Lecture 8: Oligosaccharides and Polysaccharides Flashcards
What is a glycoconjugate?
A glycan (carbohydrate) attached to a protein or lipid
What is a glycolipid?
A lipid + oligosaccharide
What is a glycoprotein?
A protein + oligosaccharide
What is a Proteoglycan?
A protein + glycosaminoglycan (polysaccharide)
Where are most oligosaccharides found?
usually found covalently linked to proteins/lipids as glycoconjugates
Do polymers of monosaccharides store information like nucleotides and proteins?
NO!
What are the main functions of polysaccharides?
energy storage and mechanical structure
What are Glucans?
homopolysaccharides of glucose
What are the 3 major types of glucans produced by plants?
amylose and amylopectin (energy storage) i.e. starch
cellulose (structural) i.e. wood, cotton
Amylose and cellulose are both ____ (branched, linear, or spiral) glucans with ___→___ glycosidic linkages
linear glucans
1→4
Of amylose and cellulose: which one is water soluble and which is not? Why?
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.
For glycogen: alpha or beta linkage? How often are the 1→6 branches? how many reducing ends and non-reducing ends?
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
For amylose: alpha or beta? how often 1→6 branches? how many reducing ends and non-reducing ends?
alpha linkages. no 1→6 branches. 1 reducing end. 1 non-reducing end (hence no branches).
Amylopectin: alpha or beta? how often 1→6 linkages? how many reducing and non-reducing ends?
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)
What glucan(s) is starch made of?
amylose and amylopectin
Name which type of linkage each of the following enzymes break:
1) amylase
2) sucrase
3) isomaltase
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
Why can humans not break down cellulose?
because we don’t have an enzyme to hydrolyze the ß1→4 linkages between 2 glucoses
Lactase can hydrolyze a ß1→4 glycosidic linkage, so why can humans not break down cellulose?
because lactase can only hydrolyze the ß1→4 linkage between galactose and glucose. cellulose is a ß1→4 linkage between 2 glucoses.
Glucose isomerase can interconvert _____ and _____ i.e. can convert D-glucose into D-fructose
aldoses and ketoses
Chitin is a ____ (linear or chiral) homopolysaccharide of _______(type of monosaccharide)
linear
D-N-acetylglucosamine (ß1→4)
What functional group differeniates cellulose and chitin?
the D-N-acetylglucosamine function group (found in chitin) that replaces the C2 OH in cellulose
What 2 monosaccharides make up peptidoglycan?
D-N-acetylglucosamine and D-N-acetylmuramic acid (ß1→4 linkages)
Name the 3 main glucans used for energy storage in living things. Name the 2 main glucans used for structural support in living things?
energy storage = glycogen, amylose, amylopectin
structural support = cellulose and chitin
