Chapter 12 Proteins

1
Chapter 12Proteins
2
Roles of Biomolecules

• Carbohydrates Lipids -
• Proteins
• Nucleic Acids -

Provide energy, precursors to biomolecules,
construct cell membranes
Catalytic, transport, regulatory,
structural, contractile, protective, storage
transmission of genetic info.
3
(No Transcript)
4
12.1 a-Amino Acids
Amino acids
building blocks of polypeptides
5
12.1 a-Amino Acids

• Amino acids
• Mammals require all 20-amino acids for protein
  synthesis.
• 10 essential amino acids

building blocks of polypeptides
6
(No Transcript)
7
12.1 a-Amino Acids
a-amino acids organized according to
R-group 1) 2) 3) 4)
8
(No Transcript)
9
(No Transcript)
10
12.1 a-Amino Acids
a-amino acids organized according to
R-group 1) 2) 3) 4)
nonpolar neutral
polar neutral
polar acidic
polar basic
11
12.1 a-Amino Acids
Notes
2º amine
Nitrogen of amine part of a ring structure
12
12.1 a-Amino Acids
H
Glycine no stereocenter All other amino acids
have D/L enantiomers
13
Box 12.1 Proteins in Diet

• minimal reserves for protein production
• proteins synthesized only when all 12 amino
  acids are present

Incomplete Protein
Complete Protein
14
Box 12.1 Proteins in Diet
Complete Protein
Incomplete Protein
Contains all needed aas
doesnt contain all needed aas
Grains (rice, corn, oats, wheat)
Contains too little Lysine
Legumes (beans, peas)
Contains too little methionine
Nuts
Like legumes
15
12.2 The Zwitterion Structure of a-amino acids

• amino acids can react with themselves to form
  a zwitterion

16
12.2 The Zwitterion Structure of a-amino acids

• amino acids can react with themselves to form
  a zwitterion

17
12.2 The Zwitterion Structure of a-amino acids

• Strong secondary forces
• solubility __________________
• Melting point ___________________

18
m.p. 314ºC
m.p. 53ºC
19
12.2 The Zwitterion Structure of a-amino acids

• pH changes affect the structure of amino acids

20
12.2 The Zwitterion Structure of a-amino acids

• pH changes affect the structure of amino acids

21
12.3 Peptides
a polyamide formed from amino acids linked by
peptide bonds
Peptide Polypeptide Protein peptide
formation
a few to hundreds/thousands of amino acids
Usually 2 polypeptides (along with other
molecules or ions)
22
12.3 Peptides
23
12.3 Peptides
Amino acids sequence and constitutional
isomers Gly Ala Ala - Gly
24
12.3 Peptides

• physiological function determined largely by
  _______________________.
• isomers
• OMIT SECTIONS
• The Peptide Bond and Ionization of Peptides

25
12.4 Chemical Reactions of Peptides
Formation of disulfide bridges
26
12.4 Chemical Reactions of Peptides
Formation of disulfide bridges
27
12.4 Chemical Reactions of Peptides
28
12.4 Chemical Reactions of Peptides
29
12.4 Chemical Reactions of Peptides
Formation of disulfide bridges
30
12.4 Chemical Reactions of Peptides
Formation of disulfide bridges
31
12.4 Chemical Reactions of Peptides
Formation of disulfide bridges
32
12.4 Chemical Reactions of Peptides
33
12.4 Chemical Reactions of Peptides
34
12.5 The 3-D Structure of Proteins
Peptide a polyamide formed from amino acids
linked by peptide bonds Polypeptide a few to
hundreds/thousands of amino acids Protein a
polypeptide is considered a protein if 1) 2)
gt 50 amino acids
Its functional as an individual molecule
35
12.5 The 3-D Structure of Proteins
Protein a polypeptide is considered a protein
if 1) 2) Ex. Hemoglobin
gt 50 amino acids
Its functional as an individual molecule
36
12.5 The 3-D Structure of Proteins
Simple Conjugated -
37
12.5 The 3-D Structure of Proteins
Levels of Structure Primary (1º) Secondary
(2º) Tertiary (3º) Quaternary (4º) 3D relation
among diff. proteins
Amino acid sequence
Conformation in a local region
When diff. 2 structures in diff. local regions
interact
38
12.5 The 3-D Structure of Proteins
Determinants of Protein Conformation 1) 2)
Bonds in linear chain
Interactions of side groups
39
What gives rise to conformation stability
1) Shielding of nonpolar amino acids from
water 2) Hydrogen bonding between peptide
groups 3) Attractive interactions between side
groups of amino acids. 4) Attractive
interactions of side groups of polar amino acids
with water 5) Disulfide bridges
40
(No Transcript)
41
(No Transcript)
42
(No Transcript)
43
(No Transcript)
44
12.5 The 3-D Structure of Proteins

