weber uiuc edu 29 August 2007 MCB150 Lecture 04 Lecture 04 29 August 2007 Announcements No classes on Monday Labor Day o No discussion sections at all next week Post lecture questions from Friday s lecture will be due on Tuesday Tips for success meeting is in 228 NHB on 7 00PM Thursday o Tomorrow is a chance to ask questions about the administration of the course o There will be no official course information at the tips meeting that is no information about microbiology Polysaccharides Major Uses of Large Polymers of Glucose Three important molecules made from glucose o Cellulose o Starch o Glycogen Cellulose Primary component of plant cell walls Very common molecule Cellulose is composed of monomers of glucose o Relatively straight chains of glucose are formed called fibrils o 1 4 glycosidic linkages Fibrils are bundled together for strength into units called fibers o Hundreds or thousands of glucose monomers o The fibrils are held together by hydrogen bonds formed with the hydroxyl groups on the glucose monomers o Any one hydrogen bond is weak but when hundreds or thousands are present serious interactions can result Cellulose Linkages The example in the notes is drawn in the standard convention with lines indicating atoms receding into or projecting out of the page Any deviations from the numbering or from the orientation of the molecules is due to a change in the three dimensional organization of the monomers in the molecule o That is if you look at the diagram you will note that every other glucose is rotated 180 degrees along the axis of the fibril Why o The first glucose is in the B configuration it is glucose o The second glucose in order to form a 1 4 glycosidic linkage must be rotated 180 degrees o Be careful with this Just because the hydrogen on the 1 carbon of the second glucose is apparently above the plane it does not make that glucose an glucose Always look to see which carbon is considered the 1 carbon and follow it around the molecule to the 6 carbon paying attention to the orientation Page 1 of 5 weber uiuc edu 29 August 2007 MCB150 Lecture 04 Fibrils are almost perfectly straight in cellulose They form hydrogen bonds to other fibrils using the hydroxyl groups o These pairings of fibrils are not due to covalent bonds Hydrogen bonds hold the fibrils adjacent to one another Fibrils are laid down in bundles called fibers in a cross hatch pattern which provides strength to the cell wall The individual glucose monomers of a fibril are very inaccessible It is hard to break the 1 4 glycosidic linkages See the note in the FAQ section of the MCB150 web site for more information on why they are stronger than 1 4 linkages Starch Starch is made by plants and is found in roots storage organs etc It too is a polymer of glucose but it is used for energy storage not as a structural unit It is an energy storage molecule Starch is made of branching polymers of glucose o These linear chains are linked by 1 4 glycosidic linkages o The branches are linked by 1 6 glycosidic linkages Starch Structure The 1 glucose is an glucose The 2 glucose is not drawn upside down here because there is no need to in order to maintain structure and shape These repeating patterns can form long chains just like with cellulose To form a branch the top glucose 1 carbon is in glucose conformation o Its 1 carbon is attached to the 6 carbon of a glucose in the chain via an 1 6 linkage o The 4 carbon of the branch can be attached to the 1 carbon of another glucose to form a branching chain Every 6 carbon is a potential branching site Glucose is the central food source on the planet The pictures in the notes include a light microscope view of stained starch granules within cells o Cells find it easier to store glucose in starch molecules pulling them off as needed than leaving the individual glucose molecules floating around o They can pull off a glucose easier than in cellulose o This is true even though glucose is the central food storage unit in plant cells Glycogen Glycogen does for animals what starch does for plants Glycogen is found in muscles and liver cells It is more efficient to store glucose in the form of clumps or polymers than it is to keep the glucose molecules around individually Page 2 of 5 weber uiuc edu 29 August 2007 MCB150 Lecture 04 o They pack tighter this way too Glycogen is highly branched o More branching makes for a tighter molecule which in turn makes it easier to move about o This is an important consideration for animal cells that need flexibility and motility As with starch fibrils are composed of 1 4 linkages while branches use 1 6 linkages The difference between starch and glycogen is the organism the molecules are found within plant vs animal and the amount of branching Glycogen Structure Same general concept as found in starch but more branching o The same structural diagram is used in the notes though it is more compact than starch Glycogen forms granules in liver tissue and muscle cells Because they are more compact the picture in the notes comes from electron microscopy We will address carbohydrates later throughout the semester These three are the only polysaccharides we will be concerned with now Thus finishes the lectures on the sugars Macromolecule 2 Proteins We are the product of our proteins and protein activity o The unique nature of cells arise from the composition and amounts of proteins contained within Genomics they study of an organism as a function of its genome Proteomics The study of an organism as a function of its proteins In other words the study of the collection of proteins proteo and protein activity within a cell o Cell A behaves differently from Cell B because of its proteins Proteins account for more than half the macromolecules in the cell Review the pie chart in the previous lecture for the breakdown of molecules in a cell o It follows that they are important Proteins are involved in all types of cell functions o Structure keratin hair fingernails o Storage albumen egg whites o Transport hemoglobin binds oxygen in red blood cells o Movement actin myosin moving muscle fibers o Regulation Metabolism Catalysis This last one is the most important of all of them in cells We ll spend the most time talking about these Most of our useful DNA instructs cells on how to make proteins o To understand the behavior of cells and the function of DNA we need to understand proteins o We need to understand the non junk useful DNA Page 3 of 5 weber uiuc edu 29