Biochemical Reactions SBI4U1

Acids produces H + ions in H 2 O pH below 7 Sour taste, conducts electricity Increase [H + ] or [H 3 O + ] ions when dissolved in water HCl (aq) + H 2 O (l)  H 3 O + (aq) + Cl - (aq)

Bases produces OH - ions in H 2 O (or accepts/ reacts with H + ions) pH above 7 Bitter taste, conducts electricity Increase [OH - ] when dissolved in water NaOH (s)  Na + (aq) + OH - (aq)

Strong/Weak Acids and Bases Depends on the degree to which they dissolve into ions Strong acids/bases completely ionize in water (e.g. NaOH, HCl) NaOH (s)  Na + (aq) + OH - (aq) HCl (aq) + H 2 O (l)  H 3 O + (aq) + Cl - (aq) 100% ionization 100%

Weak acids/bases only partially ionize in water CH 3 COOH (aq) + H 2 O (l) H 3 O + (aq) + Cl - (aq) NH 3 (aq) + H 2 O(l) NH 4 + (aq) + OH - (aq) 10% Note: double arrow  represents that reaction is reversible 1.3%

Acid-Base Buffers Cells are sensitive to pH levels –Cell processes w/ proteins and enzymes (pH 7) –Blood (pH 7.4, 0.4 increase can be fatal) Acidosis: blood pH < 7.35 Alkalosis: blood pH >7.45

Blood pH can be affected by food –Acidic fruits, wine, salad dressing –Alkaline shrimp, tonic water

Buffers Chemical systems with substances that donate/remove H + ions when pH changes Example: Carbonic acid-bicarbonate buffer H 2 O + CO 2 H 2 CO 3 HCO H +

If too acidic H + will react with HCO 3 - to produce H 2 CO 3 –Excess H + are removed from the solution to avoid decrease in pH If too basic, H 2 CO 3 will ionize to replace H + –H + ions are added to avoid increase in pH Animation:

Oxidation-Reduction Reactions Oxidation: loss of electrons (loses hydrogen or gains oxygen) Reduction: gain of electrons Redox Rxn: LEO the lion says GER LEO  loss of electrons is oxidation GER  gain of electrons is reduction

Examples: C 3 H 8 + 5O 2  3CO 2 + H 2 O LEO GER C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O LEO GER Sugars are oxidized to produce carbon dioxide and water in cellular respiration.

Condensation/Hydrolysis Rxns Condensation Rxn: formation of a covalent bond with the production of water Anabolic rxn (makes larger molecules) Hydrolysis Rxn: formation of a covalent bond with the addition of water Catabolic (breaks down into smaller molecules) Animation:

An H from one molecule combines with an OH from another. Water is released and the two molecules join. Water is added. One H goes to one molecule and the OH to the other to break them apart.

Carbohydrates Note: condensation rxn is also known as dehydration synthesis

Lipids

Protein

Nucleotide Purine: A and G Pyrimidine: C, T, U

Enzymes Activation Energy (E A ): energy required for a rxn to take place Catalyst: speeds up the rate of a chemical rxn without being consumed Enzymes: protein catalysts that increase the rate of reaction by lowering the E A

Enzymes typically end in “ase” Example: amylose + H 2 O  maltose There are many enzymes involved in digestion: peptase, lipase, maltase amylase

How Enzymes Work: Enzymes are made up of long chains of amino acids Enzymes attach to substrates in order to work Most enzymes have globular shapes with active sites –Where the substrate binds

Enzyme-Substrate Complex: enzyme with a substrate that is bound to enzyme’s active site In this rxn, a dissacharide sucrose is broken down into glucose and fructose.

Since enzymes are protein, they can become denatured if the temperature or pH change Some enzymes require assistance from cofactors of coenzymes –Coenzymes are organic molecules –Cofactors are metal ions like iron or zinc

Some substances can inhibit enzyme function: Competitive Inhibitors: similar to substrate, bind to active site and block normal substrate

Non-Competitive Inhibitors: do not compete with substrate, attach to different site, change the shape so substrate cannot bind

Enzyme activity is controlled by: 1.Restricting the production of an enzyme 2. Inhibiting or stimulating enzymes activity by the use of allosteric sites –Not the active site –Other molecules can interact with/regulate enzyme activity –If an activator binds = enzyme is functional –If an inhibitor binds = enzyme is not functional

Review Questions Why are enzymes important in biological processes? Give an example. What is an enzyme-substrate complex? Differentiate b/t competitive and non- competitive inhibition.

Things You Should Know... Redox rxns Acid/Base Buffers Condensation vs. Hydrolysis Rxn Role of enzymes Enzyme substrate complex Competitive vs. non-competitive inhibition