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2012-02-13 16:22:39
Carbs Classification Structure

Midterm week 4
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  1. 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
    • Di: sucrose
    • poly: starch (most common in diet), cellulose, glycogen (way we store glucose in liver and muscle)
  2. 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
  3. 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
  4. What form of glucose is naturally occuring in diet?
    alpha-D-glucose (OH group down on anomeric carbon)
  5. What is another word for glycosidic bond? how is this bond formed in hexoses?
    • Acetal bond
    • For hexoses, OH group from anomeric carbon interacts with OH group from carbon 4 or 6
  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
  7. What is the main polysaccharide in plants? What are the 2 types and the cahracteristics of each?
    • Starch
    • 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
  8. What is the main polysaccharide in animals?
    • Glycogen
    • Main storage form
    • has alpha-1,4 and alpha-1,6 linkages
    • Highly branches
    • Tightly packed into liver
    • Need a specific enzyme to break the alpha-1,6 linkage
  9. 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
  10. 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.
  11. 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
    • Mainly insoluble
  12. 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
    • Soluble fibres
  13. 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
  14. 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
    • Weight control
  15. 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