Download Ch. 12 note packet

Roles of Biomolecules
Carbohydrates –
Lipids –
Proteins –
1) Catalytic
2) Transport
3) Regulatory
4) Structural
5) Contractile
6) Protective
7) Storage
Nucleic Acids –
12.1  -Amino Acids
Chapter 12 - Proteins
Amino acids –
• Mammals require all 20  -amino acids for protein synthesis
• amino acids organized according to ______________. (See Table 12.1 next page)
1)
2)
3)
4)
Notes:
proline
glycine
1
2
Box 12.1 Proteins in Diet
• minimal reserves for protein production
• proteins synthesized only when all 12 amino acids present
Complete Protein
Incomplete Proteins
Grains (rice, corn, oats, wheat)
Legumes (beans, peas)
Nuts
12.2 The Zwitterion Structure of -amino acids
• Strong secondary forces
• solubility ____________________
• melting point ___________________
L-alanine
vs. L-lactic acid
12.3 Peptides
Peptide –
Polypeptide –
Protein –
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• physiological function determined largely by _________________________.
# isomers =
OMIT SECTIONS:
“The Peptide Bond” and “Ionization of Peptides”
12.4 Chemical Reactions of Peptides
Disulfide bridge formation:
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)
Ex. Hemoglobin
simple protein –
conjugated protein –
amino acid
sequence
Levels of Structure:
Primary (1°)
Secondary (2°)
Tertiary (3°)
Quaternary (4°)
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Determinants of Protein Conformation
1)
2)
• the number of allowed conformation are limited by single-bond rotation
The following Give rise to the stability of one conformation over others:
1) Shielding of nonpolar -amino acids from water
2) Hydrogen Bonding between peptide groups
3) Attractive interactions between side groups of amino acids
a) hydrophobic attractions
b) hydrogen-bonding
c) salt bridge (ionic) attractions
4) Attractive interactions of side groups of polar -amino acids with water
5) Disulfide Bridges
native conformation –
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.
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Basic Patterns of protein conformation
When favored
1) a-helix
2) b-pleated sheet
3) b-turn (b-bend)
4) Loop conformations
12.6 Fibrous Proteins
Key features:
• water-insoluble
• elongated shapes having one dimension much longer than the others
• serve as structural and contractile proteins
• usually have repetition of a single conformational pattern throughout all /most of chain
 aggregate tightly into fibers or sheets with strong secondary attractive forces,
production macroscopic structures with high strength
• described as containing no tertiary structure
• usually have quaternary structure
-keratins – structural components of hair, horn, hoofs, nails, skin, and wool
Hierarchical structure based on helical polypeptide chains
Ex. Hair
Individual polypeptides
Mostly -helices
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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.
Hierarchical structure based on helical polypeptide chains
Compared to -keratins…
• more glycine and proline
• contains little cysteine
L-hand helix
• ___________ bonding and __________ between peptide chains contribute to strength.
-keratins and Silk Fibroins
12.7 Globular Proteins
Key Features:
• don’t aggregate into macroscopic structures
Recall: highly branched molecules have ______________________________
• do metabolic work – catalysis, transport, regulation, protection
• contain large numbers of amino acids with _______________ side chains.
• possess tertiary structure
Myoglobin and Hemoglobin
Hemoglobin – in red blood cells; picks up oxygen in lungs and transports to tissues
Myoglobin – in muscle cells; picks up oxygen and stores it as reserve
Myoglobin –
• polypeptide w/ 153 -amino acids
• ¾ of residues are folded into 8 a-helical sections
•  -helices connected by short b-turns w/praline
• nonpolar residues on interior
• polar residues on exterior
Except two histidines
• prosthetic group, heme, held in cavity inside by hydrophobic attractive forces
• oxygen binds at Fe2+ site
Hemoglobin –
• 4 polypeptide chains (2  and 2 )
• -helices separated by -turns
• hydrophobic residues where myoglobin has hydrophilic which serve to
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• each polypeptide carries a _______ with is ____ ion.
• de-oxygenated hemoglobin has a 2,3-bisphosphoglycerate ion (BPG) in central
cavity.
hemoglobin w/oxygen  hemoglobin no oxygen
Carbon monoxide poisoning –
Lysozyme –
• helps dispose of bacteria after they have been killed by other means
• all four types secondary structures
12.8 Mutations: Sickle-cell Hemoglobin
KEY: protein function ultimately depends on _______________________.
genetic mutation –
• the substitution of an a-amino acid residue similar _____________________________
often has minimal effect on the three-dimensional structure and may have no effect on
function.
Ex.
_____ for Val
_____ for Glu
_____ for Ser
• The substitution of very different amino acids may result in a large change in 3-D
structure.
Ex.
_____ for Gly
_____ for Glu
_____ for Ala
Ex. Sickle-cell hemoglobin
• 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 no move easily though the
blood capillaries.
• the capillaries become inflamed, causing considerable pain.
Sickle-cell anemia –
Normal hemoglobin sickle-cell hemoglobin
Sickle-cell trait –
Val-His-Leu-Thr-Pro-Glu-Glu-Lys-…
Val-His-Leu-Thr-Pro-Val-Glu-Lys-…
• 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 _____________________.
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If Val-His-Leu-Thr-Pro-Ala-Glu-Lys-… no effect on hemoglobin function
12.9 Denaturation
Denaturation –
- alters _______________________ structures.
• denaturation involves breaking __________________ bonds unlike digestion which
breaks ________________ bonds and alters ______________ structure.
• _______________________________ resistant to denaturation
• Globular proteins have ____________ secondary forces compared to fibrous proteins
and are thus denatured ______________________.
(whipping eggs)
Methods of Denaturation:
1) Increased temperature
2) Ultraviolet and ionizing radiations
3) Mechanical Energy
4) Changes in pH
5) Organic Chemicals
6) Salts of heave metals
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7) Oxidizing and reducing Agents
Prion diseases –
Alzheimer’s Disease –
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