Highlights Carbohydrates II
1.Sorbitol is a so-called sugar alcohol that is related to D-sorbose by reduction. Sorbitol is used as an artificial sweetener because it tastes sweet, but is not readily metabolized.
2. An alpha1-4 glycosidic bond joins an aldose in the alpha configuration to an oxygen linked to carbon 4 of the next sugar. An alpha 1-6 glycosidic bond joins an aldose in the alpha configuration to an oxygen linked to carbon 6 of the next sugar. Amylose is a polymer of glucose (polysaccharide) that has almost exclusively alpha 1-4 links. Starch is a carbohydrate storage form of plants that contains amylose (and other polysaccharides). Cellulose is a polymer of glucose that has beta 1-4 links. In contrast to starch, non-ruminant animals cannot digest cellulose, but they can digest starch. Ruminant animals, like cattle, contain a bacterium in their rumen that digests the cellulose for them.
3. Glycogen is a polymer of glucose with alpha1-4 bonds and alpha 1-6 branch bonds. It is found primarily in the liver and muscles of animals.
4. Disaccharides are carbohydrates with two sugar (monosaccharide) subunits. The most common disaccharide is sucrose, which contains a subunit of glucose linked to a subunit of fructose via glycosidic bonds between each.
6. Another common disaccharide is lactose (glucose + galactose, linked in an alpha-1,4 bond). Lactose is abundant in milk. Maltose is a disaccharide of glucose. You should know what sugars compose sucrose and lactose, but you do not need to draw structures.
7. Bacterial cell walls contain carbohydrate polymers cross linked with short peptides containing D amino acids.
8. Polymers of anionic carbohydrates create "slippery" solutions in water due to the repulsion of the many negative charges.
9. Proteoglycans are molecules containing proteins linked to chemically modified (addition of negative charges) polysaccharides. Examples include heparin (inhibits blood clotting) and hyaluronic acid (lubricating material in the synovial fluid of joints). Proteo glycans are polyanionic compounds and the multiple negative charges give the water they are dissolved in a "slimey" feel.
1. Metabolism consists of the sum of all of the biochemical reactions occurring in cells.
2. Glycolysis is a metabolic pathway for the breakdown (catabolism) of glucose and related sugars. The pathway requires two ATPs to start the process and generates 4 ATPS (for a net of two ATPs) per glucose. Also generated during glycolysis are two NADHs.
3. You should know the names of all glycolysis intermediates, as well as the names of the enzyme catalyzing each reaction.
4. Hexokinase is an enzyme that catalyzes the first step in glycolysis. It uses an ATP to put a phosphate onto glucose, making glucose-6-phosphate (G6P) and ADP.
5. G6P is converted to fructose-6-phosphate (F6P) in the next step of the pathways. The enzyme catalyzing this reaction is called glucosephosphate isomerase. Hexokinase is also able to convert fructose to F6P (using ATP) in a reaction very similar to that for glucose. This means that fructose too can readily enter the glycolysis pathway. Other sugars have other ways of entering.
6. Conversion of F6P to fructose-1,6-bisphosphate is catalyzed by the enzyme phoshofructokinase (PFK) (need to know).