Chapter 7: Monosaccharides

Carbohydrates are some of the most __ molecules on earth

Abundant!

Why do bacteria need rigid cell walls?

If they didn’t, water would flood their cells and they would burst due to osmotic pressure

Name a few functions of carbohydrates

1. Fuel

2. Energy storage

3. Structure

4. Barrier/lubricant

5. Cell signaling

6. Cell adhesion

7. Cellular identity

What is sialic acid used for?

To determine the “age” of RBC in our system, to know it if should be turned over or not

What decorates the surface of the COVID spike protein?

Carbohydrates! They help the virus evade our immune system

Saccharides carbonyls come in what two forms?

Aldehydes or ketones (aldoses and ketoses)

The simplest monosaccharide contains how many C?

3!

Glucose is a __hexose. Fructose is a __hexose.

aldohexose, ketohexose

Draw D-glucose

Draw D-fructose

What are the L and D names based on?

The stereochemistry of the simplest saccharide, Glyceraldehyde

What does a horizontal line mean on a Fisher Projection? What about vertically?

• Horizontal: towards us

• Vertical: plane of paper

In a Fisher Projection, how can you tell L or D stereochemistry?

• D: Carbonyl at top, most distant -OH towards right

• L: Carbonyl at top, most distant -OH towards left

The most distant is NOT the CH₂OH

How many isomers exist for a monosaccharide with n chiral centers?

2ⁿ

What configuration are most sugars in? What configuration are most amino acids in?

• Sugars: D

• Amino Acids: L

Epimer definition

A different configuration at only ONE carbon, and NOT the one that determines L or D.

How to tell the difference between an aldose and a ketose in the name of the sugar?

a -ul is inserted in the ketone name

Ex: D-Ribose vs D-Ribulose

Ribulose is a ketone, ribose is an aldehyde

Draw D-Ribose

What 3 sugars do we need to remember?

D-fructose, D-glucose, D-ribose

Which form is dominant in aqueous solution?

Cyclic

The formation of sugar rings is an…

intramolecular cyclization

What do we call the two possible anomers of a cyclic form of a saccharide? Why can we get get these two forms?

Alpha and Beta. The -OH group can attack the carbonyl either from the front or back.

What is the most abundant form of glucose in solution?

B-D-glucopyranose

Pyranose=? Furanose=?

6 membered ring, 5 membered ring

Both with one O as part of the ring

How do we define alpha or beta? How do we determine L or D in cyclic form?

• L: Terminal carbon (the CH₂OH carbon) is pointing down

• D: Terminal carbon is pointing up

• Beta: -OH pointing same way

• Alpha: -OH opposite same way (ANTIparallel)

Mutarotation definition

Interconversion of alpha and beta anomers (ring opens and closes all the time, alpha and beta forms in a certain equilibrium, often favoring one of them)

Draw a phosphate group

Draw alpha-D-deoxyribose

How are disaccharides formed?

The -OH of one monomer attacks one of the carbons of another, forming an O-glycosidic bond

Formation of a disaccharide is an example of what kind of reaction?

Condensation

What is the reducing end of a multiple saccharide chain?

the hemiacetal residue, the anomeric -OH is still available to attack another monomer

Name the abbreviations for fructose, glucose and ribose

Fru, Glc, Rib

What does GlcNAc mean

N-acetylglucosamine

What does GlcN mean

Glucosamine

What are the 3 rules for naming di saccharides?

1. Put the non-reducing residue at the left

2. Name the reducing sugar on the right

3. Describe the linkage of the glycosidic bond

What type of glycosidic bond is lactose

Gal(B1 →4) Glc

What is interesting about sucrose?

It’s a disaccharide with no reducing end

How does Benedicts solution work?

If there is a reducing end present, the Cu⁺² in solution will oxidize, and the solution will become red. Needs the linear form though but that’s fine because the ring is always opening and closing

What is a homopolysaccharide?

Polymer made of only one monosaccharide

Name the glycosidic linkages of glycogen, starch, cellulose and chitin

• Glycogen: (alpha1→4)Glucose

• Starch: (Alpha1→4)glucose

• Cellulose: (B1→4)Glucose

• Chitin:(B1→4)GlcNac

Sooo why can’t we eat our pants?

Don’t have a digestive enzyme for the B1→4 linkage

How can O-glycosidic bonds be broken?

Boiling with acid or heating up in general

How can you analyze the type of glycosidic bond present?

Exhaustive methylation of all the -OH groups, cleavage with acid, then see which carbons have an -OH still (those were the ones involved in the linkage)