LOGO
Lecture 8:
Energy and life: Carbohydrates
International University of Sarajevo
Course lecturer :
Jasmin Šutković
16th December 2015
CHAPTER OUTLINE
International University of Sarajevo
Book chapter 20
Introduction – Energy for humans
Energy and Biochemical reactions- basics
Carbohydrates
Monosaccharide's
The Cyclic Forms of Monosaccharides
Reduction and Oxidation of Monosaccharides
Disaccharides
Polysaccharide
FOCUS ON THE HUMAN BODY:
Useful Carbohydrate Derivatives
FOCUS ON THE HUMAN BODY:
Blood Type
Introduction
 All organisms obtain energy from their surroundings to stay alive.
 In animals, the energy comes from food and is released through the
interconnected reaction pathways of metabolism.
 The end products are carbon dioxide, water, and energy:
The principal food molecules—lipids, proteins, and carbohydrates—differ in
structure and are broken down by individual pathways that are examined in
later chapters.
Energy and life
 Living things must do mechanical work —microorganisms
engulf food, plants bend toward the sun, and humans
walk about.
 All organisms must also do the chemical work of
synthesizing biomolecules needed for energy storage,
growth, repair, and replacement.
 In addition, cells need energy for the work of moving
molecules and ions across cell membranes. In humans, it
is the energy released from food that allows these
various kinds of work to be done.
The flow of energy through
the biosphere
 Our bodies do not produce energy by burning up a steak
all at once because the release of a large quantity of
energy (primarily as heat) would be harmful to us.
 Furthermore, it is difficult to capture energy for storage
once it has been converted to heat.
 We need energy that can be stored and then released in
the right amounts when and where it is needed, whether
we are running away from an angry dog, studying for an
exam, or sleeping peacefully.
Our requirements for energy:
 Energy must be released from food gradually.
 Energy must be stored in readily accessible forms.
 Release of energy from storage must be finely controlled
so that it is available exactly when and where it is
needed.
 Just enough energy must be released as heat to maintain
constant body temperature.
 Energy in a form other than heat must be available to
drive chemical reactions that are not favorable at body
temperatures.
Metabolism
ATP
Carbohydrates
 Carbohydrates can be simple or complex, having as few
as three or as many as thousand of carbon atoms.
 The glucose metabolized for energy in cells, the sucrose
of table sugar, and the cellulose of plant stems and tree
trunks are all examples of carbohydrates.
 Carbohydrates on cell surfaces determine blood type,
and carbohydrates form the backbone of DNA, the carrier
of all genetic information in the cell.
Carbohydrates
Carbohydrates, commonly referred to as sugars and starches, are
polyhydroxy aldehydes and ketones, or compounds that can be
hydrolyzed to them.
 Glucose, for example, has five hydroxyl (-OH) groups and one
aldehyde (-CHO) group:
Carbohydrates are classified into three groups:
1. Monosaccharides
2. Disaccharides
3. Polysaccharides
Monosaccharides
 Monosaccharides or simple sugars are the simplest
carbohydrates. Glucose and fructose, the two major
constituents of honey, are Monosaccharides.
Disaccharides
Disaccharides are composed of two Monosaccharides
joined together. Lactose, the principal carbohydrate in
milk, is a disaccharide.
Disaccharides contain at least one acetal carbon—a carbon
atom singly bonded to two OR (alkoxy) groups.
Polysaccharides
 Polysaccharides have three or more monosaccharides joined
together. Starch, the main carbohydrate found in the seeds and
roots of plants, is a polysaccharide composed of hundreds of glucose
molecules joined together.
Monosaccharides are drawn vertically, with
the carbonyl group at (or near) the top.
A monosaccharide is characterized by the number of
carbons in its chain.
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A triose has three carbons.
A tetrose has four carbons.
A pentose has fi ve carbons.
A hexose has six carbons.
 These terms are then combined with the words aldose and ketose to
indicate both the number of carbon atoms in the monosaccharide
and whether it contains an aldehyde or ketone.
 Example, glyceraldehyde is an aldotriose (three carbons and an
aldehyde)
Fisher projection formulas
 A carbohydrate structure is composed of chirality centers. All
carbohydrates except for dihydroxyacetone contain one or
more chirality centers.
 The simplest aldose, glyceraldehyde, has one chirality center—
one carbon atom bonded to four different groups.
 Fischer projection formulas are also used for compounds
like aldohexoses that contain several chirality centers.
 The letters D and L are used to label all monosaccharides, even
those with many chirality centers.
 The configuration of the chirality center farthest from the
carbonyl group determines whether a monosaccharide is D or L
Common monosaccharides
Glucose
 Glucose, also called dextrose, is the sugar referred to
when blood sugar is measured. It is the most abundant
monosaccharide. Glucose is the building block for the
polysaccharides starch and cellulose.
 Glucose, the carbohydrate that is transported in the
bloodstream, provides energy for cells when it is
metabolized.
 Normal blood glucose levels are in the range of 70–110
mg/dL. Excess glucose is converted to the
polysaccharide glycogen (Section 20.6) or fat.
