Building Blocks of Life An Introduction

Carbon—The Backbone of Biological Molecules

• Carbon is unparalleled in its ability to form large, complex, and diverse molecules

• Proteins, DNA, carbohydrates, and other molecules that distinguish living matter are all composed of carbon compounds

Carbon atoms can form diverse molecules by bonding to four other atoms

Electron configuration determines the kinds and number of bonds an atom will form with other atoms

With four valence electrons, carbon can form four covalent bonds with a variety of atoms◦makes large, complex molecules possible

The valences of carbon and its most frequent partners (hydrogen, oxygen, and nitrogen) are the “building code” that governs the architecture of living molecules

Macromolecules

Within cells, small organic molecules are joined together to form larger molecules

Macromolecules are large molecules composed of thousands of covalently connected atoms

polymers built from monomers

• Monomers build polymers linked together by covalent bonds

• Three of the four classes of life’s organic molecules are polymers:◦Carbohydrates◦Proteins◦Nucleic acids◦Lipids

The Synthesis and Breakdown of Polymers

Monomers form larger molecules by condensation reactions called dehydration reactions

Polymers are disassembled to monomers by hydrolysis, a reaction that is essentially the reverse of the dehydration reaction

Short polymer Unlinked monomer

Dehydration removes a watermolecule, forming a new bond

Dehydration reaction in the synthesis of a polymer

Longer polymer

Hydrolysis adds a watermolecule, breaking a bond

Hydrolysis of a polymer

Carbohydrates

Sugars and sugar polymersMonosaccharides

◦Simple sugars◦glucose

Carbonyl group

Hydroxyl group

Carbohydrates

Disaccharides◦2 or more monosaccharides joined by glycosidic

linkage, covalent bond by dehydration reaction◦Glucose + fructose sucrose

Carbohydrates

Storage◦Plant starch◦Stored energy can be broken down by

hydrolysis into glucose◦Animal polysaccharide

Glycogen◦Stored in liver and muscles◦Used for short term energy

Carbohydrates

Structure ◦Cellulose: cell walls

Requires an enzyme for animals to break it down◦Chitin: exoskeleton of arthropods and fungi

Lipids

Fats, oils, waxes◦Mix poorly with water◦Fats

Large molecules of glycerol and fatty acid chains connected by dehydration

Lipids

Cell Membranes◦Phospholipid bi-layer

Proteins

Polymer of amino acids called polypeptidesFunctions

◦Enzymes◦Storage of amino acids◦Hormones◦Motor◦Defense◦Transport◦Receptors for chemical stimuli◦structure

Proteins

Amino acids◦20 amino acids from 1000’s of proteins◦Side chains “R” determines the properties

Hydrophillic:polar Hydrophobic: non polar Hydrophillic: electric charge

Proteins

Structure◦1°

Linear chain

Proteins

2°◦Alpha helix: hair◦β pleated sheets: spider web◦Held together by hydrogen bonds between

amino groups

Proteins

3°◦Interactions between side chains “R”

Hydrogen bonds Ionic bonds Disulfide bonds Van der Waals

Proteins

4°◦Aggregation of polypeptide subunits

Collagen hemoglobin

Proteins

Denaturation◦Weak chemical bonds and interactions can be

destroyed Heat pH

Nucleic Acids

Polymer of nucleotides◦DNA and RNA