Carbohydrates Flashcards
What are the most abundant organic molecules in nature and our diet?
Carbohydrates (saccharide)
What are some of the many functions of carbohydrates?
Dietary calories Energy storage (glycogen) Cell membrane intercellular communication
What is the empiric formula of a carbohydrate?
(CH2O)n where n is greater than or equal to 3
What 2 things are monosaccharides classified by?
1) Number of carbon atoms (3 carbon = triose; 4 carbon = tetrose; 5 carbon = pentose; 6 carbon = hexose; 7 carbon = heptose; 9 carbon = nonose)
2) Carbonyl group (aldose = aldehyde group; ketose = ketone group)
Monosaccharides can be linked by ______ bonds, created by _____.
glycosidic bonds; glycosyltransferases
**1->4 connection makes a straight line ; 1->6 makes a branch
What is a disaccharide? An oligosaccharide? A polysaccharide?
Di -> 2 sugars
Oligo -> 3-10 sugars
Poly -> 10+ sugars
What is an enantiomer?
Mirror images of each other
-all sugars in humans are in D-configuration (-OH farthest from the carbonyl carbon is on the right -> “derecha”)
How can a straight chain monosaccharide become cyclic?
The aldehyde/ketone in the chain will react with an -OH group in the same chain
- if -OH (on the anomeric carbon/C-1) above the plane structure -> alpha-C
- if -OH is below the plane structure -> beta-C
What can a colorimetric test detect?
Reducing sugar in urine
-positive result -> pathology (because sugars are not normally present in urine)
What are some important disaccharides?
- Lactose = galactose + glucose
- Sucrose = glucose + fructose
- Maltose = glucose + glucose
What are some important polysaccharides?
- Branched glycogen (animal source)
- Starch (plant source)
- Unbranched cellulose (plant source)
What is an N-glycosidic bond?
Sugar is bound to a nitrogen
-type of bond in ATP
What is an O-glycosidic bond?
Sugar is bound to an oxygen
-type of bond in lactose
What is a glycoprotein?
Sugar attached to a protein
-can also have N vs O linkage
Where are carbohydrates digested?
Mouth and intestines (monosaccharides absorbed by small intestine)
What are carbohydrates digested by?
Glycoside hydrolyses
1) Endoglycosidase - hydrolyze polysaccharides (cut from the center)
2) Disaccharidase - hydrolyze disaccharides into single sugar components
What is alpha-amylase?
Salivary or pancreatic enzymes (different ones required because salivary one will be destroyed in the acidity of the stomach) that aid in digestion of carbohydrates
What does salivary alpha amylase hydrolyze?
Salivary acts briefly on dietary starch and glycogen, hydrolyzing random alpha (1->4 bonds aka straight lines)
- will not break down branches (1->6
- product = DEXTRINS (short, branched oligosaccharides)
T or F: Carb digestion halts temporarily in stomach, because high acidity inactivates salivary alpha-amylase.
True; neutralized by pancreas’ bicarbonate -> pancreatic alpha-amylase continues process in small intestine
What are the key disaccharidases in upper jejunum (lining small intestine)?
1) Maltase - cleaves 1,4 maltose -> glucose + glucose
2) Sucrase - cleaves 1,2 sucrose -> glucose + fructose
3) Lactase - cleaves 1,4 lactose -> glucose + galactose
- all products are monosaccharides
Where does intestinal absorption occur?
Mainly in duodenum and upper jejunum
What is the mechanism of absorption in GI tract -> SI tissue?
- Glucose/Galactose: co-transport with Na+ through SGLT-1 (active, energy-dependent)
- Fructose: facilitated diffusion through GLUT-5 (Na+ independent transporter)
What is the mechanism of absorption in SI tissue -> blood?
Glucose, fructose and galactose: facilitated diffusion through GLUT-2 transporter
What happens if someone has a genetic or acquired disaccharidase deficiency?
Passage of undigested carbohydrate into large intestine -> osmotic gradient that draws water from tissues into large intenstine -> osmotic diarrhea
- Bacterial fermentation of carbohydrates occurs
- Creates large volume of CO2 and H2 gas -> abdominal cramps, diarrhea, flatulence
- Causes: genetic, intestinal disease, malnutrition, drugs that injure mucosa of small intestine
What occurs in lactose intolerance?
Body lacks the enzyme lactase
- More than 70% of the world’s adults are lactose intolerant
- Up to 90% of African or Asian descent are affected
