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By the end of this section, you will be able to:
  • Discuss the role of carbohydrates in cells and in the extracellular materials of animals and plants
  • Explain the classifications of carbohydrates
  • List common monosaccharides, disaccharides, and polysaccharides

Most people are familiar with carbohydrates, one type of macromolecule, especially when it comes to what we eat. To lose weight, some individuals adhere to “low-carb” diets. Athletes, in contrast, often “carb-load” before important competitions to ensure that they have enough energy to compete at a high level. Carbohydrates are, in fact, an essential part of our diet; grains, fruits, and vegetables are all natural sources of carbohydrates. Carbohydrates provide energy to the body, particularly through glucose, a simple sugar that is a component of starch    and an ingredient in many staple foods. Carbohydrates also have other important functions in humans, animals, and plants.

Molecular structures

Carbohydrates can be represented by the stoichiometric formula (CH 2 O) n , where n is the number of carbons in the molecule. In other words, the ratio of carbon to hydrogen to oxygen is 1:2:1 in carbohydrate molecules. This formula also explains the origin of the term “carbohydrate”: the components are carbon (“carbo”) and the components of water (hence, “hydrate”). Carbohydrates are classified into three subtypes: monosaccharides, disaccharides, and polysaccharides.


Monosaccharides (mono- = “one”; sacchar- = “sweet”) are simple sugars, the most common of which is glucose. In monosaccharides, the number of carbons usually ranges from three to seven. Most monosaccharide names end with the suffix -ose. If the sugar has an aldehyde group (the functional group with the structure R-CHO), it is known as an aldose, and if it has a ketone group (the functional group with the structure RC(=O)R'), it is known as a ketose. Depending on the number of carbons in the sugar, they also may be known as trioses (three carbons), pentoses (five carbons), and or hexoses (six carbons). See [link] for an illustration of the monosaccharides.

The molecular structures of glyceraldehyde, an aldose, and dihydroxyacetone, a ketose, are shown. Both sugars have a three-carbon backbone. Glyceraldehyde has a carbonyl group (c double bonded to O) at one end of the carbon chain with hydroxyl (OH) groups attached to the other carbons. Dihydroxyacetone has a carbonyl group in the middle of the chain and alcohol groups at each end. The molecular structures of linear forms of ribose, a pentose, and glucose, a hexose, are also shown. Both ribose and glucose are aldoses with a carbonyl group at the end of chain,and hydroxyl groups attached to the other carbons.
Monosaccharides are classified based on the position of their carbonyl group and the number of carbons in the backbone. Aldoses have a carbonyl group (indicated in green) at the end of the carbon chain, and ketoses have a carbonyl group in the middle of the carbon chain. Trioses, pentoses, and hexoses have three, five, and six carbon backbones, respectively.

The chemical formula for glucose is C 6 H 12 O 6 . In humans, glucose is an important source of energy. During cellular respiration, energy is released from glucose, and that energy is used to help make adenosine triphosphate (ATP). Plants synthesize glucose using carbon dioxide and water, and glucose in turn is used for energy requirements for the plant. Excess glucose is often stored as starch that is catabolized (the breakdown of larger molecules by cells) by humans and other animals that feed on plants.

Galactose (part of lactose, or milk sugar) and fructose (found in sucrose, in fruit) are other common monosaccharides. Although glucose, galactose, and fructose all have the same chemical formula (C 6 H 12 O 6 ), they differ structurally and chemically (and are known as isomers) because of the different arrangement of functional groups around the asymmetric carbon; all of these monosaccharides have more than one asymmetric carbon ( [link] ).

Questions & Answers

state and explainfour function of a costumer service
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the circular flow model of the economy is a simplification showing how the economy works and the relationship between income,production and spending in the economy as a whole
Anna Reply
what is circular flow
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Economics is defined as the science that study human behaviour as a relationship between ends and scarce means which have alternative uses.
economics is a social science concerned with the production,distribution, and consumption of goods and services
in 2021 Amazon reduced the annual subscription fee for its prime membership service which provides free two_day shipping on many goods and other benefits, from $119 to $99. Zoppa consulting, an investment firm estimated that before the price reduction, prime had 62million subscribers globally. If so, what is the arc elasticity of demand for a prime membership.
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Differences between microeconomics and macroeconomics
tatiana Reply
Macroeconomics deal with the economy as a whole.that is an economy affect the firm ,government and the households eg.unemployment, whilst Microeconomics deal with the the decision making of households,firm and government separately.
what is Economics
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the branch of knowledge concerned with the production, consumption, and transfer of wealth and has Influence by sociology!!!!
Economics is the study of how humans make decisions when they want to fulfil their requirements and desires for goods, services and resources.
Economics is the study how humans make decisions in the faces of scarcity.
economic is the study of how human make decision in the fact of scarcity.
Economics is a social science which study human behavior as a relationship between earn and scarce mean which have alternative uses
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market structure in economics depicts how firms are differentiated and categorised based on types of goods they sell and how their operations are affected by external factors and elements.
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demand is the willingness to purchase something
demand is the potential ability or williness to purchases something at a particular price at a given period of time..
Demand refers to as quantities of a goods and services in which consumers are willing and able to purchase at a given period of time. Demand can also be defined as the desire backed by ability to purchase .
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is the production of goods in scarcity
Demand refers to as quantities of a goods and services in which consumers are willing and able to purchase at a given period of time.
Demand refers to the quantity of goods and services that a consumer is willing and able to buy at a given price over a period of time
Do high interest rate in a country increase investment
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What is the meaning of supply of labour
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what is production?
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Production is basically the creation of goods and services to satisfy human wants
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Production is the process of producing goods and services to satisfy human needs and want.
under what condition will demand curve slope upward from left to right instead of normally sloping downward from left to right
Atama Reply
how i can calculate elasticity?
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What is real wages
Emmanuella Reply
Researchers demonstrated that the hippocampus functions in memory processing by creating lesions in the hippocampi of rats, which resulted in ________.
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The formulation of new memories is sometimes called ________, and the process of bringing up old memories is called ________.
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Source:  OpenStax, Virology. OpenStax CNX. Dec 10, 2014 Download for free at http://legacy.cnx.org/content/col11724/1.1
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