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In this topic of IBDP Biology, we will learn about the first part of membranes.
The structure of membranes
Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes.
- When it comes to IBDP Biology, The 'head's have large phosphate groups, thus they are hydrophilic (attract water) or polar. These section are suited to the large water content of the tissue fluid and cytoplasm on opposite sides of the membrane.
- The fatty acid tails are non-charged, hydrophobic meaning they repel water. This creates a barrier between the internal and external 'water' environments of the cell. The 'tails' effectively create a barrier to the movement of charged molecules
- The individual phospholipids are attracted through their charges and this gives some stability. They can however move around in this plane
- The stability of the phospholipid can be increased by the presence of cholesterol molecules.
List functions of membrane proteins
Diffusion and Osmosis
- Diffusion: is the passive movement of particles from a region of higher concentration to a region of lower concentration, as a result of the random motion of particles.
- Osmosis: the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration.
Explain passive transport across membranes by simple diffusion and facilitated diffusion
- If you look at the IBDP Biology curriculum, Some molecules are so small that they pass through the membrane with little resistance
- This includes Oxygen and Carbon Dioxide
- Lipid molecules (even though very large) pass through membranes with very little resistance also.
- Larger molecules (red) move passively through the membrane via channel proteins
- These proteins(grey) have large globular structures and complex 3d-shapes
- The shapes provide a channel through the middle of the protein, the 'pore'
- The channel 'shields' the diffusing molecule from the non-charged/ hydrophobic/ non-polar regions of the membrane.
Explain the role of protein pumps and ATP in active transport across membranes
- Molecules are moved against the concentration gradient from a region of their low concentration to a region of their high concentration.
- Active mean that the membrane protein 'pump' requires energy (ATP) to function
- Referring to the IBDP Biology specification, The source of energy is ATP is produced in cell respiration
- Transported molecules enter the carrier protein in the membrane.
- The energy causes a shape change in the protein that allows it to move the molecule to the other side of the membrane.
- The sodium-potassium, pump that creates electro-chemical gradient across the cell membrane of all cells.
- Cells are -ve charged on the inside relative to the outside.
- This pump is modified in the nerve cell to create some of the electrochemical phenomena seen in nerve cells.
That's the end of Part 1~ You can go to Part 2 now!
