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75 Cards in this Set

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Empirical formula of carbs:
(CH2O)n
What is a monosaccharide?
A carbon chain w/ a carbonyl and 2 or more hydroxyls.
How are monosaccharides numbered?
From the carbonyl end.
What are the 2 types of monosaccharides?
-Ketose (ketone)
-Aldose (aldehyde)
What is ea; ketose or aldose?
-Glucose
-Fructose
glucose = aldose
fructose = ketose
How many carbons long is the last physiolog significant carbohydrate?
7
definition of chiral
carbon w/ 4 different groups attached
isomers in general are:
compounds with the same atoms but different arrangements.
What is dextrose?
D-glucose
What are anomers?
Compounds that differ in carbonyl carbon configuration.
What are epimers?
Compounds that differ in configuration at ONLY ONE SINGLE carbon other THAT IS OTHER than the carbonyl carbon.
What are enantiomers?
isomers that exist as mirror images (d/l glyceraldehyde)
What are diastereomers?
isomers differing in configuration, but that are NOT mirror images. (b/c have more than one chiral center)
What are the 5 most important monosaccharides to know?
-Ribose
-galactose
-glucose
-mannose
-Fructose
What are 2 important epimers of Glucose? At what carbon do they differ in configuration?
-galactose-> C4
-mannose -> C2
what is the relationship of fructose and glucose?
isomers; fructose is a ketose, glucose an aldose.
how does ribose compare to the other important monosaccs to know?
it has 5 carbons, not 6
what is a 3-carbon monosacch?
glyceraldehyde
which carbon determines whether a carb is L or D?
the carbon farthest from the carbonyl or ketone carbon.
What is gluconic acid (gluconate)?
Glucose with the C1 carbonyl oxidized to carbonic acid.
What is glucuronic acid (glucuronate)?
glucose with its C6 alcohol end oxidized into a carbonyl group.
What does reduction of the carbonyl end of a monosacch create?
A polyol
What product results from oxidizing glucose to a polyol?
Sorbitol
What cofactor is necessary to produce sorbitol from glucose?
NADP+ - gets reduced as glucose is oxidized to the polyol sorbitol.
What are 2 points of clinical relevance to sorbitol?
-Diabetic cataracts
-Seminal vesicles (precursor to fructose, sperm fuel)
For sperm to convert glucose to sorbitol requires how many NADPH?
2
By what mechanism are monosaccharides cyclized?
Intramolecular hemiacetal or hemiketal formation.
What forms a
-pyranose
-furanose
Pyranose - cyclization of a 6-carbon aldose
Furanose - cyclization of a 6-carbon ketose or 5-carbon aldose.
What 2 configurations result from cyclization?
Alpha or beta - referring to whether the OH group C1 is above/below the ring plane.
How is the OH configured in
-Alpha config?
-Beta config?
A = down

B - up
What is the predominant anomer in a glucose solution?
B-glucopyranose - the most stable configuration because all OH groups are equatorial.
Why is hemiacetal/ketal the mechanism used in cyclization?
It increases the carbon's susceptiblty to intramolec. nucleophilic attack.
So in cyclization of glucose, what attacks what?
C5 -OH group attacks C1 C=O group.
What is a reducing sugar?
A saccharide with a free aldehyde group capable of reducing compounds like Fe3+ or Cu2+
What is a glycosidic bond?
The result of a functional group covalently binding the anomeric carbon of a ring.
What is the CLASSIC nonreducing sugar? What does its structure consist of?
Sucrose - glucose + fructose
How many members are in the ring structures of
-Glucose
-Fructose
Glucose = 6-membered
Fructose = 5-membered
Why exactly is sucrose a nonreducing sugar?
Both anomeric carbons of glucose/fructose are linked to each other.
Why is the glycosidic bond in sucrose "alpha"1-2, not alpha-beta?
Because the "1" carbon is alpha and that is what determines the naming.
What is a disaccharide?
2 sugars linked by a glycosidic bond.
What are the 3 most common disaccharides, and what are their linkages?
Sucrose - a1,2 (glu/fru)
Lactose - B1-4 (glu/galact)
Maltose - a1-4 (glu/glu)
So how do maltose and lactose differ from sucrose?
The latter is nonreducing, the other 2 are reducing.
What is a complex polysaccharide?
A polymer of multiple sugars linked together by glycosidic bonds.
Why are polysaccharides important?
They constitute the major storage form of carbohydrates.
In what form do plants store sugar?
Starch
What are the 2 types of starch?
1. Amylose
2. Amylopectin
What is the key difference between amylose and amylopectin?
Amylose = linear w/ a-1,4 links

