2.2.6Inquiry Process
Globular and Fibrous Proteins — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 47 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 5Globular Proteins
Globular proteins mostly carry out metabolic and regulatory tasks.
Shape
- Shape Polypeptide chains fold into compact, roughly spherical molecules.
Solubility
- Solubility Hydrophilic R groups lie on the outside, so globular proteins dissolve in water.
Sequence
- Sequence The amino acid sequence is irregular, giving each protein a unique shape suited to its role.
Functions
- Functions Enzymes, antibodies, transport proteins and many hormones are globular, since they need specific shapes.
Section 2 of 5Fibrous Proteins
Fibrous proteins are mostly structural.
Fibrous Proteins
Shape
- Shape Long strands or sheets that lie side by side, forming strong fibres.
Solubility
- Solubility Many hydrophobic R groups are exposed, so fibrous proteins are generally insoluble in water.
Sequence
- Sequence Often repetitive amino acid sequences allow regular, repeating structures.
Functions
- Functions Provide strength and support, for example in tendons, skin, hair and nails.
| Feature | Globular | Fibrous |
|---|---|---|
| Shape | Compact, spherical | Long, strand-like |
| Solubility | Soluble | Insoluble |
| Sequence | Irregular | Repetitive |
| Main role | Metabolic, transport, defence | Structure, strength |
Section 3 of 5Examples
Comparing named examples shows how each shape suits a particular job in the body.
Haemoglobin
- Haemoglobin A globular protein with four polypeptides that carries oxygen in red blood cells.
Insulin
- Insulin A small globular hormone that binds to receptors and lowers blood glucose.
Collagen
- Collagen A fibrous protein with three chains in a triple helix, strong in tendons, skin and bones.
Keratin
- Keratin A fibrous protein in hair, nails and feathers, strengthened by disulfide bridges.
| Protein | Type | Location | Role |
|---|---|---|---|
| Haemoglobin | Globular | Red blood cells | Oxygen transport |
| Insulin | Globular | Blood plasma | Lowers blood glucose |
| Collagen | Fibrous | Tendons, skin, bone | Tensile strength |
| Keratin | Fibrous | Hair, nails | Tough protective covering |
Section 4 of 5Structure Fits Function
1
Enzymes need a precise active site, so a compact folded globular shape is required.
2
Haemoglobin must dissolve in the cytoplasm of red blood cells, so it is soluble and globular.
3
Collagen must resist stretching, so its chains twist together and cross-link into strong fibres.
4
Keratin must be tough and insoluble, so many disulfide bonds link its chains.
5
In each case the three-dimensional shape explains the properties and role of the protein.
Section 5 of 5Exam Checklist & Tips
2.2.6 – Key Points for the Exam
- Globular protein A compact, soluble protein with a spherical shape, usually with metabolic roles.
- Fibrous protein An elongated, insoluble protein, usually with a structural role.
- Collagen A fibrous protein with a triple helix that gives strength to connective tissue.
- Haemoglobin A globular protein with four subunits that transports oxygen.
Common Mistakes
- Saying all structural proteins are globular; they are mostly fibrous.
- Claiming fibrous proteins have no tertiary structure.
- Stating that haemoglobin is fibrous because it has four chains.
- Forgetting that solubility depends on the R groups at the surface.
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