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23 Cards in this Set
- Front
- Back
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• Describe the properties of the lipid bilayer and thegeneral structure of cell membranes.• Explain how membrane proteins and carbohydratesare associated with the lipid bilayer.• Describe the functions of membrane proteins andcarbohydrates. |
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what must a cell do in order to survive? |
be physically separated from the external environment. • allow passage of nutrients, minerals, water etc. into the cell. • excrete waste products out from the cell. • receive and act on signals from outside & send signals to othercells. |
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what is the plasma membrane |
the membrane surrounding eukaryotic cells |
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what is the role of lipids in the cell membrane? |
forms the structure that seals each cell or organelle from its external environment made up from phospholipids and cholesterol |
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what are protein responsible for in cell membranes? |
responsible for communication with the externalenvironment: comprising receptors, channels and pumps |
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what is the role of carbohydrates |
present in small amounts on the outside surface ofthe cell, either as glycoproteins or glycolipids |
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what is meant by the term amphipathic |
Phospholipid molecules have polar(hydrophilic) and non polar (hydrophobic)domains |
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describe the structure of a phospholipid |
hydrophilic head hydrophobic tail |
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what is a liposome? how has it been exploited |
spherical sac of phospholipid molecules enclosing a water droplet exploited in medicine as formed artificially to carry drugs or other substances into the tissues. |
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what is the role of cholesterol |
fits between phospholipids, membrane fluidity, the more cholesterol the more rigid and less permeable the membrane becomes important for thermoregulation- more cholesterol in colder animal species |
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What molecules can and cant cross the bilayer |
can- water other small uncharged polar molecules, hydrophobic molecules can't- large uncharged molecules (e.g. glucose), ion WE NEED PROTEINS- for them to cross |
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state 5 functions of the membrane |
- transport specific molecules - act as signal receptors -provide channels - provide structural links to other cells - for enzyme activity (enzymes sat on the membrane) |
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How can transmembrane proteins span pass through the hydrophobic interior |
Depending on the amino acid sequence of the polypeptide chains,proteins can adopt amphipathic structures: partly hydrophobic andpartly hydrophilic.• The a-helix can provide such a hydrophobic surface, one that is oftenfound spanning membranes. |
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what proteins are there? |
- integral membrane -lipid bound proteins monotopic membrane proteins peripheral membrane proteins |
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outline integral proteins |
transmembrane- one end in contact with interior the other in contact with the exterior one end hydrophobic other phillic |
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outline peripheral proteins |
attached to the exterior of the lipid bilayer easily separated from the bilayer able to be removed without harming the layer less mobile within |
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where is carbohydrate found? |
only on the exterior side of the membrane |
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what are the two types of protein-carbohydrate molecules ? |
glycoproteins - mostly protein with some sugar attached proteoglycans- very long branching carbohydrate chains |
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what is a Glycocalyx |
when carb chains form a net around cells role- traps compounds required by the cell, involved in cell-cell recognition |
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what is a GPI anchor |
connects a protein via a lipid, alter the structure of that part of the membrane |
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what are lipid rafts |
highly organised area concentration of particular transmembrane proteins involved with signalling lot more cholesterol, more rigid structure |
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what is a caveolae? |
invagination on the surface of a cell used for endocytosis, accumulate in lipid rafts |
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summary |
Membranes enclose the cell, control entry/exit of nutrients/ waste and sense external signals Membrane consists mostly of lipid and protein and are fluid structures The lipid bilayer provides the basic structure and ensures permeability |
