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.

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