Biochemistry Review

Carbohydrates


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1. Although most large molecules (macromolecules) may appear complex they are often polymers -- that is composed of many identical small molecules (monomers).

2. The empirical formula for many carbohydrates may be written (CH2O)n .

3. The simplest common carbohydrates have a three carbon backbone so their formula would be (CH2O)3.

4. Single sugars are called monosaccharides.

5. The next level of saccharide complexity involves two sugars linked together. They are represented by the disaccahride sucrose--table sugar.

6. A chain of many monosaccharides linked together is called a polysaccharide.

7. Monosaccharides may occur in a chain or a ring, and nearly every carbon will have a(n) hydroxyl (-OH) functional group attached as well as a hydrogen.

8. One of the end-carbons in most monosaccharides forms a double bond with oxygen producing an aldehyde group.

9. When a carbon within a chain has a double bond with an oxygen atom it is called a ketone.

10. The shape of simple sugar subunits in polysaccharides like amylose is a ring.

11.The most common and most important monosaccharide is dextrose or D glucose (an aldehyde).

12. Dextrose plays important roles in energy metabolism, photosynthesis, and as a subunit (monomer) for many complex carbohydrates.

13. In order to link two sugar molecules an oxygen bridge is formed between two monosaccharides. In the process a water molecule is liberated (dehydration). The bond between to adjacent sugar subunits is called a glycosidic linkage.

14. Most chemical reactions in the body such as the dehydration synthesis described above require the presence of special proteins called enzymes.

15. Most metabolic reactions are not spontaneous and must have a source of energy in order to go to completion. This energy source is typically a molecule of ATP.

16. The open chain sugar molecule has two ends; an aldehyde or a ketone end and a glyceride or repeating hydroxyl end. From which end of a sugar molecule should you begin numbering the carbon atoms? The aldehyde or ketone end.

17. When a sucrose molecule (glucose-fructose) enters your gastrointestinal tract it will be broken down by a process called hydrolitic cleavage (during which water is added by an enzyme).

18. Lactose like sucrose is a disaccharide found only in milk. This sugar is digested by infants but cannot be tolerated by most adults because they lack the enzyme necessary split it in two.

19. Two basic purposes of polysaccharides are food storage and structural properties.

20. Polysaccharides used for food storage are amylose or amylopectin (plants) and glycogen (animals)

21. The polysaccharide cellulose is found mostly in plant cells and several algae.

22. Chitin is used by arthropods (insects, spiders etc.) to form a tough exoskeleton.

23. All plant starches such as amylose and amylopectin are made almost exclusively of glucose subunits.

24. Amylose is the simplest starch--glucose molecules joined by 1-4 alpha linkages--whereas amylopectin is a highly branched polymer.

25. Amylose can become insoluble in water because it will spontaneously form a(n) helix --the secondary structure of the molecule--a shape formed by hydrogen bonding between the sugar subunits rather than with water.

26. Animal starch or glycogen provides temporary energy storage which is concentrated in muscle cells and the liver of vertebrates.

27. Glycogen is larger than amylopectin and more complex because its branches have their own branches.

28. Iodine is a substance can be used to easily identify starch because it forms a dark blue complex

*While both amylose and cellulose are formed by 1-4 dehydration linkages between glucose molecules they have vastly different properties. You should be able to describe the functional differences between these two polymers.

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29. The structural difference between cellulose and starch is based on the location of the hydroxyl group found on carbon-one of the glucose ring. As the 1-4 beta-linkages of cellulose form, every other monomer in the chain is turned over.

30. Only a few organisms have evolved an efficient enzyme, cellulase, necessary to break the beta-glycosidic linkage found in cellulose.

31. Termites and grazing animals are able to digest the cellulose in the plants they eat because of a symbiotic relationship with certain intestinal microorganisms.

32. Numerous hydrogen bonds enable cellulose to cluster into groups of 60 or 70 strands forming very strong cable-like filaments called microfibrils.

* You should be able to describe the microscopic details of plant cell walls which make them one of the strongest of biological structures. Your description should include such terms as beta glycoside linkages, microfibrils, fibrils, and laminated cell wall structure.

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33. Arthropods and fungi have evolved a structural polysaccharide called chitin which is made up of N&emdash;acetylglucosamine subunits.

34. Special polysaccharides complexed with protein form much of the jellylike substance that fills the eye and lubricating fluids of skeletal joints. Heparin is one such proteoglycan which has the vital role of inhibiting the clotting of blood.