Carbohydrates (Module 2 Lecture 1) Flashcards
How many carbons are in monosaccharides?
3-9
Define oligosaccharide.
Many monosaccharides linked together.
In what form to animals store glucose?
Glycogen
Complex carbohydrates are used in what three structures?
- Extracellular matrix (eukaryotes)
- Bacteria cell walls
- Plant cell walls
What are two functions of carbohydrates linked to proteins and lipids on the cell membrane?
- Cell-to-cell communication
2. Interactions between cells and extracellular environment.
Define triose.
A monosaccharide made of only three carbons.
What is the smallest aldose (aldehyde sugar)?
Glyceraldehide (a triose).
What is the smallest ketose (ketone sugar)?
Dihydroxyacetone (a triose).
What are the two most common sugars?
Hexoses and pentoses.
What is the most common hexose in nature?
Glucose (a D-aldose).
Describe the structure and stereochemistry of glucose and related hexoses.
- The four internal carbons are asymmetric.
2. It has multiple isomeric hexoses.
Define epimer.
An epimer is a sugar that differs from another in only the stereoconfiguration around ONE carbon.
Name two common epimers of D-glucose.
- D-mannose (epimeric at C-2)
2. D-galactose (epimeric at C-4).
What happens to glucose straight chains in aqueous solution?
- It forms a pyranose ring by C-1 aldehyde reacting with the C-5 hydroxyl to form a hemiacetal.
- Open-chain and ring forms are in equilibrium.
Explain the two anomers of glucose in solution.
- After cyclizing, D-glucose turns into two interconvertible anomers around the C-1 carbon.
- The two configurations are denoted alpha and beta.
Describe the structure and formation of fructose.
- It is a ketose.
2. It cyclizes by forming a hemiketal linkage between C-2 and C-5, forming furanose, a 5-membered ring.
Describe the formation of ribose and deoxyribose.
- Ribose is a pentose sugar formed by the cyclization of C-1 aldehyde and C-4 hydroxyl. 2. Deoxyribose is missing the OH on the C-2 carbon.
What is a modified monosaccharide and how is it commonly used by the body?
- It is a monosaccharide with at least one additional substituent (like methyl, etc.) on its basic structure.
- It is commonly used on cell surfaces.
What is a reducing sugar and why?
- A sugar that is in equilibrium with its cyclic and open chain forms.
- Such sugars reduce copper II to copper I by oxidizing the aldehyde into an acid.
How are glycosidic bonds formed?
By the reaction of monosaccharides with alcohols and amines.
What happens when O-CH3 is added to glucose?
- An O-glycosidic bond is formed in one of two possible stereoisomers.
- The products are no longer reducing sugars because they can no longer open up into open chain form.
How are oligosaccharides formed?
By linking two or more monosaccharides together with O-glycosidic bonds.
Explain the structure of maltose.
A disaccharide formed by linkage of two glucose residues (C-1 -> C-4) forming an alpha-1,4-glycosidic bond.
How are disaccharides synthesized and broken?
Via condensation (removal of two water molecules) and the reverse process, which splits the glycosidic bond, is called hydrolysis and requires two water molecules per broken glycosidic linkage.
How is lactose formed?
By linking glucose and galactose (C-1 -> C-4)
Where in the body are glucose and lactose hydrolyzed and why are they broken down here?
In the gut for the monosaccharide components to be used by individual cells.
What is glycogen made out of?
Many glucose units linked together with alpha-1,4-glycosidic linkages and then branches between these polymers made by alpha-1,6-glycosidic linkages.
Describe the function and structure of two main glucose homopolymers used in plants.
- Starch (similar to glycogen only less branched) is for mobile storage in plants.
- Cellulose is the major structural polymer in plants and is made with beta-1,4-glycosidic linkages.
- In cellulose, the beta linkages lead to fibril formation which is very strong (tensile).
- Humans cannot digest the beta-1,4-glycosidic linkages, which is why eating plants helps you go to the bathroom without gaining weight (it just washes through along with everything else in your stomach).
