What you should know from today’s lecture
• Examples and chemical basis of the diversity of proteins and their functions.
• Levels of protein structure and the chemical bonds that stabilize each level.
• 3-D structure determines biological function.
• Denaturation.
• Enzymes and catalysis.
• Enzyme cofactors, vitamins, and minerals.
• Biochemical pathways.
Function Example
Structural Muscle fiber (myosin)
Rhino horn (keratin)
Hormonal Insulin, leptin, hGH
Binding Antibodies (-globulin), receptors, snake venom
Transport Na+/K+ pump, hemoglobin, HDL
N storage Gluten, zein, albumin
Enzymes/catalytic
Sucrase, amylase, protease, nuclease
Misc. Antifreeze
Infectious Mad cow disease (prion)
The diverse functions of proteins
Fig. 3.16, p. 43
Levels of protein structure
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Why is it so hard to predict protein folding?
• Even a small protein made of just 100 amino acids has 3200 possible backbone configurations.
• The fastest supercomputers can do 1015 calculations per second.
• Even at that speed, it would take 1080 seconds to calculate the 3-dimensional shape of the small protein.
• The universe is only 1020 seconds old.
• A real protein folds in a microsecond (10-6 seconds).
Protein denaturation• Hydrogen bonds are broken,
destroying 3-D structure, and, therefore, protein function
• Denatured proteins are less soluble in water
• Covalent peptide bonds are NOT broken
• Common protein denaturants are gentle heat (100oC or less), solvents such as ethanol, even violent mechanical action such as beating an egg white
• Sometimes reversible, sometimes not
Biochemical reactionsA-P-P-PATP
A-P-P + P + energyADP
substrates(reactants)
products
Rules of thumb:•Chemical reactions proceed spontaneously from few complex molecules to a greater number of less complex molecules; from higher bond energy to lower energy•Making a more complex molecule from simpler substrates requires energy input
Catalysts• Increase the rate of a
chemical reaction
• Do not affect the equilibrium of the reaction
• Participate in the reaction but are not ‘used up’
• Are neither a substrate nor a product of the reaction
• Protein catalysts (enzymes) are exquisitely specific for their substrates and products
• Enzymes typically accelerate reaction rates by thousands or millions of times
The effect of enzymes on chemical reactions
O
OHO
OH
HO
OH
P
OO
HO
OH
HO OH
P1:19
G1P : G6P
How do enzymes work?
Lock-and-keyInduced fit
Sucrose Glucose + FructoseSucrase
Enzyme cofactors (coenzymes)
• Provide a wider range of chemically active ‘functional’ groups than are available in the 20 amino acid ‘R’ groups
• Vitamins
Example: nicotinic acid (niacin) in NADH and NADPH
• MineralsIron (Fe++) in hemoglobin
Magnesium (Mg++) in chlorophyll
Biochemical pathways