Carbohydrates

Question 1

What is a Carbohydrate?

Answer 1

A polyhydroxyaldehyde or polyhydroxyketone, or a substance which gives these compounds upon hydrolysis

Question 2

What is a monosaccharide and it’s general formula?

Answer 2

Monosaccarides are a source of energy in metabolic processes that cannot be further simplified. Their basic formula:

Cn(H2O)n, where n = the number of carbon atoms and varies from 3-8

Question 3

What are the two types of monosaccharides?

Answer 3

• Aldose = has an aldehyde group

- Ketose = has a ketone group

Question 4

How are monosaccharides named?

Answer 4

They are classified by the number of carbon atoms present. 
tri -3
tetr-4
pent-5
hex-6
hept-7
oct-8

Question 5

Are enantiomers and distereoisomers possible in carbohydrates?

Answer 5

Yes as carbohydrates have stereogenic centres

Question 6

What is a fischer projection?

Answer 6

A 2 dimensional representation of a 3 dimensional organic molecule, it is commonly used to represent monosaccharides

Question 7

How do we put molecules into the fischer projection?

Answer 7

rotate the molecule 90 degrees clockwise from the top and then 180 degrees backwards until the hydrogens are level with the plane of paper

Question 8

What is a D monosaccharide versus an L monosaccharide?

Answer 8

D-monosaccharide= the -OH group on it’s penultimate (2nd to last) carbon is on it’s right

L-monosaccharide= the -OH group on it’s penultimate carbon is on it’s left

Question 9

What form are all natural sugars found in?

Answer 9

the D form

Question 10

What are cyclic sugars?

Answer 10

When one or more series of atoms in the sugar compound connect to form a ring shape

Question 11

What are hemiacetals?

Answer 11

compounds which form as a result of aldehydes or ketones reacting with alcohols

Question 12

Which groups/compounds can become cyclic?

Answer 12

Those hemiacatels which contain 5 or 6 carbon atoms

Question 13

What is similar about monosaccharides in cyclic 5/6 membered hemiacetals?

Answer 13

They have hydroxyl and carbonyl groups in the same molecules

Question 14

What are Haworth Projections?

Answer 14

a common way of writing a structural formula to represent the cyclic structure of monosaccharides

Question 15

What is a beta and alpha anomer?

Answer 15

b- OH on the anomeric carbon is cis to the terminal -CH2OH (up)
a-OH on the anomeric carbon is trans to the terminal-CH2OH

Question 16

What are anomers and anomeric carbons?

Answer 16

Anomeric Carbon - new stereocentre resulting from cyclic hemiacetal formation

Anomers - Carbohydrates that differ based on the configuration at the anomeric carbons

Question 17

What are 5/6 membered ring structures called?

Answer 17

6 membered are called pyranose and 5 members are called furanose

For pyranoses, the 6 membered ring is more accurately represented as a strain free chair conformation

Question 18

What is a multirotation?

Answer 18

The change in specific rotation that accompanies the interconversion of a and b anomers in an aqueous solution

Question 19

What is a glycoside formation?

Answer 19

when the OH of an anomeric carbon is replaced by an OR (variable R)

Question 20

Does a gylcosidic formation change the anomeric carbon?

Answer 20

Yes. After this occurs the carbon is called the glycosidic carbon as it can no longer do multirotation

Question 21

Can all sugars bind to each other?

Answer 21

Yes as they are all alcohols

Question 22

What is the difference between an alpha and a beta link?

Answer 22

an alpha link forms below the monosaccharide and a beta forms above

Question 23

What are N-Glycosides?

Answer 23

These are compunds formed when the anomeric carbon of a cyclic hemiacetal undergoes a reaction with an NH group from an amine

Question 24

What is cellulose?

Answer 24

A polysaccharide with several thousand D-glucose units joined by beta 1,4 links.

It provides structure in plants as the H bonds can contribute to rigidity and toughness

Question 25

What is Starch?

Answer 25

A polysaccharide of inidividual glucose units joined by alpha 1,4 links

It is fully digestible and an essential part of the human diet which is only found in plant material

Question 26

What is starch made up of?

Answer 26

Amylose (20%) and Amylopectin (80%)

Question 27

Describe Amylose

Answer 27

A polysaccharide which is soluble in water and consists of several hundred to thousand D glucose units linked in long chains
it tends to curl into helices

Question 28

Describe Amylopectin

Answer 28

A polysaccharide which has up to 100,000 glucose units per molecules and an alpha 1,6 branch approximately every 25 units along the chain
it is not soluble and has a hirachial structure

Question 29

What is Glycogen?

Answer 29

Glycogen is how energy is stored in animals, it is stored in the liver and muscles
Structurally, glycogen is similar to amylopectin but much more branched