chapter 7 section 3

Question 1

What makes maltose, isomaltose, and cellobiose homodisaccharides?

Answer 1

They each contain only one kind of monosaccharide: glucose.

Question 2

How is maltose formed?

Answer 2

From starch by amylase enzymes during grain germination; hydrolyzed by diastase.

Question 3

What glycosidic linkage is found in maltose and cellobiose?

Answer 3

1→4 linkage between glucose units

Question 4

How do maltose and cellobiose differ?

Answer 4

Maltose: α-1→4 linkage; cellobiose: β-1→4 linkage.

Question 5

What is the linkage in isomaltose?

Answer 5

α-1→6 linkage between two glucose units

Question 6

What is the formal IUPAC name for maltose?

Answer 6

O-α-D-glucopyranosyl-(1→4)-D-glucopyranose

Question 7

What is β-D-lactose composed of?

Answer 7

D-galactose and D-glucose via a β-1→4 linkage

Question 8

Why is lactose a reducing sugar?

Answer 8

It has a free anomeric carbon capable of mutarotation.

Question 9

Why can most adults not digest lactose?

Answer 9

Lactase enzyme levels decrease after infancy in most populations

Question 10

What is sucrose composed of?

Answer 10

Glucose and fructose.

Question 11

How is sucrose hydrolyzed?

Answer 11

By invertase enzyme or dilute acid

Question 12

Why is sucrose called “invert sugar” after hydrolysis?

Answer 12

Optical rotation changes from positive (+66.5°) to negative due to component monosaccharides.

Question 13

re maltose, lactose, and sucrose absorbed directly in humans

Answer 13

No; they must first be hydrolyzed by maltase, lactase, or sucrase

Question 14

What is the main “blood sugar” in insects?

Answer 14

Trehalose, a nonreducing disaccharide.

Question 15

In which organisms is trehalose commonly found?

Answer 15

Insects, bacterial spores, fungi, and yeast—organisms exposed to environmental stresses.

Question 16

Why don’t honeybees use trehalose in their hemolymph?

Answer 16

their colonial lifestyle maintains stable temperature, reducing environmental stress.

Question 17

What is a proposed biological function of trehalose?

Answer 17

Acts as a natural cryoprotectant, protecting cells from freezing/thawing damage.

Question 18

Why is trehalose especially effective as a cryoprotectant?

Answer 18

It protects biological structures at low concentrations better than other polyhydroxy compounds.

Question 19

What evidence supports trehalose’s role in stress protection?

Answer 19

Trehalose levels in Saccharomyces cerevisiae rise under high salt and high temperature stress.

Question 20

How is the α or β configuration of a sugar ring determined?

Answer 20

By the position of the —OH at the anomeric carbon: α = below the ring, β = above the ring.

Question 21

What does “HOH” mean in disaccharide notation?

Answer 21

The configuration at that position can be either α or β.

Question 22

Does sucrose have a free anomeric carbon?

Answer 22

No, sucrose has no free anomeric carbon and is a nonreducing sugar.

Question 23

What defines a disaccharide?

Answer 23

Two monosaccharide units linked by a glycosidic bond.

Question 24

What is a residue in an oligosaccharide?

Answer 24

Each individual monosaccharide unit in the chain.

Question 25

Name the three most common naturally occurring disaccharides

Answer 25

Sucrose, maltose, and lactose.

Question 26

What is a mixed acetal in a disaccharide?

Answer 26

One hydroxyl comes from the monosaccharide itself, one from the other monosaccharide.

Question 27

What is the reducing end of a disaccharide?

Answer 27

The end containing the free anomeric carbon capable of oxidation.

Question 28

Why is sucrose a nonreducing sugar?

Answer 28

Both anomeric carbons are substituted, so it cannot convert to the aldehyde form.

Question 29

What is the nonreducing end of a disaccharide?

Answer 29

The end without a free anomeric carbon.

Question 30

Where are higher oligosaccharides found?

Answer 30

In both prokaryotic and eukaryotic organisms, naturally or as hydrolysis products of larger carbohydrates.

Question 31

how do higher oligosaccharides differ from disaccharides?

Answer 31

They contain more than two monosaccharide residues.