Lecture 8: Oligosaccharides and Polysaccharides

Question 1

What is a glycoconjugate?

Answer 1

A glycan (carbohydrate) attached to a protein or lipid

Question 2

What is a glycolipid?

Answer 2

A lipid + oligosaccharide

Question 3

What is a glycoprotein?

Answer 3

A protein + oligosaccharide

Question 4

What is a Proteoglycan?

Answer 4

A protein + glycosaminoglycan (polysaccharide)

Question 5

Where are most oligosaccharides found?

Answer 5

usually found covalently linked to proteins/lipids as glycoconjugates

Question 6

Do polymers of monosaccharides store information like nucleotides and proteins?

Answer 6

NO!

Question 7

What are the main functions of polysaccharides?

Answer 7

energy storage and mechanical structure

Question 8

What are Glucans?

Answer 8

homopolysaccharides of glucose

Question 9

What are the 3 major types of glucans produced by plants?

Answer 9

amylose and amylopectin (energy storage) i.e. starch
cellulose (structural) i.e. wood, cotton

Question 10

Amylose and cellulose are both ____ (branched, linear, or spiral) glucans with ___→___ glycosidic linkages

Answer 10

linear glucans
1→4

Question 11

Of amylose and cellulose: which one is water soluble and which is not? Why?

Answer 11

Amylose is water soluble because it’s alpha1→4 glycosidic linkages, which creates coils (instead of sheets) and fewer intramolecular H-bonds compared to cellulose, which then means it can form more H bonds with water.

Cellulose is not water soluble because it’s ß1→4 glycosidic linkages, which makes the glucose molecules hydrogen bond with themselves and creates flat sheets, which stack upon themselves. The intramolecular H bonding between the glucose molecules leaves few available to H bond with water; hence, water insoluble.

Question 12

For glycogen: alpha or beta linkage? How often are the 1→6 branches? how many reducing ends and non-reducing ends?

Answer 12

alpha linkages (mostly 1→4). 1→6 branches ~12-14 residues. always 1 reducing end. non-reducing ends = n + 1, where n is the #branches

Question 13

For amylose: alpha or beta? how often 1→6 branches? how many reducing ends and non-reducing ends?

Answer 13

alpha linkages. no 1→6 branches. 1 reducing end. 1 non-reducing end (hence no branches).

Question 14

Amylopectin: alpha or beta? how often 1→6 linkages? how many reducing and non-reducing ends?

Answer 14

alpha linkages. 1→6 linkages every 24-30 glucose residues. 1 reducing end only. n +1 = non-reducing ends (like glycogen, but branches will be spread more widely a part)

Question 15

What glucan(s) is starch made of?

Answer 15

amylose and amylopectin

Question 16

Name which type of linkage each of the following enzymes break:

1) amylase
2) sucrase
3) isomaltase

Answer 16

1) amylase: cleaves the alpha1→4 linkage in amylose/amylopectin
2) sucrase: hydrolyzes sucrose into glucose and fructose
3) isomaltase: hydrolyzes alpha1→6 linkages in amylopectin

Question 17

Why can humans not break down cellulose?

Answer 17

because we don’t have an enzyme to hydrolyze the ß1→4 linkages between 2 glucoses

Question 18

Lactase can hydrolyze a ß1→4 glycosidic linkage, so why can humans not break down cellulose?

Answer 18

because lactase can only hydrolyze the ß1→4 linkage between galactose and glucose. cellulose is a ß1→4 linkage between 2 glucoses.

Question 19

Glucose isomerase can interconvert _____ and _____ i.e. can convert D-glucose into D-fructose

Answer 19

aldoses and ketoses

Question 20

Chitin is a ____ (linear or chiral) homopolysaccharide of _______(type of monosaccharide)

Answer 20

linear

D-N-acetylglucosamine (ß1→4)

Question 21

What functional group differeniates cellulose and chitin?

Answer 21

the D-N-acetylglucosamine function group (found in chitin) that replaces the C2 OH in cellulose

Question 22

What 2 monosaccharides make up peptidoglycan?

Answer 22

D-N-acetylglucosamine and D-N-acetylmuramic acid (ß1→4 linkages)

Question 23

Name the 3 main glucans used for energy storage in living things. Name the 2 main glucans used for structural support in living things?

Answer 23

energy storage = glycogen, amylose, amylopectin

structural support = cellulose and chitin