What’s a Carbohydrate?
Carbohydrates are molecules composed of carbon, hydrogen and oxygen, and they include sugar and starches. Carbon Review
• Likes to form 4 covalent bonds
• Can be in the form of
– straight chain
– branched chain
– ring
The word carbohydrate literally means “watered carbon”. This can be explained by the ratio of carbon atoms to hydrogen and oxygen atoms in the a carbohydrate:
C:H:O
1:2:1
However, the general formula CH2O creates a false impression that the oxygen is supplied by water. The oxygen in a carbohydrate comes from oxygen gas. The hydrogen atoms come from a molecule of water, but only after releasing the oxygen. Glucose is a common simple sugar with the chemical formula C6H12O6. It is made by plant cells during photosynthesis and oxidized by animal cells for usable energy. There are many different types of sugar. It’s easy to identify a sugar because they all end in –ose.
What is a monomer of carbohydrates?
Monosaccharides are simple sugars. Many simple sugars have either five or six carbon atoms. Ex: Glucose and fructose (both have the chemical formula C6H12O6 but have different structures) are monosaccharides. A disaccharide is two monosaccharides linked together. Ex: Dehydration reaction of glucose + glucose = maltose (milk sugar)
Ex: Sucrose (table sugar) is a disaccharide composed of one glucose and one fructose linked together through dehydration synthesis. What is a polymer of carbohydrates? Polysaccharides are polymers composed of many monosaccharide subunits. Polysaccharides include starches, cellulose, and glycogen.
Carbohydrate Function
1. Carbohydrates are a source of quick energy for organisms. Athletes often eat "gels" during intense exercise. These gels are mostly made up of sugar and provide a quick source of energy for the athlete. Carbohydrate Function
2. When energy is not immediately needed, simple sugars get stored for later. Monosaccharides are built into long chains of carbohydrates called polysaccharides. Some common forms of energy storage are shown below. Animals store glucose as glycogen.
Glycogen – branched chains of glucose molecules that are made and stored by animals. Glycogen is more highly branched than plant starches. Plants store glucose as starch.
Starch – branched chains of glucose molecules that are made and stored by plants. They can be broken down as a source of energy by plants or when consumed by animals.
Carbohydrate Function
3. Carbohydrates can be used for structural support. Example
Example
Cellulose – a polymer of glucose monomers that has a straight, rigid structure. Cellulose makes up the cell wall of plant cells. Animals can't make cellulose. Carbohydrates can be imbedded in the cell membrane (the outer layer of cells). Cellulose is the most abundant organic molecule on Earth. Plants produce almost 1011 (100 billion) tons of cellulose a year. Example
Chitin is a polysaccharide that makes up the exoskeletons of insects and other organisms.