Carbohydrates Flashcards
Which cells utilize glucose for energy
ALL of them
The body tries to maintain blood glucose levels at what range?
70-100mg/dL
Identify the major carbohydrate constituents in the average diet.
Are they polysaccharides or disaccharides?
Starch, Sucrose and Lactose
Polysaccharides
Define the digestion of carbohydrates
Digestion converts dietary polysaccharides and disaccharides to their respective monosaccharides
Are all naturally occurring sugars in the D or L form?
D form
How can you identify the D form of glucose when written in a non cyclic fashion?
You look at the farthest asymmetric carbon from the carbonyl carbon and see what side the OH group is on. If it is on the right it is a D and if it is on the Left it is a L
The creation of a cyclic structure exists between which two carbons in a glucose molecule?
The aldehyde and the anomeric carbon
True or False
The 6 membered ring (5C + O) of glucose is considered to have a pyranose structure, while the 5 membered ring (4C + O) of fructose is considered to have a furanose structure.
True
If the hydroxyl group at position #1 points up it is a _____ form. If the hydroxyl group at position #1 points down it is a ______.
Beta
Alpha
The anomeric carbon is located on which position for glucose?
For Fructose?
On Carbon #1
On Carbon #2
Define a reducing end on a sugar molecule
The hydroxyl group on the anomeric carbon of a cyclized sugar is not linked to another sugar by a glycosidic bond
Starches can be divided into which two structural classes?
Amylose
Amylopectin
Describe the difference between Amylose and Amylopectin
Amylose consists of linear chains of glucose molecules all linked by α-1,4 bonds, while amylopectin has a branched character in which the linear chains of glucose molecules are occasionally linked α-1,6.
True or False
Starches are primarily carbohydrate storage in animals
False -
Starches = Plants
Glycogen = Animals
True or False
Glycogen resembles Amylopectin in structure
True
It resembles amylopectin in structure, but is more highly branched
Cellulose is a chief constituent of the fibrous parts of plants, and is composed of ____________in unbranched chains.
β-D-glucose units
True or False
Humans do not have any digestive enzymes that can cleave a Beta D bond (like those in cellulose) so it is indigestible
True
Name the 3 major disaccharides discussed in class
Sucrose, Lactose, Trehalose
Sucrose contains which two sugar molecules?
Glucose and Fructose
Is sucrose a reducing sugar? Why or why not?
No it is not because the anomeric carbons on the glucose and fructose molecules are occupied
What type of bond (linkage) is found in sucrose
alpha, beta, 1,2
Lactose contains which two sugar molecules?
Glucose and Galactose
Is lactose a reducing sugar? Why or why not?
Yes, the anomeric carbon on glucose can be reduced
Trehalose contains which two sugar molecules
2 Glucose molecules
What type of bond is found in trehalose?
alpha, alpha 1,1
Is Trehalose a reducing sugar? Why or why not?
No, the anomeric carbons are both occupied
Digestion is catalyzed by a family of enzymes known as _______________that hydrolyze glycosidic bonds.
glycosidases (glycoside hydrolases)
The saliva contains a digestive enzyme known as ____________which randomly hydrolyzes the interior __________ bonds between glucose residues within amylopectin, amylose, and glycogen converting the large polysaccharides to smaller entities.
salivary alpha amylase
alpha 1,4
What bonds/areas will salivary alpha amylase likely not cleave?
Terminal Ends
Near branches
Alpha 1,6 bonds
True or False
There are no digestive enzymes in the stomach that can cleave glycosidic linkages found in carbohydrates.
True
Digestion in the intestine occurs in what two phases?
Luminal and Membrane
Cholecystokinin acts on the exocrine cells of the pancreas to stimulate the release of _______.
Pancreatic alpha amylase
Other intestinal epithelial cells produce another peptide hormone _________, in response to the low pH of the gastric contents entering the intestine.
secretin
Secretin causes the pancreas to release a solution rich in _________ that helps neutralize the pH of the intestinal contents.
bicarbonate
What are the final products of α-amylase action on starch?
Maltose, maltotriose and branched dextrins
In the membrane phase, what 4 glycosidases are found protruding from the brush-boarder?
Lactase, Trehalase, Sucrase-Isomaltase complex and glucoamylase
Lactase cleaves the ______ bond between ______ and ______ molecules.
β-1,4 bond between galactose and glucose in lactose
Trehalase hydrolyzes ______bond to yield two molecules of________.
alpha, alpha 1,1 bond
glucose
Glucoamylase complex functions to cleave the ______ linkages between glucose units in oligosaccharides, starting from the _______ end of the chains.
alpha 1,4
nonreducing
Glucoamylase also hydrolyzes the α-1,4 bonds in maltose and maltotriose yielding _______.
glucose
Alpha beta 1,2 bonds between glucose and fructose are hydrolyzed by the ______ portion of the sucrase-isomaltase complex
Sucrase portion
The isomaltase portion of the sucrase-isomaltase complex cleaves which bond? What are the products of this cleavage?
Cleaves alpha 1,6 to give glucose and maltotriose
Dietary fiber is composed of carbohydrates or carbohydrate derivatives that ________(can or cannot) be digested by human digestive enzymes. Colonic bacteria convert the more soluble dietary fiber to _____, _______, and ________.
Cannot
Gases (CO2, H2 and methane), short-chain fatty acids (acetic, propionic and butyric), and lactate
What is the function of bile acids?
Emulsify fats
Absorption of the monosaccharides takes place primarily from the ________ of the small intestine and involves the “_______ border” of the epithelial cells.
lumen
brush
Monosaccharides are transported through the absorptive cells of the intestine by which two mechanisms?
Facilitated diffusion and by Na+- dependent facilitated transport (active transport)
_______ and _________ are transported by SGLT-1 into absorptive intestinal epithelial cells via active transport
Glucose and galactose
Fructose utilizes ________ for its absorption via facilitated diffusion.
GLUT-5
What 3 sugars are transported from the intestinal epithelial cells into the portal circulation by GLUT-2?
Glucose, galactose, and fructose
What is the glycemic index?
An indication of how rapidly blood glucose levels rise after consumption. The higher the number, the more rapidly blood glucose levels rise.
True or False
Lactose/Lactase are osmotically active
True
True or False
Lactose causes water to be drawn into the intestine
True
In addition to the increase in water in the intestine, what other factors contribute to the symptoms associated with lactose intolerance?
Bacterial fermentation
