Carbohydrates Flashcards
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
What is the typical function and structure of proteoglycans?
- protein conjucated to a polysaccharide glycosaminoglycan
- structural components and lubricants
- tethered to cell membrane
- highly sulfanated
Where does glycolysation occur?
In the ER and Golgi apparatus, aids in protein folding
Which enzymes are responsible for the assembly and breaking down of carbohydrates?
Broken down by glycoside hyrolayses (GHs) - general
Synthesized by glycosytransferases (GTs) - very specific
How does the influenza virus exploit GHs?
Uses neurominidase to release new virus particles using own acid
Which compounds typically act as GT donor substrates and which act as acceptors?
nucleotide phosphates - donors
hydroxl in protein, lipid, small molecule or another sugar - acceptor
