This document summarizes key aspects of lipids and proteins. It discusses the different types of lipids including fatty acids, glycerides, sterols, and phospholipids. It describes the structures and properties of saturated and unsaturated fatty acids. It also summarizes the basic structures of proteins, including the properties of alpha-amino acids like glycine and alanine, and how peptide bonds form between amino acids in the polymerization reaction.

1. Chapter 17
Lipids and Their Functions
in Biological Systems
1

2. Lipids
 Lipids are
 biomolecules that contain fatty acids or a steroid nucleus.
 soluble in organic solvents, but not in water.
 named for the Greek word lipos, which means “fat.”
 extracted from cells using organic solvents.
2

3. Lipids—one classification
 The types of lipids containing fatty acids are
 waxes
 fats and oils (triacylglycerols)
 glycerophospholipids
 prostaglandins
 The types of lipids that do not contain fatty acids are
 steroids
3

4. Lipids—one classification

5. Lipids—another classification
 Four main groups
 Fatty acids
 Saturated
 Unsaturated
 Glycerides: glycerol-containing lipids
 Nonglyceride lipids
 Sphingolipids
 Steroids
 Waxes
 Complex lipids: lipoproteins
5

6. Lipids—another classification

7. Fatty acids
 Fatty acids are
 long-chain carboxylic acids.
 typically 12-18 carbon atoms.
 insoluble in water.
 saturated or unsaturated.
Olive oil contains 84%
unsaturated fatty acids and
16% saturated fatty acids.
7

8. Fatty acids
 Fatty acids are
 saturated with all single C–C bonds.
palmitic acid, a saturated acid
 unsaturated with one or more double C=C bonds.
palmitoleic acid, an unsaturated acid
8

9. Fatty acids
 Saturated fatty acids
 contain only single C–C bonds.
 are closely packed.
 have strong attractions between chains.
 have high melting points.
 are solids at room temperature.
COOH
COOH
COOH
9

10. Fatty acids
 Unsaturated fatty acids
HOOC
 contain one or more cis
H
double C=C bonds. COOH
C
H
 have “kinks” in the fatty acid C
chains.
 do not pack closely.
“kinks” in
 have few attractions H chain
C
between chains.
C
 have low melting points. H
 are liquids at room
temperature.
10

11. Fatty acids
 Melting points of fatty acids
11

12. Waxes, fats, and oils
 Waxes are:
 esters of saturated fatty acids and long-chain alcohols.
 coatings that prevent loss of water by leaves of plants.
12

13. Waxes, fats, and oils
 Fats and oils are
 also called triglycerides.
 esters of glycerol.*
 produced by esterification.
 formed when the hydroxyl groups of
glycerol react with the carboxyl groups
of fatty acids.
*The IUPAC name for glycerol is 1,2,3-propanetriol.
13

14. Waxes, fats, and oils
 In a triglyceride, glycerol forms ester bonds with three
fatty acids.
14

15. Waxes, fats, and oils
glycerol + 3 fatty acids  triglyceride + 3 waters
O
CH2 OH HO C (C H 2 ) 1 4 C H 3
O
CH OH HO C (C H 2 ) 1 4 C H 3
O
O
CH2 OH HO C (C H 2 ) 1 4 C H 3 CH2 O C (C H 2 ) 1 4 C H 3
O
CH O C (C H 2 ) 1 4 C H 3 + 3H2O
O
CH2 O C (C H 2 ) 1 4 C H 3
15

16. Waxes, fats, and oils
 Example of a triglyceride:
O
CH2 Stearic acid
O C (C H 2 ) 16 C H 3
O
Oleic acid
CH O C (C H 2 ) 7 C H C H (C H 2 ) 7 C H 3
O
Myristic acid
CH2 O C (C H 2 ) 12 C H 3
16

17. Waxes, fats, and oils
A fat
• is solid at room temperature.
• is prevalent in meats, whole
milk, butter, and cheese.
An oil
• is liquid at room temperature.
• is prevalent in plants such as
olive and safflower.
17

18. Waxes, fats, and oils
 Oils
 have more unsaturated fats.
 have cis double bonds that cause “kinks” in the fatty acid chains.
 with “kinks” in the chains do not allow the triglyceride molecules to
pack closely.
 have lower melting points than saturated fatty acids.
 are liquids at room temperature.
18

