Monday 10 10 05

10/10/05 Lecture
Now we are starting chap 7, which is Carbohydrates, and because of time constraints we are only doing 7.1 and 7.2
HW is dues next Monday.
Next Monday is the midterm, more information about the test to come during the week.
• Carbohydrates are the most abundant biomolecules on earth. They are made by photosynthesis, in abundance, so much that 10^18 of carbohydrates are fixed every year.
• Carbohydrates provide energy, which can be stored for use later. They can also be used for cell walls.
• All carbohydrates share similar chemistry
• Figure 7-1a Simple sugars start at 3 carbons. Characterized by CH2O, number of carbons equal oxygen. Every carbon but one is in the form of an active hydroxyl group. One carbon is a carbonyl group. This has special chemical properties: when it is a terminal carbon it is called an Aldoses. When it is not it is called a Ketoses.
• Figure 7.1 b You can add carbons and make longer chains.
• Figure 7.1.c Used for RNA and DNA. The D means sugars are optically actively.
• Figure 7.2 The stereoisomers are mirror images of each other. The L form is usually not relevant biologically, a few expectations. D rotates clockwise to the light source. The two forms are nonsuperimposable.
• Figure 7.3a Active carbon with OH is on the left on the next to last carbon, or penultimate carbon, gives a D sugar. D family is relative common, L is rare. In the figure, the ones with their names in boxes are the common aldoses.
• Figure 7.3b These are the ketoses
• Figure 7-4 If you look at these three, glucose is what the others are compared to; the other two are called epimers. They vary by optical rotation on one carbon. *All are nonsuperimposable which can be a trick question on a midterm because it looks like you can on paper, don’t forget these molecules are in 3D. To make this rotation, it needs an enzyme called epimerace.
• Figure 7-5 The condensation of aldehyde or ketone. Alcohol is the nucleophile. E- is taken by the Oxygen, which makes hemiacetal / hemiketal. This is reversible, which can happen fast without catalysts. It is the carbon bonded to 2 oxygen that remains active so that another alcohol can attack making a stable acetal / ketal and water. The second half is slower so it needs more help for a catalysts then the first step.
• Figure 7-6 Rings can form among chains; it can produce alpha and beta isomers. It can attack its self because it the of the single bonds. If Carbon 4 or 6 attacks it creates rings with too much strain. If carbon 5 attacks, it gives a 6 member ring, 5 carbons, 1 oxygen. The alpha form has the OH down and H up while the beta form has the OH up and the H down. All three forms are in rapid equilibrium, called mutarotation. It is important because it will create slightly skewed amounts so you do not have 50/50 of the two forms. Enzymes are picky and will only react with 1 or the other, their docking and the placement of the H bond is dependent on which conformation it is.
• Figure 7-7 This ring forming makes pyran or furan.
• Figure 7-8 resulting rings are puckered makes chair conformations. Two possible chair forms; there is an equatorial and axial position. Axial is up and down, equatorial is out to the side. When OH is in the equatorial position, it is happier and the H likes to be in the axial position.
• Figure 7-9 You can usually play games with the 2 and 3 carbons with out affecting the function. Be aware of all the different members of the glucose family, and what makes them different.
• Figure 7-10 Sugars can be oxidized by 2 electrons can form ester by eliminating H2O. You need to have an enzyme.
• Figure 7-11 Stringing sugars together by glycosidic bonds. It is a condensation reaction. Alcohol is it the nucleophile again and attacks the hemiacetal (the carbon bonded to two oxygen.) Once again, there is the dilemma between the alcohol wanted to be basic and the hemiacetal wanted to be acidic, so you need an enzyme to help make a boat confirmation.