Carbohydrates

Question 1

What are the simplest carbohydrates? Describe what they are.
How many carbons do the smallest monosaccharides have?

Answer 1

monosaccharides- simplest carbs
They are aldehydes or ketones that contain 2 or more alcohol groups.
smallest monosaccharides have three carbons.
ex: Dihydroxyacetone, D-glyceraldehyde and L-Glyceraldehyde.

Question 2

Describe what Fischer Projections are and how they relate to monosaccharides.

Answer 2

Fischer projections are a ways of representing sugars and monosaccharides. In Fischer projection, atoms are joined to an asymmetric tetrahedral carbon atom, horizontal bonds in front of plane and vertical bonds behind plane.

Question 3

Name and define the different isomeric forms of carbohydrates.

Answer 3

Isomers- have same molecular formula, different structure
constitutional isomers- differ in order of attachment of atoms
Ex: Glyceraldehyde and Dihydroxyacetone
Stereoisomers- atoms connected in same order but differ in spatial arrangement.
Ex:
Enantiomers- non-superimposable mirror images- D and L glyceraldehyde
Diastereoisomers- isomer that are not mirror images. Ex: D altose and D glucose
Epimers- differ at one of several asymmetric carbon atoms
ex: d-glucose and D-mannose
Anomers- isomers that differ at new asymmetric carbon atom formed in ring closure
ex: alpha D Glucose, B-D Glucose

Question 4

What are examples of common monosaccharides?

Answer 4

D-Ribose (sugar in RNA) D- Deoxyribose (sugar in DNA) , D-Glucose, D-Mannose, D-Galactose, D- Fructose

Question 5

What kind of form does sugar appear in the human body? Compare and contrast D and L glucose in terms of activation.

Answer 5

In ring form. Also, all glucose in the body is D- Glucose (active); whereas, L-Glucose is not biologically active.

Question 6

Describe the chemical basis for ring formation.

Answer 6

An aldehyde can react with an alcohol to form a hemiacetal.

A ketone can react with an alcohol to form a hemiketal.

Question 7

Differentiate between the the cyclic forms of fructose and glucose.

Answer 7

In glucose, ring forms intramolecular hemiacetal (6 carbon ring) called pyranose due to resemblance to pyran.
In fructose which is a ketohexose, the intramolecular hemiketal (5 carbon ring) called furanose because of resemblance to furan.

Question 8

What occurs when a cyclic hemiacetal is formed? Differentiate between the alpha and beta anomers?

Answer 8

When cyclic hemiacetal is formed, an anomer is created.
Two types of anomers:
alpha form- hydroxyl at C- 1 is below plane of ring.
Beta form- hydroxyl at C-1 is above plane of ring.

Question 9

How does a pyranose form?

Answer 9

In D-Glucose form, the aldehyde on C-1 will react with OH of C-5 forming ring structure and intramolecular hemiacetal. Then form alpha or beta form of anomers.

Question 10

What makes Fructose so unique in its cyclic (ring) form? How does furanose form differ from pyranose form?

Answer 10

Fructose forms both the pyranose form that predominates when fructose is free in solution and furanose form, seen in fructose derivatives.
Furanose form of fructose can exist in anomeric forms just like pyranose, but Alpha and Beta forms of furanose refer to orientation of hydroxyl at C-2

Question 11

What are the two types of conformations that pyranose rings can adopt? How does the chair conformation look like? What kind of conformation does Beta-D glucopyranose adopt and why?

Answer 11

Boat and chair conformation
Chair conformation- substituents on Carbon ring atoms have 2 orientations, axial or equatorial.
Beta-D-glucopyranose adopt chair conformation because axial positions are occupied by Hydrogen atoms, reducing steric hindrance.

Question 12

What conformation of rings are more stable and why?

Answer 12

Chair conformations are more stable due to less steric hindrance between C-H groups. Larger groups are on side of chair and are more stable when they are further away from each other.

Question 13

What are reducing sugars? What are non-reducing sugars? Provide examples

Answer 13

Reducing sugars- sugars that react with oxidizing agents.
Ex: glucose
Non-reducing sugars- sugars that DO NOT react with oxidizing agents (no free carbonyls)
Ex: sucrose

Question 14

What is the composition of a glucose solution? Why does open chain form react with oxidizing agents?

