments:
? Cystinuria
? Histidinemia
? Phenylketonuria (PKU)
? Methylmalonyl CoA mutase deficiency e. Albinism
? Homocystinuria
? Alkaptonuria
? Maple syrup urine disease
? Cystathioninuria
? Tyrosinemia
Catabolism of Phenylalanine and Tyrosine with genetic disorders
Catabolic pathways of five aa to -ketoglutarate and associated disorders
Summary of Amino acid Catabolism
Fig18.15: Lehninger Principles of Biochemistry by David L Nelson
Genetic disorders related to Amino-acid catabolism
Table 18.2: Lehninger Principles of Biochemistry by David L Nelson
Catabolism of Phenylalanine and Tyrosine with genetic disorders
Homogentisate Oxidase/
Neonatal Tyrosinemia or
Or p-hydroxyphenylpyruvate hydroxylase
Fig18.23: Lehninger Principles of Biochemistry by David L Nelson
Alternative pathways for catabolism of phenylalanine in PKU
? Phenylalanine and phenylpyruvate accumulate in
blood and tissues and are excreted in urine--hence
name "phenylketonuria"
? Phenylpyruvate, excreted as either decarboxylated
to phenylacetate or reduced to phenyllactate
? Phenylacetate gives a characteristic odor to urine,
(for detection of PKU in infants)
Fig18.25: Lehninger Principles of Biochemistry by David L Nelson, 6th Ed.
Disorder related to phenylalanine catabolism
Phenylketonuria (PKU): Genetic defect in phenylalanine hydroxylase, first
enzyme in catabolic pathway for phenylalanine, is responsible for PKU, most
common cause of elevated levels of phenylalanine (hyperphenylalaninemia)
Excess phenylalanine is transaminated to Phenylpyruvate
The "spil over" of Phenylpyruvate (a phenylketone) into urine
High concentration of phenylalanine itself gives rise to brain dysfunction.
Cont--
Phenylalanine hydroxylase requires cofactor tetrahydrobiopterin,
which carries electrons from NADH to O2 and becomes oxidized to
dihydrobiopterin
It is subsequently reduced by enzyme dihydrobiopterin reductase in
a reaction that requires NADH
Diet low in phenylalanine can prevent mental retardation of PKU
Disorder related to Tyrosine catabolism
Alkaptonuria: Metabolic defect in alkaptonuria is a defective homogentisate
oxidase the enzyme that catalyzes homogentisate to Maleylacetoacetate
Large amounts of homogentisate are excreted and urine darkens on
exposure to air due to oxidation of excreted homogentisate
This autooxidizes to the corresponding quinone, which polymerizes to
form an intensely dark color
Late in disease, there is arthritis and connective tissue pigmentation
(ochronosis) due to oxidation of homogentisate to benzoquinone acetate,
which polymerizes and binds to connective tissue
Type I Tyrosinemia
Several metabolic disorders are associated with tyrosine catabolic
pathway
Probable metabolic defect in type I tyrosinemia (tyrosinosis) is at
fumarylacetoacetate hydrolase
Untreated acute and chronic tyrosinosis leads to death from liver
failure, renal tubular dysfunction, rickets and polyneuropathy
Type II Tyrosinemia
Alternate metabolites of tyrosine are also excreted in type II
tyrosinemia (Richner-Hanhart syndrome), a defect in tyrosine
aminotransferase produces accumulation and excretion of tyrosine
and metabolites
Leads to eye and skin lesions and mental retardation
Type III Tyrosinemia
Neonatal Tyrosinemia or type III tyrosinemia, due to lowered activity of p-
hydroxyphenylpyruvate
dioxygenase/
p-hydroxyphenylpyruvate
hydroxylase
It can cause learning problems, seizures, and loss of balance
Therapy employs a diet low in protein, tyrosine and phenylalanine
Catabolic pathways of five aa to -ketoglutarate
Proline dehydrogenase/
1-pyrroline-5-carboxylate dehydrogenase/
Fig18.26: Lehninger Principles of Biochemistry by David L Nelson
Disorder related to Proline catabolism
Type I hyperprolinemia
Metabolic block in type I hyperprolinemia is at proline
dehydrogenase/proline oxidase
Some individuals with hyperprolinemia type I exhibit seizures,
intellectual disability, or other neurological or psychiatric problems
Type II hyperprolinemia
Metabolic block in type II hyperprolinemia is at 1-pyrroline-5-
carboxylate dehydrogenase, which also participates in catabolism of
arginine, ornithine, and hydroxyproline
It leads to seizures or intellectual disability.
Two Clinical-cases discussed
Reference Books
17
1) Lehninger Principles of Biochemistry, 6th Ed.
2) Harper's Il ustrated Biochemistry, 30th edition
3) Biochemistry, Lippincott's Il ustrated Reviews, 6th Ed
Thank you
This post was last modified on 05 April 2022