Carbohydrates

Question 1

Functions of carbohydrates

Answer 1

1) Energy stores (glycogen, starch).
2) Components of structural material
(e.g. chitin for insect exoskeletons).
3) Parts of other important
macromolecules – DNA and RNA,
glycoproteins, and glycolipids.
4) Signalling function (recognition of cell surface molecules on other cells)

Question 2

general formula for carbohydrates

Answer 2

C: H O:
1 : 2: 1
carbohydrates are hydrates of carbon with the
general formula Cx(H2O)x

Question 3

Characteristics of monosaccharides

Answer 3

1. Monosaccharides are colourless, crystalline solids that are
   soluble in water and other polar solutions – in other words
   monosaccharides are hydrophilic.
2. Monosaccharides have names ending with “ose”.
   Glucose, Ribose, Deoxyribose….
3. Most have a sweet taste

Question 4

Continued

Answer 4

4. The backbone of the monosaccharide is a carbon chain with
   all carbons joined by single covalent bonds.
   Glucose when solubilised, they form a ring structures
   5- Monosaccharide chains contain a single carbonyl group
   (C=O)

Question 5

If it contains an aldehyde
carbonyl group.

Answer 5

aldose
D-Glyceraldehyde

Question 6

If it contains a ketone
carbonyl group

Answer 6

ketose
Dihydroxyacetone

Question 7

Common 6-carbon monosaccharides

Answer 7

Glucose
Most abundant sugar in nature; in many foods, e.g.
bread, pasta, fruit, cereals.
Most of the carbohydrates we eat are converted into
glucose for energy.

Fructose
Naturally occurring in foods such as honey & fruit.

Galactose
In nature primarily found as part of lactose (milk sugar).

Mannose A by-product of metabolism, also found in some fruitsand vegetables.

Question 8

Monosaccharides have chirality

Answer 8

The chiral carbon which
determines whether a
carbohydrate is in the D
or L configuration is the
one furthest from the
carbonyl group

In glucose
Carbons 2-5 are chiral
C6 = Not a chiral carbon. Chiral
carbon should have 4
different atoms/groups
attached to it!

Question 9

Which chiral carbon
determines D/L
configuration?

Answer 9

C5
D-glucose and L-glucose
are enantiomers.

Question 10

Enantiomers

Answer 10

1- Do they have the same chemical formula? YES
2- Do they have chiral carbons? YES
3- Can they be superimposed? NO
4- Are they mirror images? NO

Question 11

diastereomers.

Answer 11

1- Do they have the same chemical formula?
2- Do they have chiral carbons?
3- Can they be superimposed?
4- Are they mirror images?
YES
YES
NO
NO
These molecules are called diastereomers.

Question 12

Hexoses…..

Answer 12

Same Chemical Forumula

Question 13

How many diastereomers can a molecule have?

Answer 13

A molecule with n chiral carbons has (2n-2) diastereomers.
Example:
A molecule with 4 chiral carbons will have 24-2 = 14 diastereomers.

Question 14

carbon derived from the carbonyl carbon is known as

Answer 14

the anomeric carbon

Question 15

D-glucose

Answer 15

The ring has 6 members
Rings with 6 members are
called pyranose rings.

Question 16

Fructose

Answer 16

Fructose is a ketose
The ring has 5 members
Rings with 5 members are
called furanose rings.

Question 17

Common furanose monosaccharides

Answer 17

Deoxyribose is part of the structure of DNA
Ribose is part of RNA.

Question 18

Forming carbohydrate polymers

Answer 18

Monosaccharides are joined together to form
disaccharides, oligosaccharides and polysaccharides by
condensation reactions.
 Covalent bonds that form between a carbohydrate and
another molecule are called glycosidic bonds (this
other molecule does not need to be another
carbohydrate).

Question 19

Maltose

Answer 19

Condensation reaction between α-D-glucose + either α or β-D-glucose
Covalent bond is α-1,4-glycosidic
Formula is: C12H22O11

Question 20

Sucrose

Answer 20

Condensation reaction between α-D-glucose + b-D-fructose
Covalent bond is α-1,2-glycosidic
Formula is: C12H22O11

Question 21

Lactose

Answer 21

Condensation reaction between b-D-galactose + a/b-D-glucose
Covalent bond is b-1,4-glycosidic
Formula is: C12H22O11

Question 22

Cellobiose

Answer 22

Condensation reaction between b-D-glucose + b-D-glucose
Covalent bond is b-1,4-glycosidic
Formula is: C12H22O11

Question 23

Why are some bonds named as a bonds and some b?

