Lab 3: Carbohydrate Characterization Flashcards
What is a carbohydrate?
Organic compound composed of carbon, hydrogen and oxygen
What are the two main functions of carbohydrates?
1) Source of energy for the cells
2) Intermediate-term energy source (starch for plants and glycogen for animals)
What are simple sugars called?
Monosaccharides
Are monosaccharides and disaccharides soluble in water?
Yes, both of them are
What is the function of cellulose?
Adds strength and stiffness to a plant’s cell wall
What is the most common carbohydrate in the human diet? Where is it contained?
- Starch
- Potatoes, wheat, corn, rice
What are the bonds in glycogen?
- a(1-4) glycosidic bonds
- a(1-6) branches
Where is glycogen primarily stored?
Muscle and liver
After food is ingested and starches are broken into monosaccharides, where are they transported to?
To the liver, among other tissues
Where does glycogen synthesis primarily happen?
In the liver
What is the energy source in glycogen synthesis? What does it convert? To what?
- Energy source: UTP
- Converts glucose-1-phosphate to UDP-glucose
What is the enzyme that catalyzes the a(1-4) glycosidic bonds in glycogen synthesis?
Glycogen synthase
What is needed to form glycogen branches? (2)
- Glycogenin (protein)
- Amylotransglycosylase (enzyme)
What do glycogenin and amylotransglycosylase catalyze?
Transfer residues from the non-reducing end of the chain to the C6 hydroxyl group of a glucose molecule in the middle
What limits branching?
If a chain does not contain a sufficient number of residues
What enzyme is used in glycogenolysis?
- Glycogen phosphorylase
- Glycogen debranching enzyme
What is the role of glycogen phosphorylase?
Attacks the Pi on the a(1-4) linkages between glucose units at one end
What is glucose?
- Aldose
- Hexose
- Reducing
- Monosaccharide
What is fructose?
- Ketose
- Hexose
- Reducing
- Monosaccharide
What is xylose?
- Aldose
- Pentose
- Reducing
- Monosaccharide
What is sucrose?
- Non-reducing disaccharide
- Made of glucose and fructose monosaccharides
What is Benedict’s test used for?
Tests for the presence of reducing sugars
What is Bial’s test used for?
Tests for pentoses
What is Seilwanoff’s test used for?
Tests for ketoses
What is Molisch’s test used for?
Tests for all carbohydrates
Why do heifers have high blood glucose?
Due to their young age, they require high quantities of glucose to serve as nutrients, which assures proper growth and cognitive development
Why do pregnant cows have low blood glucose?
Because glucose is constantly withdrawn from the blood to provide nutrients for the fetus to grow
Why do peak lactation cows have the lowest blood glucose?
Because glucose is withdrawn from the blood to make the disaccharide lactose, composed of glucose and galactose
What is Benedict’s reagent made of?
- Anhydrous sodium carbonate (alkali)
- Sodium citrate
- Copper sulfate
What happens when a reducing sugar is heated with an alkali?
- Transformed into a reactive enediol
- Reduces Cu2+ from the copper sulfate to Cu+
What happens to the Cu+ in Benedict’s test?
Converted to insoluble red copper oxide
What is the role of sodium citrate in Benedict’s test?
Preserves Cu2+ ions, avoiding their deterioration to Cu+ in storage
What is a positive reaction to Benedict’s test?
When a clear blue solution becomes a brick-red precipitate
Why does sucrose react negatively to Benedict’s test?
The glycosidic bond prevents it from isomerizing to its free ketone and aldehyde form, which prevents it from reacting with Benedict’s reagent
What is Bial’s reagent made of?
- Orcinol
- HCl
- FeCl3
What is the role of HCl in Bial’s test?
- Dehydrates pentose sugars
- Forms furfural
What does furfural react with in Bial’s test?
- In a condensation reaction, furfural reacts with orcinol and ferric ions from FeCl3
- Forms a bluish product
What is a positive reaction to Bial’s test? What is a negative reaction?
- Positive (pentoses): bluish product
- Negative (hexoses): green, red, or brown products
What is Seilwanoff’s reagent made of?
- HCl
- Resorcinol
What is the role of HCl in Seilwanoff’s test?
- Dehydrates the ketone groups of ketoses
- Forms furfural
What does furfural react with in Seilwanoff’s test?
- In a condensation reaction, furfural reacts with resorcinol
- Forms a clear red wine complex in under 5 minutes without a precipitate
What is a positive reaction to Seilwanoff’s test? What is a negative reaction?
- Positive: clear red wine complex under 5 minutes
- Negative: light colours, and slowly
Why does sucrose react positively to Seilwanoff’s test?
Hydrolyzed by HCl into its monosaccharides to form a red product, indicating the presence of a ketose (fructose)
What is Molish’s reagent made of?
- H2SO4
- a-naphthol
What is the role of H2SO4 in Molisch’s test?
- Dehydrates pentoses to furfural
- Dehydrates hexoses to 5-hydroxymethyl furfural
What is the role of a-naphthol in Molisch’s test?
Furfural derivatives react with a-naphthol to produce a purple band between H2SO4 and the sugar olution
What is a positive reaction to Molisch’s test?
- Positive (monosaccharides): fast
- Negative (disaccharides): slow