• Attractive interactions between side groups of
  amino acids.
• a. Hydrophobic attractions
• b. Hydrogen bonding
• c. Salt-bridge
• Attractive interactions of side groups of polar
  amino acids with water
• ex. globular proteins
• fibrous proteins

45
5) Disulfide bridges
3º 4º
46
12.5 The 3-D Structure of Proteins
Native protein Concept Check (pg. 389)
Hydrogen bonding between peptide groups is mainly
responsible for the secondary structure of
polypeptides. Disulfide bridges and secondary
interactions between side groups are mostly
responsible for the tertiary and quaternary
structures of proteins. Disulfide bridges are
more resistant to environmental changes such as
those in temperature and pH than are the various
secondary attractive forces.
47
(No Transcript)
48
12.6 Fibrous Proteins

• Key Features
• Solubility ____________
• elongated shapes having one dimension much
  longer than the others.
• serve as ___________ and _________ proteins

Water insoluble
structural
contractile
49
12.6 Fibrous Proteins

• Key Features cont
• usually have repetition of a _______________
  throughout all or most of chain ?
• described as containing no ________ structure.
• usually have ___________ structure

Single conformational pattern
aggregate tightly into fibers/sheets
tertiary
quaternary
50
12.6 FibrousProteins
a-keratins Structural component of hair, skin,
nails, horns, hoofs, and wool.
51
The hierarchical structure of a strand of hair
explains many of the hairs properties.
52

• strong physical strength
• springiness

53
Intermolecular disulfide bridges between
polypeptide chains in a protofibril
Stabilizes the packing into coiled conformations
54
(No Transcript)
55
(No Transcript)
56
12.6 FibrousProteins
collagen Major stress-bearing component of
connective tissues such as bone, cartilage,
cornea, ligament, teeth, tendons, and the fibrous
matrices of skin and blood vessels.
57
The triple helix of collagen explains its
strength and flexibility
Contains more __________ and ___________ contains
little ____________
58
12.7 Globular Proteins

• Key Features
• dont aggregate into macroscopic structures

Recall highly branched molecules have
__________ intermolecular forces.
weaker
59
12.7 Globular Proteins
60
Globular proteins do metabolic work 1) 2) 3) 4) C
ontain large s of aas with _____________ side
chains
catalysis
transport
regulation
protection
hydrophillic
Myoglobin - __________ cells
muscle
61
Heme is held in the cavity by hydrophobic
attractive forces
Fe2 is held in the center by free electron pairs
of the 4 Ns and by ionic attractions with an
interior histidine residue.
62

• Hemoglobin in ________ cells
• ____ polypeptide chains (___ a and ___ b)
• a-helices separated by b-turns

63
(No Transcript)
64
(No Transcript)
65
12.8 Mutations
KEY Protein function ultimately depends on
___________
66
genetic mutation an alteration in the DNA
structure of a gene that may in turn produce a
change in the primary structure of a protein.
67
Normal hemoglobin Val-His-Leu-Thr-Pro-Glu-Glu-Ly
s- Sickle-cell hemoglobin Val-His-Leu-Thr-Pro
-Val-Glu-Lys-
68
regions critical to binding oxygen ___________
changed sickling is the aggregation of the
hemoglobins (hydrophobic attractions between the
hydrophobic pocket and residue 6 (Val)
Sickle-cell anemia found in ______________________
_ likely because of the high incidence of
_______________.
are NOT
western Africa
malaria
69
deoxygenated red blood cells containing
sickle-cell hemoglobin take on an elongated
sickle shape instead of the normal biconcave disk
shape. the sickled cells aggregate together
into long rodlike structures that do not move
easily though the blood capillaries.
the capillaries become inflamed, causing
considerable pain.
70
12.9 Denaturation
Denaturation Loss of native conformation
brought about by a change in environmental
conditions, resulting in loss of physiological
function alters _______________________
structures. denaturation involves breaking
__________________ bonds unlike digestion which
breaks _______________ bonds and alters
______________ structure. _____________________
are resistant to denaturation Globular
proteins have ____________ secondary forces
compared to fibrous proteins and are thus
denatured ______________________.
71
12.9 Denaturation
1) Increased Temperature 2) UV and
ionizing radiations - 3) Mechanical energy -
Increased motion disrupts non-covalent
attractions Ex. Cooking, sterilization (curling
hair)
Causes chemical reactions
Violent mixing (whipping eggs)
72
(No Transcript)
73
12.9 Denaturation
4) Changes in pH -
Interferes with salt bridge interactions ( )
charged basic groups become ____ if pH gt 7 ( )
charged acidic groups become ____ if pH lt 7
74
(No Transcript)
75
12.9 Denaturation
5) Organic Chemicals -
Ex. Alcohol (passes through cell walls and
denatures bacterial proteins)
76
6) Salts of heavy metals -
Pb2, Hg2, and Ag react with sulfhydryl groups
of cysteine residues to form metal disulfide
bridges
77
12.9 Denaturation
7) Oxidizing and reducing agents
Forms and cleaves disulfide bridges