There are 4 classes of large molecules that make up the majority of living things. They are called Macromolecules. Since macromolecules are generally made up of many smaller molecules and atoms, they are referred to as polymers. Polymers are made up of smaller units known as monomers.
The macromolecules of life are:
- nucleic acids
We will look at each to determine the make-up, functions and examples as found in living things.
Ever wonder where life's molecular building blocks come from? If so, take a look at the Molecular Logic Project's nifty concept map. The Molecular Logic Project's mission is to improve the ability of all students to understand fundamental biological phenomena in terms of the interactions of atoms and molecules.
In order to gain a better understanding of macromolecules and the molecular building blocks that comprise them, you may want to visit and use MolviZ.Orgwhich contains a number of molecular visualization resources initiated and authored or managed by Eric Martz (University of Massachusetts, Amherst).
Carbon compounds are found in all living things and are called organic compounds. Several properties of carbon contribute to its versatility:
- Carbon has four electrons in its outer energy shell and thus can form 4 covalent bonds with other elements or with other carbon atoms. These bonds can be single bonds, double bonds, or triple bonds.
- Carbon can also form long chains of molecules as well as rings and other complex structures.
Inorganic compounds are those that do not contain carbon; many are also essential to life. Water, nitrate and phosphate compounds are required, but are not organic. Exceptions to the 'carbon' rule are Carbon Dioxide and Carbon monoxide. They contain carbon, but are not considered organic.
Just to make sure you get the idea: Carbon (solid), Hydrogen (gas), Oxygen (gas), and Nitrogen (gas) are among the four most common elements found in living organisms (just remember CHON). These four elements are also notable for being the least massive (and having the lowest atomic number) in their group in the periodic table.
Carbohydrates - macromolecules composed of carbon, hydrogen and oxygen in a ratio of 1:2:1.
Ex: glucose, C6H12O6
Carbohydrates are sugars; sugars can be simple monomers, such as glucose or fructose, or complex polymers, such as starch.
Polysaccharides are large sugar molecules composed of many smaller units, linked together in complex arrangements. Starch and cellulose (as depicted in the 3D model below), made by plants and glycogen found in animals are types of polysaccharides. Starches and glycogen are used to store energy; cellulose is the structural component of cell walls.
Disaccharides are sugar molecules with only two monomers; table sugar is an example of a disaccharide. These types of sugars are generally used as a source of energy.
This is sucrose, a common disaccharide.
Here's another representation of sucrose as well.
Monosaccharides are the monomer units of carbohydrates; they are glucose, fructose and galactose.
Lipids are macromolecules composed of mostly carbon and hydrogen chains; primarily fats, waxes oils and steroids
Monomers (single) units of lipids are made of fatty acids attached to a glycerol molecule. They usually combine in a ratio of 1 glycerol to 3 fatty acids. What you see below is ball and stick model of glycerol. Glycerol is a type of alcohol with a hydroxyl group on each of its three carbons.
Glycerol along with 3 fatty acids make a monomer of lipid.
Add a few things to glycerol (like fatty acids) and you have the ingredients for substances that are extremely useful to living things. For example, triglyceride is glyceride in which the glycerol is esterified with three fatty acids. You'll find it in stuff like vegetable oil and animal fats.
Examples of lipids are fats, oils, waxes and steroids. Lipids are not soluble in water. The fatty acids can be saturated or unsaturated.
- Saturated fatty acids contain the maximum number of hydrogens. These molecules are 'flat' and tend to pack solidly like bricks. Thus saturated fats are usually solid at room temperature. Animal fat and butter are typical saturated fats.
- Unsaturated fatty acids contain 1 or more double bonds. Double bonds prevent them from holding the maximum number of hydrogens. This causes the carbon chain to bend into odd shapes so that they will not pack solidly. Thus unsaturated fats are generally liquid at room temperature. Vegetable oil is usually unsaturated.
- Polyunsaturated fatty acids contain more than one double bond.
Lipids have a lot of important jobs in living things. Some of these are:
They form waterproofing (waxes) act as
- chemical messengers (steroids),
- store energy (fats and oils), and
- form cell membranes (phospholipids).
To learn more about lipids, click here to visit J. Stein Carter's webpage devoted to the topic.
Nucleic acids - macromolecules containing hydrogen, oxygen, nitrogen, carbon and phosphorus and are associated with organism's genetic code.
Monomer (single) units of nucleic acids are called nucleotides. One nucleotide consists of a 5-carbon sugar, a phosphate group and a nitrogen base.
Two examples of nucleic acids are deoxyribonucleic acid (DNA), and ribonucleic acid (RNA).
The function of nucleic acids is to store and transmit genetic information (chemical instructions about how living things should form and operate). You will learn much more about nucleic acids in a future unit of study.
Proteins - macromolecules containing carbon, hydrogen, oxygen and nitrogen; proteins are considered the building blocks of tissue
Monomer units of proteins are called amino acids.
Amino acids can link together and form molecules called proteins.
Proteins perform several critical jobs in cells. Functions of proteins include:
- controlling the rate of chemical reactions (enzymes do this),
- regulating cell processes,
- forming structural components of certain cells,
- transporting substances into and out of cells,
- helping to fight disease.
One of the most important types of proteins is called an enzyme:
- Enzymes act as biological catalysts (a catalyst is a chemical that speeds up chemical reactions within the cell.)
- Enzymes are able to speed up the rate in which chemical reactions occur by reducing the activation energy (energy needed to start a chemical reaction).
- Enzymes work by providing a place for reactants to come together at a lower energy level so the products can come together faster.
- The reactants are called substrates and when they join together with the enzyme, an enzyme-substrate complex is formed; it is here that the substrates are converted into products and then released. The enzyme will remain unchanged after the chemical reaction occurs and can be used over and over to complete the same reaction.
Enzymes can be synthetic (they can build up) or hydrolytic (they can breakdown or digest). They are very specific for their substrates. Most end in -ase .
SUBSTRATE... ENZYME ... PRODUCTS
- Protein... Protease...> Amino Acids
- Lipids... Lipase...> 3 Fatty Acids and Glycerol
- Maltose... Maltase...> 2 Glucose molecules
Enzymes must have the best environmental conditions to operate most efficiently. This is called their optimum enzyme activity.
The three (3) conditions that limit enzyme activity are:
- Temperature: Conditions can't be too hot or too cold. Just like Goldilocks, the temperature has to be just right!
- pH: Conditions can't be too acidic or basic. They have to be just right. Remember pH measures the Hydrogen Ion concentration in a solution (the more H+ the stronger the acid).
- Substrate and Enzyme concentration: The amount of each that is present must be--you guessed it--just right! There has to be sufficient amounts of each for the reaction to work.