1. The Molecules of Life
Chapter 3

2. Polymers Are Built of Monomers
Organic molecules are formed by living organisms.
Carbon-based core
The core has attached groups of atoms called functional groups.
The functional groups confer specific chemical properties on the organic molecules.

3. Five principal functional groups
Found In
Group
Structural
Formula
Ball-and-
Stick Model O– P O OH C H N
Lipids
Proteins
DNA,
ATP
Carbohydrates
Carboxyl
Carbonyl
Hydroxyl
Amino
Phosphate 3

4. Macromolecules
The building materials of the body are known as macromolecules because they can be very large.
There are four types of macromolecules:
Proteins
Nucleic acids
Carbohydrates
Lipids

5. Macromolecules
Large macromolecules are actually assembled from many similar small components, called monomers.
The assembled chain of monomers is known as a polymer.

6. Dehydration Synthesis
All polymers are assembled the same way.
A covalent bond is formed by removing a hydroxyl group (OH) from one subunit and a hydrogen (H) from another subunit.

7. Dehydration Synthesis
Because this amounts to the removal of a molecule of water (H2O), this process of linking together two subunits to form a polymer is called dehydration synthesis. H
Energy HO
H2O

8. Hydrolysis H2O H Energy HO
The process of disassembling polymers into component monomers is essentially the reverse of dehydration synthesis.
A molecule of water is added to break the covalent bond between the monomers.
This process is known as hydrolysis. H HO
Energy
H2O

9. Proteins
Proteins are complex macromolecules that are polymers of many subunits called amino acids.

10. Proteins
The covalent bond linking two amino acids together is called a peptide bond.
The assembled polymer is called a polypeptide. O C N H
H2O R
Amino acid OH
Polypeptide chain

11. Proteins
Amino acids are small molecules with a simple basic structure, a carbon atom to which three groups are added:
an amino group (—NH2)
a carboxyl group (—COOH)
a functional group (R)
The functional group gives amino acids their chemical identity.
There are 20 different types of amino acids.

12. Proteins Protein structure is complex.
The order of the amino acids that form the polypeptide is important.
The sequence of the amino acids affects how the protein folds together.

13. Proteins
The way that a polypeptide folds to form the protein determines the protein’s function.
Some proteins are comprised of more than one polypeptide.

14. Proteins There are four general levels of protein structure: Primary
Secondary
structure
β-pleated sheet
α-helix
Tertiary
Quaternary
Amino acids
Primary
There are four general levels of protein structure:
Primary
Secondary
Tertiary
Quaternary

15. Proteins
Primary structure—the sequence of amino acids in the polypeptide chain.
Determines all other levels of protein structure.
Amino acids
Primary
structure

16. Proteins
Secondary structure forms because regions of the polypeptide that are nonpolar are forced together; hydrogen bonds can form between different parts of the chain.
The folded structure may resemble coils, helices, or sheets. N H C O
Secondary
structure
β-pleated sheet
α-helix

17. Proteins Tertiary structure—the final 3-D shape of the protein.
The final twists and folds that lead to this shape are the result of polarity differences in regions of the polypeptide.
Tertiary
structure

18. Proteins
Quaternary structure—the spatial arrangement of proteins comprised of more than one polypeptide chain.
Quaternary
structure

19. Proteins The shape of a protein affects its function.
Denaturation
Folded
protein
Denatured protein
The shape of a protein affects its function.
Changes to the environment of the protein may cause it to unfold or denature.
Increased temperature or lower pH affects hydrogen bonding, which is involved in the folding process.
A denatured protein is inactive.

20. Proteins
Active-site
cleft
Enzymes are globular proteins that have a special 3-D shape that fits precisely with another chemical.
They cause the chemical that they fit with to undergo a reaction.
This process of enhancing a chemical reaction is called catalysis.