Amylopectin = branched w/ a-1,4 and a-1,6 links. Branches every 10-12 residues.
What is the major structural molecule in plants? What type of links, so similar to what storage polysaccharide?
Cellulose - B-1,4 linkages
-Similar to amylose (linear)
Why is cellulose important?
Animals cant digest it b/c they lack the enzymes for catalyzing the hydrogen bond created by this stereochemistry.
How do animals store glucose?
As glycogen
What plant storage polysacch. does glycogen resemble?
Amylopectin - has both linear a-1,4 and branched a-1,6 links.
For glycogen, what is its unique
-Advantage
-Disadvantage
Adv: allows for compact storage of lots of glucose

Dis: mixed linkages require two diff. enzymes for breakdwn
What type of glycosidic bond is found in nucleosides? What sugar?
N-glycosidic - Ribose sugar bound to a purine/pyrimidine
What type of glycosidic bonds are found in membrane sugars? What protein residues?
O-linked (Serine) or
N-linked (Asparagine)
What bad thing happens with sugars and proteins?
Non-specific glycosylation
what is the most common type of non-specific glycosylation?
Sugar reacts w/ primary NH3 of lysine to form a SCHIFF'S BASE
What can happen to a schiff's base?
Contains a hydroxyl group that can undergo an Amadori rearrangement.
Why is an amadori rearrangemnet bad?
Its last step is irreversible so you're left with an undo-able glycosylated protein.
What disease is non-spcf glycosylation a problem espec?
Diabetes - results in AGE (advanced glyc. endproducts)
Which sugar is table sugar?
Sucrose
What are the important dietary carbs to remember?
Glu/Fru (mono)
Suc/Lac (di)
Amylopectin/Amylose (starch)
Glycogen/Cellulose (undigestble)
What sugar is in legumes?
Raffinose
Why is raffinose important?
bacteria digest it in the intestines which causes gas.
What enzyme catalyzes the first step of starch/glycogen digestion?
Alpha-amylase in saliva and pancreatic juice in stomach
What does a-amylase do?
An endosaccharidase; attacks the a-1,4 linkages.
What are the products of a-amylase digestion?
Maltose, maltotriose, and a-limit dextrin.
What is the 3 next enzymes in starch digestion?
a-glucosidase, sucrase, lactase
What 3 sugars result from digestion that mammalian cells use for fuel?
Glucose
Galactose
Fructose
What kind of transport is required for enterocytes to take up Glu/Galact/Fructose?
Glucose - active
Galactose - active
Fructose - passive
What transporter does fructose use to get into enterocytes?
GLUT5
What transports Glu/Galactose into enterocytes?
SLGT-1
What is the mechanism of SLGT-1 operation?
It is facilitated active transport - uses the Na gradient established by an ATP pump on the basolateral membrane.
How do all 3 sugars pass from enterocytes into the blood stream? What specific transporter?
Via passive diffusion through GLUT2
What are 2 relatively common problems with carb metabolism?
1. Lactose insufficnecy - in children; decreases w/ age
2. Lack of enzymes for cellulose and Raffinose
Why is the inability to digest cellulose good?
It provides fiber in feces that keeps it hydrated.