Скачать или смотреть 12.Glycoproteins | Structure, Functions & Clinical Aspects | Medical Biochemistry | USMLE Step 1

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Glycoproteins | Structure, Functions & Clinical Aspects | Medical Biochemistry | MBBS | USMLE Step 1

👋 Hey future doctors and biochem learners! Did you know that many cell surface molecules, hormones, enzymes, and immunoglobulins are actually glycoproteins? 🧩 These proteins with attached carbohydrate chains are critical for cell adhesion, recognition, immunity, and signaling.

In this lecture, we’ll cover the structure, functions, and clinical aspects of glycoproteins, making it a high-yield topic for MBBS, NEET PG, FMGE, and USMLE Step 1. 🧬📚

🌟 Structure of Glycoproteins

Definition: Proteins covalently bonded to oligosaccharide chains (carbohydrate content usually Less than 10%).

Attachment Types:
• N-linked glycosylation: carbohydrate attached to asparagine residue (in ER).
• O-linked glycosylation: carbohydrate attached to serine or threonine (in Golgi).

Carbohydrates involved: Glucose, galactose, mannose, N-acetylglucosamine, sialic acid, fucose.

🌟 Functions of Glycoproteins

1️⃣ Cell Recognition & Adhesion

Cell surface receptors, selectins, integrins.

Blood group antigens (ABO system).

2️⃣ Immune Function

Immunoglobulins (antibodies).

MHC (major histocompatibility complex) molecules.

3️⃣ Enzymes & Hormones

Many hormones (TSH, LH, FSH) are glycoproteins.

Lysosomal enzymes are glycosylated for targeting.

4️⃣ Structural Role

Mucins (protective glycoproteins in secretions).

Basement membrane components.

5️⃣ Protective & Stability Functions

Glycosylation prevents protein degradation.

Increases solubility and stability.

🩺 Clinical Aspects

I-Cell Disease (Mucolipidosis II): Failure of mannose-6-phosphate tagging → lysosomal enzymes secreted outside instead of entering lysosome.

Congenital Disorders of Glycosylation (CDG): Defects in N-linked glycosylation → developmental delay, failure to thrive.

Cancer: Altered glycoproteins help tumor cells evade immunity.

Viral Infections: Many viral proteins (e.g., HIV gp120) are glycoproteins aiding entry into host cells.

Blood Groups: ABO antigens are glycoproteins/glycolipids.

🎯 Exam Integration

N-linked = Asn (ER), O-linked = Ser/Thr (Golgi).

Glycoproteins = blood group antigens, immunoglobulins, hormones, receptors.

I-cell disease = mannose-6-phosphate tagging defect.
👉 Favorite for recall and clinical vignette questions in USMLE & NEET PG.

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❓Should we cover Glycosaminoglycans & Proteoglycans as the next lecture, since they are the other major group of carbohydrate–protein complexes in connective tissue biochemistry? Drop your request in the comments below! 😊

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