Answer 14

1/3 alpha anomer, 2/3 beta anomer, and less than 1% open-chain form.
since the 2 anomeric forms are in equilibrium that passes through open-chain form, the free open chain form, reacts with oxidizing agents.

Question 15

What is HbA1c? What can it be used for?

What happens when carbs and proteins form a reaction with one another?

Answer 15

HbA1c is the glycated form of Hemoglobin or Hemoglobin Alc. This forms when a reducing sugar like glucose reacts with Hemoglobin, forming a fully functional product HbA1c.
determining amount of HbA1c in blood can help monitor long-term control of blood glucose levels in diabetics.
reactions between carbs and proteins, impair protein function.
modifications called advanced glycation end products have been implicated in number of pathological conditions.

Question 16

*Differentiate between an O-Glycosidic bond and N-glycosidic bond.
How do carbohydrates interact with phosphates?

Answer 16

O-Glycosidic bond- bond formed between anomeric carbon atom of glucose and OH group of another molecule; product is glycoside
N-glycosidic bond- formed between anomeric carbon of glucose and an amine.
Carbohydrates also from ester to linkages to phosphates.

Question 17

What is a glycosidic bond?

Answer 17

A covalent bond that joins carbohydrate to another molecule (carb or amine, OH)

Question 18

*What is an asymmetric carbon atom?

Answer 18

Asymmetric carbon- chiral carbon attached to 4 different atoms.

Question 19

Understand ring formation of aldoses and ketoses What are α and β
anomers?

Answer 19

m

Question 20

• Understand ring formation of aldoses and ketoses What are α and β
  anomers?

Answer 20

.j

Question 21

*Understand how the human blood groups, ABO come about and the consequences of
transfusing the wrong blood types. What do all of the blood groups share? What are their differences?

Answer 21

The human ABO blood groups reflect the specificity of glycotransferases.
All blood groups shared the oligosaccharide foundation called O.
Blood group A- N-acetlyglucosamine is added to the O by a specific glycosyltransferase
Blood group B- galactose is added by another glycosyltransferase
Blood type O produces NO active glycosyltransferase.

Question 22

• Define what glycoproteins are and understand the different forms of glycoproteins and their linkages

Answer 22

Glycoprotein- proteins with carbohydrates attached.
Three classes of Glycoproteins:
1. Glycoproteins: protein is the largest component by weight. serve a variety roles, including membrane proteins.
2. Proteoglycans- protein attached to polysaccharide called Glycosaminoglycan. By weight, carbohydrate are largest. serve as structural role and lubricants
3. Mucins or Mucoproteins- protein attached to carbohydrate by N-acetlyglucosamine. They are predominantly carbs (weight)
Mucins serve as lubricants.

Question 23

*What are the characteristics of cellulose, starch and glycogen?
What makes cellulose unique and which compound aids in digestion for humans.

Answer 23

Cellulose- homopolymer of glucose units linked by Beta 1,4 glycosidic bonds. Beta linkage creates straight chain of interacting cellulose molecules, forming strong fibrils
Starch and Glycogen are alpha linkages that form compact hollow cylinders for accessible storage.

mammals cannot digest cellulose and other plant fibers. However, soluble fibers like polygalacturonic acid aid in digestion.

Question 24

*Understand what an oligosaccharide is and what enzymes synthesize them.
How are the substrates for this enzyme activated.

Answer 24

Oligosaccharide- made up of 2 monosaccharides linked by O-glycosidic bonds.
Enzymes called Glycosyltransferases catalyze the formation of glycosidic bonds.
Monosaccharide substrate for glycosyltransferase are activated by attachment to Uridine diphosphate (UDP)

Question 25

What are three common disaccharides? Which enzymes cleave these common disaccharides? Provide examples.

Answer 25

Sucrose, lactose and Maltose are the common disaccharides.
Enzymes located on outer surface of intestinal epithelium cleave the sugars.
Ex: Sucrase cleaves sucrose (table sugar), Lactase cleaves lactose (milk sugar) and Maltase cleaves maltose.
Lactose and Maltose are 1,4 linkages.
Lactase and other enzymes that hydrolyze carbs located on microvilli of intestinal epithelial cells.

