WEEK 4: CARBOHYDRATES: DIGESTIBLE AND INDIGESTIBLE Flashcards
1
Q
Carbohydrates Classification
A
Monosaccharides – simplest carbohydrates – C6H12O6 (glucose) Disaccharides – 2 monosaccharides bound – C12 H22O11 (maltose) Polysaccharides – many monosaccharides bound – complex carbohydrates: glycogen, starch, fibre – (C6 H12 O6)n
2
Q
Monosaccharide
A
6 CARBON SINGLE UNITS: – Glucose – Fructose – Galactose – Sugar alcohols: xylitol, mannitol and sorbitol (= low calorie sweeteners) 5 CARBON SINGLE UNITS: - Ribose - Deoxyribose
3
Q
Glucose
A
- A hexose, C6H12O6
- Most abundant monosaccharide
- Consumed as sucrose
(glucose + fructose) - Constitutes “blood sugar level”
- GLUT4 is insulin dependent
- Undergoes glycolysis or glycogenesis
4
Q
Fructose
A
- Varies from glucose in that the carbonyl group is on C-2 rather then C-1
- Is the sweetest monosaccharide
- Found in fruit, honey, vegetables
- Cell uptake is not insulin dependent
- Thought to be a good sugar because blood sugar level only measures glucose… but it does get transformed to glucose inside the cell
5
Q
Galactose
A
- Differs from glucose only in the orientation of the OH group around C-4
- With glucose, forms lactose (milk sugar)
- Also present in some vegetables
- Is the least sweet of the
monosaccharides - Converted to glucose in the liver
6
Q
Role of Carbohydrates
A
- The basis of structural tissue in plants e..g cellulose
- Source of energy and blood glucose homeostasis
- Substrate in the biosynthesis of other compounds: e.g. fat, ribose in ribonucleic acid
- Cell to cell recognition and communication: saccharides are used in the formation of glycoproteins that sit on the surface of cells
7
Q
Glycoprotein cell receptors
A
- surface carbohydrates on cells serve as points of attachment for other cells
8
Q
Galactosemia
A
- reduction in the metabolism of galactose to glucose due to deficient galactokinase or other metabolism genes
- galactose build-up leads to bacterial infections, mental retardation and cataracts
- management: switch to soy formula at infancy, throughout life avoid dairy product, organ meats and some fruit, nuts and vegetables containing galactose
9
Q
Sugar Alcohols
A
- derivatices of mono, di or polysaccharides
- class of polyols, 1 OH group attached to each carbon
- not fully absorbed in SI, femented by bacteria in LI - therefore used as low energy sweeteners
- with large quantities may induce bloating, diarrhoea and flatulence as water is drawn into the colon and bacterial fermentation
- occurs naturally in some fruit and vegetable but usually issues from hydrogenation of sugars (sorbitol, mannitol, xylitol) or via fermentation of sugars (erythritol)
10
Q
Pentose Monosaccharides
A
- ribose and deoxyribose
- contains 5 carbons
- essential part of cells genetic material - RNA and DNA
- body makes own sypply via pentose phosphate pathway
11
Q
Pentose Monosaccharides
A
- ribose and deoxyribose
- contains 5 carbons
- essential part of cells genetic material - RNA and DNA
- body makes own sypply via pentose phosphate pathway
- found in nuts, meat, dairy, veges and is part of riboflavin
12
Q
Disaccharides
A
- two monosaccarides linked together by a condensation reaction
- alpha or beta glycosidic bonds
- maltose, lactose, sucrose
13
Q
Maltose
A
- glucose to glucose with alpha 1,4 glycosidic bond
- energy tor sprout growth
- used in food production in cereals, candies and brewing
14
Q
Lactose
A
- galactose to glucose with beta 1,4 glycosidic bond
- milk sugar
15
Q
Sucrose
A
- glucose to fructose with alpha 1,2 glycosidic bond
- table sugar, sugarcane, in fruit
