Carbohydrates Flashcards
Monosaccharides:
Where is the functional group located on an aldose? Ketose?
Aldose= first carbon; ketose= second carbon
- What is an isomer?
- Stereoisomers/enantiomers are what? What are the designated as?
- Difference between a D and L sugar?
- Compounds with the same chemical formula but different structural formula
- Mirror images of each other but are not superimposable (like right and left hand); designated as D or L sugars
- D: -OH is on the right; L: -OH is on the left (L sugars are usually the toxic ones)
Pyranose vs furanose?
Pyranose is 6 membered ring; furanose is 5 membered
- What is an anomeric carbon?
- What is an anomer?
- Difference between beta hydroxyl and alpha hydroxyl
- A carbon with a functional group attached
- Cyclic structures with 2 possible forms
- Beta= OH is above the plane; alpha= OH is below the plane (they are reciprocal)
~ we can digest alpha bonds but not beta
- What is happening during a reducing sugar assay?
2. Name two sugars that are NOT reducing sugars
- You are breaking the cyclic ring and turning it to its linear form
- Sucrose and Threhalose
Monosaccharides
- What is a deoxysugar?
- What is an amino sugar?
- What is a sugar alcohol?
- H replaces the OH on carbon 2
- NH2 replaces OH on carbon 2
- Reduction of the carbonyl carbon (aldehyde or ketone group)
Example of a common sugar alcohol
Where is it predominantly found?
N-acetylglucosamine 6-sulfate
Proteoglycans
Disaccharides are formed by?
Glycosidic bond (anhydride bond) formed by the condensation between the hydroxyl group of the anomeric carbon of one mono. And a hydroxyl group of another mono
Disaccharides:
Lactose has what kind of glycosidic bond?
Why is lactose a reducing sugar?
Beta (1->4)
Because the anomeric end of the glucose is free (not involved in linkage)
~Free anomeric carbon can exist in the alpha or beta configuration
Disaccharides
Sucrose glycosidic bond?
Is sucrose a reducing sugar?
Alpha1 -> beta2 glycosidic bond
No because both anomeric carbons are not free (both are involved in glycosidic linkage)
Difference between homopolysaccharides and heteropolysaccharides
Name 3 homo
Homo is composed of one type of monosaccharide; hetero contains 2 or more types
Homo= starch, glycogen, and cellulose
Starch:
- What are the 2 main constituents?
- Difference between the two?
- Amylose and amylopectin
- Starch is 15-20% amylose, amylose is longer, non branching helical structure, ideal for storage
Amylopectin is 80-85%, shorter branched chains, each molecule has one reducing end
- What is glycogen
- Structure of glycogen is similar to ___; whats the difference?
- Why is glycogen able to be rapidly mobilized
- Carb storage molecule in vertebrates
- Amylopectin; it has more branch points
- Because of the presence of non reducing ends
Heteropolysaccharides are often referred to as:
Glycosaminoglycans (GAGs)
- Digestion in the mouth is done by what enzyme?
- What kind of enzyme is it? And what kind of bonds does it break down?
- Products?
- Salivary a-amylase (ptylin)
- An endoglycosidase; only alpha(1->4) bonds
- Primarily alpha-limit dextrins
What continues digestion of alpha-1,4 bonds in the stomach?
Mechanism?
Products?
Pancreatic amylase
In duodenum, acidic stomach contents are neutralized by bicarbonate secreted by the pancreas
Glucose, disaccharides (maltose and isomaltose), trisaccharides (maltotriose), oligosaccharides (limit dextrins)
What two enzymes are responsible for the final conversion of carbs into monosaccharides
Examples of these types of enzymes?
Oligosaccharidases and disaccharidases
Lactase, sucrase, maltase, isomalase
Disaccharidases are bound to ?
What kind of bonds may they cleave?
Gut epithelium (brush border enzymes on the intestinal epithelium)
Beta glycosidic linkages
Major monosaccharide products? (3)
Glucose, fructose, and galactose
2 major mechanisms responsible for absorption of carbs from the intestinal lumen:
- Active transport against a concentration gradient by SGLT1 (occurs with Na+ symport)
- Facilitative transport with the concentration gradient (uses GLUT transporters)
Which organ does each transporter act on:
- GLUT1
- GLUT2
- GLUT3
- GLUT4
- GLUT5
Which of these is insulin dependent?
- Blood brain barrier
- Pancreas and liver (also kidney and intestine)
- Brain (neurons and CNS)
- Adipose tissue and muscle
- Intestine
GLUT4 (if you have high blood sugar, it means your adipose and muscle are not picking up glucose)
- What is significant about GLUT2?
2. What monosaccharide does GLUT5 accept?
- Its an Na+ independent monosaccharide transporter that accepts all 3 monosaccharides
- Only fructose
Lactase is a non-inducible enzyme. What does that mean?
Intolerance cannot be reverese by repeated ingestion of milk; you are most likely to become lactose intolerant when you don’t drink milk that often
What is primary lactose intolerance?
Secondary?
Primary= inherited as a recessive trait
Secondary= results from injury to small intestine (more common in infancy)
Diagnosis of lactose intolerance:
- Lactose tolerance test
- Breath hydrogen test
- What test do you use for infants/young children?
- Ingest 50g of lactose; lactose intolerant individuals will have an increase in blood glucose of less than 20 mg/dL
- More common; since lactose intolerant individuals cannot digest lactose, it is fermented by colon bacteria that produces hydrogen which you can detect in your breath
- Neither of these, use a stool acidity test
