1.3 Syllabus
U1. Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules.
Cell Membrane: Cell membranes are made of phospholipids, molecules composed of a phosphate head and a lipid tale
Phospholipids: Molecules composed of a phosphate head and a lipid tale. This makes phospholipids amphipathic.
-Phosphate head: Hydrophilic (Polar) = Attracted to water
-Tails: Hydrophobic (Non-polar)= Not attracted to water (Consists of 2 hydrocarbon chains)
- When phospholipids mixed with water, phosphate head is attracted to water and hydrocarbon tail is attracted to each other and not attracter to water. This forms double layer
-Membrane needs to be fluid enough for cell to move
- Properties of the Phospholipid Bilayer: The bilayer is held together by weak hydrophobic interactions between the tails. Hydrophilic / hydrophobic layers restrict the passage of many substances. Individual phospholipids can move within the bilayer, allowing for membrane fluidity and flexibility. This fluidity allows for the spontaneous breaking and reforming of membranes (endocytosis / exocytosis)
Phospholipids: Molecules composed of a phosphate head and a lipid tale. This makes phospholipids amphipathic.
-Phosphate head: Hydrophilic (Polar) = Attracted to water
-Tails: Hydrophobic (Non-polar)= Not attracted to water (Consists of 2 hydrocarbon chains)
- When phospholipids mixed with water, phosphate head is attracted to water and hydrocarbon tail is attracted to each other and not attracter to water. This forms double layer
-Membrane needs to be fluid enough for cell to move
- Properties of the Phospholipid Bilayer: The bilayer is held together by weak hydrophobic interactions between the tails. Hydrophilic / hydrophobic layers restrict the passage of many substances. Individual phospholipids can move within the bilayer, allowing for membrane fluidity and flexibility. This fluidity allows for the spontaneous breaking and reforming of membranes (endocytosis / exocytosis)
U2. Membrane proteins are diverse in terms of structure, position in the membranes and function.
-Primary Function: Form barrier through which ions and hydrophilic molecules do not easily pass. It is carried out by phospholipid bilayer.
- Integral Proteins (Carrier and channel protein): Permanently embedded in hydrocarbon chains in centre of membrane. Many go all way through.
- Peripheral protein: Usually have temporary association with the membrane ,
Related Question:
Q. Write down functions of membrane protein
Answer:
-Cell to cell communication
-Channels for passive transport
-Active transport
-Cell Adhesion
-Immobilized Enzymes embedded in the membrane
-Electron carriers
-Binding site for Hormone
- Integral Proteins (Carrier and channel protein): Permanently embedded in hydrocarbon chains in centre of membrane. Many go all way through.
- Peripheral protein: Usually have temporary association with the membrane ,
Related Question:
Q. Write down functions of membrane protein
Answer:
-Cell to cell communication
-Channels for passive transport
-Active transport
-Cell Adhesion
-Immobilized Enzymes embedded in the membrane
-Electron carriers
-Binding site for Hormone
U3. Cholesterol is a component of animal cell membranes
Cholesterol: Makes the phospholipids pack more tightly and regulate the fluidity and flexibility of the membrane. Mostly hydrophobic and restrict movement of phospholipid molecule. It reduces fluidity of membrane and permeability of membrane to hydrophilic particles ions.
→It makes the membrane less permeable to very small water-soluble molecules that would otherwise freely cross
→It functions to separate phospholipid tails and so prevent crystallization of the membrane
→It helps secure peripheral proteins by forming high density lipid
- Type of lipid: Steroids -> Interact with fatty acid tails of phospholipids to moderate properties of the membrane.
- Disrupt regular packing of hydrocarbon tails of phospholipid molecules a
→It makes the membrane less permeable to very small water-soluble molecules that would otherwise freely cross
→It functions to separate phospholipid tails and so prevent crystallization of the membrane
→It helps secure peripheral proteins by forming high density lipid
S1. Drawing of the fluid mosaic model.
S2. Analysis of the falsification of the Davison-Danielli model that led to the Singer-Nicolson model.
Evidences that have falsified Davison-Danielli Model:
-Presence of globular proteins with phospholipid bilayer
-Non polar amino acids cause proteins to remain embedded in membranes
-Presence of globular proteins with phospholipid bilayer
-Non polar amino acids cause proteins to remain embedded in membranes