Proteins, Carbohydrates and Fats

Learning Goals Student will be able to: 1) Understand that the building blocks of living organisms are polymers 2) Explain the formation of proteins, simple carbohydrates and fats from biological monomers

Success Criteria Students will be able to: 1) explain how proteins are constructed from amino acids through a peptide bond (amide link) 2) explain how carbohydrates such as starch and cellulose are created from simple sugars and disaccharides. 3) explain how fats and oils are created from triglycerides and fatty acids

Natural Polymers biological macromolecules – proteins, carbohydrates, nucleic acids, fats and lipids of high molecular mass have a variety of physical and chemical properties the smaller monomers (amino acids, simple sugars, glycerol and fatty acids) tend to be soluble which allows them to be transported in our blood. the polymers are solids and form the structures of our body

Proteins – Natural Polyamides proteins make up about one half of our dry body weight – muscles, skin, cartilage, tendons, nails and protein molecules like hemoglobin and enzymes. All proteins are constructed from the same set of monomers called amino acids. there are 20 amino acids (see the diagram). You will need to understand these in more detail in Biology. As the name suggests amino acids contain two functional groups amines and carboxylic acids.

Amino Acids note the amine group and the carboxylic acid group in the generalized amino acid structure above Find the amine and carboxylic acid functional groups in these 8 simple amino acids.

Amino Acids amino acids that our bodies cannot synthesize are called essential amino acids. These amino acids must be obtained by eating.

Amino Acids See page in Nelson 12 There are 20 amino acids in total. Notice the amine group (NH 2 or NH 3 + ) and the carboxylic acid group (COOH, COO - ) on each amino acid.

Amino Acids Line Drawings Notice the amine group (NH 2 or NH 3 + ) and the carboxylic acid group (COOH, COO - ) on each amino acid.

Formation of proteins from amino acids The carboxylic acid group of one amino acid links with amine group of another amino acid in a condensation reaction. The link is called a peptide bond, however you learned it earlier as the amide link. A dipeptide is formed from the reaction of two amino acids

Formation of proteins from amino acids The first diagram shows glycine reacting with alanine. The second diagram shows a few repeats of amino acids.

…eventually enough amino acids link up to form a protein This is called the primary protein structure

Chiral Molecules

Protein Structure Primary Structure of Proteins – a polymer chain formed by linked amino acids (see previous page) Secondary Structure of Proteins - if you noticed from the chart of 20 amino acids that some have polar and non-polar groups. These groups attract each other (Van der Waals, H-bonds, etc.) to form either an alpha helix (like DNA) or a beta-pleated 2- dimensional sheet.

The tertiary structure developing from the secondary and primary protein structure.

Protein Structure Tertiary Structure of Proteins – the alpha helix and pleated sheets attract each other causing the protein to coil into “twisted ribbon” shapes. Proteins like hemoglobin and hormones twist into tight “balls” or “globular shapes so that they can pass through narrow blood vessels. Quaternary Structure of Proteins – several tertiary structures attract each other to form complexes. Hemoglobin is formed from 4 tertiary protein sub- units.

Denaturing of Proteins Denaturing is the breakdown of proteins caused by the breaking of weaker bonds like Van der Waals forces and H-bonds. Denaturing is caused by heating, change of pH, addition of organic solvents (acetone, formaldehyde, etc.) The function of the protein is severely disrupted – bonds within the tertiary and secondary structures of proteins is lost along with its 3-D structure.

Polymers of Sugar Carbohydrates have the formula C x (H 2 O) y, which explains the derivation of the name – “hydrated carbon” Glucose is C 6 H 12 O 6 or C 6 (H 2 O) 6 is a simple sugar called a monosaccharide.

Monosaccharide structure Monosaccharides fall into 2 groups – aldoses like glucose because they have an aldehyde group (like glucose) and ketoses because they have a ketone group (like fructose) 3 simple monosaccharides often found in food. Notice that they have 6 carbons (hexoses). Some monosaccharides have 5 sugars (riboses)

Monosaccharide structure This shows monosaccharides in their more correct ring structures.

Disaccharides Disaccharides form when monosaccharides combine in a condensation reaction. Table sugar is sucrose. Enzymes are used to break down disaccharides in the body. people who lack the enzyme lactase cannot break down the sugar lactose

Polysaccharides Carbohydrates can be subdivided into three levels based on their number of saccharide molecules – mono-, di- and polysaccharides. Polysaccharides are long polymer chains of saccharides.

Polysaccharides The three most common polysaccharides are starch, cellulose and glycogen.

Starch and Glycogen Starches are the main energy storage for plants such as rice, corn or wheat (seeds) and potatoes or carrots (tubers) Starch is a polymer of glucose. Glycogen is produced by animals as a ready energy source Glycogen is stored in muscles and the liver. Our digestive tracts have enzymes that can break down starch and glycogen.

Cellulose Cellulose is also a polymer of glucose but there are different linkages. Cellulose is produced by plants for support. It is insoluble. Humans cannot digest cellulose – we often refer to it as dietary fiber Animals such as ants and cows digest cellulose with the aid of bacteria in their guts.

Nucleic Acids

Fats and Oils Fats and oils are triglycerides which are esters formed from an alcohol (glycerol) and long- chained carboxylic acids called fatty acids. Glycerol is an alcohol with 3 carbons and 3 –OH groups. 3 fatty acid chains are attached to the glycerol – they may or may not be the same fatty acid – usually they are different

Forming Fats Fatty acids usually have even numbers in the body as they are formed from successive addition of ethanoic acid molecules in a cyclic reaction. Fatty acids (which are long chain carboxylic acids) then react with glycerol (a polyalcohol) to form fats by creating an ester link.

Lipids Lipids are formed when glycerol (a polyalcohol) reacts with fatty acids Ester bonds are formed between the alcohol group of glycerol and the carboxylic acid group of the fatty acid. Monoglyceride = glycerol + 1 fatty acid Diglyceride = glycerol + 2 fatty acids Triglyceride = glycerol + 3 fatty acid – most fats fall into this category

Saturated vs. Unsaturated Fats

If there are double bonds somewhere along the carbon chain of a fatty acid, it is unsaturated. If there are no double bonds, the fatty acid or fat is saturated. unsaturated fats are mostly better for your health because they are easier for our bodies to digest. Mono-unsaturated fatty acid is a fatty acid that has just one double bond. Polyunsaturated fatty acids have multiple double bonds.

Saturated vs. Unsaturated Fats The cis-isomer introduces a kink into the molecule that prevents the fats from stacking efficiently as in the case of fats with saturated chains. This decreases intermolecular forces between the fat molecules, making it more difficult for unsaturated cis-fats to freeze; they are typically liquid at room temperature. Trans fats may still stack like saturated fats, and are not as susceptible to metabolization as other fats.

How are Hydrogenated Trans-Fats Made? The process of hydrogenation forms saturated fats (artificially) by blasting the polyunsaturated vegetable oil with hydrogen atoms forming a trans-fat. This is called hydrogenation. A hydrogen atom is bound to the backbone of the fat, making it more stable and even solid at room temperature. This solid, creamy substance has an unnatural chemical distribution rarely found in nature. In fact, these fats are actually too stable and our body even has trouble breaking them down.