2.3.4Inquiry Process
Glycolipids and Glycoproteins — IB Biology HL Revision Notes & Topical Questions
5 min read 6 parts Lesson 50 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 6Structure and Position
Carbohydrate chains attached to membrane lipids and proteins form a coat on the cell exterior.
Glycolipid
- Glycolipid A lipid with a carbohydrate chain attached, found in the outer layer of the plasma membrane.
Glycoprotein
- Glycoprotein A membrane protein with carbohydrate chains attached, also exposed on the outer surface.
Glycocalyx
- Glycocalyx The carbohydrate-rich layer on the outside of many animal cells, formed by these molecules.
Orientation
- Orientation The carbohydrate chains always project out of the cell and never into the cytoplasm.
| Molecule | Anchor | Attached group |
|---|---|---|
| Glycolipid | Lipid in bilayer | Carbohydrate chain |
| Glycoprotein | Protein in bilayer | Carbohydrate chain |
Section 2 of 6Functions
Functions
Cell recognition
- Cell recognition The chains work as labels that identify the cell type, such as the antigens on red blood cells.
Self and non-self
- Self and non-self The immune system uses surface markers to tell the body's own cells from foreign ones.
Cell adhesion
- Cell adhesion Carbohydrate chains help cells bind to their neighbours when forming tissues.
Receptors
- Receptors Some carbohydrate chains bind hormones or other signal molecules.
Section 3 of 6Additional Roles
The coat also affects how cells interact with their environment.
Protection
- Protection The glycocalyx forms a cushion against physical damage and protects the membrane from enzymes.
Water retention
- Water retention Sugar chains attract water and give a hydrated layer at the cell surface.
Pathogen entry
- Pathogen entry Some viruses and bacteria attach to specific surface carbohydrates to enter cells.
Cell communication
- Cell communication Changes in surface carbohydrates can alter how neighbouring cells respond.
Section 4 of 6Making Membrane Sugars
1
Lipids and proteins are made in the endoplasmic reticulum.
2
Carbohydrate chains are added to them in the endoplasmic reticulum and Golgi apparatus.
3
The completed molecules are packaged into vesicles.
4
Vesicles move to the plasma membrane and fuse with it.
5
This fusion places the carbohydrate chains on the outer surface.
Section 5 of 6Worked Example
Question
- A transplanted kidney is attacked by the recipient's immune system.
- Explain how the molecules on the surface of the kidney cells are involved.
- Cells carry glycoproteins and glycolipids whose carbohydrate chains act as recognition markers.
- The donor kidney cells have markers that differ from those of the recipient.
- The recipient's immune cells detect these as foreign antigens and attack the cells carrying them.
- Matching donor and recipient markers closely, and giving immunosuppressant drugs, reduces rejection.
Answer The surface carbohydrate markers are recognised as non-self, which triggers an immune response.
Section 6 of 6Exam Checklist & Tips
2.3.4 – Key Points for the Exam
- Glycolipid A lipid molecule with a carbohydrate chain attached.
- Glycoprotein A protein molecule with a carbohydrate chain attached.
- Glycocalyx The carbohydrate layer covering the outside of the cell membrane.
- Antigen A surface molecule that can trigger an immune response.
Common Mistakes
- Placing the carbohydrates inside the cell; they face outward.
- Saying glycolipids are proteins.
- Forgetting the vesicle route from Golgi to membrane.
- Describing recognition as a function of cholesterol.
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