Plasma MembranesPlasma Membranes2. Structure2. Structure

Plasma Membrane StructurePlasma Membrane Structure

Double phospholipid Double phospholipid bilayerbilayer

Head – hydrophilic (water Head – hydrophilic (water loving)loving)

Tails – hydrophobic (water Tails – hydrophobic (water loathing)loathing)

Lipids give membrane Lipids give membrane flexibility (eg cholesterol)flexibility (eg cholesterol)

Single celled organisms Single celled organisms use this flexibility to engulf use this flexibility to engulf food & excrete excess food & excrete excess waterwater

Plasma Membrane ProteinsPlasma Membrane Proteins

May be surface proteins, or penetrate throughMay be surface proteins, or penetrate through Present to enable the cell to exchange substances and detect Present to enable the cell to exchange substances and detect

particular properties of the external environmentparticular properties of the external environment Different proteins have different characteristics for different functionsDifferent proteins have different characteristics for different functions

Transport ProteinsTransport Proteins

Openings on both sides of the membraneOpenings on both sides of the membrane Allows some substances through membraneAllows some substances through membrane eg ions. In nerve cells this causes a rapid change in eg ions. In nerve cells this causes a rapid change in

potential difference (charge) across membrane, and potential difference (charge) across membrane, and explains how charge of nerve impulse is transmittedexplains how charge of nerve impulse is transmitted

Receptor ProteinsReceptor Proteins

Bind hormones and Bind hormones and other cell controllersother cell controllers

Not all cells have the Not all cells have the same receptor proteinssame receptor proteins

Different functions – Different functions – different receptor different receptor proteinsproteins

Allows for cellular Allows for cellular differentiation in differentiation in multicellular organismsmulticellular organisms

Recognition Proteins – AntigensRecognition Proteins – Antigens

Act as markers which Act as markers which allow the immune allow the immune system to distinguish system to distinguish between self and non-between self and non-self cellsself cells

Unique to personUnique to person If non-self cells seen, If non-self cells seen,

immune system immune system destroys themdestroys them

Important in transplants Important in transplants and blood transfusionand blood transfusion

Antigens of human blood group system

Adhesion ProteinsAdhesion Proteins

Link cells together in Link cells together in multicellular organismsmulticellular organisms

Present on cells such Present on cells such as epithelial cells as epithelial cells (surface cells, and (surface cells, and lining cells of eg gut), lining cells of eg gut), white blood cells, white blood cells, platelets (involved in platelets (involved in blood clotting), and blood clotting), and endothelial cells (cells endothelial cells (cells lining blood vessels)lining blood vessels)

Toxins and Plasma MembranesToxins and Plasma Membranes Different toxins have different effectsDifferent toxins have different effects S. aureus (golden staph) inserts itself into plasma S. aureus (golden staph) inserts itself into plasma

membranes forming channelsmembranes forming channels Tetanus and Botulism toxins both are neurotoxins Tetanus and Botulism toxins both are neurotoxins

causing paralysis (opposite ways)causing paralysis (opposite ways) Venoms are neurotoxic, also necrotoxicVenoms are neurotoxic, also necrotoxic Toxins act by inhibiting nerve signals (inhibiting PD or Toxins act by inhibiting nerve signals (inhibiting PD or

overexciting), lysing membranes, making new overexciting), lysing membranes, making new membrane channels, interfering with metabolism, membrane channels, interfering with metabolism, targeting cytoplasmic componentstargeting cytoplasmic components

Alcohol also can dissolve in the plasma membrane, Alcohol also can dissolve in the plasma membrane, altering its organisation and functionaltering its organisation and function

QuestionsQuestions

Why are proteins important in membrane Why are proteins important in membrane structure?structure?

Why is membrane structure important in Why is membrane structure important in medicine?medicine?

How does the composition of different cell How does the composition of different cell membranes affect the actions of hormones? membranes affect the actions of hormones?

How have we used this information on How have we used this information on phospholipids to produce new products?phospholipids to produce new products?

BioZone questions pages 89 & 90BioZone questions pages 89 & 90 Can you find any inherited membrane disorders Can you find any inherited membrane disorders

on the internet?on the internet?

SoapSoap Soap ‘micelle’ – Soap ‘micelle’ –

hydrophobic tail and hydrophobic tail and hydrophilic headhydrophilic head

Grease and oil attract Grease and oil attract dirt and are immiscible in dirt and are immiscible in waterwater

When soap and water When soap and water and grease/oil mixed, and grease/oil mixed, micelles break up the oilmicelles break up the oil

Grease and oil and the Grease and oil and the dirt with them are dirt with them are trapped inside micelles trapped inside micelles and can be rinsed awayand can be rinsed away

Activity – Blood groupingActivity – Blood grouping http://www.youtube.com/watchhttp://www.youtube.com/watch

?v=H4qkwW-Fl3E?v=H4qkwW-Fl3E Antigen-antibody reaction Antigen-antibody reaction

causes red cell clumping causes red cell clumping if the antigen is present if the antigen is present on the membrane of the on the membrane of the red cellsred cells

ABO and Rh system ABO and Rh system important (transfusion important (transfusion reactions and Rh reactions and Rh incompatibility in incompatibility in pregnancy)pregnancy)

The answer is in The answer is in membranes!membranes!

Inherited Membrane DisordersInherited Membrane Disorders

Cystic fibrosis (Chloride channels)Cystic fibrosis (Chloride channels) Menkes disease, Wilson’s disease (Cu transport)Menkes disease, Wilson’s disease (Cu transport) Fanconi-Bickel syndrome (glucose transport)Fanconi-Bickel syndrome (glucose transport) Haemachromatosis (iron absorption receptor)Haemachromatosis (iron absorption receptor) Liddle’s syndrome (Na/K channel in kidneys)Liddle’s syndrome (Na/K channel in kidneys) Long QT syndrome (K channel - heart)Long QT syndrome (K channel - heart) Hyperkalaemic periodic paralysis (K channel - muscles)Hyperkalaemic periodic paralysis (K channel - muscles) Nephrogenic diabetes insipidus (ADH receptor in Nephrogenic diabetes insipidus (ADH receptor in

kidneys)kidneys) Glucose/galactose malabsorption (Na/Glu transporter)Glucose/galactose malabsorption (Na/Glu transporter) Cystinuria (pos. charged aa transporter in kidneys)Cystinuria (pos. charged aa transporter in kidneys)