Chapter 6 – Energy flow in the life of a cell What is energy? What principles govern energy? How is energy utilized in biochemical reactions? How is energy carried in cells? How do cells control chemical reactions?

What is energy? Potential energy—stored energy 2. Kinetic energy—energy of movement

What is energy?

What principles govern energy? First law of thermodynamics Total energy remains constant in a closed system b. Energy cannot be created or destroyed

Second law of thermodynamics In an isolated system, any change causes the quantity of concentrated, useful energy to decrease Energy is converted from more useful to less useful forms Organization of matter and energy 1) Concentrated energy is more ordered (complex) chemically 2) Entropy—all processes in an isolated system result in an increase in randomness and disorder

How is energy utilized in biochemical reactions? A. Uses of energy in living things 1. Movement, metabolism, response to stimuli B. Energy flow in ecosystems

How is energy utilized in biochemical reactions? A. Energy is stored in the chemical bonds of biological molecules

How is stored chemical bond energy released so work can be accomplished?

How is energy utilized in biochemical reactions? Energy releasing chemical reactions are exergonic High energy reactants → Low energy products

How is energy utilized in biochemical reactions? Endergonic reactions Low energy reactants → high energy products

Chemical reactions and activation energy Why does a match not spontaneously burn?

How is energy utilized in biochemical reactions?

Endergonic chemical reactions Do endergonic reactions create energy? How can the product(s) of an endergonic reaction have more energy than the reactants?

How is energy utilized in biochemical reactions? Exergonic reaction provides energy to drive endergonic reactions

How is energy utilized in biochemical reactions? How is the energy that is released from an exergonic reaction harnessed and directed to drive its associated endergonic reaction? Energy carrier molecules a. ATP and electron carrier molecules

Biology: Life on Earth (Audesirk) Figure: 06.4 Title: ADP and ATP Caption: A phosphate group is added to (a) ADP (adenosine diphosphate) to make (b) ATP (adenosine triphosphate). In most cases, only the last phosphate group and its high-energy bond are used to carry energy and transfer it to endergonic reactions within a cell. In much of the remainder of the text, we will employ the shorthand representations of ATP and ADP. Chapter 1

Biology: Life on Earth (Audesirk) Figure: 06.UN04a Title: ATP synthesis Caption: ATP synthesis. Chapter 1

Biology: Life on Earth (Audesirk) Figure: 06.UN04b Title: ATP breakdown Caption: ATP breakdown. Chapter 1

How is energy utilized in biochemical reactions? Biology: Life on Earth (Audesirk) How is energy utilized in biochemical reactions? Figure: 06.5 Title: Coupled reactions within living cells Caption: Exergonic reactions (such as glucose metabolism) drive the endergonic reaction of ATP synthesis from ADP. The ATP molecule moves to a part of the cell where the breakdown of ATP liberates some of this energy to drive an essential endergonic reaction (such as protein synthesis). The ADP and phosphate are recycled to the exergonic reactions; they will be converted back to ATP. The overall reaction is “downhill”: More energy is produced by the exergonic reaction than is needed to drive the endergonic reaction. The extra energy is released as heat. Chapter 1

Biology: Life on Earth (Audesirk) Figure: 06.6 Title: Electron carriers Caption: Electron-carrier molecules such as nicotinamide adenine dinucleotide (NAD+) pick up electrons generated by exergonic reactions and hold them in high-energy outer electron shells. Hydrogen atoms are often picked up simultaneously. The electron is then deposited, energy and all, with another molecule to drive an endergonic reaction, typically the synthesis of ATP. Chapter 1

In exergonic chemical reactions, reactants have more energy than products. energy is destroyed by the reaction. reactants have less energy than products. reactant and product molecules possess equal amounts of energy. Both 1 and 2 are correct.

Why is photosynthesis considered an endergonic reaction in an isolated plant? The sun provides the activation energy necessary to drive the reactions of photosynthesis. Energy is created during photosynthesis. Sugar has less energy than the sun. Energy is released during photosynthesis. Low-energy reactants are converted into high-energy products.

Body fat is composed of lipids created by dehydration synthesis reactions to store energy. Which of the following statements concerning the energy in this system is true? Creating body fat violates the 1st law of thermodynamics since energy is being created Creating body fat violates the 2nd law of thermodynamics as complex lipids are more ordered than the fatty acids they are made from Creating body fat violates both the 1st and 2nd laws of thermodynamics The laws of thermodynamics do not apply to body fat, because these laws deal with energy, not body fat None of these statements are true

How do cells control chemical reactions? A. Activation energy requirements for all the chemical reactions occurring in an organism are too high B. Catalysts reduce activation energy requirements

How do cells control chemical reactions? Enzymes catalyze reactions in living organisms Bring reactant molecules close together 2. Make bonds easier to break

How do cells control chemical reactions? Enzymes are synthesized by cells Most enzymes are proteins

Biology: Life on Earth (Audesirk) Figure: 06.8 Title: Activation energy controls the rate of chemical reactions Caption: High activation energy (black curve) means that reactant molecules must collide very forcefully in order to react. Only very fast-moving molecules will collide hard enough to react, so reactions with high activation energies proceed slowly at low temperatures, where most molecules move relatively slowly. Catalysts lower the activation energy of a reaction (red curve), so a much higher proportion of molecules move fast enough to react when they collide. