Carbohydrates 3

Question 1

What is the general formula for carbohydrates?

Answer 1

CnH2nOn OR Cn(H2O)n.

Question 2

What is the formula for pentose monosaccharides?

Answer 2

C5H10O5.

Question 3

What is the formula for hexose monosaccharides?

Answer 3

C6H12O6.

Question 4

Explain the difference between pyranose monosaccharides and furanose polysaccharides.

Answer 4

Pyranose monosaccharides have SIX carbon atoms in their ring.

Furanose monosaccharides have FIVE carbon atoms in their ring.

Question 5

What is a stereoisomer?

Answer 5

An isomer that has the atoms in the molecule in the same order, but the 3D arrangement of atoms in the space differs (e.g. they are flipped upside down, or left to right etc.).

Question 6

These hexose pyranoses are……………?They all have the chemical formula C6H12O6.

Galactose
Glucose
Mannose

Answer 6

Stereoisomers.

Question 7

What makes a carbon atom ‘chiral’ in a carbon ring?

Answer 7

Chiral carbon atoms must be attached to four DIFFERENT groups attached to them, therefore each covalent bond the carbon atom forms is unique!

Question 8

True or false? Monosaccharides cannot be structurally rearranged, they are permanently in one form.

Answer 8

False! When dispersed in water, monosaccharides can structurally rearrange, causing variations in the anomeric carbon.

Question 9

What is an anomeric carbon? Where is it found in the ring and linear forms of a monosaccharide?

Answer 9

In a ring carbon, the anomeric carbon is the one which forms a bond with the hydroxyl (OH) group and the ring oxygen.

In a linear monosaccharide, te anomeric carbon is the carbonyl carbon of the aldehyde or ketone.

Question 10

Which are more stable? Linear or cyclical monosaccharides?

Answer 10

Cyclical.

Question 11

Monosaccharides can react with each other in …………………….. reactions to form ………………… linkages.

Answer 11

Condensation, glycosidic.

Question 12

What are heteropolysaccharides?

Answer 12

Polysaccharides made from more than one form of monosaccharide.

Question 13

Name two linear homopolysaccharides.

Answer 13

Amylose and cellulose.

Question 14

Give an example of a linear heterosaccharide.

Answer 14

Inulin.

Question 15

Amylopectin and glycogen both have what monosaccharide composition and geometry?

Answer 15

They are both branched homopolysaccharides.

Question 16

Arabinoxylan and galactomannan both have what monosaccharide composition and geometry?

Answer 16

They are both branched heteropolysaccharides.

Question 17

What dictates the secondary structure of polysaccharides?

Answer 17

Glycosidic linkages - the orientation on the anomeric carbon, either alpha or beta, and the bond position on the connecting sugar.

Question 18

Amylose is a polymer of glucose with alpha 1,4 linkages. Cellulose is a polymer of glucose with beta 1,4 linkages. What impact does this difference in linkages have on their secondary structures?

Answer 18

Amylose is a helical structure.
Cellulose is a linear structure.

Question 19

Name the carbohydrate:

‘formed in plants in photosynthesis and the calvin cycle. A small molecule which is easily transported through plants. Can form polysaccharides for energy storage and react with proteins and lipids. Essential for short-term energy management’.

Answer 19

Simple sugars.

Question 20

In food and feed, what contributes to the perceived sweetness of foods and adds texture. It can also be fermented to form ethanol and acids, for example in kombucha.

Answer 20

Simple sugars.

Question 21

In vivo, what can be rapidly absorbed in the small bowel and facilitates nutrient transport through the blood. It is crucial for cellular energetic processes and any excess can be converted to glycogen for storage.

Answer 21

Simple sugars.

Question 22

What forms long-term energy reserves in plants and is composed of two polysaccharides, amylose and amylopectin?

Answer 22

Starch.

Question 23

What can disrupt the native granular structure of starch to make it easier for humans to digest? Name this process.

Answer 23

Heat, shear and water. Gelatinisation.

Question 24

Name some of the uses of non-starch polysaccharides in food production.

Answer 24

Thickening, emulsification and gelling.

Question 25

What are some of the challenges with carbohydrate analysis?

Answer 25

They rarely exist alone and need to be separated from other nutrients and potentially other carbohydrates.

The large, complex structures might need to be processed before they can be analysed.

Question 26

Why can monosaccharides be difficult to distinguish from one another?

Answer 26

They have very simlar structures.

Question 27

Are these quantative or descriptive carbohydrate analysis?:

Total carbohydrates
Total sugar
Total fibre

Answer 27

Quantitative.

Question 28

Are these quantitative or descriptive carbohydrate analysis?:

Average molecular weight
Carbohydrate structure
Monosaccharide composition

Answer 28

Descriptive.

Question 29

How can total sugars be separated into simple sugars, starches and dietary fibre?

Answer 29

Fractionation.

Question 30

To fractionate simple sugars from total carbohydrates, what solution should the sample be placed in?

Answer 30

When a sample is placed in a solution of 70% alcohol/water the simple sugars will be solubilised.

Question 31

When fractionating carbohydrates, once simple sugars have been removed how can starch and dietary fibre be separated?

Answer 31

Starches are enzymatically hydrolysed to simple sugars, to leave the dietary fibre.

Question 32

Which method of analysing carbohydrates by determining the concentration of sugars is reliable and repeatable and lead to standardised methods?

Answer 32

Spectroscopy.

Question 33

What is a benefit and a drawback of liquid carbohydrate analysis?

Answer 33

Benefit - rapid analysis.

Drawback - limited by other nutrients potentially affecting the accuracy.

Question 34

What does a pycnometer, hydrometer and densitometer measure?

Answer 34

Carbohydrate content in a liquid using density.

Question 35

Which apparatus provides a direct measure of mass/volume. It is only accurate at 25c, usually requires a large sample volume…but it’s cheap!

Answer 35

Pycnometer.

Question 36

Which apparatus infers cabohydrate content through buoyancy. It has to be calibrated for the specific application and usually requires a large volume…but it’s cheap!

Answer 36

Hydrometer.

Question 37

Which apparatus uses high-precision piezoelectronics to infer carbohydrate content. It can measure at different temperatures, does not require a large sample volume and is highly accurate…but it’s expensive!

Answer 37

Densitometer.