Chapter 3

MOLECULES OF LIFE

Molecules of life-From structure to function

� Molecules of life are organic compounds� Contain carbon and at least one hydrogen

atom and have one or more functional group

Carbon’s Bonding Behavior� Versatile bonding behavior� Most organic compound have a carbon back

bone to which functional group is attached

An Organic Compound: Glucose� Four models

Molecules of life-From structure to function

Functional Group

� They are common in carbohydrates, lipids, and nucleic acids

� The seven functional groups that are most important in the chemistry of life:� Hydroxyl group

� Carbonyl group

� Carboxyl group

� Amino group

� Sulfhydryl group

� Phosphate group

� Methyl group

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Functional Groups

Molecules of life-From structure to function

What cells Do To Organic compoundsMetabolism- Activities by which cells acquire and use

energyMetabolic Reactions

Condensation– Two molecules covalently bond into a larger oneHydrolysis – Reverse of condensationA molecule splits into smaller ones

Condensation and Hydrolysis

Molecules of life-From structure to function

� Monomer – Small molecules that are repeating subunits in a polymer

� Example. Sugar is a monomer of starch

Carbohydrates – The most abundant ones

Carbohydrates – they are organic compounds that consist of Carbon, Hydrogen, Oxygen in a 1:2:1 ratio

Carbohydrates

Monosaccharides Oligosaccharides Polysaccharides

Carbohydrates – The most abundant ones

Monosaccharides (one sugar unit) � simplest carbohydrates

� have at least two hydroxyl group, one ketone or aldehyde group bonded to a carbon backbone

� most are water soluble

Simple Sugars: Glucose and Fructose

Carbohydrates – The most abundant ones

Oligosaccharides� Short chain carbohydrate

� Example. Formation of Sucrose molecule

Oligosaccharides: Sucrose

Carbohydrates – The most abundant ones

Polysaccharide (complex carbohydrate)� They are straight or branched chains of many

monomers

� Example :� Starch – plant polysaccharide

� Glycogen – animal polysaccharide

� Cellulose – plant cell wall

� Chitin – exoskeleton of arthropods

Chloroplast

(b) Glycogen: an animal polysaccharide

Starch

GlycogenAmylose

(a) Starch: a plant polysaccharide

Amylopectin

Mitochondria Glycogen granules

0.5 µm1 µm

Complex Carbohydrates: Bonding Patterns

Starch Cellulose

Complex Carbohydrates: Starch, Cellulose, and Glycogen

Complex Carbohydrates: Chitin

Greasy, Oily – Must be LipidsLipids

� They are fatty, oily or waxy organic compounds that are insoluble in water

� Many lipids incorporate fatty acids

Fats� They are lipids with one, two or three fatty acids

� Triglycerides� Have three fatty acid tail linked to glycerol

� Example : Most neutral fats such butter and vegetable oil

Fatty Acids

glycerol

three fatty acid tails Triglyceride, a neutral fat

Greasy, Oily – Must be Lipids� Saturated fat

� Fatty acid backbone with a single covalent bond� Solid at room temperature� Example : Animal fat, butter

� Unsaturated fat� Fatty acids with one or more double covalent

bonds� Liquid at room temperature� Example : Vegetable oil

Greasy, Oily – Must be Lipids� Phospholipids

� They have a polar head with a phosphate in it and two non polar fatty acid tails

� Abundant in cell membrane

� Waxes� They are firm water-repellent lipids with long

tightly packed fatty acid tails bonded to long chain alcohols or carbon rings

Phospholipids� Main component of

cell membranes � Hydrophilic head,

hydrophobic tails

Greasy, Oily – Must be Lipids� Cholesterols and other sterols

� Lipids with a rigid backbone of four carbon rings

� No fatty acid tails

� All eukaryotic cell membranes contain sterols

� In animal tissue cholesterol is most common

Sterols: Cholesterol� Membrane components; precursors of other

molecules (steroid hormones)