Question 26

What does it mean when one is referred as lactose intolerant?

Answer 26

Someone that lacks the enzyme lactase that will break down lactose into glucose and galactose.

Question 27

What is significant behind the enzyme invertase?

Answer 27

Invertase was the enzyme that Michaelis and Menten investigated in their classic study; established that the reate of invertase reaction is proportional to concentration of enzyme substrate complex predicted by equation.

Question 28

What are polysaccharides? what is a homopolymer? Provide an example of a compound that is both a polysaccharide and homopolymer and describe how its units are linked.

Answer 28

Polysaccharide- large polymeric oligosaccharides
Homopolymer-a polysaccharide where all of monosaccharides in the polysaccharides are the same.
Glycogen is a polysaccharide and homopolymer. It is the storage form of glucose in animal cells.
The glucose units in glycogen are linked by alpha 1,4 glycosidic bonds, while the branches are formed by alpha 1, 6 glycosidic bonds every 12 glucose units.

Question 29

Name the storage form of glucose in animals. How many storage forms of glucose are there in plants? What are they?

Answer 29

In animals, storage form of glucose is glycogen.
In plants, there are 2 storage forms of glucose”
1. Amylose- linear polymer of glucose units linked by alpha 1,4 glycosidic bonds.
2. Amylopectin- branched polymer, alpha 1, 6 glycosidic bond for every 30 alpha 1,4 glycosidic bonds.

Question 30

Describe the 2 different forms that carbohydrates are attached in all classes of Glycoproteins, and what amino acids are involved.

Answer 30

In all glycoproteins, carbs are attached to either the Nitrogen atom in side chain of Asparagine (N-linkage) or to the Oxygen atom of the side chain of Serine or Threonine (O-linkage)

Question 31

What are the structures involved in all N-Linked Polysaccharides?

Answer 31

All N-Linked polysaccharides consist of common pentasaccharide core made of three mannoses, six-carbon sugar, and 2 N-acetlygulcosamine units.
additional monosaccharides can be attached to core.

Question 32

What kind of molecule is the Erythroprotein (hormone)?
How is it formed and what is it’s function?
How does glycosylation affect Erythoprotein?

Answer 32

Erythropoietin is a glycoprotein secreted by the kidney into the blood that stimulates production of red blood cells.
Glycosylation of Erythropoietin will enhance stability of protein in the blood.
What endurance athletes inject themselves, increase EPO production.

Question 33

Elaborate more on what gylcosaminoglycans in proteogylcans are composed of.
What is the role of proteogylcans?

Answer 33

Proteoglycans are proteins attached to glycosaminoglycans , which make up 95% of proteoglycan by weight.
These Glycosaminoglycans are made of repeating units of a disaccharide, one of which is a derivative of an amino acid sugar and one that carries a negative charge, either as carboxylate or sulfate.
Ex: Heparin, keratan sulfate, Dermatan sulfate, Hyaluronate
glycosaminoglycans- can occur in synovial joints, shock absorbers

Question 34

what is Mucopolysaccharidoses?

Answer 34

pathological conditions Like Hurler disease, that result from the inability to degrade proteoglycans.

Question 35

What is cartilage composed of and how do they function?

Also explain the roles of different glycosaminoglycans in cartilage and other structures.

Answer 35

Cartilage is composed of proteoglycan Aggrecan and collagen.
cartilage can serve as shock absorber
The glycosaminoglycan component of Aggrecan cushions joints by releasing water on impact (feet push down when walking) and then rebinding water (as pressure releases)
Chitin, is also a glycosaminoglycan found in exoskeleton and wing of insects , and one of the most abundant carbohydrates in the world.

Question 36

What is the most abundant proteoglycan that is seen in cartilage and what does it compose of?

Answer 36

Aggrecan- composed of keratan sulfate and Chondroitin sulfate units, linked by Hyaluronate (glycosaminoglycan)

Question 37

What are human blood groups based on? What may occur in case of transfusing the wrong blood type?

Answer 37

blood groups based on protein glycosylation patterns.
If you transfuse blood that is not compatible to your own blood type, your body will treat it as an antigen (foreign) and produce antibodies, attacking RBC’s