Biology 102 Lecture 10: Energy Flow in Cells (Part 1) Alternate title: “How life on earth can exist despite the fact that the universe is falling apart”

Lecture outline 1. Some perspective: “Where we’ve been and where we are going…” 2. Energy and the Universe: The two basic laws of thermodynamics 3. How does energy flow in chemical reactions? 4. How is energy “carried” between coupled reactions?

1. Some perspective… Last few lectures have focused on the puzzle pieces Last few lectures have focused on the puzzle pieces  Atoms and bonds  Organic molecules (structure and function)  Parts of a cell (structure and function) Remaining lectures build towards understanding of how these pieces fit together... Remaining lectures build towards understanding of how these pieces fit together...  For example…

2. Energy and the Universe Life on earth is basically a little pocket of order in a universe tending toward disorder. Life on earth is basically a little pocket of order in a universe tending toward disorder.

The two basic laws of thermodynamics Law 1: QUANTITY of energy Law 1: QUANTITY of energy  The Universe (or any closed system) has a constant amount of energy. Energy cannot be created or destroyed, but only changed in form.  So, what is “energy”?  So, what is “work”?

The two basic laws of thermodynamics (cont.) Forms of energy Forms of energy  Potential energy  Stored energy  Examples…  Kinetic energy  Energy in motion  Examples,,, Recap: Law 1 Recap: Law 1

The two basic laws of thermodynamics Law 2: QUALITY of energy Law 2: QUALITY of energy  Left to itself, any system spontaneously undergoes conversion to less organized forms  Energy becomes more randomly dispersed in form (often dissipating as heat) and less able to do work. Heat: Increased random movement of molecules Heat: Increased random movement of molecules

The entire universe is proceeding irrevocably toward complete disorder So how is it that life can exist on earth? So how is it that life can exist on earth?

3. How does energy flow in chemical reactions? What is a chemical reaction? What is a chemical reaction?  Making and breaking of chemical bonds Implications of the second law: Implications of the second law:  Orderly reactants to less ordered products releases energy (EXERGONIC)  Examples…

Implications of the second law (cont.) Implications of the second law (cont.)  Less ordered reactants to more orderly products requires energy (ENDERGONIC)  Examples…

Two key reactions important in living systems Photosynthesis Photosynthesis  THE major way energy from the sun is incorporated into organisms  ENDERGONIC Cellular respiration Cellular respiration  THE major way cells of most organisms obtain energy for chemical reactions  EXERGONIC

Activation energy Initial input of energy required to start reactions (both exergonic and endergonic) Initial input of energy required to start reactions (both exergonic and endergonic)

4. How is energy carried between “coupled” reactions? What are coupled reactions? What are coupled reactions?  Examples ATP is the principle energy carrier that allows coupling of reactions ATP is the principle energy carrier that allows coupling of reactions  The basics: ATP produced during an exergonic reaction provides energy to for endergonic reactions

What’s so great about ATP? 1. High energy phosphate bonds! 2. Convenient size unit

What’s so great about ATP? Bonds easily formed for easy energy transfer from a high energy compound to ATP Bonds easily formed for easy energy transfer from a high energy compound to ATP Bonds are unstable to easily give up energy in a reaction Bonds are unstable to easily give up energy in a reaction

Coupled reactions within living cells Glucose breakdown (cellular respiration) produces ATP Glucose breakdown (cellular respiration) produces ATP Protein synthesis requires ATP breakdown Protein synthesis requires ATP breakdown

Electron carriers