Carbohydrates & Glycobiology

Question 1

Functions of Carbohydrates (4)

Answer 1

1. Energy source
2. Energy storage
3. Structural component of cell walls and exoskeletons
4. Informational molecules in cell - cell signalling (regulates cell - cell communication)

Question 2

Carbohydrate formula

Answer 2

Cn(H2O)n

Question 3

What is an aldose

Answer 3

A carbohydrate with aldehyde functionality

Question 4

What is a ketose

Answer 4

A carbohydrate with ketone functionality

Question 5

What are enantiomers

Answer 5

Stereoisomers that are non superimposable mirror images

Question 6

What are diasteromers

Answer 6

Two sugars that have identical molecular formulas, different arrangement of atoms and are not enantimers (mirror images)

Question 7

What are epimers

Answer 7

Sugars that differ in stereochemistry at only one chiral center. They are not mirror images and are not enantiomers.

Question 8

What carbohydrate structure predominates under normal physiological conditions and why?

Answer 8

Cyclic/ ring structure. Because they are lower in energy and are more stable than open chain structures.

Question 9

Alpha anomer of glucose structure

Answer 9

The OH group (hydroxyl grp) is facing the opposite direction than the CH2OH group

Question 10

Beta anomer of glucose structure

Answer 10

OH (hydroxyl) group is facing the same direction as the CH2OH group.

Question 11

How is the cyclic structure formed?

Answer 11

The nucleophilic alcohol attacks the electrophilic carbonyl carbon, allowing formation of a hemiacetal. This results in the linear carbohydrate forming a ring structure. The carbonyl carbon is reduced to an alcohol.

Question 12

After the cyclisation of monosaccharides what does the former carbonyl carbon become?

Answer 12

It becomes a new chiral center, called the anomeric carbon at C1 of an aldose & C2 of a ketose.

Question 13

What is a pyranose

Answer 13

Six membered oxygen containing ring

Question 14

What is a furanose

Answer 14

Five membered oxygen containing ring

Question 15

What occurs to form amino sugars

Answer 15

An NH2 group replaces one of the OH groups in the hexose.

Question 16

What occurs to form deoxy sugars

Answer 16

Substitution of H for OH produces a deoxy sugar

Question 17

What occurs to form acidic sugars

Answer 17

Made by oxidation of carbonyl carbon or hydroxyl carbon or both.

Question 18

What is the O-glycosidic bond formed between

Answer 18

An anomeric carbon and a hydroxyl carbon

Question 19

Which part of the molecule is reducing

Answer 19

The second molecule, with the hemiacetal is reducing

Question 20

Which part of the molecule is non reducing

Answer 20

The anomeric carbon involved in the glycosidic bonding is non reducing

Question 21

What is sucrose made of

Answer 21

Glucose + fructose

Question 22

What is lactose made of

Answer 22

Glucose + galactose

Question 23

What is maltose made of

Answer 23

Glucose + glucose

Question 24

How is a disaccharide formed

Answer 24

• Formed from two monosaccharides
• The OH of one glucose molecule condenses with the hemiacetal of the other glucose molecule
• This happens with the elimination of H2O
• A glycosidic bond is formed

Question 25

Reducing sugar

Answer 25

Sugar has the ability to participate in oxidation or reduction rxns due to the free oxygen in the OH group at the end of the molecule

Question 26

Non reducing sugar

Answer 26

Sugar doesn't have the ability to participate in oxidation or reduction rxns due to the oxygens in the anomeric carbons being bound by the glycosidic bond

Question 27

What does the product have after an O-glycosidic bond (bond between two anomeric carbons) is formed

Answer 27

The product has two acetal groups and no hemiacetals

Question 28

What linkages do glucose monomers form to form glycogen

Answer 28

Alpha 1 - 4 linkages

Question 29

What is glycogen

Answer 29

* A branched homopolysaccharide of glucose

Question 30

Function of glycogen

Answer 30

It is the main storage polysaccharide in animals

Question 31

What is starch a mixture of

Answer 31

Two homopolysaccharides of glucose: amylose & amylopectin

Question 32

Function of starch

Answer 32

It is the main storage polysaccharide in plants

Question 33

How is cellulose structured

Answer 33

It's a linear homopolysaccharide of glucose

Question 34

What linkages are found in cellulose

Answer 34

Glucose monomers form beta 1 - 4 glycosidic linkages

Question 35

How is chitin structured

Answer 35

It's a linear homopolysaccharide of N-acetylglucosamine

Question 36

What linkages are in chitin

Answer 36

N-acetylglucosamine monomers form beta 1-4 linked chains

Question 37

Structure of amylose (tyoe & repeating unit)

Answer 37

Linear homopolysaccharide of glucose with alpha 1-4 glycosidic bonds

Question 38

Structure of amylopectin (type & repeating unit)

Answer 38

Branched homopolysaccharide of glucose with alpha 1-4 glycosidic bonds

Question 39

What are glycosaminoglycans

Answer 39

A special type of polysaccharides that consist of repeating disaccharide units which are modified to contain an amino grp (either N-acetyl-glucosamine or N-acetyl-galactosamine) and some negatively charged grps (uronic acids or galactose and sulfate esters)

Question 40

Where are glycosaminoglycans found and what is their function

Answer 40

Found in our joints and act as a shock absorber/ buffer/ lubricant

Question 41

What are proteoglycans

Answer 41

Proteins that are attached to glycosaminoglycans

Question 42

What are glypicans

Answer 42

protein that is anchored to a lipid membrane

Question 42

What are syndecans

Answer 42

protein has a single transmembrane domain

Question 43

4 functions of proteoglycans

Answer 43

1. Joint lubricants 2. Structural components of connective tissue 3. Bind cell to ECM 4. Regulate movement of molecules through the matrix

Question 44

Main components of ECM

Answer 44

* proteoglycan aggregates * collagen fibres * elastin (a fibrous protein)

Question 45

What is a glycoprotein

Answer 45

Carbohydrate attached to a protein via its anomeric carbon to amino acids on the protein

Question 46

What amino acids commonly form glycoproteins

Answer 46

Ser, Thr, Asn (Serine, Threonine, Asparagine)

Question 47

What are glycolipids

Answer 47

Lipids with covalently bound oligosaccharide