BioChem: Carbohydrates

Erythropoetin (EPO)

* a glycoprotein hormone * EPO. is responsible for RBC production *has 4 oligosaccharide groups *presence of oligosaccharide groups protect EPO from cellular degradation * hormonal regulation

Name 6 monosaccharides

* alpha-D-glucose *alpha-D-fructose *alpha-D-Galactose *alpha-D-mannose *beta-D-ribose *beta-2-Deoxy-D-ribose

Describe the reaction formation of maltose.

* alpha-D-glucose (OH pointed down) is a hemiacetal at anomeric carbon (R1, R2, OH, H) *beta-D-glucose (OH pointed down) has a alcohol group *the OH of alpha-D-glucose and H form together to get water; release of H20 [CONDENSATION] *glycosidic bond (an acetal) is formed between alpha-d-glucose and beta-d-glucose. forming 1-4 bond *there is no longer a free anomeric carbon therefore can no longer go back to aldehyde *Final product: non-reducing end + reducing end (hemiacetal on C1 from b-d-glucose) * Final product name: maltose

A reducing sugar

*A sugar that can reduce other compounds *have a free anomeric carbon *can be picked up by Tollen's or Benedicts reagent

D-Arabinose

*aldose * 5 Carbons

D-xylose

*aldose * 5 Carbons *monosaccharide absorbed from gut, *excreted in kidneys. *d-xylose test used to measure GI mucosal damage. measure blood/urine levels after admin

D-Ribose

*aldose * 5 Carbons *component of RNA and ATP

What are the two types of polysaccharides?

*homopolysaccharides *heteropolysaccharides

Cyclization of Monosaccharides

*nucleophilic OH attacks the electrophilic carbonyl carbon (intramolecular nucleoattack) --> hemiacetal * As a result, the linear carbohydrate forms a ring structure * At the completion of the structure, carbonyl carbon is reduced to an alcohol *orientation of the alcohol around the carbon is variable and transient (can be B or alpha)

Epimer

*subtype of diatereomers *differ in configuration at exactly one chiral carbon

Anomeric Carbon

*the new chiral center formed in ring closure; *it was the carbon containing the carbonyl in the straight-chain form

Mutarotation

-spontaneous change of configuration about C1 (occurs more rapidly if rxn is catalyzed w/ acid or base) -Exposing hemiacetal rings to water causes them to spontaneously cycle b/w open & closed forms -b/c the substituents on the single bond b/w C1 and C2 can rotate freely, either the α or β anomer can be formed

What are 3 main functions of carbohydrates?

1. energy source and energy storage 2. structural components 3. informational molecules in cell-cell signaling

What are the 3 major size classes of carbohydrates?

1. monosaccharides 2. oligosaccharides 3. polysaccharides

Anomer

A sugar diastereomer differing only in the position of the hydroxyl at the anomeric carbon

Which of the following monosaccharides is NOT an aldose? A)Maltose B) Fructose C) Glucose D) Glyceraldehyde E) Ribose

A. Maltose

Reactivity of carbohydrates: hemiacetals & hemiketals

Aldehyde and ketone carbons are electrophilic Alcohol oxygen atom is nucleophilic

What is an aldose?

An aldose is defined as a monosaccharide whose carbon skeleton has an aldehyde group. *They are primarily found in plants.

Which of the following are reducing sugars? More than one answer can apply A) Sucrose B) Lactose C) Maltose

B&C Sucrose's glycosidic bond occurs at both anomeric carbons of the monomers therefore it is a non-reducing sugar.

All are true about starch, except? A) It is a mixture of 2 homopolysaccharides of glucose B) Serves as a energy storage polysaccharide in animals C) Serves as a energy storage polysaccharide in plants D) It has less branches than glycogen E) Amylopectin (a starch) branch points occur with alpha 1-6 links every 24-30 residues

B.

What is the general formula for most of carbohydrates?

Cn(H2O)n

What is the difference between D-isomers and L-isomers?

D-isomers: hydroxyl group on chiral carbon is pointed to the RIGHT L-isomers: hydroxyl group on chiral carbon is pointed to the LEFT

Al are true about glycogen, except? A) It is a branched homopolysaccharide of glucose B) Serves as a energy storage polysaccharide in animals C) It is highly branched D) it has only non-reducing ends E) it has both non-reducing and reducing ends F) glucose monomers form an alpha 1-4 linked changes G) the branch points occur with alpha 1-6 links every 8-12 residues

D.

All of the following are true about disaccharide except: A) two monosaccharides join together via glycosidic bond B) The glycosidic bond is between an anomeric carbon & hydroxyl carbon C) the glycosidic bond b/w monomers is more stable and less reactive than the hemiacetal at the second monomer D) the glycosidic bond b/w monomers is less stable and more reactive than the hemiacetal at the second monomer E) the second monomer with the hemiacetal is reducing F) the anomeric carbon involved in the glycosidic linkage is nonreducing

D.

