Carbohydrates Flashcards
Functions of carbohydrates
energy source energy storage structural component immune function intercellular communication
General formula of carbohydrates
(CH2O)n [hydrate of carbon)
How many sugar units are in monosaccharides, disaccharides, oligosaccharides and polysaccharides?
monosaccharides = 1 disaccharides = 2 oligosaccharides = 3-10 polysaccharides = 11->100
What are the generic names of monosaccharides and how are they classified
classified by number of carbon atoms 3 = triose 4 = tetrose 5 = pentose 6 = hexose 7 = heptose 9 = nonose
What is an aldose?
aldehyde functional group present
-ose
eg. glucose
RCOH
What is a ketose?
ketone functional group present
-ulose
eg. fructose (should really be called fructulose)
R1COR2
Define isomer
compounds that have the same chemical formula but different structures
Define epimer
carbohydrate isomers that differ in configuration around only one specific carbon atom
Define enantiomer
pairs of structures that are mirror images of each other
non-superimposable mirror images
What are D and L designations?
based on configuration of single asymmetric carbon atom in glyceraldehyde
L-glyceraldehyde = hydroxyl group below carbon backbone plane
D-glyceraldehyde = hydroxyl group above carbon backbone plane
for sugars with more than one chiral centre, D + L refers to the farthest asymmetric carbon atom from the carbonyl group
most naturally occurring sugars = D isomers
What is a pyranose ring?
5 carbon atoms and one oxygen atom
What is a furanose ring?
4 carbon atoms and one oxygen atom
What is the different between beta and alpha glucose anomers
cyclisation of monosaccharides creates an anomeric carbon atom
beta anomer = hydrogen below plane of ring on carbon 1
alpha anomer = hydrogen above plane of ring on carbon 1
alpha and beta glucose anomers are in equilibrium and can interconvert
Describe sucrose
disaccharide of glucose + fructose
alpha 1-2 beta glycosidic bond between glucose + fructose
Describe maltose
disaccharide of glucose + glucose
alpha 1-4 glycosidic bond between glucoses
major degradation product of starch
Describe lactose
disaccharide of glucose and galactose
beta 1-4 glycosidic bond between galactose and glucose
in mammalian milk
Describe cellulose
structural polysaccharide in plants
beta 1-4 glycosidic bonds between glucose molecules
major constituent of plant cell walls
humans cannot digest as no enzymes to break bonds
Describe starch
storage polysaccharide in plants
alpha 1-4 glycosidic bonds between glucose molecules
amylose = unbranched + only alpha 1-4 linkages
amylopectin = branched (every 20-30 residues) + mainly alpha 1-4 linkages, branches = alpha 1-6 linkages
Describe glycogen
storage polysaccharide in animals
branched (every 8-10 residues)
mainly alpha 1-4 linkages, branches = alpha 1-6 linkages
What are the 3 sites of digestion of carbohydrates?
mouth = salivary alpha amylase hydrolysing alpha 1-4 bonds, yields maltose + dextrin
small intestine = pancreatic alpha amylase, more maltose + dextrin
upper jejunum = brush border membrane-associated oligosaccharidases + disaccharidases of intestinal mucosal cells, yields glucose, fructose + galactose
How are different carbohydrates absorbed?
monosaccharides are absorbed by intestinal mucosal cells:
- glucose + galactose = sodium-dependent cotransporter-1 (SGLT-1)
- fructose = sodium-independent monosaccharide transporter (GLUT-5)
all 3 monosaccharides are transported from the intestinal cells into the portal circulation by GLUT-2
What can deficiencies in carbohydrate degradation cause?
lactose intolerance
sucrose/isomaltose intolerance
Symptoms of sugar intolerance
undigested carbohydrates pass into large intestine = osmotic diarrhoea
bacterial fermentation of carbohydrate produces large volumes of carbon dioxide and hydrogen = abdominal cramps, diarrhoea, flatulence
How are patients with sugar intolerance managed?
withholding dietary sugar
enzyme replacement therapy