19. Waxes, fats, and oils
 Unsaturated fatty acid chains with kinks cannot pack
closely.
olive oil
19

20. Waxes, fats, and oils
 Percent saturated and unsaturated fatty acids
20

21. Chemical reactions of fatty acids
 In hydrogenation1, double bonds in unsaturated fatty acids
react with H2 in the presence of a Ni or Pt catalyst.
O
O
CH2 O C (C H 2 ) 5 C H C H (C H 2 ) 7 C H 3
CH2 O C (C H 2 ) 1 4 C H 3
O
Ni O
CH O C (C H 2 ) 5 C H C H (C H 2 ) 7 C H 3 + 3 H2
CH O C (C H 2 ) 1 4 C H 3
O
O
CH2 O C (C H 2 ) 5 C H C H (C H 2 ) 7 C H 3
CH2 O C (C H 2 ) 1 4 C H 3
glyceryl tripalmitoleate glyceryl tripalmitate
1See Chapter 11, pages 363-365, Power point slides 35-39
21

22. Chemical reactions of fatty acids
 Unsaturated fatty acids can be
 cis with bulky groups on same side of C=C.
 trans with bulky groups on opposite sides of C=C.
22

23. Chemical reactions of fatty acids
 Most naturally occurring
fatty acids have cis
double bonds.
 During hydrogenation,
some cis double bonds are
converted to trans double
bonds.
 In the body, trans fatty acids
behave like saturated fatty
acids.
 Why would trans fatty
acids behave like
saturated fatty acids,
while cis fatty acids do
not?
23

24. Chemical reactions of fatty acids
 In hydrolysis2, ester bonds are split by water in the
presence of an acid, a base, or an enzyme.
O
CH2 O C (C H 2 ) 1 4 C H 3
O
H+
CH O C (C H 2 ) 1 4 C H 3 + H 2O
O
CH2 O C (C H 2 ) 1 4 C H 3 CH2 OH
O
CH OH + 3 HO C (C H 2 ) 1 4 C H 3
CH2 OH
2See Chapter 14, pages 472-473, Power point slides 31-33
24

25. Chemical reactions of fatty acids
In saponification, a fatty acid or
O triglyceride reacts with a strong base
CH2 O C (C H 2 ) 1 4 C H 3 to form an alcohol or glycerol, and
the salt(s) of fatty acid(s).
O
CH O C (C H 2 ) 1 4 C H 3 + 3NaOH
O CH2 OH
CH2 O C (C H 2 ) 1 4 C H 3
CH OH O
+ 3 N a + -O C (C H 2 ) 1 4 C H 3
“soap”
CH2 OH

26. Triglycerides
 Glycerides are lipid esters.
 A triglyceride places fatty acid chains at each alcohol
group of a molecule of glycerol.
glycerol portion
fatty acid
chains
26

27. Triglycerides
 Triglycerides undergo three fundamental reactions, identical
to those studied in carboxylic acids.
Triglyceride
H2O, H+ H2, Ni
NaOH
Glycerol More saturated
Fatty Acids triglyceride
Glycerol
Fatty Acid Salts
27

28. Glycerophospholipids
 Glycerophospholipids are
 the most abundant lipids in cell membranes.
 composed of glycerol, two fatty acids, phosphate, and an amino
alcohol.
Fatty acid
example
Fatty acid
Glycerol
Amino
PO4
alcohol
28

29. Cholesterol and steroid hormones
 A steroid nucleus consists of
 three cyclohexane rings, and
 one cyclopentane ring.
 The rings are fused (joined along one side).
29

30. Cholesterol and steroid hormones
 Cholesterol
 is the most abundant steroid in the body.
 has methyl (-CH3) groups, an alkyl chain, and an -OH attached to the
steroid nucleus.
30

31. Cholesterol and steroid hormones
 A steroid is any natural or synthetic compound based on
the four-fused-ring structure in cholesterol.
cortisone
testosterone
progesterone
31

32. Protein Structure and Function
Chapter 18
32

33. 2. The α-amino acids
 Amino acids
 are the building blocks of proteins.
 contain a carboxylic acid group
33

34. 2. The α-amino acids
 Amino acids
 are the building blocks of proteins.
 contain a carboxylic acid group and an amino group
34

35. 2. The α-amino acids
 Amino acids
 are the building blocks of proteins.
 contain a carboxylic acid group and an amino group on the alpha
() carbon.
35

36. 2. The α-amino acids
 Amino acids
 are the building blocks of proteins.
 contain a carboxylic acid group and an amino group on the alpha
() carbon.
 are ionized in solution.
H2O
ionized
form
36

