How much do CHO make up of our diet? What are the most common mono, di, and polysaccharides?
It makes up the majority of our diet
Mono: glucose, galactose, fructose - smallest and absorbable
poly: starch (most common in diet), cellulose, glycogen (way we store glucose in liver and muscle)
What are the main functions of trioses, pentoses and hexoses? What is the anomeric carbon? What kinds of bonds do they form?
Triose: metabolites of glucose
Pentose: components of RNA and DNA
Hexoses: nutrionally the most important
Anomeric carbon is the functional carbonyl group
Form glycosidic bonds
Why is stereoisomerism important? Which stereospecificty is most improtant nutrionally?
Most biological systems are stereospecific
D-monosaccharides are nutrionally more improtant because enzymes for CHO digestion and metabolism are stereospecific for D sugars
What form of glucose is naturally occuring in diet?
alpha-D-glucose (OH group down on anomeric carbon)
What is another word for glycosidic bond? how is this bond formed in hexoses?
For hexoses, OH group from anomeric carbon interacts with OH group from carbon 4 or 6
What are the common disaccharides? Where are the found and what are the bonds associated in each?
1. Sucrose: major dissacharide in diet - glucose alpha (1-2) fructose - involves both anomeric carbons (enzyme specific for bond)
2. Lactose: milk and milk products - galactose beta (1-4) glucose - not both anomeric carbon - enzyme specificity is highest at birth
3. Maltose: primarily from starch breakdown, beer - glucose alpha (1-4) glucose - not both anomeric carbons
What is the main polysaccharide in plants? What are the 2 types and the cahracteristics of each?
Amylose: linear, unbranched - alpha-1,4 linkage
Amylopectin: branched at alpha-1,6 bonds which allows for storage of glucose units as branches can be more tightly packed - also has alpha-1,4 linkages
What is the main polysaccharide in animals?
Main storage form
has alpha-1,4 and alpha-1,6 linkages
Tightly packed into liver
Need a specific enzyme to break the alpha-1,6 linkage
What are the characterisitics of dietary fibre concerning solubility? Difference between insoluble and soluble?
Water-holding ability: ability of a fibre to hold water and create a viscous solution
Adsorptive ability: ability of a fibre to bind enzymes and nutrients as passing through tract therefore nutrients aren't available to be used
Solubility does not equal digestibility does not equal fermentability
Insoluble: decrease transit time through the gut, increase fecal bulk - more constipation
Soluble: increase transit time (things move more slowly), delay gastric emptying, delay absorption - has benefits in disease states
What are the characterisitics of cellulose?
Both a dietary and functional fibre
Functional fibre: isolated non digestable CHO that has been shown to have beneficial physiological effects in humans therefore added to good
Homopolysaccharide of glucose
Linear polymer of beta-1,4 glucose - dont have enzymes to break beta bond but bacteria do
Poorly fermented by gut bacteria
In bran, legumes, nuts, peas etc.
What are the characteristics of hemicellulose?
Heteropolysaccharide that varies between plants
Both alpha and beta conformation
Contain pentoses and hexoses - xylose is the msot common sugar (bonds are also indigestible by human enzymes
Can be branched or linear
Solubility and fermentability depend on the sugar composition
In bran, whole grains, buts and some veggies and fruits
What are the characterisitics of pectin?
Both dietary and functional fibre
Part of the primary cell wall of plants
Backbone of unbranched alpha-1,4 linked D-galacturonic acid (indigestible)
Stable at low pH
Highly fermented by gut bacteria
Rich in fruits
What are the characterisitcs of resistant starch?
Not digested by humans
4 main types, termed RS1-4
Typcially found in plant cell walls
Resistant to amylase activity that digests regular starch
Converys some advantages of soluble and insoluble fibres
NAmericans consume about 10g per day
Chemically related to starch but has many health benefits related to dietary fibres
what are the health benefits of dietary fibre?
Maintains function and health of gut
Decreases constipation - insoluble fibre types increase bulk which stimulates walls of the digestive system
Increases satiety because the food moves more slowly (soluble fibres) - causes delayed gastric emptying
What are the health benefits of soluble fibre?
Decrease cardiovascular disease risk by lowering blood cholesterol - binds bile acids, excreted from body therefore need to use more cholesterol to produce more bile (mechanism by which choelsterol lowering drugs work)
Effects on blood glucose - delays gastric emptying which leads to less of a spike in blood glucose after a meal which slows down appearance of glucose in blood stream