21. Nucleic Acids
Nucleic acids are very long polymers that store information.
Comprised of monomers called nucleotides.
Each nucleotide has 3 parts:
a five-carbon sugar
a phosphate group
an organic nitrogen-containing base

22. Nucleic Acids There are five different types of nucleotides.
Information is encoded in the nucleic acid by different sequences of these nucleotides. N O P –O O– R C H
H3C 4 5 1 3 2 2 8 7 6 3 9 4 5 1
Structure of nucleotide
Nitrogenous base
Nitrogenous bases
Guanine
Uracil (RNA only)
Sugar
Thymine (DNA only)
Cytosine
Phosphate group
H in DNA
OH in RNA
Adenine OH
CH2
NH2
(a)
(b)

23. Nucleic Acids There are two types of nucleic acids:G C A T
Phosphodiester bond
Hydrogen bonds
between nitrogenous
bases
Sugar-phosphate
“backbone” OH
There are two types of nucleic acids:
Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)
RNA is similar to DNA except that
it uses uracil instead of thymine
it is comprised of just one strand
it has a ribose sugar

24. Nucleic Acids The structure of DNA is a double helix because:
There are only two base pairs possible
Adenine (A) pairs with thymine (T)
Cytosine (C) pairs with Guanine (G)
Properly aligned hydrogen bonds hold each base pair together.
A sugar-phosphate backbone comprised of phosphodiester bonds gives support.

25. A G C T
G and C can align to form
three hydrogen bonds.
A and T can align to form
two hydrogen bonds.
G and T cannot properly
align to form hydrogen
bonds.
A and C cannot properly

26. Nucleic Acids The structure of DNA helps it to function.
The hydrogen bonds of the base pairs can be broken to unzip the DNA so that information can be copied.
Each strand of DNA is a mirror image so that the DNA contains two copies of the information.
Having two copies means that the information can be accurately copied and passed to the next generation.

27. Carbohydrates
Carbohydrates are monomers that make up the structural framework of cells and play a critical role in energy storage.
A carbohydrate is any molecule that contains the elements C, H, and O in a 1:2:1 ratio.

28. Carbohydrates The sizes of carbohydrates varies:
Simple carbohydrates—consist of one or two monomers.
Complex carbohydrates—are long polymers.

29. Carbohydrates Simple carbohydrates are small.
Monosaccharides consist of only one monomer subunit.
An example is the sugar glucose (C6H12O6).
Disaccharides consist of two monosaccharides.
An example is the sugar sucrose, which is formed by joining together glucose and fructose.

30. Carbohydrates Complex carbohydrates are long polymer chains.
Because they contain many C-H bonds, these carbohydrates are good for storing energy.
These bond types are the ones most often broken by organisms to obtain energy.
The long chains are called polysaccharides.

31. Carbohydrates
Plants and animals store energy in polysaccharide chains formed from glucose.
Plants form starch.
Animals form glycogen.
Some polysaccharides are structural and resistant to digestion by enzymes.
Plants form cellulose cell walls.
Some animals form chitin for exoskeletons.

32. Lipids Lipids—fats and other molecules that are not soluble in water.
Lipids are nonpolar molecules.
There are many different types of lipids.
fats
oils
steroids
rubber
waxes
pigments

33. Lipids Fats are converted from glucose for long-term energy storage.
Fats have two subunits
1. fatty acids
2. glycerol
Fatty acids are chains of C and H atoms, known as hydrocarbons.
The chain ends in a carboxyl (—COOH) group.

34. Saturated and unsaturated fats
Because there are 3 fatty acids attached to a glycerol, another name for a fat is triglyceride H C O
(a) Fat molecule (triacylglycerol)
Glycerol
backbone
Fatty acids

35. Lipids
Fatty acids have different chemical properties due to the number of hydrogens that are attached to the non-carboxyl carbons
If the maximum number of hydrogens are attached, then the fat is said to be saturated.
If there are fewer than the maximum attached, then the fat is said to be unsaturated.

36. Saturated and unsaturated fatsH H H H C C C C H H
(b) Hard fat (saturated): Fatty
acids with single bonds
between all carbon pairs
(c) Oil (unsaturated): Fatty acids
that contain double bonds
between one or more pairs
of carbon atoms

37. Phospholipids Biological membranes involve lipids.
Phospholipids make up the two layers of the membrane.
Cholesterol is embedded within the membrane.
Outside of cell
Carbohydrate chains
Cell
membrane
Membrane proteins
Phospholipid
Cholesterol
Inside of cell