Chapter 5 Directions and Rates of Biochemical Processes

Energy Organisms are able to live because of their constant input of energy

Types of Energy Chemical energy Thermal energy Radiative energy Potential and Kinetic Energy Electrical energy Mechanical energy

Key Energy Laws Energy cannot be created or destroyed –The total amount of energy in the universe is constant. Energy can be converted from one form to another –Often, some of that energy is lost as heat.

Energy used for: –Metabolism –Cellular growth –Cell reproduction The remainder of energy is lost as heat

Most organisms get their energy from the sun –Photosynthesis Animals get their energy by eating those organisms that get their energy directly or indirectly from the sun

Metabolic Pathways Catabolic –Break down food molecules –Release energy Anabolic –Generate molecules needed by the cell –Require energy Coupled pathways –Energy produced by catabolic reactions is used to generate larger necessary molecules

Thermodynamics and Order Second Law of Thermodynamics –There is a universal tendency for things to become disordered –Systems will change spontaneously towards those conditions that are the most likely

Entropy Measurement of the disorder of a system –Greater the disorder = Greater the entropy –Systems will spontaneously change towards arrangements with more entropy So how are cells/organisms/etc. so darn ordered? Figure 3-3 Essential Cell Biology (© Garland Science 2010)

Order Becoming ordered REQUIRES ENERGY Chemical reactions that generate order: –Need energy to occur –Release heat Heat energy is transferred to the surroundings Figure 3-5 Essential Cell Biology (© Garland Science 2010)

Amount of heat released into the surroundings will increase its disorder This disorder needs to be/will more than enough to compensate for the order generated by the chemical reaction

Where does this heat come from? First Law of Thermodynamics –Energy can be converted from one form to another Energy can not be created or destroyed Energy need to create chemical bonds, but some of that energy will be lost –Chemical energy to thermal energy Figure 3-6b Essential Cell Biology (© Garland Science 2010)

Recap……. Catabolic processes break down molecules and release energy –Ex: digesting and breaking down food Anabolic processes build molecules and require energy –Ex: Building proteins Processes that require energy are coupled to (tied to) processes that release energy

Recap continued….. A coupled reaction will proceed as long as the overall disorder in the system increases –Entropy –Order = requires energy, releases heat –Disorder = heat used to increase

Energy and Catalysis Energetic pathways in the body are regulated by ENZYMES –Proteins –Each reaction in the body is catalyzed by a specific enzyme Combine molecules OR break a molecule apart –Metabolic pathway Different enzymes working in sequence to form chains of reactions

Why do we need enzymes? Can help speed up chemically favorable reactions –Spontaneous, increase disorder Not all chemical reactions are favorable –They increase order –Enzymes LOWER THE ACTIVATION ENERGY needed to make the reaction happen

Energy to start a reaction Chemical reactions occur because molecules collide with each other Can add energy to a system by: –____________ temperature –____________ pressure –Using an enzyme –**increase the chance that the molecules will run into each other**

Enzyme structure Protein Active site –Site of catalysis –Metal ion Substrate –a.k.a. ligand

How does binding even happen? Crowded! Diffusion Molecular rate of motion Initially weak interactions can lead to strong ones Strong association means a slow rate of dissociation Figure 3-23 Essential Cell Biology (© Garland Science 2010)

Inhibiting enzyme activity Competitive inhibition –Active site Noncompetitive inhibition –Not at the active site

Enzyme inhibitors ACE (angiotensin converting enzyme) inhibitors –Targets high blood pressure Reverse transcriptase inhibitors –Targets HIV

ACE Inhibitors Angiotensin II Causes muscles surrounding blood vessels to contract Narrows blood vessels What will this narrowing cause?

Angiotensin I converted to Angiotensin II by ACE No ACE = no increase in blood pressure

ACE inhibitors are non-selective –Interaction between a zinc atom in the enzyme and a chelating group in the inhibitor –More side effects!

HIV

Activation Energy Energy barrier that molecules may need to get over to get to a lower energy state Probability of molecules getting together to make a reaction happen –Some may need help!

Reverse transcriptase Uses virus’s genetic material (RNA) to make DNA This DNA is then incorporated into the host cell’s DNA –Used to make virus proteins

AZT Inhibits reverse transcriptase Thymidine analog –Lacks –OH group Reverse transcriptase cannot proceed! –Stops working…no DNA made

Food Chemistry Lab Moving it to Wednesday/Thursday –Bring in food any time before then! Materials and Methods –Typed Materials and Methods section needs to be turned in on Wednesday –Six sections A. Materials B. Preparation of test liquid C. Test for simple sugars using Benedict’s solution D. Test for starches using Lugol’s iodine E. Test for proteins using Biuret solution F. Test for fats using Sudan IV

Back to general properties of enzymes… In any chemical reaction, there is a defined amount of energy needed to make the reaction happen –Activation energy Increasing the kinetic energy of molecules helps them overcome the energy barrier What the limitations of increasing kinetic energy in vivo?

Figure 3-12 Essential Cell Biology (© Garland Science 2010) Enzymes lower the activation energy of a reaction –Spatially bring reactants together

Enzymes: –Do not change the free energy of the reactants or the products –Are not used up in the chemical reaction