plasma membranes Flashcards
What is the fluid mosaic model?
Theory of cell membrane structure with proteins embedded in a sea of phospholipids
What are the roles of membranes at the surface of cells?
Separate cell components from its external environment, regulate transport of materials in and out of the cell, contains enzymes involved in specific metabolic pathways, have antigens so that the immune system recognises the cell as ‘self’, release chemical signals, contain receptors for chemical signals and may be the site for chemical reactions
What are the roles of membranes within cells?
In mitochondria, folded membranes called cristae give a large surface area for reactions in aerobic respiration, the inner membranes of chloroplasts called thylakoids membranes house chlorophyll and are the site of some reactions in photosynthesis, and all organelles in eukaryotes are membrane bound to separate their contents from the cytoplasm
What are the functions of proteins spanning the plasma membrane?
Some will have pores and act as channels to allow charged ions to pass, some will be carriers which - by changing their shape - carry specific molecules across the membrane, and others may be attached to the carrier proteins (peripheral proteins) and function as enzymes, antigens or receptor sites for complementary signalling chemicals eg hormones
What is the glycocalyx?
A covering on the outside of the cell membrane made up of carbohydrate chains either attached to lipids (glycolipids) or proteins (glycoproteins) in the membrane that attract water and dissolved solutes helping the cell to interact with its watery surroundings and obtain dissolved substances
What is the role of cholesterol in a membrane?
Cholesterol disrupts the regular packaging of the phospholipids and regulates fluidity in the membrane, maintaining mechanical stability and resisting the effects of temperature changes on the structure of the membrane
How are neurone cell membranes different to that of a typical cell?
The protein channels and carriers in the plasma membrane covering the long axon allow entry and exit of ions to bring about the conduction of electrical impulses, and they also have a myelin sheath formed by flattened cells wrapped around a few times, and this membrane is made of 20% protein and 76% lipid
How is the plasma membrane of white blood cells different to that of a typical cell?
Contains special protein receptors that enable them to recognise the antigens on foreign cells, usually from invading pathogens and from organ transplants
How is the structure of inner membranes of mitochondria different from that of a typical cell membrane?
They are 76% protein and 24% lipid, because the inner membranes contain many electron carriers that are made of protein, and hydrogen ion channels associated with ATP synthase enzymes
What is the biological definition of diffusion?
Movement of molecules from an area of high concentration of that molecule to an area of low concentration; it may or may not be across a membrane; it does not involve metabolic energy (ATP)
What is the definition of facilitated diffusion?
Movement of molecules from an area of high concentration of that molecule to an area of low concentration, across a partially permeable membrane via protein channels or carriers; it does not involve metabolic energy (ATP)
What factors affect the rate of simple diffusion?
Temperature - increase means molecules have more kinetic energy so rate increases, diffusion distance - thicker membrane means slower the rate, surface area - more diffusion can take place over a larger surface area, size of diffusing molecule - smaller ions or molecules diffuse faster, concentration gradient - steeper gradient means faster rate
What is the definition of osmosis?
Passage of water molecules down their water potential gradient, across a partially permeable membrane
What is the definition of water potential
Measure of tendency of water molecules to diffuse from one region to another. It is measured in kilopascals (kPa) and the highest water potential is 0 (pure water)
What is cytolysis?
In animal cells, if a lot of water molecules enter the cell due to it being placed in a high water potential solution, it may swell and burst as the plasma membrane breaks
