Carbohydrates — Overview & Importance in Biology

What Are Carbohydrates Made Of?

Carbohydrates are made up of one or more simple sugars. More commonly known as starches, they are the main source of energy for most living things.

You're probably wondering, "Well, what is a simple sugar?"

Simple sugars are small sugar molecules, which are also called monosaccharides. This literally translates to "one sugar". You've probably heard of a few kinds of simple sugars before, such as glucose and fructose.

A simple carbohydrate (monosaccharide) is made of carbon, hydrogen, and oxygen atoms in a 1:2:1 ratio. These carbohydrates can be drawn in a couple of different ways, but they all represent the same thing. Four types of drawings are shown below for a simple sugar.

Simple sugars can bond together to form long chains, called complex sugars or complex carbohydrates.

When the complex sugar is made of two monosaccharides, it's called a disaccharide. (Note that di- means two, so this translates to "two sugars".)

Regular table sugar, sucrose, is a compound made of both glucose and fructose.

Polysaccharides are macromolecules formed from monosaccharides. Poly- means "many".

Animals use a polysaccharide called glycogen (sometimes called animal starch) to store excess sugar. If your blood sugar ever gets too low, glycogen will be broken down into glucose for more energy.

Plants also use polysaccharides (starch) for storing excess sugars. They use the complex carbohydrate called cellulose for structural strength. Large amounts of cellulose are present in wood and paper.

$$\color{#8925AE}{\text{Vocabulary Review:}}$$

$\color{#8925AE}{\text{Monomer}}$ : Any molecule that can react with other molecules of the same or different makeup to form a chain, or polymer

$\color{#8925AE}{\text{Polymer}}$ : A chain of monomers made of a specific type of compound

$\color{#8925AE}{\text{Macromolecule}}$ : A polymer that has a large (macro) molecular mass. There are four main types in organisms: carbohydrates, proteins, lipids, and nucleic acids

$\color{#8925AE}{\text{Monosaccharide}}$ : The most basic types of sugars, called simple sugars

$\color{#8925AE}{\text{Polysaccharide}}$ : A polymer of simple sugars. They are called complex carbohydrates

$\color{#8925AE}{\text{Carbohydrate}}$ : A polymer of sugars or starch monomers

What Are Carbohydrates?

Carbohydrates are sugars. They are the primary energy storage molecule for life on Earth.

Structure of Carbohydrates

Carbohydrates are made of carbons, hydrogens, and oxygens. The hydrogen bonds between the hydrogens and oxygens in carbohydrates typically make them dissolve easily in water. These hydrogen bonds also make hydrolysis reactions possible. Hydrolysis reactions are where the carbohydrates react with water to break down into smaller molecules. This allows them to be used as a source of energy.

Carbohydrate monomers have a simple chemical formula with a ratio of 1 carbon atom to 2 hydrogen atoms to 1 oxygen atom. These bond with other monosaccharides to make polysaccharides, which are polymers. Glucose is the most important monosaccharide. It is used by organisms in cellular respiration to produce usable energy for the body.

Where Do Carbohydrates Come From?

Plants perform photosynthesis to make carbohydrates using energy from the sun, water, and $CO_2$ (carbon dioxide). Animals eat and break down the very same carbohydrates to make energy in the form of ATP. This process is called cellular respiration.

Disaccharides

When two monosaccharides are bonded together, they are called disaccharides. (It helps to remember that di means two and mono means one.) Examples of disaccharides include sucrose and lactose. These are easily broken down by animals and bacteria to get glucose, which is then used for cell functions.

Polysaccharides

Large strings or clusters of monosaccharides are called polysaccharides (poly- means "many"). They are also called complex carbohydrates. Polysaccharides are used either as energy storage molecules or as structural molecules.

Examples include glycogen, cellulose, starch, and chitin. Glycogen stores energy in humans (in the liver), while starch performs the same function in plants. Cellulose makes up plant cell walls, giving them their square shape. Finally, chitin is what makes up the hard exoskeletons of insects.

In our daily lives, examples of carbohydrates include bread, pasta, and candy. They also show up a lot in processed foods. But despite the negative press they get in fad diets and from some celebrities, carbohydrates are necessary for survival.

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