Lipids, Membranes, and Transport PDF

Lipids, membranes and transport    **MLO6.    **Describe the structure of the principle biological molecules contained within cells, i.e. DNA, RNA, carbohydrates, proteins, and lipids.\      **MLO9.    **Describe the basic structure of cell membranes and understand its importance in cellular compar...

Lipids, membranes and transport    **MLO6.    **Describe the structure of the principle biological molecules contained within cells, i.e. DNA, RNA, carbohydrates, proteins, and lipids.\      **MLO9.    **Describe the basic structure of cell membranes and understand its importance in cellular compartmentalisation and maintaining osmolality. Explain the ways in which ions and large molecules are transported across cell membranes. Lipids are hydrophobic molecules and are water insoluble. They are formed of fatty acids Fatty acids: - Long hydrocarbon chain - Carboxyl group - Hydrocarbon groups are non polar - Water insoluble - Saturated (fatty acids) have no double bonds, are solid at room temperature and very important for cell membrane - Unsaturated (fatty acids) have one or more double bonds, if hydrogen atoms are on the same side of the double bond called cis-unsaturated fatty acids, if opposite, trans-unsaturated fatty acids - Cis-unsaturated fatty acids are more healthy Triglycerides are formed of 3 fatty acids and glycerol - In animal fats, triglyceride made of saturated fatty acid - In plant fats, triglyceride made of unsaturated fatty acid Triglycerides: - Hydrophobic/completely water insoluble Phospholipids: - Glycerol attached to 2 fatty acids and one polar head (phosphocholine) - Phosphor group attaches to choline - Amphipathic meaning it has a polar head and non polar head/body Steroids: - Made of cholesterol - Cholesterol has four carbon rings - Hepatocytes have enzyme for production of cholesterol - Important for rigidity in cell membrane - Important precursor for synthesis of hormones - Vitamin D has a steroid structure Cell partitions: - Separate out different parts of the cell - Might be to raise the concentration of a substance in one particular area - Might want to separate organelles with different functions - Signalling within cell Phospholipid membrane: - Hydrophilic head on the outside, hydrophobic tails inside - Doesn't allow large or charged molecules through Diffusion: - Passive movement of a molecule down its concentration gradient Osmosis: - Passive movement of water molecules down water potential gradient Active transport: - The net movement of molecules from an area of low to high concentration, against the concentration gradient hence requiring ATP Facilitated diffusion: - The movement of molecules that are not able to cross the membrane independently, perhaps because of size or charge Ion channels: - Protein that makes a hole/pore in the membrane - Can be opened and closed by various mechanisms - Don't use energy - High carrying capacity - Selective to specific ions Carrier molecules: - Uniporters: Allow ions to go one way - Symporters: Allow two molecules of different kinds to move together, can use concentration gradient to power this carrier - Antiporters: Allow two molecules of different kinds to move in two opposite directions, can use diffusion gradient of one to power the pumping of the other Aquaporins: - Water channels - Allow osmotic movement of water - Made of four subunits and each subunit has a pore down the middle Moodle recap quiz Q: An ion channel is a -? A: simple pore in the membrane, selectively permeable and usually opened and closed in a controlled manner Q: What do carriers do -?\ A: Bind to the molecule and change shape to transport it across Q: What do aquaporins do? A: Play a role in osmosis Q: What are some characteristics of ion channels?\ A: Contain a central water filled pore, have gate in the pore which opens and closes, are selective for certain ions Q: What features would favour a molecule diffusing through the plasma membrane?\ A: Small size, readily soluble in oil, non-polar Using the sodium-glucose pump as an example, what do these things do? Q: Antiporter A: Binds sodium on the outside of the cell, and pumps calcium out of the cell against calcium's concentration gradient Q: Active transporter A: Binds sodium inside the cell and releases it on the outside, using ATP Q: Symporter A: Binds sodium on the outside of the cell, and pumps glucose into the cell down its concentration gradient Q: Ion channel A: Opens in response to voltage, and allows chloride to leave the cell Q: Uniporter A: Binds glucose on the outside of the membrane where its concentration is higher and release it on the inside Q: What are some of the features of plasma membranes?\ A: Found inside cells, as well as on the outside, formed of 2 layers of phospholipid