Chapter 3: Chemistry of Life

Macromolecules

Macromolecules• There are many molecules that comprise

living organisms and many of them are quite large.

• As such, they are called macromolecules.

• There are 4 main macromolecules that comprise living organisms:

1. Proteins.

2. Lipids.

3. Carbohydrates.

4. Nucleic acids.

Macromolecules

• Three of the four classes (carbohydrates, protein, and nucleic acids) are comprised of polymers which are long molecules made up of the same or similar subunits covalently linked together.

• The subunits that are linked together are called monomers.

Macromolecules

• The synthesis and breakdown of macromolecules is governed by a series of condensation/dehydration or hydrolysis reactions.

Condensation Reactions

• In a condensation reaction (aka a dehydration reaction) monomers are added to a growing polymer and a water molecule is given off--hence the name dehydration reaction.

• These reactions require energy and the action is carried out by enzymes.

Hydrolysis

• Hydrolysis is the process that adds a water molecule to a polymer giving one of the monomers.

• This occurs during digestion and it makes the large molecules useable by our bodies by producing smaller subunits that our cells can uptake.

• The four main types of macromolecules can be broken down further and analyzed.

Carbohydrates• Carbohydrates are molecules

consisting of carbon, hydrogen, and oxygen.

• The three classifications are monosaccharides or simple sugars, disaccharides or double sugars, and polysaccharides which are 3 or more sugars linked together forming a sugar polymer.

• They are involved in storage functions, structural functions, and cell recognition functions.

Monosaccharides

• Monosaccharides generally have the formula CnH2nOn.

• C6H12O6, for example.

Disaccharides• A disaccharide, such as sucrose and

lactose are joined together by a glycosidic linkage--a covalent bond between 2 monosaccharides by a dehydration reactions.

Disaccharides

• The fruit of a plant is often a great source of sucrose (the most common disaccharide) consists of glucose and fructose.

• It’s the most common because as the plants form it during photosynthesis, this is where it gets stored.

Polysaccharides

• When monosaccharides are glycosidically linked together thousands of times, polysaccharides are formed.

• There are 3 main types of polysaccharides, structural, storage, and those involved in cell to cell recognition.

Structural or Storage?

• There are actually 2 forms of glucose, α and β, and the form is determined by the placement of a hydroxyl group.

Structural or Storage?

• In α-glucose, the -OH group is below the ring structure and in β-glucose, it is above the ring structure.

Structural Polysaccharides

• In structural polysaccharides, strong materials are built to provide strength and support for the organism.

• A good example of this is cellulose.

Structural Polysaccharides

• Plant cell walls are comprised of cellulose which gives them strength. Some animals such as cows can digest cellulose, but humans can’t.

• For us, it is called “insoluble fiber” and is found in many fruits and vegetables.

Storage Polysaccharides• Although the starch and cellulose

molecules are comprised of glucose molecules, the different types of glucose give them vastly different uses.

• For example starch can be used by humans for food, cellulose can’t.

Storage Polysaccharides• There are two

main types of storage polysaccharides: That which is found in plants (starch), and that which is found in animals (glycogen).

• Glycogen is branched, and starch is helical.

Proteins• Proteins are another

class of macromolecules consisting of many monomers linked together by peptide bonds forming polymers.

• Enzymes are protein polymers that act as catalysts within cells.

Proteins• Polymers of amino acids are called

polypeptides and the same 20 amino acids form all polypeptides.

• Proteins consist of one or more of the polypeptides coiled into a specific conformation.

Proteins• Amino acids are

organic molecules containing a carboxyl group and an amino group.

• These are each bounded to a central carbon atom which also has an amino acid attached to it.

α carbon

Amino Group

Carboxyl Group

Proteins

• There are 2 groups that are linked together to form a peptide bond.

• A peptide bond is a dehydration reaction which links the amino group of one amino acid to the carboxyl group of a different amino acid yielding water in the process.

Proteins

• Once amino acids are added to the polypeptide, they begin to interact with the other amino acids on the growing polypeptide.

• The sequence then determines the 3D conformation the protein will take.

• The conformation of the protein determines how it will function.

Proteins

• An enzyme is an example and the conformation it takes determines how it functions when it interacts with a substrate.

• There are 4 different types of protein structure: 1°, 2°, 3°, and 4°.

Proteins--Primary Structure

• The primary structure is the specific sequence of amino acids.

Proteins--Secondary Structure

• The secondary structure of the polypeptide is the coiled and/or folded patterns that emerges as the amino acids begin to interact with one another (H-bonds) not from the R-groups, but from the backbones of the amino acids.

Proteins--Secondary Structure

• There are two main types of secondary protein structure, the α-helix and the β-pleated sheet.

• The α-helix is a delicate coil held together by H-bonds.

• The β-pleated sheet forms when 2 polypeptides are aligned side by side and hydrogen bond along their lengths.

Proteins--Tertiary Structure

• The tertiary structure of the protein is due to the interactions of the R-groups on the amino acids.

Proteins--Quaternary Structure

• The quaternary structure of a protein occurs when 2 or more polypeptide chains interact with each other to form a large, functional protein.

Nucleic Acids

• Nucleic acids store and transmit information about a protein’s primary structure.

• There are 2 types of nucleic acids: RNA and DNA.

• DNA provides the necessary information for guiding its own replication.

• It also guides RNA synthesis and using RNA controls protein synthesis.

Nucleic Acids

• DNA is the information that controls the cell. This information is used to create messenger RNA that interacts with the cells protein synthesizing machinery (ribosomes) to create the proteins that run the cell.

• DNA--> RNA --> Protein

Lipids

• There are three classes of lipids:

• Fats (Fatty acids)• Phospholipids

• Steroids

• Waxes

Lipids

• Lipids are not polymers, they are long chain fatty acids attached via a dehydration reaction to a glycerol head.

Lipids

• The fatty acid portion is a long hydrocarbon usually 16 to 18 carbons in length.

• These portions are hydrophobic and this makes fats hydrophobic.

• Fatty acids can be classified as saturated or unsaturated as we often hear about in nutrition.