NUTR 3210 Lecture Notes - Lecture 5: Active Transport, Facilitated Diffusion, Aldose
27 Jun 2018
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Learning outcomes
Describe the classification and structure of carbohydrates, including fiber
Describe the digestion and absorption of dietary carbohydrates
Describe the function of dietary carbohydrates in the human body
Describe the metabolism of dietary carbohydrates, and predict how metabolism would change
under different conditions
Describe the impact of dietary carbohydrates on human health
Apply principles of nomenclature to novel CHO structures
Introduction to carbohydrates
Carbohydrates are composed of three elements - carbon, hydrogen, and oxygen with a general
formula of Cm(H2O)n
The term carbohydrate originated from early research observations that molecules of water
seemed to be attached to chains of carbon, or "hydrates of carbon" - this interpretation is wrong.
We will describe them as poly hydroxy aldehydes and ketones, but the name carbohydrates
continues to be used
Carbohydrates are a major source of fuel or energy in the body - they represent about 50% of
the calories consumed in the North American diet
CHO fraction does not contain essential nutrients - not to be confused with essential
metabolites
The sugar molecule, glucose, is what life on Earth is based on - plants, algae, and cyanobacteria
use photosynthesis to produce glucose, which is then interconverted throughout the food chain,
providing structures and energy for maintenance of land and aquatic ecosystems
There are several chiral carbons in each sugar molecule, making stereoisomers an important
consideration to understanding carbohydrate chemistry
Fortunately, natural enzymes are typically stereospecific, meaning that the sugar molecules
made by the enzymes of photosynthesis tend to be in a certain isomeric form
Another important property of many sugars is that they switch between linear, or open,
structures and ring, or closed structures
oThese are spontaneous, non-enzymatic reactions, and when a new chiral carbon is
formed in this way, it may form different stereoisomers
Carbohydrate classification
CHO can be divided into two groups: simple and complex sugars
Simple sugars (mono- and disaccharides)
oMonosaccharides are the simplest form of CHO molecules
The most common monosaccharides are the 6-carbon chains or hexoses, where
glucose is the most abundant
Other monosaccharides include pentoses, which are critical for making DNA and
RNA, and trioses, which have critical roles in metabolism, for example pyruvate
oDisaccharides form through the glyosidic linking of two monosaccharides
Include natural sugars like sucrose and lactose - these are the two main dietary
disaccharides
Maltose is also considered a disaccharide, although it is a partial breakdown
product of starch or glycogen, formed in food processing or during digestion
Complex sugars
oOligosaccharides consist of short chains of monosaccharides, joined together by
glycosidic bonds
find more resources at oneclass.com
find more resources at oneclass.com
oPolysaccharides are longer chains of 6 or more monosaccharides which often have
hundred or thousands of units
Include starches like amylose and amylopectin, and potentially glycogen from
animal sources
From plant sources, there are insoluble fibers, including cellulose, hemicellulose,
and soluble fibers with different mixtures of sugars and bond types
Isomerization is important in this unit - amylose and cellulose have the same linear glucose
structure except for the isomerization of the linkages between the glucose molecules
oAmylose is a soluble digestible starch whereas cellulose is an insoluble, poorly
fermented, fiber
Monosaccharide nomenclature
In addition to the hydroxyl groups (-OH) sugars possess a functional carbonyl group (=O), which
can be either (a) an aldehyde, or (b) a ketone
oAn aldehyde is present at the end of the chain of carbons, while a ketone will be found
somewhere within the chain
oSugars with an aldehyde group are called aldoses, while those with a ketone group are
called ketoses
Sugars can become ring structures due to reactivity of the carbonyl group, the second lowest
hydroxyl group bends around and attacks the carbonyl carbon. This is non-enzymatic, and there is
a rapid equilibrium between linear and ring forms that we will discuss further
oGlucose forms a 6-sided ring with one tail and fructose forms a 5-sided ring with 2 tails,
due to aldose vs. ketose structures
find more resources at oneclass.com
find more resources at oneclass.com
The carbon of the carbonyl group, whether is an aldehyde or a ketone, is referred to as the
anomeric carbon and the full naming system is in part based on where the anomeric carbon is
located within the sugar
The anomeric carbon is the carbon that comes from the carbonyl carbon of the ketone or
aldehyde of the open-chain form of the molecule
Stereoisomerism
Stereoisomerism refers to the characteristic shared by molecules that can be mirror images of
each other - the two structures cannot be superimposed on each other
Stereoisomerism happens in all molecules that have a chiral carbon, in which each of the four
groups bound to the carbon is structurally different
oTwo hydrogens bound to a carbon will not be chiral
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Describe the classification and structure of carbohydrates, including fiber. Describe the digestion and absorption of dietary carbohydrates. Describe the function of dietary carbohydrates in the human body. Describe the metabolism of dietary carbohydrates, and predict how metabolism would change under different conditions. Describe the impact of dietary carbohydrates on human health. Apply principles of nomenclature to novel cho structures. Carbohydrates are composed of three elements - carbon, hydrogen, and oxygen with a general formula of cm(h2o)n. The term carbohydrate originated from early research observations that molecules of water seemed to be attached to chains of carbon, or "hydrates of carbon" - this interpretation is wrong. We will describe them as poly hydroxy aldehydes and ketones, but the name carbohydrates continues to be used. Carbohydrates are a major source of fuel or energy in the body - they represent about 50% of the calories consumed in the north american diet.
