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Lecture 6

BIOL 112 Lecture 6: Lecture 6

10 Pages
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Department
Biology (Sci)
Course Code
BIOL 112
Professor
Frieder Schoeck

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Lecture 6 Why Chemistry and biology say that breaking and forming things require or release energy? Biology looks at the whole reaction. All happens at the same time (braking and forming a covalent bond happens at the same time). Chemistry looks at the equation more theoretically and biology looks at the overall result. Sugars are complicated molecules. Purlple is starcht. Startch is storage product to provide energy for plants. In green we can see cell walls also made of sugars. Cell walls are for strucutre. Polysaccharides. Ex: cellulose or starch. The smallest sugar you can get has 3 carbon atoms. Every carbon atom carries one functional group (either a hydroxyl or carbonyl). Hydroxyl: OH, there are usually lots of these. Carbonyl: CO, usually one of them. Sugars always have the same number of carbon atoms and oxygen atoms. Depending on where the CO (carbonyl) is: If it is in the end it is called an aldose and if it’s in the middle it is called a ketose. Fruit is aldose. Sugars and alchohols arerelated. Sugars justcarry moreof thealchohol (hydroxil) groups.That is why it is easy to make alchohol from sugar. There are different isomers in sugars. Isomers is whenever you have the same molecular formula but oneofthegroups isattachedinadifferentwaytoacarbonatom.Thesetwomolecules havedifferent structures and properties. Chemically they are different. Optical isomers are important for sugar. The grey ball in the middle is a carbon atom. If there are two optical isomers we call them asymmetric carbon atoms. A group can be any combination of atoms, the main point is that it has to be different. Four different groups attached to the central carbon atom. The optical isomers mirror each other. Amino acids have two types of isomers but they only use one of them to create proteins. Glucose (in grapes) and galactose (in milk) are very different sugars. They are optical isomers of each other at the carbon atom position 4. Carbon 2, 3, 4, and 5 are asymmetric because they have 4 different groups attached to them. Carbon 1 has only 3 different groups attached to it, while carbon 6 has 3 DIFFERENT groups attached to it because H group is there twice. Sugars typically do not appear linearly. They are usually closed and form a ring. The carbonyl group forms a covalent bond with the OH. This results in forming a ring. When we form the additional covalent bond and form the ring, we convert the carbon 1 into being an asymmetric carbon atom, because now it has four different groups. When we form this ring, we can form 2 polymers depending on if the OH points up or down. Whenwehaveasingleglucosemolecule.Itopensandclosesbetweenringandlinear,andsometimes it’s in the alpha or in the beta form. When we form a glyosidic linkage, we stably connect two isomers with a covalent bond, it is stable. There are many different potential glyosidic linkages. The two important linkages for biology are: Alpha1-4 and Beta1-4. Because these are used in nature. Thealpha1-4linkage:weneedoneglucoseinthealphaposition(hydroxylgrouppointingdownward) and the other glucose it does not matter what position it has because the reaction occurs with the hydroxyl group at carbon position4. This one is a disaccharide called Maltose.Eventually we form the polysaccharide starch. The alpha bond is now stable but the end can still vary. The succession of alpha 1-4 links gives you starch. When its unbranched and its one long polysaccharide it’s called amylose. Reducing end: We can oxidase the end when it opens up. Occasionally, starch can have branches. And these are vertical(1-6 linkages because they are at the carbon 6) and thencontinue with horizontalalpha 1-4 links.When its branched wecallit amylopectin in plants and glycogen in animal and humans. The beta 1-4 We start with one glucose in the beta position (a beta glucose) which means that the hydroxyl group is poin
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