1) Lipids are biomolecules that include fatty acids and steroids. They are nonpolar and insoluble in water. The main types are fatty acids, glycerides, sphingolipids, and steroids. 2) Fatty acids can be saturated or unsaturated. Saturated fatty acids are solid at room temperature due to close packing, while unsaturated fatty acids contain kinks that prevent close packing and result in lower melting points and liquid form. 3) Triglycerides are the main form of lipids in fats and oils. They consist of a glycerol molecule bonded to three fatty acid molecules. Fats are solid at room temperature due to higher saturated fatty acid content,

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

2. 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.

3. 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

4. 4
Lipids—one classification

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

6. 6
Lipids—another classification

7. 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.

8. 8
Fatty acids
Fatty acids are
saturated with all single C–C bonds.
unsaturated with one or more double C=C bonds.

9. 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

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

11. 11
Fatty acids
Melting points of fatty acids

12. 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.

13. 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.

14. 14
In a triglyceride, glycerol forms ester bonds with three
fatty acids.

15. 15
glycerol + 3 fatty acids  triglyceride + 3 waters
Waxes, fats, and oils
OHCH2
OH
OHCH2
CH
O
(CH2)14CH3CHO
O
(CH2)14CH3CHO
O
(CH2)14CH3CHO
+ 3H2O
O
O
C (CH2)14CH3
CH O
O
C (CH2)14CH3
CH2 O
O
C (CH2)14CH3
CH2

16. 16
(CH2)12CH3
O
C
CH(CH2)7CH3(CH2)7CH
O
C
O
(CH2)16CH3C
O
O
OCH2
CH2
CH
Waxes, fats, and oils
Example of a triglyceride:
Stearic acid
Oleic acid
Myristic acid

17. 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.

18. 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.

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

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

21. 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.
CH(CH2)7CH3(CH2)5CH
O
C
CH(CH2)7CH3(CH2)5CH
O
C
CH(CH2)7CH3(CH2)5CH
O
C
O
O
OCH2
CH2
CH
O
(CH2)14CH3C
O
(CH2)14CH3C
O
(CH2)14CH3C
O
O
OCH2
CH2
CH
+ 3 H2
Ni
glyceryl tripalmitoleate glyceryl tripalmitate
1See Chapter 11, pages 363-365

22. 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.

23. 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?

24. 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.
OCH2
OCH
OCH2
OHCH2
OHCH
OHCH2 O
(CH2)14CH3CHO
H2O
O
(CH2)14CH3C
O
(CH2)14CH3C
O
(CH2)14CH3C
H+
+
+
2See Chapter 14, pages 472-473

25. 25
Chemical reactions of fatty acids
O
O
C (CH2)14CH3
CH O
O
C (CH2)14CH3
CH2 O
O
C (CH2)14CH3
CH2
+ 3NaOH
Na+ -
O
O
C (CH2)14CH33
OH
CH OH
CH2 OH
CH2
+
“soap”
In saponification, a fatty acid or
triglyceride reacts with a strong base
to form an alcohol or glycerol, and
the salt(s) of fatty acid(s).

26. 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

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

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

29. 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).

30. 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.

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

32. 32
Chapter 18
Protein Structure and Function

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

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

35. 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.

36. 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

37. 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

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

39. 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.

40. 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 for monosaccharides, Fischer projections for amino
acids have the most oxidized group at the top.
L-alanine D-alanine L-cysteine D-cysteine

41. 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.

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

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

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

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

46. 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

47. 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.

48. 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

49. 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)

50. 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.

51. 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

52. 52
4. The primary structure of proteins
The primary structure of a protein is the amino acid
sequence of the protein’s peptide backbone.
There are 20 amino acids which can be arranged in varying
orders.
The length of the peptide backbone can vary.

53. 53
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
SH
CH2
CH3
S
CH2
CH2CH O
O-
CCH
H
N
O
CCH
H
N
O
CCH
H
N
O
CCHH3N
CH3
CH3CH
Ala─Leu─Cys─Met

54. 54
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.

55. 55
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.

56. 56
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”.

57. 57
5. The secondary structure of proteins
Top view of the α-helix, looking down into the “barrel.”
The side chains (-R) point out.

58. 58
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.

59. 59
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.

60. 60
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.

61. 61
6. The tertiary structure of proteins
salt bridge
hydrophobic
interactions
hydrogen
bonds
disulfide
bonds

62. 62
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.

63. 63
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

64. 64
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

65. 65
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
interactive forces are broken.

66. 66
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.
Denaturation of Protein by Strong Acid

67. 67
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.