1. The Living World George B. Johnson Jonathan B. Losos Chapter 4
Fifth Edition
George B. Johnson
Jonathan B. Losos
Chapter 4
Molecules of Life
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. 4.1 Polymers Are Built of Monomers
Organic molecules are formed by living organisms
have a core based around carbon
the core has attached groups of atoms called functional groups
the functional groups confer specific chemical properties on the organic molecules

3. 4.1 Polymers Are Built of Monomers
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
Large macromolecules are actually assembled from many similar small components, called monomers
the assembled chain of monomers is known as a polymer

4. 4.1 Polymers Are Built of Monomers
All polymers are assembled the same way
a covalent bond is formed by removing an hydroxyl group (OH) from one subunit and a hydrogen (H) from another subunit
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

5. Figure 4.2 (a) Dehydration synthesis

6. 4.1 Polymers Are Built of Monomers
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

7. Figure 4.2(b) Hydrolysis

8. 4.2 Proteins
Proteins are complex macromolecules that are polymers of many subunits called amino acids
the covalent bond linking two amino acids together is called a peptide bond
the assembled polymer is called a polypeptide
Table 4.1 amino acids, polypeptide

9. Table 4.2 The many functions of proteins

10. 4.2 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

11. 4.2 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
the way that a polypeptide folds to form the protein determines the protein’s function
some proteins are comprised of more than one polypeptide

12. 4.2 Proteins There are four general levels to protein structure
Primary
Secondary
Tertiary
Quaternary

13. 4.2 Proteins
Primary structure – the sequence of amino acids in the polypeptide chain
This determines all other levels of protein structure
Figure 4.5 Levels of protein structure (circle the primary structure)

14. 4.2 Proteins
Secondary structure forms because regions of the polypeptide that are non-polar are forced together
The folded structure may resemble coils, helices, or sheets
Figure 4.5 Levels of protein structure (circle the secondary structure)

15. 4.2 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
Figure 4.5 Levels of protein structure (circle the tertiary structure)

16. 4.2 Proteins
Quaternary structure – the spatial arrangement of proteins comprised of more than one polypeptide chain
Figure 4.5 Levels of protein structure (circle the quaternary structure)

17. 4.2 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

18. 4.2 Proteins
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

19. 4.2 Proteins Proteins fold specifically
the folding process is helped by special proteins called chaperone proteins
these proteins somehow correct a misfolded protein
defective chaperon proteins may play a role in certain genetic disorders that involve defective proteins
Cystic fibrosis
Alzheimer’s

20. 4.3 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
there are five different types of nucleotides
information is encoded in the nucleic acid by different sequences of these nucleotides

21. 4.3 Nucleic Acids 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

22. 4.3 Nucleic Acids The structure of DNA is a double helix because
there are only two base pairs possible
Adenosine (A) pairs with thymine (T)
Cytosine (C) pairs with Guanine (G)
the bond holding together a base pair is hydrogen bond
a sugar-phosphate backbone comprised of phosphodiester bonds gives support

23. Figure 4.12 The DNA double helix

24. 4.3 Nucleic Acids The structure of DNA helps it to function
the hydrogen bonds of the base pairs can be easily broken to unzip the DNA so that information can be copied
each strand of DNA is a mirror image so 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

25. 4.4 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
the sizes of carbohydrates varies
simple carbohydrates – made up of one or two monomers
complex carbohydrates – made up of polymers

26. 4.4 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 two monosaccharides, glucose and fructose

27. 4.4 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

28. 4.4 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

29. Table 4.3 Carbohydrates and their function

30. 4.5 Lipids
Lipids – fats and other molecules that are not soluble in water
lipids are non-polar molecules
lipids have many different types
fats
oils
steroids
rubber
waxes
pigments

31. 4.5 Lipids
Fats are converted from glucose for long-term energy storage
fats have two subunits
fatty acids
glycerol
fatty acids are chains of C and H atoms, known as hydrocarbons
the chain ends in a carboxyl (-COOH) group

32. Figure 4.17(a) Saturated and unsaturated fats
Because there are 3 fatty acids attached to a glycerol, another name for a fat is triglyceride

33. 4.5 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

34. Figure 4.17(b,c) Saturated and unsaturated fats

35. 4.5 Lipids Biological membranes involve lipids
phospholipids make up the two layers of the membrane
cholesterol is embedded within the membrane
Figure 4.16 Lipids are a key component of biological membranes

36. Inquiry & Analysis
Which of the three pH values represents the highest concentration of hydrogen ions?
How does pH affect the release of oxygen from hemoglobin?
pH effects on protein function