Roles of Biomolecules
Carbohydrates – Lipids –
Proteins – 1) Catalytic 2) Transport 3) Regulatory 4) Structural 5) Contractile 6) Protective 7) Storage Nucleic Acids –
Chapter 12 - Proteins
12.1 -Amino Acids 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)
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 –
• 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°)
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)
• _____________________ between peptide groups is mainly responsible for the
What type of attraction would exist between side chains of the following amino acids?
1) 2) 3)
a) Pro-His b) Ser-Tyr c) Pro-Phe d) Lys-Glu e) Ser-Val
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:
• solubility _________________
• elongated shapes having one dimension much longer than the others
• serve as _____________ and _____________ proteins
• usually have repetition of a __________________________________ throughout all or most of chain
• described as containing no __________________structure
• usually have ______________________ structure
-keratins –
Hierarchical structure based on helical polypeptide chains
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 _____________ and _____________
• contains little _________________
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 – __________________, __________________, ______________________, and _______________________
• contain large numbers of amino acids with _______________ side chains.
• possess ____________________ structure
Myoglobin and Hemoglobin
Hemoglobin – in _____________ cells; picks up oxygen in lungs and transports to tissues Myoglobin – in _____________ cells; picks up oxygen and stores it as reserve
Myoglobin –
• polypeptide w/ _____ -amino acids
Except two histidines
• prosthetic group, heme, held in cavity inside by hydrophobic attractive forces
• oxygen binds at _______ site
Hemoglobin –
• _______ polypeptide chains ( ___ and ___ )
• -helices separated by -turns
• hydrophobic residues where myoglobin has hydrophilic which serve to
• 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 Normal hemoglobin - Val-His-Leu-Thr-Pro-Glu-Glu-Lys-…
sickle-cell hemoglobin Val-His-Leu-Thr-Pro-Val-Glu-Lys-…
If Val-His-Leu-Thr-Pro-Ala-Glu-Lys-… no effect on hemoglobin function 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 not move easily though the blood capillaries.
• the capillaries become inflamed, causing considerable pain.
Sickle-cell anemia – Sickle-cell trait – 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
5) Organic Chemicals
6) Salts of heavy metals
7) Oxidizing and reducing Agents