Answer 23

alpha glycosidic bonds are formed when the OH on the C1
(anomeric carbon) is below the ring
beta glycosidic bonds are formed when the OH on the C1
(anomeric carbon) is above the ring.

Question 24

Starch

Answer 24

 energy store of plants
 Very large polymer of a-D-glucose.
Amylopectin: Branched polymer (every 24-30 glucose
molecules there is a branch).
 Glucose monomers are linked through a-1,4-
glycosidic bonds.
 The bond linking branches to the main chain is an
a-1,6-glycosidic bond.
Amylose: Linear polymer. Glucose monomers are
linked through a-1,4-glycosidic bonds.

Question 25

Glycogen

Answer 25

 energy store of animals
 Very large polymer of a-D-glucose with
many branches
Branched polymer (every 8-12 glucose molecules
there is a branch).
 Glucose monomers are linked through a-1,4-
glycosidic bonds.
 The bond linking branches to the main chain is
an a-1,6-glycosidic bond.

Question 26

Cellulose

Answer 26

 for structural support in plant cell walls
 Very large, unbranched polymer of b-D-glucose.
 Most abundant polysaccharide on earth.
 Humans cannot digest cellulose. We do
not have the correct enzymes (called
cellulases) to break the b-1,4-glycosidic
bonds.

Question 27

Chitin

Answer 27

 structural component of insects, molluscs and
fungi cell walls
Polymer of: N-acetylglucosamine
(shortened to GlcNAc).
This molecule contains:
b-D-glucose
Amino group
Acetyl group

Question 28

Continued

Answer 28

 Chitin is a polymer of N-acetylglucosamine
 The covalent bond linking the GlcNAc monomers is b-1,4-glycosidic.

Question 29

GLYCOSYLATION

Answer 29

Cellular process that attaches an oligosaccharide to a protein.
Can occur as the protein is being made or is added afterwards
(post-translational modification).
Estimated that more than half of proteins made in eukaryotic
cells are glycosylated.

Question 30

Continued

Answer 30

Creates a diversity of structures – vastly increases the
number of functions proteins can perform.
 Position the carbohydrate is attached.
 Types of sugars attached.
 Short or long chains.
 Branched or unbranched.
Glycoproteins
Structure is mostly protein with short, linear, oligosaccharides
added on.
Proteoglycan
Structure is mostly polysaccharides held together by a protein
chain.

Question 31

Types of Glycoprotein

Answer 31

Glycoproteins are classified by the type of the glycosidic
bond that connects the carbohydrate to the protein.
There are 2 main types of glycoproteins:
N-linked and O-linked
~90% of glycoproteins are N-linked.

Question 32

Production of glycoproteins

Answer 32

N-linked glycoproteins are
formed in the endoplasmic
reticulum and then the golgi.
O-linked glycoproteins are
made in the golgi.

Question 33

N-linked glycoproteins

Answer 33

Connects the sugar and protein through a nitrogen atom that
is on either an asparagine or lysine amino acid.
Functions include:
 Cell-cell adhesion.
 Cell signalling.
 Host-pathogen
recognition.
Only found in eukaryotes and
Archaea, not Bacteria

Question 34

Cell surface glycoproteins are used by viruses

Answer 34

• Haemagglutinin and Neuraminidase are
  receptors on the flu virus protein coat.
• Haemagglutinin binds to specific N-linked
  glycoproteins on the cell it wants to
  infect.
• Neuraminidase cleaves an oligosaccharide
  in the cell membrane to disconnect the
  virus.

Question 35

O- linked glycoprotein

Answer 35

Connects the sugar and protein through an oxygen atom that is
on either a serine, threonine or hydroxy-lysine amino acid.
Found in eukaryotes, Archaea and Bacteria.
Functions include:
 ABO blood groups.
 Extracellular matrix component.
 Shock absorption in joints.

Question 36

Proteoglycans

Answer 36

The polysaccharide chains within the proteoglycans change the
properties of water to a slimy, gel-like texture.
This texture is a useful function in cartilage, mucus and
synovial fluid in joints.
They provide shock absorption because they are surrounded by
a lot of water and can release it when pressure is applied.
Proteoglycans also provide structural support as part of the
extracellular matrix in eukaryotic cells.