All are true about cellulose, except? There is more than 1 correct answer A) It is found in the cell wall of plants B) It is a fibrous, tough, water-insoluble substance C) It is a linear, unbranched homopolysaccharide D) It has alpha-configuration and linked by alpha 1-4 glycosidic bonds E) It has beta-configuration and linked by beta 1-4 glycosidic bonds F) Most vertebrate animals can use cellulose as fuel source

D. in cellulose, glucose residues have beta-configuration F. Most animals cannot use cellulose as a fuel source b/c they lack the enzyme to hydrolyze (breakdown) the beta 1-4 linkages *some ruminants (cows, cattle, sheep) & termites live symbiotically with microorganisms that produce cellulase which hydrolyzes the beta 1-4 linkages.

Which of the following is a NOT a reducing sugar? A) Fructose B) Glucose C) Glyceraldehyde D) Ribose E) Sucrose

E. Sucrose b/c glycosidic bond b/w two anomeric carbons

What is a metabolic benefit of having many nonreducing ends in glycogen and starch?

Glycogen and amylopectin have 1 reducing end, but MANY nonreducing ends Enzymatic processing occurs simultaneously in many nonreducing ends

Which homopolymer, glycogen or starch, is better for digestion? Why?

Glycogen has more nonreducing ends (due to higher branching frequency) so there is faster & more complete enzymatic digestion of glycogen compared with starch

What is similar and different about homopolysaccharides and heteropolysaccharides?

Homopolysaccharides consists of one monomer unit Heteropolysaccharides consists of multiple monomer units Boths homo- & heteropolysaccharides can be unbranched (one type of glycosidic bond) or branched (multiple types of glycosidic bond)

IF the is more than 1 chiral carbon, how can you determine if it is a D-isomer or L-isomer?

In its long chain form, select the farthest chiral carbon from the aldehyde and if it points the RIGHT (it is D) if it points to the LEFT (it is L)

Viral Interactions & glycoproteins

Influenza virus has 2 glycoproteins on its viral coat: hemagglutinin (HA) and neuraminidase (NA)

What is a ketose?

Ketose is a monosaccharide whose carbon skeleton has a ketone group.

What is the ring structure of beta-D-Glucose?

OH group around anomeric carbon is facing up

True or False? D-Glucose and L-Glucose in open chain form are enantiomers.

TRUE. . Enantiomers are stereroisomers (same functional group but different spatial arrangements), but mirrored

reducing agent

The electron donor in a redox reaction.

True or false? Glycosidic bonds in glycogen and starch create non-reducing ends, but NOT reducing ends.

True

Most homopolysaccharides are used for energy storage. True or false?

True Example: glycogen, starch, and cellulose

True or false? All monosaccharides are reducing sugars

True Glucose is a reducing sugar

Glucose a reducing sugar. True or false?

True.

True or false? A reducing sugar that has a free anomeric carbon exists it can be a hemiacetal which can 'open up' which is more reactive than a acetal. CHECK!!

True.

True or false? Carbohydrates can be covalently linked with proteins and lipids.

True.

True or false? Polysaccharides do not have a defined molecular weight

True. Contrast to protein b/c no template is used to make polysaccharides *polysaccharides are often in a state of flux (monomers are added or removed depending what is needed by organism)

Both homopolymers and heteropolymers are used for structural support. True or false?

True. Example: collagen

All of the following are epimers to D-glucose, true or false? D-mannose D-galactose

True. *D-Glucose and D-Mannose are epimers *D-Glucose and D-Galactose are epimers

What is a condensation reaction?

When two molecules bond through the loss of a water molecule.

What is a polysaccharide?

a complex carbohydrates that is made up of more than two monosaccharides.

What is a hemiacetal?

aldehyde + alcohol When aldehydes are attacked by OH (alcohols), hemiacetal is formed *basis of cyclization of sugars

glycosylated hemoglobin (HbA1C)

blood test used to diagnose diabetes and monitor its treatment by measuring the amount of glucose bound to hemoglobin in the blood

How are carbohydrates produced?

by photosynthesis in plants - produced from CO2 and H20

Constitutional Isomers

different functional groups

What are the simplest monosaccharides

glyceraldehyde and dihydroxyacetone (not chiral)

Enantiomers

isomers that are mirror images of each other

What is a hemiketal?

ketone + alcohol *When ketones are attacked by OH (alcohols), hemiketals form *basis of cyclization of sugars

The simplest carbohydrates are

monosaccharides (either aldehydes or ketones with 2 or more hydroxyl groups)

Stereoisomers

same functional groups, different spatial arrangements

Isomer

same molecular formula, different structure

Diastereomers

stereoisomers (same functional groups, different spatial arrangements) that are not mirror images

What is hydrolysis?

the chemical breakdown of a compound due to reaction with water.

ABO blood types

the human blood group system based on the presence or absence of antigens on red blood cells *determined by type of glycosylation present on proteins on the surface of RBCs *all 4 blood types have O oligosaccharide sequence, but A & B have additional sugar molecules attached tot his base seuqence (AB has both)

protein glycosylation

the process by which we covalently attached a carbohydrate molecule onto a protein Most glycoproteins are bound to oligosaccharide units

True or false? Reducing sugars have a free anomeric carbon

true

True or false? Reducing sugars have a free anomeric carbon.

true.

What is a disaccharide?

two monosaccharides joined together