Biochemistry Mega Revision - Part 1

Introduction

• Lecture on important points and must-know topics in Biochemistry.
• First part of the series, with subsequent classes planned.
• Other free live classes on the app and a schedule for these classes.
• 20% subscription discount for medical PG students, use code 'Dr Nikita'.
• Available courses and offers for different student groups and exams.

Amino Acids

Groups in Amino Acids

• Guanidinium: Arginine
• Benzene: Phenylalanine
• Phenol: Tyrosine
• Imidazole: Histidine
• Pyrolidine: Proline
• Thioether linkage: Methionine
• Indole: Tryptophan
• Tryptophan & vitamin B3: 60mg Tryptophan forms 1mg Niacin.

Acidic and Basic Amino Acids

• Acidic: Aspartic acid, Glutamic acid
• Basic: Histidine, Arginine (most basic), Lysine

Essential and Non-Essential Amino Acids

• Essential: Phenylalanine, Valine, Threonine, Tryptophan, Isoleucine, Methionine, Histidine, Arginine, Leucine, Lysine
• Semi-Essential: Arginine, Histidine

Glucogenic & Ketogenic Amino Acids

• Both: TIP (Tryptophan, Isoleucine, Phenylalanine, Tyrosine)
• Purely Ketogenic: Leucine, Lysine

Branched-Chain Amino Acids

• LIV: Leucine, Isoleucine, Valine
• Maple Syrup Urine Disease (MSUD): Defect in branched-chain ketoacid dehydrogenase.

Amino Acid to Vitamin Conversion

• Tryptophan -> Niacin (B3), Significant in carcinoid syndrome.

Amino Acid Metabolism Disorders

Phenylketonuria (PKU)

• Enzyme: Phenylalanine hydroxylase deficiency
• Features: Blonde hair, Intellectual disability, Musty odor, Avoid phenylalanine, supplement tyrosine

Tyrosinemia Types

• Type 1 (Tyrosynosis): Hepatorenal, Fumarylacetoacetate hydrolase, Increased HCC risk.
• Type 2 (Richner-Hanhart): Oculocutaneous involvement.
• Type 3: 4-Hydroxyphenylpyruvate dioxygenase defect, Neonatal benign.

Homocystinuria

• Features: Marfanoid habitus, Early stroke/MI, Lens subluxation inferomedial
• Conversion: Homocysteine -> Methionine (B12 dependent), Homocysteine -> Cysteine (B6 dependent)

Alkaptonuria

• Enzyme: Homogentisate oxidase deficiency
• Features: Black urine on standing, Ochronosis, Arthritis risk

Glycogen Storage Disorders

Type 1 (Von Gierke's)

• Enzyme: Glucose-6-phosphatase deficiency
• Features: Severe fasting hypoglycemia, Hepatomegaly, Hyperlipidemia, Lactic acidosis, Doll-like faces

Type 2 (Pompe's)

• Enzyme: Acid maltase (α-glucosidase)
• Features: Cardiomegaly, Heart failure

Type 3 (Cori's)

• Enzyme: Debranching enzyme deficiency
• Features: Hepatomegaly, Short outer branches

Type 4 (Andersen's)

• Enzyme: Branching enzyme deficiency
• Features: Liver cirrhosis, Long polysaccharide chains

Type 5 (McArdle's)

• Enzyme: Muscle glycogen phosphorylase
• Features: Exercise-induced cramps, Second wind phenomenon

Type 6 (Hers)

• Enzyme: Hepatic glycogen phosphorylase
• Features: Mild hypoglycemia

Type 7 (Tauri's)

• Enzyme: Muscle phosphofructokinase
• Features: Exercise cramps, Hemolytic anemia

Lysosomal Storage Disorders

Gaucher's Disease

• Enzyme: Glucocerebrosidase
• Features: Bone pain, Pancytopenia, Hepatosplenomegaly, Tissue paper macrophages

Niemann-Pick Disease

• Enzyme: Sphingomyelinase
• Features: Hepatosplenomegaly, Cherry-red spot, Foam cells, Zebra bodies

Tay-Sachs Disease

• Enzyme: Hexosaminidase A
• Features: Cherry-red spot, No hepatosplenomegaly, Onion skin lysosomes, Startle reflex

Miscellaneous

Creatine Synthesis

• Amino Acids: Glycine, Arginine, Methionine
• Steps: Kidney -> Liver -> Muscle

Glutathione

• Amino Acids: Glutamate, Cysteine, Glycine
• Functional Component: Cysteine

Hormone-Sensitive vs Lipoprotein Lipase

• Hormone-Sensitive: Catabolic, Active during fasting
• Lipoprotein Lipase: Anabolic, Active postprandial, Stimulated by insulin