Cell Membrane (1)

Water

- IMPORTANT because it serves as the universal solvent in biological systems (living organisms), and makes up 70% or more of the weight in cells

- Solutes (e.g. sugars, organic acids, and some of the amino acids) that have an affinity of water and therefore dissolve readily in it are called hydrophilic. [Hydrophilic = Hydro (Water) + “Philic” (Loving)]
- Molecules that are not very soluble in water, such as lipids and some proteins found in biological membrane, are termed hydrophobic
- Some biological macromolecules, notable proteins and phospholipids, have both hydrophobic and hydrophilic regions on the same molecule. Such molecules are known as amphipathic molecules.

Phospholipids

-  Lipids with phosphate groups (PO₄^3-) that are hydrophilic while hydrocarbon chairs are hydrophobic

-  When phospholipid molecules come into contact with water, they tend to line up polar heads in water and hydrocarbon tails away from water

Cell Surface Membrane Structure

Fluid Mosaic Model

Fluid- a bilayer that allows both phospholipids and proteins to move about laterally

Mosaic- collage of proteins randomly distributed in the bilayer

Model- a hypothesis proposal supported by evidence

- Fluid goes through transverse diffusion (flip-flop) or lateral diffusion (frequent)

Cell membrane (mosaic) Structure and Composition

Proteins

• Interspersed randomly among phospholipids
• 2 main types
• Peripheral / Extrinsic proteins
• Loosely attached at charged surface / hydrophilic part of phospholipid bilayer
• Integral / Intrinsic proteins
• Either partially penetrating the phospholipid bilayer or spanning the membrane entirely
• Proteins partially embedded in phospholipid bilayer:
• Contains both hydrophilic and hydrophobic regions to interact with charged heads and hydrocarbon tails of phospholipid bilayer respectively

Glycoproteins (Also a type of protein but slightly different)

• Interspersed among phospholipids
• Consists of carbohydrate chains bound to peripheral proteins and hydrophilic regions of integral proteins that occur on exterior surface of outer membrane
• Carbohydrate chains involved in recognition of same cell type or adhesion of cells to neighboring cells for immune response

Glycolipids

• Interspersed among phospholipids
• Consists of carbohydrate chains bound to two hydrophobic hydrocarbon tails
•              Involved in recognition of same cell type or cell signaling pathways

Cholesterol

• Interspersed among phospholipids
• Essential in maintaining membrane fluidity

Extra :)

Why do you not feel pain?

You will feel pain from your nerve cells, so as long as you don’t touch your nerve cells, it will be okay. Areas where you hardly feel pain: Elbow XD

Seafood has a lot of cholesterol. Why?

Cold temperature. Cholesterol helps you adapt to a cold environment, and prevents the membrane from becoming frozen.