 Galactose is one of the two monosaccharides that
form the disaccharide lactose
 Galactose is a stereoisomer of glucose, since the
position of a hydrogen atom and hydroxyl group at a
single chirality center are different in the two
monosaccharides
Fructose
 Fructose is one of two monosaccharides that form
the disaccharide sucrose.
 D-Fructose, often called levulose or fruit sugar found in
honey and is almost twice as sweet as normal table
sugar with about the same number of calories per gram.
 Fructose is produced commercially in large quantities by
hydrolysis of cornstarch to make high fructose corn
syrup.
FOCUS ON HEALTH & MEDICINE
MONITORING GLUCOSE LEVELS
 In order to make sure that their blood glucose
levels are in the proper range, individuals with
diabetes frequently measure the concentration of
glucose in their blood.
 A common method for carrying out this
procedure today involves the oxidation of
glucose to gluconic acid using the enzyme
glucose oxidase.
How it work in practice?
 In the presence of glucose oxidase, oxygen (O2) in the air oxidizes
the aldehyde of glucose to a carboxyl group. The O2, in turn, is
reduced to hydrogen peroxide, H2O2.
 In the first generation of meters for glucose monitoring, the H2O2
produced in this reaction was allowed to react with another organic
compound to produce a colored product.
 The intensity of the colored product was then correlated to the
amount of glucose in the blood. Test strips used for measuring
glucose concentration in the urine are still based on this technology.
Disaccharides
 Disaccharides are carbohydrates composed
of two monosaccharides.
 Disaccharides are acetals, compounds that
contain two alkoxy groups (OR groups) bonded
to the same carbon.
 All disaccharides contain at least one acetal that joins the rings
together. Each ring is numbered beginning at the anomeric carbon,
the carbon in each ring bonded to two oxygen atoms.
 The glycosidic linkage that joins the two monosaccharides in a
disaccharide can be oriented in two different ways, shown with
Haworth projections in structures A and B.
FOCUS ON HEALTH & MEDICINE
LACTOSE INTOLERANCE
 Lactose is the principal disaccharide found in milk from
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both humans and cows.
Compared to other mono and disacharisdes lactose is
not really sweet!
Lactose is digested in the body by enzyme lactase.
Individuals who are lactose intolerant no longer
produce this enzyme, and so lactos cannot be properly
digested, causing abdominal cramps and diarrhea.
Lactose intolerance is especially prevalent in Asian and
African populations whose diets have not traditionally
included milk beyond infancy.
FOCUS ON HEALTH & MEDICINE
SUCROSE AND ARTIFICIAL SWEETENERS
 Sucrose, the disaccharide found in sugarcane and the compound
generally referred to as “sugar,” is the most common disaccharide in
nature
 Sucrose’s pleasant sweetness has made it a widely used ingredient
in baked goods, cereals, bread, and many other products
 To reduce caloric intake while maintaining sweetness, a variety of
artifi cial sweeteners have been developed. These include
aspartame, saccharin, and sucralose (Figure 20.3). These
compounds are much sweeter than sucrose, so only a small amount
of each compound is needed to achieve the same level of perceived
sweetness.
 A relative sweetness scale ranks the sweetness of carbohydrates
and synthetic sweeteners, as shown in Table 20.1.
Polysaccharides
 Polysaccharides contain three or more
monosaccharides joined together. Three prevalent
polysaccharides in nature are cellulose, starch, and
glycogen, each of which consists of repeating glucose
units joined by glycosidic bonds.
Celluloze
 Cellulose is found in the cell walls of nearly all plants,
where it gives support and rigidity to wood, plant stems,
and grass (Figure 20.4). Wood, cotton, and flax are
composed largely of cellulose.
 In some cells, cellulose is hydrolyzed by an enzyme
called a 𝛃-glycosidase, which cleaves all of the β
glycoside bonds, forming glucose.
 Humans do not possess this enzyme, and therefore
cannot digest cellulose. Other animals have bacteria
containing this enzyme in their digestive systems, so they
can derive nutritional benefi t from eating grass and
leaves.
Celluloze
Starch
 Starch is the main carbohydrate found in
the seeds and roots of plants. Corn, rice,
wheat, and potatoes are common foods
that contain a great deal of starch.
 Starch is a polymer composed of
repeating glucose units joined in 𝛂
glycosidic linkages. The two common
forms of starch are amylose and
amylopectin.
 Amylose, which comprises about 20% of
starch molecules, has an unbranched
skeleton of glucose molecules with 1→4-𝛂glycoside bonds.
 Amylopectin, which comprises about 80%
of starch molecules, consists of a
backbone of glucose units joined in 𝛂
glycosidic bonds, but it also contains
considerable branching along the chain.
GLYCOGEN
 Glycogen is the major form in which
polysaccharides are stored in animals.
 Glycogen, a polymer of glucose containing
𝛂 glycosidic bonds, has a branched
structure similar to amylopectin, but the
branching is much more extensive
(Figure 20.6).
FOCUS ON THE HUMAN BODY
BLOOD TYPE
 Human blood is classified into one of four types using the
ABO system discovered in the early 1900s by Karl
Landsteiner.
 There are four blood types—A, B, AB, and O. An
individual’s blood type is determined by three or four
monosaccharides attached to a membrane protein of red
blood cells. These monosaccharides include:
End of chapter
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