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Transport across cell membranes - Coggle Diagram
Transport across cell membranes
Structure of the cell surface membrane
Phospholipids
The hydrophobic tails point into the centre of the cell-surface membrane as they are repelled by water.
A bi-layer is formed from phospholipids, forming a membrane.
Functions
Allow lipid-soluble substances to enter and leave the cell.
Prevent water-soluble substances entering and leaving the cell.
Make the membrane flexible and self-sealing.
The hydrophilic heads point to the outside of the cell-surface membrane as they are attracted to water on both sides.
The cell-surface membrane is the name specifically given to the plasma membrane that surrounds cells and forms the boundary between the cell cytoplasm and the external environment. Every organism will have a cell surface membrane except a virus.
All membranes around and within all cells have the same basic structure known as the plasma membrane.
Cholesterol
Functions
Make the membrane less fluid at high temperatures.
Prevent leakage of water and dissolved ions from the cell.
Reduce lateral movement of other molecules including phospholipids.
The cholesterol molecules are very hydrophobic, this helps to prevent the loss of water and dissolved ions from the cell.
Cholesterol occurs within the phospholipid bi-layer of the cell-surface membrane and add strength to it.
The cholesterol molecules also help pull the fatty acid tails of the bi-layer together to limit their movement without making the membrane too rigid.
Proteins
Functions
Allow active transport across the membrane through carrier proteins.
Form cell-surface receptors for identifying cells.
Act as channels transporting water-soluble substances across the membrane.
Help cells adhere together.
Provide structural support.
Act as receptors for substances like hormones.
Carrier proteins completely span the bi-layer. They bind to larger molecules, like glucose and amino acids, then change their shape in order to transport these large molecules across the membrane.
Protein channels completely span the bi-layer. They form water-filled tubes to allow water-soluble substances to diffuse across the membrane.
Proteins occur in the surface of the bi-layer. These proteins can act to either give mechanical support to the membrane or as cell receptors for molecules.
Glycolipids
Glycoproteins
Diffusion
Osmosis
Active transport
Co-transport