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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