The Chemical BuildingBlocks of Life

Chapter 3

Adapted by G. Cornwall, Ph.D. From Raven’s Biology, McGraw Hill Publishing

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Carbon• Framework of biological

molecules consists primarily of carbon bonded to – Carbon– O, N, S, P or H

• Can form up to 4 covalent bonds• Hydrocarbons – molecule

consisting only of carbon and hydrogen– Nonpolar– Functional groups add chemical

properties

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Isomers• Molecules with the same

molecular or empirical formula– Structural isomers– Stereoisomers – differ in

how groups attached• Enantiomers

– mirror image molecules– chiral– D-sugars and L-amino

acids

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Macromolecules• Polymer – built by linking

monomers• Monomer – small,

similar chemical subunits

• Three things to keep track of in all four macromolecules– What is the Monomer – What is the Polymer– What is Bond

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• Dehydration synthesis– Formation of large molecules by the removal of water– Monomers are joined to form polymers

• Hydrolysis– Breakdown of large molecules by the addition of

water– Polymers are broken down to monomers

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Carbohydrates

• Molecules with a 1:2:1 ratio of carbon, hydrogen, oxygen

• Empirical formula (CH2O)n

• C—H covalent bonds hold much energy– Carbohydrates are good energy storage

molecules– Examples: sugars, starch, glucose

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Monosaccharides

• Simplest carbohydrate• 6 carbon sugars play important roles

• Glucose C6H12O6

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• Fructose is a structural isomer of glucose• Galactose is a stereoisomer of glucose• Enzymes that act on different sugars can

distinguish structural and stereoisomers of this basic six-carbon skeleton

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Disaccharides

• 2 monosaccharides linked together by dehydration synthesis

• Used for sugar transport or energy storage

• Examples: sucrose, lactose, maltose

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Polysaccharides• Long chains of monosaccharides

– Linked through dehydration synthesis

• Energy storage– Plants use starch– Animals use glycogen

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Polysaccharides

• Structural support– Plants use cellulose– Arthropods and fungi use chitin

Nucleic acids

• Polymer – nucleic acids• Monomers – nucleotides

– sugar + phosphate + nitrogenous base

– sugar is deoxyribose in DNA or ribose in RNA

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– Nitrogenous bases include• Purines: adenine and guanine• Pyrimidines: thymine, cytosine, uracil

– Nucleotides connected by phosphodiester bonds

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Deoxyribonucleic acid (DNA)• Encodes information for

amino acid sequence of proteins– Sequence of bases

• Double helix – 2 polynucleotide strands connected by hydrogen bonds– Base-pairing rules

• A with T (or U in RNA)• C with G

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Ribonucleic acid (RNA)

• RNA similar to DNA except– Contains ribose instead of

deoxyribose– Contains uracil instead of

thymine

• Single polynucleotide strand

• RNA uses information in DNA to specify sequence of amino acids in proteins

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Other nucleotides

• ATP adenosine triphosphate– Primary energy currency of the cell

• NAD+ and FAD+

– Electron carriers for many cellular reactions

Card Quiz A

The addition of water to break a chemical bond is termed –

Dehydration synthesis Hydrolysis Condensation Disassociation

Card Quiz A

The monomers of DNA are covalently bonded together. These bonds are called phosphodiester bonds.

This is true This is false

Card Quiz A

Which of the following is not part of a nucleotide? 5 carbon sugar Phosphate group Fatty acid chain Nitrogenous base

Card Quiz A

Dehydration synthesis – Is used to link monomers Removes water to form bonds Is involved in protein synthesis All of the above

Card Quiz A

If a strand of DNA has a sequence ATCCTAG, what would be the complementary sequence?

CGAAGAT TAGGATC TACCGGA CGAAGTC

Card Quiz Answers

Blue Green Red

Yellow Red

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ProteinsProtein functions include:

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• Proteins are polymers– Composed of 1 or more long, unbranched chains– Each chain is a polypeptide

• Amino acids are monomers• Amino acid structure

– Central carbon atom– Amino group– Carboxyl group– Single hydrogen– Variable R group

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• Amino acids joined by dehydration synthesis– Peptide bond

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• Polypeptide chains fold in various ways to form the final 3-D shape

• The shape of a protein determines its function

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4 Levels of protein structure1. Primary structure – sequence of amino

acids (beads on a string)

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1. Secondary structure – interaction of groups in the peptide backbone helix sheet

3. Tertiary structure – final folded shape of a globular protein

– Stabilized by a number of forces– Final level of structure for proteins consisting

of only a single polypeptide chain

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4. Quaternary structure – arrangement of individual chains (subunits) in a protein with 2 or more polypeptide chains

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Additional structural characteristics

• Motifs – Common elements of secondary structure

seen in many polypeptides– Useful in determining the function of unknown

proteins

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• Domains– Functional units within a larger structure– Most proteins made of multiple domains that

perform different parts of the protein’s function

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• Once thought newly made proteins folded spontaneously

• Chaperone proteins help protein fold correctly

• Deficiencies in chaperone proteins implicated in certain diseases– Cystic fibrosis is a hereditary disorder

• In some individuals, protein appears to have correct amino acid sequence but fails to fold

Chaperones

Denaturation

• Protein loses structure and function

• Due to environmental conditions– pH– Temperature– Ionic concentration of

solution

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Lipids

• Loosely defined group of molecules with one main chemical characteristic– They are insoluble in water

• High proportion of nonpolar C—H bonds causes the molecule to be hydrophobic

• Fats, oils, waxes, and even some vitamins

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Fats• Triglycerides

– Composed of 1 glycerol and 3 fatty acids

• Fatty acids – Need not be identical– Chain length varies– Saturated – no double bonds between carbon

atoms• Higher melting point, animal origin

– Unsaturated – 1 or more double bonds• Low melting point, plant origin

– Trans fats produced industrially

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Phospholipids• Composed of

– Glycerol– 2 fatty acids – nonpolar “tails”– A phosphate group – polar “head”

• Form all biological membranes

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• Micelles – lipid molecules orient with polar (hydrophilic) head toward water and nonpolar (hydrophobic) tails away from water

• Phospholipid bilayer – more complicated structure where 2 layers form– Hydrophilic heads point outward– Hydrophobic tails point inward toward each

other

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Other Kinds of Lipids

Card Quiz B

What is the function of chaperonin proteins? Denaturation of polypeptides Assembling amino acids Regulation of gene expression Folding proteins

Card Quiz B

Which lipid forms membranes? Triglycerides Steroids Phospholipids Terpenes

Card Quiz B

Which of the following is not a function of proteins? Catalyzes chemical reactions Transport of material Structural components of tissues All of the above are protein functions

Card Quiz B

Which of the following is an amino group? -OH -C=O -COOH -NH2

Card Quiz B

Lincosamides are a class of antibiotics that inhibit peptide bond formation. What type of biological molecule would be effected?

Lipids Proteins Nucleic Acids Carbohydrates

Card Quiz B

What happens when a lipid is hydrogenated? Hydrogen is added to the fatty acid chains The melting point is raised The lipid is converted into a saturated fat The fatty acid chain is straightened All of the above

Card Quiz Answers

Yellow Red

Yellow Red

Yellow Green