Скачать или смотреть 1. Proteins: Classification & Higher-Order Structure | Biochemistry | MBBS 1st Year | USMLE Step 1

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Proteins: Classification & Higher-Order Structure | Medical Biochemistry | MBBS 1st Year | USMLE Step 1

👋 Hey future doctors and biochem learners! Proteins are the workhorses of the cell — performing structural, enzymatic, hormonal, transport, and immune functions. But to truly understand how proteins work, we need to study their classification and higher-order structure. 🧩

This lecture simplifies protein types, levels of structure, stabilizing bonds, and clinical disorders in a way that is exam-friendly and conceptually clear. Perfect for MBBS, NEET PG, FMGE, and USMLE Step 1 preparation. 🧬📚

🌟 Protein Classification

1️⃣ Based on Composition

Simple proteins: yield only amino acids on hydrolysis (e.g., albumin, globulin).

Conjugated proteins: protein + non-protein moiety (prosthetic group). Examples:
• Glycoproteins (carbohydrate)
• Lipoproteins (lipid)
• Metalloproteins (metal ion)
• Nucleoproteins (nucleic acid)

Derived proteins: partially hydrolyzed forms (peptones, peptides).

2️⃣ Based on Shape

Fibrous proteins: elongated, structural role (collagen, keratin, elastin).

Globular proteins: compact, functional role (enzymes, hemoglobin, immunoglobulins).

3️⃣ Based on Function

Enzymes, Hormones, Structural proteins, Transport proteins, Immunoproteins, Storage proteins.

🌟 Higher-Order Structure of Proteins

1️⃣ Primary Structure (1°)

Linear sequence of amino acids linked by peptide bonds.

Genetic mutations alter primary structure → e.g., Sickle cell anemia (Glu → Val in Hb β-chain).

2️⃣ Secondary Structure (2°)

Local folding into α-helix and β-pleated sheets.

Stabilized by hydrogen bonds between backbone atoms.

Clinical link: Prion diseases involve abnormal β-sheet accumulation.

3️⃣ Tertiary Structure (3°)

3D folding of a single polypeptide chain.

Stabilized by hydrogen bonds, hydrophobic interactions, ionic bonds, disulfide bridges.

Determines functional conformation of globular proteins (enzymes).

4️⃣ Quaternary Structure (4°)

Association of two or more polypeptide subunits.

Example: Hemoglobin (α₂β₂).

Allows cooperativity and allosteric regulation.

🩺 Clinical Correlations

Collagen disorders: Osteogenesis imperfecta, Ehlers–Danlos syndrome.

Hemoglobinopathies: Sickle cell anemia, Thalassemias.

Protein misfolding diseases: Alzheimer’s, Parkinson’s, Prion diseases.

🎯 Exam Integration

Primary → peptide bonds, Secondary → H-bonds, Tertiary → multiple interactions, Quaternary → subunit assembly.

Classification (simple, conjugated, fibrous, globular) is a repeated question in MBBS & USMLE.

Always connect structure to function and pathology for clinical recall.

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❓Want us to create a separate lecture on Protein Denaturation & Folding Disorders (with clinical links like Alzheimer’s and Prion disease)? Drop your request in the comments below! 😊

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