Biology 112 Chapter 5 Macromolecules

All living things are made up of four classes of large biological molecules: carbohydrates, lipids, proteins, and nucleic acids Molecular function relates to molecular structure Diversity of molecular structure is the basis for the diversity of life.

Most macromolecules are Polymers Polymer = Large molecule consisting of many identical or similar subunits (monomers) connected together. Three of the four classes of life’s organic molecules are polymers: Carbohydrates Proteins Nucleic acids

Synthesis of Polymers Condensation (dehydration) reactions = polymerization reactions during which monomers are covalently linked. This produces a net removal of one water molecule for each covalent linkage formed.

Breakdown of Polymers Hydrolysis = reaction process that breaks covalent bonds between monomers by the addition of water molecules.

Unity and Diversity A limitless variety of polymers can be built from a small set of monomer building blocks. Each cell has thousands of different kinds of macromolecules Macromolecules vary among cells of an organism, vary more within a species, and vary even more between species. Unity…only about common monomers are used Diversity…emerges as these universal building blocks are arranged in different ways.

Carbohydrates Carbohydrates include sugars and the polymers of sugars The simplest carbohydrates are monosaccharides, or single sugars Monosaccharides Major nutrient for cells. Glucose is most common. Can be produced by photosynthesis from CO 2, H 2 O and sunlight. Energy stored in their chemical bonds which is harvested by cellular respiration. Their carbon “skeletons” are the raw material for other organic molecules Are the monomers for polysaccharide polymers Many form ring structures in aqueous solutions

Disaccharides A disaccharide is formed when a dehydration reaction joins two monosaccharides This covalent bond is called a glycosidic linkage.

Polysaccharides Storage Polysaccharides Starch Glycogen Structural Polysaccharides Cellulose Chitin

Lipids Lipids are the one class of large biological molecules that do not form polymers The unifying feature of lipids is having little or no affinity for water. They are hydrophobic. They are nonpolar. Lipids are hydrophobic because  they consist mostly of hydrocarbons, which form nonpolar covalent bonds The most biologically important lipids are fats, phospholipids, and steroids

Fats Fats are constructed from two types of smaller molecules: glycerol and fatty acids Glycerol is a three-carbon alcohol with a hydroxyl group attached to each carbon A fatty acid consists of a carboxyl group attached to a long carbon skeleton In a fat, three fatty acids are joined to glycerol by an ester linkage, creating a triacylglycerol, or triglyceride

Fat synthesis

Saturation Fatty acids vary in length (number of carbons) and in the number and locations of double bonds Saturated fatty acids have the maximum number of hydrogen atoms possible and no double bonds Unsaturated fatty acids have one or more double bonds

Fats made from saturated fatty acids are called saturated fats, and are solid at room temperature. (Most animal fats are saturated) Fats made from unsaturated fatty acids are called unsaturated fats or oils, and are liquid at room temperature. (Plant fats and fish fats are usually unsaturated) A diet rich in saturated fats may contribute to cardiovascular disease through plaque deposits Hydrogenation is the process of converting unsaturated fats to saturated fats by adding hydrogen Hydrogenating vegetable oils also creates unsaturated fats with trans double bonds These trans fats may contribute more than saturated fats to cardiovascular disease

Functions of Fats: Energy storage! A high energy compact form of fuel storage. Insulates against heat loss Cushions some vital organs in mammals (Kidneys)

Phospholipids Composed of glycerol, 2 fatty acids and a phosphate group ( and usually an additional chemical group attached to the phosphate. Hydrophilic heads Hydrophobic tails Spontaneously form a phospholipid bilyer in an aqueous environment Major constituents of biological membranes.

Phospholipids

Steroids Some hormones are steroids. (estrogen, testosterone) Steroids are common components of animal membranes (cholesterol)

Proteins Polypeptides = polymers of amino acids in a specific sequence that are linked by peptide bonds. Amino acids Carboxyl group Amino group A variable R group specific to each amino acid. The physical and chemical properties of these groups give the uniqueness to each amino acid. (polar/nonpolar ; charged/uncharged ; acidic/basic) 20 common amino acids

Amino Acids

Peptide bonds

Protein structure A protein’s function depends upon its unique conformation!!!! 4 levels of protein structure Primary --unique A.A. sequence Secondary-- regular repeated coiling or folding Alpha helix Beta pleated sheet Tertiary -- irregular contortions due to bonding between side chains (R groups) Weak interactions Hydrogen bonds Ionic bonds Hydrophobic interactions Covalent bonds – Disulfide bridges Quaternary -- results when two or more polypeptide chains form one macromolecule

Primary structure

Secondary structure

Tertiary structure

Quaternary structure

Denaturation Denaturation = a process that alters a protein’s native conformation and biological activity.

Protein Functions

Sickle-Cell Disease A slight change in primary structure can affect a protein’s structure and ability to function Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin

Nucleic Acids Nucleic acids are polymers of nucleotides linked together by condensation reactions. (DNA and RNA)

Nucleotides Nucleotides are composed of : 5-carbon sugar phosphate group nitrogenous base Pyrimidines Cytosine Thymine Uracil Purines Adenine Guanine Nucleotide functions: monomers for nucleic acids transfer of chemical energy (ATP) act as electron acceptors

The Roles of Nucleic Acids There are two types of nucleic acids: Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA) DNA provides directions for its own replication DNA directs synthesis of messenger RNA (mRNA) and, through mRNA, controls protein synthesis Protein synthesis occurs in ribosomes

Inheritance is based on the precise replication of DNA

Evolution DNA and Proteins can serves as measures of evolution The more closely related species have more similar sequences of DNA and therefore also more similar proteins.