2.4 Membranes Flashcards
State the function of the phospholipid bilayer and outline it’s structure
Acts as a barrier against all molecules except the smallest (O2, CO2). Made up of hydrophilic phosphate heads facing outwards, and the hydrophobic fatty tails (made of hydrocarbons) facing into the middle of the bilayer.
State the function of integral proteins.
Within the bilayer. Usually span from one side of the phospholipid bilayer to the other. Are usually involved in transporting substances across the membrane.
Name the two kinds of integral proteins
Carrier proteins and channel proteins
State the function of carrier proteins
Transport specific substances across the cell membrane.
State the function of channel proteins
Allow specific molecules/ions to pass through from one side of the membrane to another.
Outline the function of peripheral proteins
External to the bilayer, and sit on its surfaces. The ones of the outside are often involved with cell communication and recognition. The ones on the inside are involved in maintaining the cell’s shape.
State the function of cholesterol
Binds together lipids in the plasma, reducing its fluidity.
State the function of glycoproteins
Usually involved in cell recognition (part of the immune system)
List the functions of membrane proteins
Transport Recognition Adhesion Communication Enzymes
(Trace)
Define diffusion
Diffusion is the passive movement of particles from an area of high concentration to an area if low concentration.
Define osmosis
Osmosis is the diffusion of water molecules across a partially permeable membrane from an area of low solute concentration to an area of high solute concentration.
Define passive tranport
Passive transport is when no energy (ATP) is used for the movement of molecules from one side of the membrane to the other.
Define simple diffusion
Involves small or non-polar molecules passively diffusing through the membrane.
Define facilitated diffusion
Movement of large or polar molecules/ions across the plasma membrane. They must travel through channel or carrier proteins. Each channel allows only a specific substance through. There is no control over direction of movement.
Define active transport
The movement of materials across a membrane against the concentration gradient (from low to high). Requires energy (ATP).
Explain the role of protein pumps and ATP in active transport.
Active transport relies in specific protein pumps in the lipid bilayer. ATP triggers a conformational change in the pump, moving particles across the membrane.
Explain how vesicles are used to transport secretory products from the RER to the plasma membrane
A vesicles containing synthesised proteins pinches off from the RER and transports the proteins yo the Golgi apparatus, where thy are modified to glycoproteins. A vesicles then pinches off the GA, and travels to the plasma membrane.
Define exocytosis
When a vesicles travels to the plasma membrane and merges with it, secreting its products.
Define endocytosis
When the plasma membrane envelops extra cellular fluid to form a vesicles within the cell.
State the two main types of endocytosis
Phagocytosis and pinocytosis
Define phagocytosis
The process by which large particles are engulfed by the cell via a vesicles. This allows quick entry for a large amount of substance.
Define pinocytosis
The process by which fluid is engulfed into the cell via a vesicle.
Describe how the membrane can change shape, break and reform during endocytosis and exocytosis
The membrane is principally held together by relatively weak hydrophobic associations between phospholipids. This allows for membrane fluidity and flexibility, as the phospholipids can move about to some extent.
Outline the structure of a phospholipid
Polar head made of phosphate and glycerol.
Non-polar tail made if two fatty acid chains.
