Topic 2. The Molecules of Life

I. Carbon and the Molecular Diversity of Life

September 19, 2005 Biology 1001

Putting Life In Its Chemical Context

96% of living matter is made up of 4 elements – C, O, H, and N

The Importance of Carbon Carbon enters the biosphere by photosynthesis from CO2

Carbon forms large, complex, and diverse molecules

The macromolecules of life - proteins, carbohydrates, lipids, & nucleic acids - are all compounds of carbon bonded to O, H, N, S, P & other elements

The versatility of carbon underlies biological diversity

The study of the compounds of carbon is called organic chemistry

The Properties of Carbon

• The carbon atom has 4 electrons in its outermost energy shell, a property called tetravalenceThis electron configuration gives carbon covalent

compatibility with many different elements

Carbon forms molecules that can branch in up to four directions

Carbon also forms double and triple covalent bonds

A diverse array of molecules is possible - like these hydrocarbons

Carbon’s Versatile Electron Configuration

Isomers – Another Level of Diversity

Molecules with the same molecular formula but different structures and properties

There are structural isomers, geometric isomers, and enantiomers of carbon compounds

Structural

Geometric

Enantiomers

Organic Polymers Another level in the hierarchy of biological organization is

reached when small organic molecules are joined together to form macromolecules Macromolecules are giant molecules composed of 1000’s

of atoms covalently bonded together

Most macromolecules are polymers, composed of monomers Three of the classes of organic molecules are polymers –

carbohydrates, proteins and nucleic acids The fourth class, lipids, are complex macromolecules but

not technically polymers

Carbohydrates The Monomers

Simple sugars or monosaccharides Glucose, fructose, galactose

Double sugars or disaccharides Sucrose, maltose, lactose

The Polymers Polysaccharides

Starch, glycogen, cellulose, chitin Functions of Carbohydrates

Fuel for cellular respiration – the mono- and disaccharides Storage of fuel – Starch (plants) & glycogen (animals) Structural support – cellulose (plants) & chitin (animals)

The Structure of CarbohydratesMono- and Disaccharides

Polysaccharides

Proteins The Monomers

Amino acids

The Polymers Polypeptides Proteins

Protein Functions Enzymes, support, transport, storage, hormones, cell receptors, movement, antibodies

Eg. Transport - Hemoglobin

Eg. Enzyme - Lysozyme

Eg. Structural protein – Spider silk

Nucleic Acids The Monomers

The nucleotides – Adenine, Guanine, Cytosine & Thymine or Uracil

The Polymers The polynucleotides - Deoxyribonucleic Acid

(DNA) & Ribonucleic Acid (RNA)

Functions DNA stores & transmit hereditary information DNA & RNA are required for protein synthesis

The Structure of Nucleic Acids

Lipids Large hydrophobic molecules with diverse

functions

Three biologically important groups: the fats, the phospholipids, and the steroids

The functions of lipids Long-term energy storage (fats) Components of cell membranes (phospholipids & the

steroid cholesterol) Hormones (steroids)

The Structure of Lipids

FATSPhospholipids

Cholesterol

Topic 2. The Molecules of LifeII. The Origin of Life

September 21, 2005 Biology 1001

A Four-Stage Hypothesis Scientists hypothesize that chemical and physical

processes on the early Earth led to the formation of very simple living cells in four phases:

1. The abiotic synthesis of small organic molecules2. The joining of these small molecules (monomers) into

polymers3. The packaging of these molecules into “protobionts”,

small droplets with membranes that maintain an internal chemistry different from the environment

4. The origin of self-replicating molecules that would make inheritance possible

Stage 1 – A Testable Hypothesis

The Oparin-Haldane Hypothesis

In the 1920’s, A.I. Oparin and J.B.S. Haldane independently hypothesized that the Earth’s early atmosphere had been an electron-adding (reducing) environment in which organic molecules could have formed from inorganic precursors.

Stage 1 – A Testable HypothesisThe Miller-Urey Experiment Figure 26.2

Inquiry: Can organic molecules form in reducing atmosphere?

Experiment: Set up conditions in laboratory thought to have existed on Early Earth. A reducing atmosphere of H2, CH4, NH3 and water vapour. A warmed flask as the primerval sea. Sparks as lightning. A condenser to cool the atmosphere and simulate rain.

Results: A variety or organic compounds including amino acids.

Conclusion: Organic molecules, the first step in the origin of life, can form in a reducing atmosphere.

The Early Earth – A Reducing Atmosphere?