2.3.2Additional lessons
Membrane Proteins — IB Biology SL Revision Notes & Topical Questions
5 min read 4 parts Lesson 21 of 142
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 4Types of Membrane Protein
Integral proteins
- Integral proteins Embedded in the bilayer and amphipathic, with hydrophobic regions in the core;
- some span both layers.
Peripheral proteins
- Peripheral proteins Hydrophilic proteins attached to one surface of the membrane, either inside or outside the cell.
Transmembrane
- Transmembrane Proteins crossing the full bilayer have hydrophobic regions in the core and hydrophilic regions in contact with water.
Mobility
- Mobility Many membrane proteins can drift within the bilayer, which contributes to the fluid mosaic model.
Variety
- Variety A single membrane may contain many different proteins, each specific to a particular molecule or task.
Part 2 of 4Functions of Membrane Proteins
A useful memory aid is that proteins transport, receive signals, catalyse reactions, attach cells and identify cells.
Functions of Membrane Proteins
Transport
- Transport Channel and carrier proteins move specific ions and molecules across the bilayer.
Receptors
- Receptors Proteins with binding sites for hormones or neurotransmitters pass the signal into the cell.
Enzymes
- Enzymes Membrane-bound enzymes are held in position next to their substrates and catalyse reactions on the membrane surface.
Adhesion and recognition
- Adhesion and recognition Proteins link cells together and identify cells to others, using glycoproteins as markers.
Cell-to-cell communication
- Cell-to-cell communication Receptor proteins let a cell respond to chemical messages from other cells, which coordinates activity in a tissue.
Part 3 of 4Membrane Transport Processes
1
Simple diffusion moves small non-polar molecules, such as oxygen, down a concentration gradient with no energy or protein.
2
Facilitated diffusion uses channel or carrier proteins to move ions and polar molecules down their concentration gradient, without ATP.
3
Osmosis is the passive movement of water across a partially permeable membrane from lower to higher solute concentration.
4
Active transport uses carrier proteins, called pumps, to move substances against the concentration gradient.
5
ATP is hydrolysed in active transport, and the energy changes the shape of the pump so that the substance is moved across.
| Process | Needs protein? | Needs ATP? | Direction |
|---|---|---|---|
| Simple diffusion | No | No | Down the gradient |
| Facilitated diffusion | Yes | No | Down the gradient |
| Active transport | Yes | Yes | Against the gradient |
Part 4 of 4Exam Checklist & Tips
2.3.2 – Key Points for the Exam
- Integral protein A protein embedded in the phospholipid bilayer.
- Peripheral protein A protein attached to the membrane surface.
- Channel protein A protein forming a pore through which specific ions pass by facilitated diffusion.
- Carrier protein A protein that changes shape to move a specific substance across the membrane.
- Active transport Movement of substances against a concentration gradient using energy from ATP.
Common Mistakes
- Saying facilitated diffusion needs ATP; it is passive.
- Describing active transport as movement down the concentration gradient.
- Stating that peripheral proteins pass through the membrane; that describes transmembrane integral proteins.
- Forgetting that each transport protein is specific for one type of ion or molecule.
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