Proteins – Diversity in structure and Function

Protein� It is an organic compound composed of one

or more chains of amino acids

� Amino acids

� They have an amino group, carboxyl group, a hydrogen atom, and an R group

� R group is different for each amino acid

Protein Structure� Built from 20 kinds of amino acids

Proteins – Diversity in structure and Function

� A protein is formed by condensation of amino acids

� Peptide bond joins the amino group of one amino acid with a carboxyl group of other

� Polypeptide – A chain with several amino acids

Protein Synthesis

Proteins – Diversity in structure and Function

Levels of Protein StructurePrimary Structure � Unique sequence of amino acids

Secondary Structure� Polypeptide chains form sheets and coils

Tertiary Structure� Sheets and coils pack into functional domains

a Protein primarystructure: Aminoacids bonded in apolypeptide chain.

Proteins – Diversity in structure and Function

b Protein secondarystructure: A coiled(helical) or sheet likearray, held in placeby hydrogen bonds( dotted lines) betweendifferent parts of thepolypeptide chain.

helical coil sheet

c Protein tertiary structure: A chain’s coiled parts, sheetlikearrays, or both have folded and twisted into stable, functionaldomains, including clusters, pockets, and barrels.

barrel

Proteins – Diversity in structure and Function

Quaternary Structure� Two or more polypeptide chains bond

together� Example – Enzymes, Hemoglobin� Other protein structures

� Glycoproteins� Lipoproteins� Fibrous proteins

d Protein quaternarystructure: Many weakinteractions hold twoor more polypeptidechains together asa single molecule.

Importance of Protein Structure� Changes in amino acid sequence have drastic

consequences

� Sometimes a mutation in DNA results in an amino acid substitution that alters a protein’s structure and compromises its function� Example: Hemoglobin and sickle-cell anemia

Importance of Protein StructureHemoglobin� An oxygen transport protein in red blood

cells

� Four Globin chains -2 alpha globin,2 beta globins

� Globin chains holds a iron containing hemegroup

alpha globin

beta globin beta globin

alpha globin

b Hemoglobin is one of the proteins with quaternar y structure. Itconsists of four globin molecules held together by h ydrogen bonds.To help you distinguish among them, the two alpha g lobin chainsare shown here in green, and the two beta globins a re in brown.

Sickle-Cell Mutation

VALINE HISTIDINE LEUCINE GLUTAMATEVALINETHREONINE PROLINE

sickle cell

normal cell

b One amino acid substitution results in theabnormal beta chain in HbS molecules. Insteadof glutamate, valine was added at the sixthposition of the polypeptide chain.

c Glutamate has an overall negative charge; valinehas no net charge. At low oxygen levels, this difference gives rise to a water-repellent, sticky patch on HbS molecules. They stick togetherbecause of that patch, forming rod shaped clumps that distort normally rounded red blood cells into sickle shapes. (A sickle is a farm tool that has a crescent-shaped blade.)

Sickle-Cell Mutation

Protein – Denaturation� Protein’s function as long as they stay in

coiled, folded, and packed form.

Denaturation – Unraveling of three dimensional structure by shifts in pH, detergent, heat

� Hydrogen bonds are disrupted

Normal protein Denatured protein

Denaturation

Renaturation

Nucleotides� Function as energy carriers, enzyme helpers,

messengers

� Building block for DNA & RNA

� ATP - Energizes many kinds of molecules by phosphate-group transfers

NucleotidesNucleotide structure, 3 parts:

� Sugar

� Phosphate group

� Nitrogen-containing base

NucleotidesNucleic Acids– DNA & RNA� Single or double stranded chains of nucleotides� DNA (deoxyribonucleic acid)� Double stranded nucleic acid with 4kinds of

nucleotide monomers� Adenine, Guanine, thymine, &Cytosine� Sugar – phosphate forms the back bone and

hydrogen bond between the bases joins the two strand

Nucleotides of DNA

covalentbonding incarbonbackbone

hydrogen bondingbetween bases

NucleotidesRNA (ribonucleic acid)� Four kinds of nucleotide monomers

� Uracil, Adenine, Guanine, Cytosine