Chapter 5 Plasma Membranes Flashcards
Describe the structure of the phospholipids in the plasma membrane
The polar hydrophilic phosphate heads face outwards interacting with the surrounding aqueous solutions while the non polar hydrophobic fatty acid tails face inwards forming the inner core of the phospholipid bilayer.
State the different components that make up the cell surface membrane
Cholesterol
Glycolipids
Extrinsic proteins
Intrinsic proteins consisting of carrier proteins, channel proteins and glycoproteins.
What are intrinsic proteins?
Transmembrane proteins embedded through both layers of the membrane.
Eg, channel and carrier proteins
What is function of channel proteins?
Provide a hydrophilic channel for passive movement of polar molecules and ions down a concentration gradient.
What is the function of carrier proteins?
Involved in the passive and active transport of substances into cells by changing the protein shape.
What is the structure of a glycoprotein?
Intrinsic protein which have attached carbohydrate chains.
What is the function of glycoproteins?
Act as receptors for cell signalling
Eg, neurotransmitters, hormones, drugs and antibodies are able to bind to these receptors to initiate a response
Help to stabilise the membrane by forming hydrogen bonds with surrounding water molecules
What is the structure of glycolipids?
Lipids with attached carbohydrate chains
What is the function of glycolipids?
Act as cell markers or antigens for cell recognition in the immune system.
What are extrinsic proteins?
Proteins free on the membrane surface or bound to an intrinsic protein.
They are only bound on one side of the bilayer but can be bound on either side.
What is the structure of cholesterol?
Lipid with a hydrophilic and hydrophobic end.
They are positioned between the phospholipids in the membrane bilayer with the hydrophilic end interacting with the polar phosphate heads and the hydrophobic end interacting with the fatty acid non polar tails.
What is the function of cholesterol?
Regulates the membranes fluidity
The more cholesterol there is, the less fluid that is able to pass through making the membrane less permeable.
State why the way cholesterol is structured is significant to the phospholipid bilayer
Cholesterol adds stability to membranes without making them to rigid.
State the two different types of membranes
Plasma membranes at the surface of cells
Membranes within cells
State the functions of a plasma membrane
-Act as a barrier between the cell and the surrounding aqueous environment
-Partially permeable to control what substances enter and leave the cell
-Allow recognition by other cells
-Allow cell communication
State the function of membranes within cells
-Act as a barrier between organelles and cytoplasm of cell so functions of organelles are more efficient
-Form vesicles to transport substances to different areas of the cell
-Partially permeable so control what substances enter and leave the organelle
-Sites of chemical reactions
-Compartmentalisation- separate membrane bound areas
What is the function of the phospholipid bilayer?
Acts as a barrier to control what substances enter and leave the cell
What molecules are prevented from diffusing across the phospholipid bilayer?
Water soluble substances such as ions
What molecules are able to diffuse through the phospholipid bilayer?
Fat soluble substances such as vitamins are able to dissolve in the bilayer and pass directly through.
The smaller and less polar the molecule the faster it is able to diffuse across the membrane.
State the name of the model that represents all the components of the plasma membrane
Fluid Mosaic model
Why do cell membranes have a fluid mosaic structure?
Phospholipids are free to move (fluid)
Embedded proteins can vary in shape, size and position
Describe the role of the plasma membrane in cell signalling
A cell will release a messenger molecule
(eg hormone) that travels to the target cell
The messenger molecule will be detected as it binds to a receptor on its cell membrane
Proteins in the cell membrane act as these receptors- they have specific shapes meaning only the messenger molecules with a complementary shape are able to bind.
Describe the roles of the cell membrane receptors when drugs are taken
Drugs can bind to the receptors on cell membranes
The drugs either trigger a response or block the receptor and prevent it from working.
Describe the role of plasma membranes during chemical reactions
Proteins need to be in particular positions for chemical reactions to occur.
State the factors which can affect the membrane structure
Temperature
Solvents
Describe and explain how changing temperature affects membrane permeability
Lower temperatures (below zero) mean the phospholipids don’t have as much kinetic energy so cannot move as much. The membrane becomes rigid and the proteins in the membrane deform increasing the permeability of the structure. Ice crystals can forms which pierce the membrane increasing permeability further.
Between 0 and 45 degrees the phospholipids are able to move and are not packed as tightly together- partially permeable. Increasing temperature increases the kinetic energy of the phospholipids so the permeability of the membrane also increases.
Higher temperatures exceeding 45 degrees means the bilayer melts and breaks down so the overall permeability of the membrane increases. Channel and carrier proteins deform so they cannot control what enters of leaves cell. Water inside the cell expands putting pressure on the membrane.
