Carbohydrates Flashcards
What are the simplest carbohydrates? Describe what they are.
How many carbons do the smallest monosaccharides have?
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.
Describe what Fischer Projections are and how they relate to monosaccharides.
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.
Name and define the different isomeric forms of carbohydrates.
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
What are examples of common monosaccharides?
D-Ribose (sugar in RNA) D- Deoxyribose (sugar in DNA) , D-Glucose, D-Mannose, D-Galactose, D- Fructose
What kind of form does sugar appear in the human body? Compare and contrast D and L glucose in terms of activation.
In ring form. Also, all glucose in the body is D- Glucose (active); whereas, L-Glucose is not biologically active.
Describe the chemical basis for ring formation.
An aldehyde can react with an alcohol to form a hemiacetal.
A ketone can react with an alcohol to form a hemiketal.
Differentiate between the the cyclic forms of fructose and glucose.
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.
What occurs when a cyclic hemiacetal is formed? Differentiate between the alpha and beta anomers?
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.
How does a pyranose form?
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.
What makes Fructose so unique in its cyclic (ring) form? How does furanose form differ from pyranose form?
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
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?
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.
What conformation of rings are more stable and why?
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.
What are reducing sugars? What are non-reducing sugars? Provide examples
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
What is the composition of a glucose solution? Why does open chain form react with oxidizing agents?
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.
What is HbA1c? What can it be used for?
What happens when carbs and proteins form a reaction with one another?
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.
*Differentiate between an O-Glycosidic bond and N-glycosidic bond.
How do carbohydrates interact with phosphates?
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.
What is a glycosidic bond?
A covalent bond that joins carbohydrate to another molecule (carb or amine, OH)
*What is an asymmetric carbon atom?
Asymmetric carbon- chiral carbon attached to 4 different atoms.
Understand ring formation of aldoses and ketoses What are α and β
anomers?
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- Understand ring formation of aldoses and ketoses What are α and β
anomers?
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*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?
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.
- Define what glycoproteins are and understand the different forms of glycoproteins and their linkages
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.
*What are the characteristics of cellulose, starch and glycogen?
What makes cellulose unique and which compound aids in digestion for humans.
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.
*Understand what an oligosaccharide is and what enzymes synthesize them.
How are the substrates for this enzyme activated.
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)
