Carbohydrates

Question 1

Name 6 functions of carbohydrates

Answer 1

1. Energy
2. Structure
3. Extracellular matrix
4. Signalling and development
5. Protein folding
6. Components of DNA

Question 2

What are the basic properties of all carbohydrates?

Answer 2

• Carbon based molecules rich in hydroxyl groups

- Empirical formula: (CH2O)n

Question 3

What are monosaccharides?

Answer 3

• Most simple form of carbohydrates

- Either aldehydes (aldose) or ketones (ketose) with >2 hydroxyl groups

Question 4

What is the configuration of a monosaccharide defined by?

Answer 4

• Asymmetric carbon atom furthest from the aldehyde/keto group
  (Most sugars have a D configuration)

Question 5

When can diasterioisomers occur?

Answer 5

• > 3 carbon atoms

- Number of isomers = 2^n (where n= number of asymmetric carbon atoms)

Question 6

What are constitutional isomers?

Answer 6

Have identical molecular formula but differ in how their atoms are ordered

Question 7

How do epimers and anomers differ?

Answer 7

epimers - differ at one of several asymmetric carbon atoms

anomers - differ at a new asymmetric carbon atom formed on ring closure

Question 8

Why do monosaccharides adopt cyclical forms?

Answer 8

Lower energy conformation

Question 9

What types of rings to glucose and fructose form?

Answer 9

Glucose - C5 hydroxyl group attacks O of C1 aldehyde to form 6 C ring hyranose (hemiacetal - aldehyde)
Fructose - C5/C6 hydroxyl group attacks O of C2 ketone to form 5C ring of furanose/pyranose (Hemiaketal - ketone)

Question 10

What are the two common forms of pyranose?

Answer 10

Boat and chair

Question 11

What is the difference between axial and equatorial?

Answer 11

axial - nearly perpendicular to the average plane of the molecule
equatorial - nearly parallel to the average plane of the molecule

Question 12

What is the common conformation of furanose rings?

Answer 12

envelope - either C-2 or C-3 is out of plan on the same side as C5 (endo-pucker)

Question 13

What are anomers?

Answer 13

Different forms of carbohydrates created by an assymetric carbon

• In glucose this is C1
• In fructose this is C2

Question 14

How do alpha and beta anomers differ?

Answer 14

alpha - hydroxyl group is on the opposite side of the ring as C6
beta - hydroxyl group is on the same side of the ring as C6
note: C5 on fructose

Question 15

What are 3 common reactants for monosaccharides

Answer 15

• alcohols
• amines
• phosphates

Question 16

How does an O-glycosidic bond form?

Answer 16

• oxygen atom of n alcohol and anomeric carbon of a monosaccharide
• between two sugars

Question 17

How does an N-glycosidic bond form?

Answer 17

Anomeric carbon of sugar linked to nitrogen atom of an amine group

Question 18

Name 3 common disaccharides

Answer 18

sucrose, lactose, maltose

Question 19

What differentiates a reducing and non-reducing sugar

Answer 19

reducing - free hydroxyl at anomeric position allowing ring to open, exists in equilibrium (e.g glucose)
non-reducing - anomeric carbon is involved in bonding

Question 20

Describe the structure of glycogen

Answer 20

• Branched

- Mostly consists of alpha 1,4 glycosidic bonds between glucose

Question 21

Describe the structure of starch

Answer 21

• Linear
• glucose joined by alpha 1,4 glycosidic bonds (amylose)
• alpha 1,6 glycosidic bonds ( amylopectin)

Question 22

What is the structure of chitin and cellulose

Answer 22

cellulose - linear polymer of glucose B-1,4

chitin - linear molecules of N-acetyly glucosamine joined by B-1,4 glycosidic bonds

Question 23

By which type of linkage do carbohydrates link to nulceic acids?

Answer 23

N-glycosidic bonds

Question 24

How do carbohydrates typically attach themselves to proteins?

Answer 24

• Attach to asparagine via N-glycosidic

- Attach to serine/threonine via O-glycosidic

Question 25

What is the typical function and structure of proteoglycans?

Answer 25

• protein conjucated to a polysaccharide glycosaminoglycan
• structural components and lubricants
• tethered to cell membrane
• highly sulfanated

Question 26

Where does glycolysation occur?

Answer 26

In the ER and Golgi apparatus, aids in protein folding

Question 27

Which enzymes are responsible for the assembly and breaking down of carbohydrates?

Answer 27

Broken down by glycoside hyrolayses (GHs) - general

Synthesized by glycosytransferases (GTs) - very specific

Question 28

How does the influenza virus exploit GHs?

Answer 28

Uses neurominidase to release new virus particles using own acid

Question 29

Which compounds typically act as GT donor substrates and which act as acceptors?

Answer 29

nucleotide phosphates - donors

hydroxl in protein, lipid, small molecule or another sugar - acceptor