37. 2. The α-amino acids
 Amino acids
 are the building blocks of proteins.
 contain a carboxylic acid group and an amino group on the alpha
() carbon.
 are ionized in solution.
 all have a different side chain.
H2O
ionized
form
37

38. 2. The α-amino acids
 Examples of amino acids
 glycine
 alanine
38

39. 2. The α-amino acids
 All but one of the amino acids have a chiral carbon. The α
carbon is attached to
 a carboxylate group (COO-),
 a protonated amino group (-NH3+),
 a hydrogen atom, and
 a side chain (R group).
 Glycine has R = H, which gives it two hydrogens attached to
the α carbon and no chiral carbon.
39

40. 2. The α-amino acids
 Each amino acid (except glycine) can exist as one of two
stereoisomers.
 Only L- isomers of amino acids are found in proteins.
 Recall that mainly D- isomers of monosaccharides exist in nature.
 As is true for monosaccharides, Fischer projections for
amino acids have the most oxidized group at the top.
L-alanine D-alanine L-cysteine D-cysteine
40

41. 2. The α-amino acids
 Amino acids are classified based on the nature of their side
chains.
 Nonpolar amino acids are hydrophobic and have hydrocarbon side
chains.
 Polar amino acids are hydrophilic and have polar or ionic side
chains.
 Acidic amino acids are hydrophilic and have acidic (carboxylic acid)
side chains.
 Basic amino acids are hydrophilic and have amino side chains.
41

42. 2. The α-amino acids
 Nonpolar: The R group is H, alkyl, or aromatic.
glycine alanine valine leucine isoleucine
phenylalanine tryptophan methionine proline
42

43. 2. The α-amino acids
 Polar: the R group is an alcohol, thiol, or amide
serine threonine tyrosine
glutamine asparagin cysteine
e
43

44. 2. The α-amino acids
 Acidic: The R group is a carboxylic acid.
aspartate glutamate
44

45. 2. The α-amino acids
 Basic: The R group is an amine.
histidine lysine arginine
45

46. 3. The peptide bond
 A peptide bond is an amide bond that forms between the
carboxyl group of one amino acid and the amino group of
the next amino acid.
glycine alanine
+ H2O
46

47. 3. The peptide bond
 Naming peptides
 For small peptides, the general name “peptide” is preceded by a
prefix indicating how many amino acids were condensed to form the
peptide.
 The peptide formed on the previous slide is a dipeptide.
 The end of the peptide with the free NH3+ group is called the N-
terminal amino acid.
 The end of the peptide with the free –COO- group is called the C-
terminal amino acid.
47

48. 3. The peptide bond
 Naming peptides (cont.)
 The root name of a peptide is the name of the C-terminal amino acid,
which uses its entire name.
 For all other amino acids in the peptide, the ending –ine is changed
to –yl.
 The amino acids are named in order starting with the N-terminal
amino acid.
 A peptide composed of aspartine, glutamine, and serine (in
that order) would be named:
aspartyl-glutamyl-serine
48

49. 3. The peptide bond
 The structures of small peptides are based on a repeating
backbone:
N—C—C—N—C—C—N—C—C
 α-amino group (N)
 α-carbon (always attached to H and R)
 α-carboxyl group (C)
49

50. 3. The peptide bond
 Draw the structure of aspartyl-glutamyl-serine.
 This is a tripeptide, so the backbone will have three repeats.
 The left end is the N-terminal amino acid and the right end is the C-
terminal amino acid.
 The carboxyl carbons all have a carbonyl and the α carbons all have
a hydrogen.
50

51. 3. The peptide bond
 Draw the structure of aspartyl-glutamyl-serine. (cont.)
 Each α carbon has the R group characteristic of the particular amino
acid.
 aspartame
 glutamate
 serine
51

52. 4. The primary structure of proteins
 Primary structure is the amino acid sequence of the
polypeptide chain.
 It is the result of covalent bonding (peptide bonds) between amino
acids.
 Each protein has a different primary structure with different
amino acids in different places along the chain.
CH3
CH3 S
CH CH3 SH CH2
CH3 O CH O CH2 O CH2 O
-
H 3N CH C N CH C N CH C N CH C O
H H H
Ala─Leu─Cys─Met
52

53. 4. The primary structure of proteins
 Insulin was the first protein to have its primary structure
determined.
 It has a primary structure of two polypeptide chains linked
by disulfide bonds.
 One chain (A) has 21 amino acids and the other (B) has
30 amino acids.
53

