Carboydrates Flashcards
What are the functions of carbs?
- Energy source
- Immune functions
- Intracellular communication
- Energy storage
- Structural functions e.g. cell walls of bacteria, or exoskeletons of insects, cellulose of cell wall of plants.
Classification and general structure of carbohydrates?
- Consist of carbon, oxygen and hydrogen
- Ratio of H to O = ~ 2:1
- General formula = (CH2O)n
Monosaccharides - 1 sugar unit
Disaccharides- 2 sugar units
Oligosaccharides 3-10 sugar units
Polysaccharides- 11 to >100 sugars units
How does the body obtain monosaccharides?
Present in the diet or obtained via digestion of more complex carbohydrates.
Can be synthesised in the body from non-carbohydrate sources (glucogenesis) - their external supply is therefore not required for survival.
How are monosaccharides classified?
- Their number of carbon atoms
- Any functional groups
No of C atoms:
- 3= triose e.g. glyceraldehyde
- 5= pentose e.g. ribose & deoxyribose
- 6-= hexose e.g. glucose
Functional group:
- contains an aldehyde group- aldoses (-ose ending)
- contains a ketone group- ketoses (-ulose ending)
- The first carbon is the carbon attached to the carbonyl group e.g. ketone
- Black wedges = above plane
- Dotted wedge = below plane
What are the 3 important monosaccharides & their source?
- Glucose
- Source= diet, degradation of glycogen, gluconeogenesis
- Preferred energy source of brain. Required energy source of cells with few or no mitochondria. Essential in exercising muscle - Fructose
- Source= fruits, vegetables, honey
- Sweeter than glucose - Galactose
- Source= dairy products
- Less sweet than glucose
Define isomers
Compounds that have the same chemical formula but different structures
Define epimers. Give 2 examples?
Carbohydrate isomers that differ in configuration around only 1 specific carbon atom.
e.g. glucose & galactose are C4 epimers
e.g. Glucose & mannose are C2 epimers
Define enantiomers
Pairs of structures that are mirror image of each other & non-superimposable
They are a type of stereoisomer & have this property due to chiral carbons (have 4 different groups attached to C atom)
How does cyclisation of a monosaccharide occur? What are the common ring structures? Define anomeric carbon.
99% of monosaccharides w/ 5 or more carbon atoms form a ring structure.
The carbonyl functional group reacts w/ hydroxyl group.
- 5C + 1O = pyranose ring
- 4C + 1O = furanose ring
Cyclisation creates an anomeric carbon atom because the -OH group can end up above the plane of the C atoms or below.
- So a molecule of D-glucose can form an α-anomer or a β-anomer.
NOTE- view diagram on notes!
Give 3 examples of dietary disaccharides - include their monomers, bonds & sources.
Formed from 2 identical or different monosaccharide units linked together by aglycosidic bond.
- Sucrose
- Monomers= glucose + fructose
- Bonds= α-1,2-β-glycosidic bond
- Source= prevalent in sugar cane & table sugar - Maltose
- Monomers= glucose + glucose
- Bonds= α-1,4-glycosidic bond
- Source= starch. malt sugar - Lactase
- Monomers= Glucose + galactose
- Bonds= β-1,4-glycosidic bond
- Source= mammalian milk. milk sugar
Explain the bonding in disaccharides?
- Numbered according to the number of the carbon atom the bond is attached to.
- Also according to the position of the anomeric carbon atoms in the ring.
- If the hydroxyl group is in the alpha configuration, the bond is an α-glycosidic bond.
- e.g. In sucrose, the bond is an α-1,2-β-glycosidic bond because
-OH of glucose in alpha configuration on carbon 1 has reacted w/ OH group of fructose in beta configuration on carbon 2.
What are the 3 important polysaccharides?
- Starch
- Amylose
- Amylopectin - Cellulose
- Glycogen
Explain the source, function, structure, monomers, bonds & digestion of Starch.
- Amylose
- Source= plants, seeds & tubers.
- Function= stores carbs in plants
- Structure= unbranched, spiral
- Monomers= α-glucose
- Bonds= α-1,4-glycosidic bonds
- Digestion= Amylases secreted by salivary glands & pancreas digest amylopectin, releasing glucose, maltose & isomaltose.
- Amylopectin
- Source= plants, seeds & tubers.
- Function= stores carbs in plants
- Structure= Branched (every 20-30 residues), spiral
- Monomers= α-glucose
- Bonding= α-1,4- & α-1,6-glycosidic bonds
Explain the source, function, structure, monomers, bonds & digestion of Cellulose.
Source= plant cell walls
Function= structural polysaccharides for plants
Structure= Unbranched
Monomers= β-glucose
Bonds= β-1,4-glycosidic bonds
Digestion= Important as dietary fibre as humans don’t have the enzyme to digest cellulose.
Explain the source, function, structure, monomers, bonds & digestion of Glycogen.
Source= Liver & skeletal muscle
Function= Carbohydrate storage molecule in humans.
Structure= Branched (every 8-10 residues)
Monomers= α-glucose
Bonds= α-1,4- & α-1,6-glycosidic bonds
Digestion= The high level of glycogen branching means that the molecule has a large number of free ends - allows for rapid degeneration to glucose.
