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Types of Carbohydrates

Types of Carbohydrates. Section 17.1. Four Types of Carbohydrates. Monosaccharides Contain a single sugar unit Examples: glucose and fructose Disaccharides Contain two monosaccharides units joined through bridging oxygen atoms AKA glycosidic bond Examples: sucrose and lactose.

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Types of Carbohydrates

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  1. Types of Carbohydrates Section 17.1

  2. Four Types of Carbohydrates • Monosaccharides • Contain a single sugar unit • Examples: glucose and fructose • Disaccharides • Contain two monosaccharides units joined through bridging oxygen atoms AKA glycosidic bond • Examples: sucrose and lactose

  3. Four Types, continued • Oligosaccharides • Three to ten monosaccharide units joined by glycosidic bonds • Polysaccharides • Long, often highly branched, chains of monosaccharides • Examples: starch, glycogen, and cellulose

  4. Monosaccharides • Composed of carbon, hydrogen and oxygen • Most follow the general formula (CH2O)n • All names end in –ose • Two types • Ketose – monosaccharide that contains a ketone carbonyl group • Aldose – monosaccharide that contains an aldehyde carbonyl group

  5. Ketose OR Aldose?

  6. Ketose ORAldose

  7. Another system – number of carbons • Another system of nomenclature tells us the number of carbon atoms in the main skeleton. • 3 carbon triose • 4 carbon tetrose • 5 carbon pentose • 6 carbon hexose • Etc.

  8. Triose, tetrose, pentose, etc?

  9. Answers Triose Pentose Hexose

  10. Combining the two systems Aldose Triose Aldotriose D-Glyceraldehyde Aldose Hexose Aldohexose D-Glucose Ketose Hexose Ketohexose D-Fructose

  11. Chiral Objects • Chiral compounds have the same number of atoms arranged differently in space. • A chiral carbon atom has four different groups attached.

  12. Mirror Images • The three-dimensional structure of a chiral compound has a mirror image. • Your hands are chiral. Try to superimpose your thumbs, palms, back of hands, and little fingers. Is it possible? Why or why not?

  13. Chiral or NOT? Determine if there is a chiral carbon in each compound. A B

  14. Solution A Yes, 4 different B No, the groups are attached 2 H atoms to the second C atom are identical

  15. D and L Notation • D,L tells to which of the two chiral isomers we are referring. • If the –OH group on the next to the bottom carbon atom points to the right, the isomer is a D-isomer; if it points left, the isomer is L. • The D form is usually the isomer found in nature.

  16. D notation

  17. Glucose

  18. Homework Complete problems 17.3 and 17.4 on page 472; 17.5 and 17.6 on page 474-5; 17.24, 17.25, and 17.26 on page 493

  19. Importance of Glucose • Most important sugar in the human body. • Glucose is broken down in glycolysis and other pathways to release energy for body functions • The concentration of glucose in the blood is carefully controlled by insulin and glucagon. • Normal blood glucose levels are 100-120 mg/100mL

  20. Importance of Glucose • Insulin stimulates the uptake of the excess glucose by most of the cells in the body. • 1-2 hrs after eating the glucose levels return to normal. • If glucose concentrations drop too low, the individual feels lightheaded and shaky. When this happens, glucagon stimulates the liver to release glucose in the blood.

  21. Diabetes / Hypoglycemia and Glucose • Type I diabetes or diabetes mellitus – caused by the inability to produce the hormone insulin; If untreated, end up with high blood sugar • Type II diabetes or adult-onset diabetes – caused by insulin resistance (body fails to properly use insulin) combined with a relative insulin deficiency; If untreated, end up with high blood sugar • Hypoglycemia – caused by the over excretion of insulin in response to a rise in blood sugar; If untreated, end up with low blood sugar

  22. Structure of glucose • In reality, the open-chain form of glucose is present in very small concentrations in cells. • In most cases, the cyclic intramolecular hemiacetal is formed. • The hydroxyl group on C-5 reacts with the aldehyde group to form a hemiacetal. • Two isomers are formed because a new chiral carbon is created.

  23. 6 α-D-glucose 5 1 1 4 2 6 2 3 3 5 4 4 1 5 2 6 3 D-glucose β-D-glucose

  24. Haworth Structure for D-Glucose • Write –OH groups on the right (C2, C4) down • Write –OH groups on the left (C3) up • The new –OH on C1 has two possibilites: down for  form, up for  form

  25. α-D-glucose O

  26. β-D-glucose O

  27. You Try This One! Write the cyclic form of -D-galactose

  28. Solution -D-galactose O

  29. Benedict’s reagent • Benedict’s reagent – a basic buffer solution that contains Cu2+ ions • It readily oxidizes the aldehyde group of aldoses to form a brick red Cu2O precipitate. • It will also oxidize ketoses because of the –OH group on the carbon next to the carbonyl group.

  30. Reducing Sugars • Reducing sugar – a sugar that can be oxidized by Benedict’s reagent • All monosaccharides and the common disaccharides (except sucrose) are reducing sugars.

  31. Use of Benedict’s reagent • Benedict’s reagent was commonly used to qualitatively monitor excess glucose in the urine by diabetics to insure proper dosage of insulin. • These have been replaced by blood glucose tests that are more accurate.

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