BIOL 380 Lecture Notes - Lecture 3: Sorbitol, Mannitol, Carbohydrate
26 May 2018
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BIOL 380 – Lecture 3 – Carbohydrates
What are carbohydrates?
- One of the three macromolecules
- Important source of energy for all cells
- Preferred energy source for nerve cells
- Composed of carbon. Hydrogen and oxygen
- Good sources: fruits, vegetables and grains
Glucose
- Most abundant carbohydrate
- Produced by plants through photosynthesis
Simple carbohydrates
- Contain one or two molecules
- Commonly referred to as sugars
o Monosaccharides contain one molecule
▪ Glucose, fructose and galactose
o Disaccharides contain 2 molecules
▪ Lactose, maltose and sucrose
o Sugar alcohols provide less energy and are used as sweeteners
▪ Mannitol (seaweed) and sorbitol (corn)
Monosaccharides
- glucose is a isomer of galactose
- structural isomer = fructose
- don't really find pure glucose as a normal component
of any type of nutritional source
- fructose does occur alone, mainly in fruits
- galactose also is not found generally in foods on its own. usually found bound to glucose, as
LACTOSE
- don't know structures
Disaccharides
- lactose = galactose + glucose
o beta bond
- maltose = glucose + glucose
o alpha bond
- sucrose = glucose + fructose
o alpha bond
complex carbohydrates
- long chains of glycose moelcules
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find more resources at oneclass.com
- oligosaccharides contain 3 to 10 monosaccharides
- most polysaccharides consist of hundreds to thousands of glucose molecules
1. starch
2. glycogen
3. fibers
complex carbohydrate: Starch
- plants store carbohydrates as starch
o amylose – straight chain of glucose
o amylopectin – branched chain of glucose
▪ branched = inc SA for exposure to
digestive enzymes
o resistant starch (fiber) – glucose molecules linked by beta bonds are largely indigestible
▪ we do not have an enzyme that breaks down beta bond
▪ resistant starch is classified as a type of fiber
- sources: grains, legumes, fruits & vegetables
complex carbohydrate: glycogen
- storage form of glycose in animals (humans)
- not found in food and therefore not a source of dietary carbohydrate
o lose most of glycogen during preparation
- stored in the liver and muscles
- when blood glucose levels are low, and you need to raise them to feed teh tissues of your body,
your liver releases the stored glucose by breaking down that stored glycogen
- muscles first use ATP reserves, but once empty they break down glycogen into glucose, but your
muscles don't release glucose into blood stream they use it for themselves
complex carbohydrate: fiber
- compossed of long polysaccharide chains
o dietary fibers are non-digestible parts of plants (support structure of leaves and stems
ect)
o functional fibers are non-digestible forms of carbohydrates extracted from plants or
manufactured in a laboratory and have known health benefits
▪ eg., guar gum, cellulose, psyllium and pectin
o total fiber = dietary fiber + functional fiber
- fibers can be classified as soluble and insoluble
1. soluble fibers
o dissolve in water; viscous and gel-forming when wet
o fermentable; digested by intestinal bacteria
o loes lood holesteol does’t seueste holesteol fo the lood, ut deeases
how much you absorb into the blood)
o found in citrus fruits, berries, oats and beans
o e.g. pectin, gum and mucilage (ex. Psyllium)
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find more resources at oneclass.com
2. insoluble fibers
o do not dissolve in water, non -viscous and most
of them are not digested
o cannot be fermented by bacteria in the colon
o promote regular bowel movements and
alleviate constipation
o good sources: whole grains, seeds, legumes,
fruits and vegetables
o e.g. lignins and cellulose
carbohydrate digestion
- Digestion breaks
polysaccharides
and disaccharides
into
monosaccharides
which then get absorbed into the mucosal cells lining the small intestine
- MOUTH
o Salivary amylase begins carbohydrate digestion in the mouth
o Breaks carbohydrates down to maltose
o Disaccharides not broken down in the mouth
o Carbohydrate digestion does not occur in the stomach because the acid in the stomach
inactivates the salivary amylase enzyme
- Most chemical digestion of carbohydrates occurs in the SMALL INTESTINE
o Pancreatic amylase produced in the pancreas and secreted into the small intestine
o Digests carbohydrates to maltose
- Additional enzymes in the microvilli (brush border membrane)
digest disaccharides to monosaccharides
o Maltase to glucose glucose
o Sucrose to glucose fructose
o Lactase to glucose galactose
- Monosaccharides are absorbed into the enterocyte of the small
intestine and then enter the bloodstream
carbohydrate absorption
- monosaccharides are absorbed into the cells lining the small
intestine
o glucose and galatose by active transport
o fructose by facilitated diffusion
▪ takes longer
▪ less likely to raise blood sugar levels as quickly
Carbohydrate digestion
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Commonly referred to as sugars: monosaccharides contain one molecule, glucose, fructose and galactose, disaccharides contain 2 molecules. Lactose, maltose and sucrose: sugar alcohols provide less energy and are used as sweeteners, mannitol (seaweed) and sorbitol (corn) Monosaccharides glucose is a isomer of galactose structural isomer = fructose. Disaccharides lactose = galactose + glucose: beta bond. Maltose = glucose + glucose: alpha bond sucrose = glucose + fructose, alpha bond complex carbohydrates long chains of glycose moelcules. Most polysaccharides consist of hundreds to thousands of glucose molecules: starch, glycogen, fibers complex carbohydrate: starch. Not found in food and therefore not a source of dietary carbohydrate lose most of glycogen during preparation stored in the liver and muscles. When blood glucose levels are low, and you need to raise them to feed teh tissues of your body, your liver releases the stored glucose by breaking down that stored glycogen.
