Membranes Flashcards
What are the roles of plasma membranes at the surface of cells?
Separate cell contents from the outside environment
Cell recognition and signalling Regulating transports of materials into/ out of cells
What are the roles of plasma membranes within cells?
Form organelles
Isolate the contents of an organelle Site for attachment of enzymes and ribosomes
Provide selective permeability- controls what goes into/out of organelles
Creation of concentration gradients or specific environments (pH)
What kind of barriers are plasma membranes?
Partially permeable
Describe the role of phospholipids in the plasma membrane.
They form a bilayer seperating the cell from the outside
They are fluid and move around freely
They control what goes in and out of the cell
They are permeable to small and/or non-polar molecules, but are impermeable to large molecules and ions
They have a hydrophobic head and a fatty acid tail
Describe the role of cholesterol in the plasma membrane.
Gives the membrane stability by sitting between the fatty acid tails, making the barrier more complete and preventing molecules like water passing the membrane
Describe the role of glycolipids in the plasma membrane.
They are used in cell signalling, cell surface antigens and cell adhesion
(phospholipid molecules with a carb part attached)
Describe the role of proteins in the plasma membrane.
Channel proteins allow the movement of some substances i.e large molecules like sugar, through the plasma membrane
Carrier proteins actively move substances across the plasma membrane
Describe the role of glycoproteins in the plasma membrane.
Act as antigens
Enable the identification of cells as self or non-self
Act as receptors or binding sites for hormones
Act as receptors on transport proteins to trigger movement
Allow cell adhesions to hold cells together in a tissue
Allow water molecules to stabilise the membrane
Outline the effect of changing temperature on structure and permeability.
Increasing temperature means the molecules have more kinetic energy, the increased movement will make the membrane leaky, so molecules that do not usually move in/out of the cell can do so.
The membrane structure is disrupted as the phosphilipd bilayer melts, membranes and proteins denature and the membrane becomes more permeable.
Explain the term cell signalling.
Process that leads to communication and coordination between cells, e.g. hormones binding to their receptors on the cell surface membrane to trigger a response. It allows cell recognition and the coordination of the action of different cells
Explain the role of membrane bound receptors as sites where hormones and drugs can bind.
The Target Cells have a receptor which is complementary to the hormone, meaning that it can bind to the receptor cells, triggering the desired internal response. Drugs have also been developed which bind to the receptor molecules on cells.
Give examples of drugs that bind to the receptor molecules on cells.
Beta-blockers are used to prevent a muscle from increasing heart rate to dangerous levels and some drugs use to treat schizophrenia mimic a natural neuron transmitter that some individuals cannot reproduce.
Define passive transport.
The transport of a molecule without the use of energy.
Define diffusion.
The net movement of molecules from an area of high concentration to an area of low concentration, small non-polar substances and water diffuse through the bilayer between phospholipid molecules
Define facilitated diffusion.
Large and charged molecules can’t diffuse.
Channel proteins form pored in the bilayer which are specific to only one ion and are often gated.
Carrier proteins are specific to only 1 molecules, once this molecule fits in the carrier changes shape to allow the molecule through the membrane.
