Lecture 16: Carbohydrate Structure and Transport Flashcards
1
Q
Carbohydrates
A
- Energy producing macronutrient found in diet
- Recommended dietary intake: 130 g/day
- Each g of glucose produces 4 kcal of energy
2
Q
Simplest Monosaccharide
A
-Triose(three carbons)
3
Q
Carbohydrate Numbering
A
- Alpha carbon is most oxidized
- eg. carboxyl group
4
Q
Carbohydrate Configuration
A
- 2^x
- x = chirals
- L or D assigned to asymmetric chiral carbon furthest away to the carbonyl
5
Q
Diversity of Sugar Structures
A
- Sugars all have chemical formula (CH2O)n
- Sugars can often be found in ring structures
- lowest energy structure
6
Q
Carbohydrate Cyclization
A
- Aldehydes, ketones, and hydroxyl groups are very reactive
- Aldehyde/ketone carbonyl undergo nucleophilic attack by hydroxyl groups
- Intramolecular reactions for a 5 member furan ring or 6 member pyran ring
- Alpha carbohydrate: OH on bottom
- Beta carbohydrate: OH on top
7
Q
Anomeric Carbons are Chiral
A
- Intramolecular cyclization is reversible in solution through linear chain
- Chirality of cyclic structures can be detected by mutarotation(change in optical rotation of polarized light), following interconversion between alpha and beta anomer
- Reactivity of aldehydes also means sugars can react with other molecules but only in linear form
8
Q
Carbohydrate Modification
A
- Sugars can be phosphorylated, methylated, or N-containing functional groups can be added
- Hydroxyls can be removed
- Increases complexity of carbohydrate structure
9
Q
Carbohydrate Terminology
A
- Isomers: Same molecular formula, different structure
- Constitutional Isomers: different order of functional group binding
- Stereoisomers: Same formula/order
- Enantiomers: Non-superimposable mirror images
- Diastereomers: Not mirror images
- Epimer: differ at one asymmetric carbon
- Anomer: Differ at a newly formed asymmetric C in ring structure
10
Q
Glycosidic Bond
A
- Glycosidic bond formation is a condensation reaction where H2O is lost
- Cleaving glycosidic bonds requires H2O(hydrolysis)
- Monosaccharides are joined by glycosidic linkages to form disaccharides and more complex structures
11
Q
Other types of glycosidic bonds
A
- Intermolecular glycosidic bonds are formed between a hydroxyl or amine, and a reactive anomeric carbon with another molecule
- Glycoproteins may be O linked(Ser/Thr) or N linked(Asn)
12
Q
Complex Carbohydrates
A
- Amylose: alpha - 1,4
- Lactose: beta- 1,4
- Amylopectin: alpha - 1,6
- Sucrose: alpha - 1,2
13
Q
Polysaccharides
A
- Large sugar polymers(thousands of monosaccharides), linked in linear or branched fashion
- Important for energy storage, cellular structure and recognition
- Homeopolymer: same monosaccharides
- eg. Glycogen and starch(homoglycans)
- Heteropolymer: Different monosaccharides
- eg. sugars found in glycoproteins(heteroglycans)
14
Q
Starch
A
Amylose: Unbranched glucose units. alpha(1,4) linkages
- Amylopectin: Linear glucose chains joined by alpha(1,4) linkages. alpha(1,6) linkages at branch points once every 30 glucose units
15
Q
Cellulose
A
- Most abundant organic compound, serving structural role in plants
- Unbranched chains of glucose joined by beta(1,4) linkages with many H bonds
- Cellobiose is a disaccharide of glucose
- Humans don’t produce cellulase(cannot break down cellulose)