54. 5. The secondary structure of proteins
 When the primary sequence of the polypeptide folds into
regularly repeating structures, secondary structure is
formed.
 Secondary structure results from hydrogen bonding between the
amide hydrogens and carbonyl oxygens of the peptide bonds.
54

55. 5. The secondary structure of proteins
 The α-helix is the most common type of
secondary structure.
 Features:
 a three-dimensional spatial arrangement of
amino acids in a polypeptide chain.
 held by H bonds between the H of –N-H
group and the O of C=O of the fourth amino
acid down the chain.
 a corkscrew shape that looks like a coiled
“telephone cord”.
55

56. 5. The secondary structure of proteins
 Top view of the α-helix, looking down into the “barrel.”
 The side chains (-R) point out.
56

57. 5. The secondary structure of proteins
 The second most common secondary structure is the β-
pleated sheet.
 The β-pleated sheet consists of polypeptide chains arranged side
by side with hydrogen bonds between chains.
 Side chains (-R) are above and below the sheet.
 This structure is typical of fibrous materials like silk.
57

58. 6. The tertiary structure of proteins
 Soluble proteins are usually
globular proteins.
 A third level of structure, tertiary
structure, is added to the primary
and secondary structures.
 Areas of α-helix and β-pleated
secondary structure are folded in
on themselves and held in place
by the forces responsible for
tertiary structure.
58

59. 6. The tertiary structure of proteins
 Crosslinks in tertiary structures involve attractions and
repulsions between the side chains (-R) of the amino acids
in the polypeptide chain.
 Hydrophobic interactions: attractions between nonpolar groups.
 Hydrophilic interactions: attractions between polar groups and
water.
 Salt bridges: ionic interactions between acidic and basic amino
acids.
 Hydrogen bonds: between H and oxygen or nitrogen.
 Disulfide bonds: covalent links between sulfur atoms of two
cysteine amino acids.
59

60. 6. The tertiary structure of proteins
salt bridge
hydrophobic
interactions
disulfide
bonds
hydrogen
bonds
60

61. 7. The quaternary structure of proteins
 Quaternary structure is the arrangement of subunits or
peptides that form a larger protein.
 A subunit is a polypeptide chain having primary, secondary, and
tertiary structural features that is a part of a larger protein.
 Quaternary structure is maintained by the same forces which are
active in maintaining tertiary structure.
 Hemoglobin consists of four polypeptide chains as subunits.
61

62. 8. Overview of protein structure
 Primary structure:
 Amino acid sequence
 Results from formation of covalent peptide
bonds between amino acids
 Secondary structure:
 Includes α-helix and β-sheet
 Hydrogen bonding between amide
hydrogens and carbonyl oxygens of the
peptide bonds
62

63. 8. Overview of protein structure
 Tertiary structure:
 Overall folding of the entire
polypeptide chain
 Interactions between different amino
acid side chains
 Quaternary structure:
 Concerned with topological, spatial
arrangement of two or more
polypeptide chains
 Involves both disulfide bridges and
noncovalent interactions
63

64. 10. Denaturation of proteins
 Denaturation involves the disruption of bonds in the
secondary, tertiary and quaternary protein structures.
 Denaturation is the loss of organized structure of a globular protein.
 Denaturation does not alter primary structure.
 Causes of denaturation:
 heat and organic compounds that break apart H bonds and disrupt
hydrophobic interactions.
 acids and bases that break H bonds between polar R groups and
disrupt ionic bonds.
 heavy metal ions that react with S-S bonds to form solids.
 agitation such as whipping that stretches peptide chains until bonds
break.
64

65. 10. Denaturation of proteins
 Heat: As the temperature rises, molecules move and vibrate
more. The weaker hydrogen bonds are the first to break.
 pH: Amino acids include basic (amino) and acidic
(carboxylate) groups. An excess of H+ or OH- changes ionic
interactions involving these groups.
 Organic solvents: Alcohols disrupt hydrogen bonding
because they take part in it themselves. The nonpolar
portions of alcohols disrupt nonpolar interactions.
65

66. 10. Denaturation of proteins
 Detergents: The hydrophobic region of detergents disrupts
hydrophobic interactions in proteins.
 Heavy metals: Metal cations such as mercury or lead can
bond with negative side chains and disrupt their
interactions. They can also bind to sulfur and disrupt
disulfide bonds.
 Mechanical stress: Shaking or whipping can disrupt the
intermolecular forces that maintain the conformation of the
protein.
66