An Introduction to Carbohydrates

1. An Introduction to Carbohydrates Chapter 5

2. Structure • Carbohydrates have the generalized chemical formula (CH2O)n • Contain a carbonyl, several hydroxyl functional groups, and many carbon-hydrogen (C–H) bonds.

3. Glucose- aldehyde Fructose- ketone Monosaccharides • Simple sugars • Vary in the placement of the carbonyl group • Aldehyde sugar (aldose) • On the end • Ketone sugar (ketose) • In the middle

4. Monosaccharides • Number of carbon atoms varies • Three (a triose), five (a pentose), and six (a hexose). • Carbon atoms are numbered starting at the end closest to the carbonyl group • Vary in the placement of hydroxyl group • Have the same chemical formula but different structures • Form ring structures in solution

5. Monosaccharides

6. Monosaccharides

7. Polysaccharides • Form from monosaccharides through a condensation reaction • Glycosidic linkage between hydroxyls

8. Polysaccharides • Linkages can be the same or different • Starch- plant storage material • a-glucose monomers joined by a-1,4-glycosidic bonds • Forms a helix • Branches when an a-1,6-glycosidic bond forms, called amylopectin • Unbranched form is amylose

9. Starch

10. Glycogen • Animals store carbohydrates as glycogen • Short term storage, ~ a day

11. Cellulose • The primary component of the plant cellwall • b-glucose linked by a-1,4-glycosidic bonds

12. Starch granules in potato tuber cells Glucosemonomer STARCH Glycogen granules in muscle tissue GLYCOGEN Cellulose fibrils ina plant cell wall CELLULOSE Cellulosemolecules Figure 3.7 Storage Polysaccharides

13. Chitin • N-acetylglucosamine monomers • Cell walls of fungi and algae • Major component of insect and crustacean exoskeletons

14. Peptidoglycan • Bacterial cell walls are composed primarily of peptidoglycan • Made of alternating N-acetyl-muramic acid (M) and N-acetyl-glucosamine (G) monosaccharides • Joined by b-1,4-glycosidic linkages. • M monomer is linked to a chain of amino acids, and peptide bonds link the amino acid chains of adjacent strands

15. Peptidoglycan

16. Role of Carbohydrates

17. Role of Carbohydrates • Building blocks in the synthesis of other molecules • Indicate cell identity • Store chemical energy • Form fibrous structural materials that protect cells.

18. Cell Identity • Carbohydrates help identify a cell • Display information on the outer surface of cells in the form of glycoproteins—proteins with covalent bonds to carbohydrates • Key molecules in cell-cell recognition and cell-cell signaling. • Also important in defense

19. Cell Identity

20. Energy Production and Storage • Most carbohydrates are formed by photosynthesis • Transforms the energy of sunlight into the chemical energy of C–H bonds • Converts CO2 to carbohydrate • The electrons in C–H bonds are shared more equally and held less tightly than they are in C–O bonds

21. Energy Production and Storage

22. Energy Production and Storage • Carbohydrates are electron donors in redox reactions that produce ATP: • CH2O + O2 + ADP  CO2 + H2O + ATP. • The free energy in ATP is used to drive endergonic reactions and perform cell work.

23. Energy Production and Storage • As CO2 molecules are reduced (gain electrons), they also gain protons (H+), so that the resulting compounds contain many C–H bonds • Fatty acids have even more C–H bonds, and consequently more free energy, than carbohydrates • Better stores than carbohydrates

25. How they store energy • Starch and glycogen are good glucose stores because the enzymes amylase and phosphorylase, catalyze reactions that release glucose subunits, which can then be used in the production of ATP.

26. Structural Carbohydrates • Structural polysaccharides form long strands with bonds between adjacent strands • Strands can be organized into fibers or layered in sheets • Gives cells and organisms strength and elasticity

27. Structural Carbohydrates