Ochem Exam 3 Flashcards
What is the prevalent form of monosaccharides with 5 or 6 carbon atoms?
Cyclic structures
Cyclic structures are the most common forms of monosaccharides, allowing for more stable configurations.
How do cyclic structures of monosaccharides form?
They form when the hydroxyl group on carbon 5 reacts with the aldehyde or ketone group.
This reaction is a key step in the cyclization of monosaccharides.
What is the first step in drawing the cyclic structure for glucose?
Number the carbon chain and turn it clockwise to form a linear open chain.
This helps visualize the structure before cyclization.
In forming the cyclic structure of glucose, which carbon bonds to oxygen to close the ring?
Carbon 5 bonds to oxygen, which then connects to carbon 1.
This bond forms the cyclic structure, completing the ring.
In the cyclic structure of glucose, where is the carbon 6 group placed?
Above the ring.
The positioning of carbon 6 is important for distinguishing between different forms of glucose.
How do you differentiate a-D-Glucose from B-D-Glucose?
The -OH on carbon 1 is down for a-D-Glucose and up for B-D-Glucose.
This difference in orientation affects the properties and functions of the sugars.
What happens when a-D-Glucose and B-D-Glucose are placed in solution?
They interconvert, with a-D-Glucose converting to B-D-Glucose and vice versa, forming an equilibrium.
This dynamic equilibrium is significant in biological systems.
What is the percentage composition of a-D-Glucose, B-D-Glucose, and open-chain glucose in solution?
a-D-Glucose (36%), B-D-Glucose (64%), open-chain glucose (trace amounts).
This composition illustrates the predominance of B-D-Glucose in solution.
What type of sugar is fructose?
Fructose is a ketohexose.
As a ketohexose, fructose has a ketone functional group and six carbon atoms.
Which carbon atoms react to form the cyclic structure of fructose?
The -OH on carbon 5 reacts with the C=O on carbon 2.
This reaction is crucial for the formation of fructose’s cyclic structure.
What is the cyclic form of a-D-Galactose?
A six-membered ring similar to glucose, but with different hydroxyl group orientation on carbon 4.
The unique orientation of the hydroxyl group affects the properties of a-D-Galactose.
What are reducing sugars?
Monosaccharides that oxidize to give a carboxylic acid and undergo reaction in the Benedict’s test.
Which monosaccharides are considered reducing sugars?
Glucose, galactose, and fructose.
What happens when D-glucose is oxidized?
It forms D-gluconic acid.
What color change occurs in the Benedict’s test for reducing sugars?
Blue Cu²⁺ solution reduces to form red Cu precipitate.
What is produced when monosaccharides undergo reduction?
Sugar alcohols, also known as alditols.
What is the reduction product of D-glucose?
D-glucitol, also called sorbitol.
What is a disaccharide?
A disaccharide consists of two monosaccharides.
Which monosaccharides form maltose?
Glucose + Glucose
Which monosaccharides form lactose?
Glucose + Galactose
Which monosaccharides form sucrose?
Glucose + Fructose
What is another name for maltose?
Malt sugar
How is maltose obtained?
From the hydrolysis of starch.
What type of bond links glucose molecules in maltose?
a-1,4-glycosidic bond
Where is maltose commonly used?
Cereals, candies, and brewing.
Which monosaccharides make up lactose?
B-D-galactose and a- or B-D-glucose
What type of glycosidic bond is in lactose?
ß-1,4-glycosidic bond
Where is lactose found?
Milk and milk products.
Where is sucrose obtained from?
Sugar cane and sugar beets.
Which monosaccharides make up sucrose?
a-D-glucose and B-D-fructose
What type of glycosidic bond is in sucrose?
a,ß-1,2-glycosidic bond
What is the reference sweetness value for sugars?
Sucrose, with a value of 100.
What are polysaccharides?
Polysaccharides are polymers of D-glucose.
Polysaccharides are large molecules made up of many monosaccharide units.
Which polysaccharides are made of a-D-glucose?
Amylose, amylopectin, and glycogen.
These polysaccharides are important energy storage forms in plants and animals.
Which polysaccharide is made of ß-D-glucose?
Cellulose.
Cellulose is a structural component in the cell walls of plants.
What type of glycosidic bonds does amylose have?
a-1,4-glycosidic bonds.
These bonds link the glucose units in a linear fashion.
What is the structure of amylose?
A continuous (unbranched) chain of a-D-glucose.
This structure allows amylose to form a helical shape.
What type of glycosidic bonds does amylopectin have?
a-1,4-glycosidic bonds and a-1,6-glycosidic bonds (for branching).
The a-1,6 bonds create branching points in the molecule.
What is the structure of amylopectin?
A branched-chain polysaccharide of a-D-glucose.
This branching allows for more rapid release of glucose when needed.
What is glycogen?
A polysaccharide that stores a-D-glucose in muscle.
Glycogen serves as a key energy reserve in animals.
How does glycogen compare to amylopectin?
Glycogen is more highly branched than amylopectin.
This higher branching affects its solubility and accessibility for enzymatic breakdown.
What type of glycosidic bonds does cellulose have?
ß-1,4-glycosidic bonds.
These bonds create a rigid structure that is resistant to enzymatic breakdown.
Why can’t humans digest cellulose?
Humans cannot break down ß-1,4-glycosidic bonds.
This is due to the lack of enzymes capable of hydrolyzing these specific bonds.
