The Chemical Building
Blocks of Life
Chapter 3
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
2
3
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
4
Macromolecules
Polymer – built by linking monomers
 Monomer – small, similar chemical subunits

5
Making and Breaking Polymers

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
6
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
7
Monosaccharides






Simplest carbohydrate
6 carbon sugars play important
roles
Glucose C6H12O6
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
8
Disaccharides
2 monosaccharides linked together by
dehydration synthesis
 Used for sugar transport or energy
storage
 Examples: sucrose, lactose, maltose

9
Polysaccharides

Long chains of
monosaccharides
◦ Linked through
dehydration synthesis

Energy storage
◦ Plants use starch
◦ Animals use glycogen

Structural support
◦ Plants use cellulose
◦ Arthropods and fungi use
chitin
10

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
11

Amino acids joined by dehydration synthesis
◦ Peptide bond
12
NONAROMATIC
AROMATIC
Nonpolar
CH3 CH3
CH3
CH3
CH3 CH3
CH
CH2
CH
NH
CH2
C
H C
CH3
CH2
CH2
H3N+ C C O–H3N+ C C O– H3N+ C C O– H3N+ C C O– H3N+ C C O– H3N+ C C O–
H O
Alanine
(Ala)
H O
Valine
(Val)
H O
Leucine
(Leu)
H O
Isoleucine
(Ile)
H O
Phenylalanine
(Phe)
H O
Tryptophan
(Trp)
Polar uncharged
NH2
O
O
OH
CH3
CH2
H
H C
OH
NH2
C
CH2
CH2
CH2
H3N+ C C O–H3N+ C C O– H3N+ C C O– H3N+ C C O– H3N+ C C O–
H O
Glycine
(Gly)
H O
Serine
(Ser)
H O
Threonine
(Thr)
H O
Asparagine
(Asn)
H O
Glutamine
(Gln)
Charged
NH2
C
O–
O
C
O
CH2
C C
HC
C N CH
H
CH2
C
CH2
CH2
H3N+
O–
O–
H O
Glutamic
acid (Glu)
H3N+
C C
NH+
O–
H O
Aspartic
acid (Asp
H3N+ C
C
O–
H O
Histidine
(His)
NH2+
CH2 NH3+
NH
CH2
CH2
CH2
CH2
CH2
CH2
H3N+ C
C
H O
Lysine
(Lys)
O–
OH
C
H3N+
C C O–
CH2
H3N+ C C O–
H O
Tyrosine
(Tyr)
SPECIAL FUNCTION
CH3
S
SH
CH
CH2CH2
2
CH
2
CH2
CH2CH C O–
–
–H3N+ C C O
+
H3N C C O
NH+2
O
H O
H O
Proline
Methionine Cysteine
(Pro)
(Met)
(Cys)
H O
Arginine
(Arg)
13
Proteins
Protein functions include:
1. Enzyme catalysis
2. Defense
3. Transport
4. Support
5. Motion
6. Regulation
7. Storage
14
4 Levels of structure
The shape of a protein determines its function
1. Primary structure – sequence of amino acids
2. Secondary structure – interaction of groups in
the peptide backbone

◦
◦
a helix
b sheet
15
4 Levels of structure
3.
Tertiary structure – final folded shape of
a globular protein
◦
◦
4.
Stabilized by a number of forces
Final level of structure for proteins
consisting of only a single polypeptide chain
Quaternary structure – arrangement of
individual chains (subunits) in a protein
with 2 or more polypeptide chains
16
17
Additional structural characteristics

Motifs
◦ Common elements of secondary structure
seen in many polypeptides
◦ Useful in determining the function of
unknown proteins

Domains
◦ Functional units within a larger structure
◦ Most proteins made of multiple domains that
perform different parts of the protein’s
function
18
19
Chaperones



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
20
Denaturation
Protein loses
structure and
function
 Due to
environmental
conditions

◦ pH
◦ Temperature
◦ Ionic concentration of
solution
21
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22
Nucleic acids


Polymer – nucleic acids
Monomers – nucleotides
◦ sugar + phosphate +
nitrogenous base
◦ sugar is deoxyribose in
DNA or ribose in RNA
◦ Nitrogenous bases include
 Purines: adenine and guanine
 Pyrimidines: thymine, cytosine,
uracil
◦ Nucleotides connected by
phosphodiester bonds
23
24
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
25
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

26
Other nucleotides

ATP adenosine triphosphate
◦ Primary energy currency of the cell

NAD+ and FAD+
◦ Electron carriers for many cellular reactions
27
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

28
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
29
30
Phospholipids

Composed of
◦ Glycerol
◦ 2 fatty acids – nonpolar “tails”
◦ A phosphate group – polar “head”

Form all biological membranes
31
32

Micelles – lipid molecules orient with polar
(hydrophilic) head toward water and nonpolar
(hydrophobic) tails away from water
33

Phospholipid bilayer – more complicated
structure where 2 layers form
◦ Hydrophilic heads point outward
◦ Hydrophobic tails point inward toward each other
34