All cells have a permeable membrane with an equally distinctive structure. In this IBDP Biology blog, we will learn:
- The structure of cell membrane
- How materials go in and out of cell
- Diffusion and Osmosis
Structure of cell membrane
Hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of the cell membrane:
- Hydrophobic molecules are not attracted to water, but are attracted to each other.
- The phosphate head is hydrophilic and the two hydrocarbon tails are hydrophobic. In water, phospholipids form double layers with the hydrophilic heads in contact with water on both sides and the hydrophobic tails away from the centre.
- 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 tissuefluid 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.
PHOSPHOLIPID STRUCTURE
- hydrophobic tail/hydrophillic head
- head made from
- glycerol
- and
- phosphate
- tail made from
two fatty acids
ARRANGEMENT IN MEMBRANE
- form a
- bilayer
- heads face outside
the membrane/ tails face inside the membrane
- there is a
hydrophobic interior and a hydrophillic exterior
Transport materials within a cell
1. After proteins have been synthesized by ribosomes they are transported to the rough endoplasmic reticulum where they can be modified.
2. The protein is moved through the rER and modified.
3. A spherical vesicle is formed form the end of the rER with the protein inside.
4. The vesicle migrates to the golgi apparatus.
5. Vesicle and golgi membranes fuse. The protein is released into the lumen of the golgi apparatus.
6. The golgi modifies the protein further by adding lipid or polysaccharides to the protein.
7. A new vesicle is formed from golgi membrane which then breaks away. The vesicles migrates to the plasma membrane.
8. The vesicle migrates to the plasma membrane fuses and secretes content its contents out of the cell. A process called exocytosis.
Diffusion and Osmosis
Diffusion: 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.
Some molecules are so small that they pass through the membrane with littleresistance
- 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 structuresand complex 3d-shapes
- The shapes provide a channel through the middle ofthe protein, the 'pore'
- The channel 'shields' the diffusing molecule from the
non-charged/ hydrophobic/ non-polar regions of the membrane.
And we're done!
References
https://www.google.com/url?sa=i&url=https%3A%2F%2Ftenor.com%2Fview%2Fcartoon-cute-thumbs-up-good-job-good-work-gif-15493930&psig=AOvVaw25FmzcQTdujti3V_7InkFd&ust=1625158891575000&source=images&cd=vfe&ved=0CAoQjRxqFwoTCMCjoubqv_ECFQAAAAAdAAAAABAJ
https://www.google.com/url?sa=i&url=https%3A%2F%2Fen.wikibooks.org%2Fwiki%2FBiochemistry%2FMembranes_and_Lipids&psig=AOvVaw3kXmrBYu0Lb-q4S55dPM4p&ust=1625156411378000&source=images&cd=vfe&ved=0CAoQjRxqFwoTCPiJjcjhv_ECFQAAAAAdAAAAABAT
https://www.google.com/url?sa=i&url=http%3A%2F%2Fib.bioninja.com.au%2Fstandard-level%2Ftopic-1-cell-biology%2F14-membrane-transport%2Fvesicular-transport.html&psig=AOvVaw0xe2spgiNEoetxi9v6hnr6&ust=1625156715016000&source=images&cd=vfe&ved=0CAoQjRxqFwoTCMDDrdviv_ECFQAAAAAdAAAAABAJ
Drafted by Venetia (Biology)