2.3.2Inquiry Process
Membrane Proteins — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 49 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.
Part 1 of 5Integral and Peripheral Proteins
Proteins are positioned in the membrane according to the chemistry of their surface.
Integral proteins
- Integral proteins Embedded in the bilayer and amphipathic, with hydrophobic regions in the core and hydrophilic regions in the water.
Transmembrane
- Transmembrane Many integral proteins span both layers, with parts on each side of the membrane.
Peripheral proteins
- Peripheral proteins Hydrophilic proteins that attach to the membrane surface or to integral proteins and can be on either side.
Variation
- Variation Membranes with many reactions, such as mitochondrial inner membranes, contain a very high proportion of protein.
| Feature | Integral | Peripheral |
|---|---|---|
| Position | Within the bilayer | On the surface |
| Polarity | Amphipathic | Hydrophilic |
| Removal | Difficult, needs detergent | Easy, mild salt solutions |
Part 2 of 5Functions
Functions
Transport
- Transport Channel proteins form pores for ions and polar molecules, and carrier proteins change shape to move a specific substance across.
Receptors
- Receptors Bind signals such as peptide hormones and neurotransmitters and trigger a response inside the cell.
Enzymes
- Enzymes Immobilised enzymes catalyse reactions at the surface, often in sequences, such as digestive enzymes in the gut lining.
Recognition and adhesion
- Recognition and adhesion Glycoproteins identify cells, while cell adhesion molecules hold cells together.
Part 3 of 5Transport Proteins in Detail
Channel proteins
- Channel proteins Provide a water-filled pore and are specific to a given ion;
- some are gated and open in response to a signal.
Carrier proteins
- Carrier proteins Bind a solute, change shape and release it on the other side, as in facilitated diffusion.
Pumps
- Pumps Use ATP to move substances against a concentration gradient, as in the sodium-potassium pump.
Specificity
- Specificity Each protein fits only one kind of solute, which lets the cell control its internal chemistry.
Part 4 of 5Link to Structure
1
Amino acids with non-polar R groups form the parts that sit in the bilayer core.
2
Polar and charged amino acids lie on the surfaces and line the channels.
3
Peripheral proteins bind loosely to the membrane by weak interactions.
4
Integral proteins can move laterally through the fluid bilayer, but some are anchored to the cell skeleton.
5
The pattern of proteins therefore depends on the function of each membrane.
Part 5 of 5Exam Checklist & Tips
2.3.2 – Key Points for the Exam
- Integral protein A protein embedded within the phospholipid bilayer.
- Peripheral protein A protein attached to the surface of the membrane.
- Channel protein A protein forming a pore through which specific ions or molecules can pass.
- Carrier protein A protein that changes shape to move a specific substance across the membrane.
- Receptor A protein that binds a specific signal molecule and triggers a response.
Common Mistakes
- Saying peripheral proteins span the membrane; this is true of integral proteins.
- Stating that carrier proteins form open pores.
- Confusing channels with pumps; pumps need energy.
- Believing proteins are fixed in position in the membrane.
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