LOGO

International University of Sarajevo

Lecture 8:Energy and life: Carbohydrates

Course lecturer :

Jasmin Šutković

16th December 2015

CHAPTER OUTLINE International University of Sarajevo

Introduction – Energy for humansEnergy and Biochemical reactions- basics

Carbohydrates Monosaccharide's The Cyclic Forms of MonosaccharidesReduction and Oxidation of

MonosaccharidesDisaccharidesPolysaccharide FOCUS ON THE HUMAN BODY:Useful Carbohydrate DerivativesFOCUS ON THE HUMAN BODY:Blood Type

Book chapter 20

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 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.

Polysaccharides

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.

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 & MEDICINEMONITORING 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 & MEDICINELACTOSE INTOLERANCE

Lactose is the principal disaccharide found in milk from 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 & MEDICINESUCROSE 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 𝛂glycosidic 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-𝛂-glycoside bonds.

Amylopectin, which comprises about 80% of starch molecules, consists of a backbone of glucose units joined in 𝛂glycosidic 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 BODYBLOOD 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

Read the Complete chapter 20 !!!!