Carbohydrates Flashcards
(29 cards)
Name 6 functions of carbohydrates
- Energy
- Structure
- Extracellular matrix
- Signalling and development
- Protein folding
- Components of DNA
What are the basic properties of all carbohydrates?
- Carbon based molecules rich in hydroxyl groups
- Empirical formula: (CH2O)n
What are monosaccharides?
- Most simple form of carbohydrates
- Either aldehydes (aldose) or ketones (ketose) with >2 hydroxyl groups
What is the configuration of a monosaccharide defined by?
- Asymmetric carbon atom furthest from the aldehyde/keto group
(Most sugars have a D configuration)
When can diasterioisomers occur?
- > 3 carbon atoms
- Number of isomers = 2^n (where n= number of asymmetric carbon atoms)
What are constitutional isomers?
Have identical molecular formula but differ in how their atoms are ordered
How do epimers and anomers differ?
epimers - differ at one of several asymmetric carbon atoms
anomers - differ at a new asymmetric carbon atom formed on ring closure
Why do monosaccharides adopt cyclical forms?
Lower energy conformation
What types of rings to glucose and fructose form?
Glucose - C5 hydroxyl group attacks O of C1 aldehyde to form 6 C ring hyranose (hemiacetal - aldehyde)
Fructose - C5/C6 hydroxyl group attacks O of C2 ketone to form 5C ring of furanose/pyranose (Hemiaketal - ketone)
What are the two common forms of pyranose?
Boat and chair
What is the difference between axial and equatorial?
axial - nearly perpendicular to the average plane of the molecule
equatorial - nearly parallel to the average plane of the molecule
What is the common conformation of furanose rings?
envelope - either C-2 or C-3 is out of plan on the same side as C5 (endo-pucker)
What are anomers?
Different forms of carbohydrates created by an assymetric carbon
- In glucose this is C1
- In fructose this is C2
How do alpha and beta anomers differ?
alpha - hydroxyl group is on the opposite side of the ring as C6
beta - hydroxyl group is on the same side of the ring as C6
note: C5 on fructose
What are 3 common reactants for monosaccharides
- alcohols
- amines
- phosphates
How does an O-glycosidic bond form?
- oxygen atom of n alcohol and anomeric carbon of a monosaccharide
- between two sugars
How does an N-glycosidic bond form?
Anomeric carbon of sugar linked to nitrogen atom of an amine group
Name 3 common disaccharides
sucrose, lactose, maltose
What differentiates a reducing and non-reducing sugar
reducing - free hydroxyl at anomeric position allowing ring to open, exists in equilibrium (e.g glucose)
non-reducing - anomeric carbon is involved in bonding
Describe the structure of glycogen
- Branched
- Mostly consists of alpha 1,4 glycosidic bonds between glucose
Describe the structure of starch
- Linear
- glucose joined by alpha 1,4 glycosidic bonds (amylose)
- alpha 1,6 glycosidic bonds ( amylopectin)
What is the structure of chitin and cellulose
cellulose - linear polymer of glucose B-1,4
chitin - linear molecules of N-acetyly glucosamine joined by B-1,4 glycosidic bonds
By which type of linkage do carbohydrates link to nulceic acids?
N-glycosidic bonds
How do carbohydrates typically attach themselves to proteins?
- Attach to asparagine via N-glycosidic
- Attach to serine/threonine via O-glycosidic
