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Terms in this set (51)
Carbohydrates are constructed from what?
Carbon, oxygen, and hydrogen atoms that occur in a proportion that approximates that of a "hydrate of carbon," CH2O, accounting for the term carbohydrate.
Carbohydrates comprise what two major classes?
Simple carbohydrates and complex carbohydrates.
Simple carbohydrates include
monosaccharides and disaccharides.
Complex carbohydrates include
Oligosaccharides containing 3 to 10 saccharide units and polysaccharides containing more than 10 units.
Monosaccharides are structurally
-The simplest form of carbohydrate, since they cannot be reduced in size
The most abundant monosaccharide in nature and the most important nutritionally is...
The six-carbon sugar glucose
Disaccharides consist of what?
Two monosaccharide units joined by covalent bonds.
Sucrose, consisting of one glucose and one fructose residue is what?
Nutritionally the most significant
Oligosaccharides consist of what?
Short chains of monosaccharide units that are also joined by covalent bonds.
Which oligosaccharides occurs most frequently in nature?
Polysaccharides are what?
Long chains of monosaccharide units that may number from several into the hundreds or even thousands
The major polysaccharides of interest in nutrition are what?
Glycogen, found in certain animal tissues, and starch and cellulose, both of plant origin.
All these polysaccharides consist of only...
Carbohydrates play three principal functional roles in animals and plants.
-First, large polysaccharides often provide structural support and shape to cells and other parts of organisms.
-In their second principal role, carbohydrates function as storage compounds.
-The third principal functional role of carbohydrates is as transport compounds.
The most important structural carbohydrate in animals is the polysaccharide...
chitin, which is the principal component of the exoskeletons of insects and many other arthropods.
The structural polysaccharides of plants and algae, which include cellulose and hemicelluloses, are
Enormously abundant in ecosystems and thus are potentially major food sources for animals.
What are the two most abundant organic compounds in the biosphere?
Chitin and cellulose
Like the structural carbohydrates, the storage carbohydrates are
They are accumulated and broken down far more dynamically than
Starch, a form of polymerized glucose...
is one of the principal storage carbohydrates in plants.
Glycogen, also a form of polymerized glucose...
is the principal storage carbohydrate in animals.
•The "value" of stored glycogen is primarily that...
It is a source of energy.
Glycogen, however, is far inferior to lipids as a general energy-storage compound for the following reason...
Molecules of glycogen are highly hydrated in the tissues of living animals, and because of the added weight of their water of hydration, they yield a low amount of energy per unit of total weight.
This attribute of glycogen probably explains why the amount of glycogen stored by animals and humans is typically...
far less than the amount of lipid stored.
Glycogen serves mainly as a store of...
glucose that in turn serves as a chemically specific energy source for certain tissues and metabolic processes that require glucose as their energy source.
The central nervous system in vertebrates requires glucose as its principal fuel; moreover...
The fastest mechanism of ATP production in vertebrate skeletal muscles (anaerobic glycolysis) also requires glucose as its fuel
Stores of glycogen supply glucose energy to the what?
Brain and skeletal muscles in times of need.
The transport carbohydrates are small molecules—monosaccharides or disaccharides—found where?
dissolved in the blood or other moving body fluids.
When the body fluids travel from one place to another....
the dissolved carbohydrates move with them—thereby, for example, transporting energy from place to place.
Glucose is the principal blood transport carbohydrate ("blood sugar") in vertebrates and most other groups of animals...
although many insects employ the disaccharide trehalose in this role
The carbon chains used to synthesize carbohydrates may be derived from...
dietary proteins or from the glycerol components of dietary lipids, as well as from dietary carbohydrates.
There are no essential carbohydrates
animals can synthesize all the carbohydrates they need. (Still needed for gut microbiome).
The one noteworthy "nutritional problem" that animals have with carbohydrates is that
many animals are unable to digest cellulose, chitin, or some of the other structural polysaccharides.
The digestion of polysaccharides proceeds in two steps:
-The first step involves carbohydrases produced by the salivary glands and pancreas.
-The second step uses brush border enzymes.
The digestion of polysaccharides involves two enzymes:
salivary amylase and pancreatic alpha-amylase.
Carbohydrate digestion begins in the mouth during mastication, through the action of salivary amylase from....
the parotid and submandibular salivary glands.
Salivary amylase breaks down starches into a mixture composed mostly of...
disaccharides and trisaccharides.
Salivary amylase continues to digest the starches and glycogen in food for 1 to 2 hours before...
stomach acids render the enzyme inactive.
Only a small amount of digestion takes place over this period because...
the enzymatic content of saliva is not high.
In the duodenum, pancreatic alpha-amylase breaks down what?
the remaining polysaccharides (about 90% of total carbohydrates ingested).
Any disaccharides or trisaccharides produced, and any present in the food, are...
not broken down further until they contact the intestinal mucosa.
Brush border enzymes of the intestinal microvilli break disaccharides and trisaccharides...
into monosaccharides prior to absorption.
The enzyme maltase splits bonds between...
the two glucose molecules of the disaccharide maltose.
Sucrase breaks the disaccharide sucrose into...
glucose and fructose
Lactase hydrolyzes the disaccharide lactose into...
a molecule of glucose and one of galactose.
If the intestinal mucosa stops producing lactase, the animal or person becomes...
The intestinal epithelium then absorbs the monosaccharides by...
facilitated diffusion and cotransport mechanisms.
Both methods involve...
A Carrier Protein
The simple sugars that are transported into the intestinal epithelial cell at its apical surface diffuse through...
They then reach the interstitial fluid by...
facilitated diffusion across the basolateral surfaces.
These monosaccharides diffuse into the capillaries of the villus for...
eventual transport to the liver in the hepatic portal vein.
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