Metabolism 1 Notes - activation energy, catalysts, ATP, enzymes PDF

Preview

Summary

activation energy, catalysts, ATP, enzymes...

Description

1.

2.

3.

6.1 The Flow of Energy in Living Systems a. Energy can take many forms i. Energy: capacity to do work ii. Kinetic energy: energy of motion iii. Potential energy: stored energy (objects that are not actively moving but have capacity to do so iv. Forms of energy: mechanical energy, heat, sound, electric current, light, or radioactivity 1. Most common: heat 2. Measured in kilocalorie a. 1 calorie is the heat required to raise temperature of one gram of water one degrees C b. The Sun provides energy for living systems i. The Sun provides energy for living systems ii. Sunlight provides earth with more than 13x1023 calories iii. Photosynthesis: energy absorbed from sunlight is used to combine small molecules (H20 and C) into more complex ones (sugar) 1. Energy from sunlight is stored as potential energy in the covalent bonds between atoms in the sugar molecules 2. Breaking the bonds requires energy 3. C-H bonds require lots of energy to break and breaking those bonds provide a lot of energy c. Oxidation-reduction reactions transfer electrons while bonds are made or broken i. During a chemical reaction, the energy stored in chemical bonds may be used to make new bonds ii. Atom or molecule that loses and electron: oxidized iii. An atom or molecule that gains an electron: reduced iv. Oxidation and reduction take place together so chemical reactions of this sort are called oxidation-reduction or redox reactions 6.2 The Laws of Thermodynamics and Free Energy a. Handout Summary i. Writing chemical reactions: reactants on left, products on right ii. Chemical reaction may either result in net release of energy or require net input of energy iii. Measure changes in energy levels in terms of free energy (G) iv. Higher number of G means that the substance has more free energy v. Reactions that result in a net release of energy are exergonic 1. Net release of energy meant that reaction products have less free energy than initial reactants vi. Endergonic reactions: net gain of free energy 1. Products have more free energy than reactants b. Spontaneous chemical reactions require activation energy i. Activation energy 1. Before new chemical bonds can form, even bonds that contain less energy, existing bonds must first be broken, and that requires energy input 2. Activation energy: extra energy needed to destabilize existing chemical bonds and initiate a chemical reaction 3. Rate of exergonic reaction depends on the activation energy required for the reaction to begin a. Reactions with larger activation energies tend to proceed more slowly because fewer molecules succeed in getting over the initial energy hurdle b. Rate of reaction increased in 2 ways: i. Increasing the energy of reacting molecules ii. Lowering activation energy ii. How catalysts work 1. Stressing particular chemical bonds can make them easier to break 2. Catalysis: process of influencing chemical bonds in a way that lowers activation energy needed to initiate a reaction 3. Catalysts exert action by affecting an intermediate stage (transition state) in a reaction a. Energy needed to reach this intermediate stage is the activation energy b. Catalysts stabilize this transition state, thus lowering activation energy 6.3 ATP: The Energy Currency of Cells a. Cells store and release energy in the bonds of ATP i. The structure of ATP 1. ATP is composed of 3 smaller components a. 1st: five carbon sugar, ribose, which serves as the frame work to which the other subunits are attached b. 2nd: adenine: organic molecules composed of 1 C-N rings c. 3rd: 3 phosphates ii. How ATP stores energy

4.

1. Key to ATP storing energy lies in triphosphate groups 2. Phosphate groups highly repel each other bc negative charge 3. Unstable bonds holding phosphates together have low activation energy and are easily broken by hydrolysis 4. When broken, transfer a lot of energy 5. Hydrolysis of ATP has a negative change in G 6. When hydrolyzed: ADP + P i b. ATP hydrolysis drives endergonic reactions i. Cells use ATP to drive endergonic reactions ii. Reactions don’t occur spontaneously bc their products possess more free energy than their reactants c. ATP cycles continuously i. Instability of ATP’s phosphate bonds prevents it from being a good long-term energy-storage molecule ii. Cells use exergonic reactions to provide the energy needed to synthesize ATP from ADP + P i iii. Then they use the hydrolysis of ATP to provide energy to drive the endergonic reactions needed 6.4: Enzymes: Biological Catalysts a. chemical reactions within living organisms are regulated by controlling the points at which catalysis takes place b. An enzyme alters the activation energy of a reaction i. Enables enzyme to stabilize a temporary association between substrates ii. By bringing 2 substrates together in the correct orientation, an enzyme lowers activation energy required for new bonds to form c. Active sites of enzymes conform to fit the shape of substrates i. Most enzymes have one or more pockets called active sites ii. Substrates bind to active sites and form enzyme-substrate complex...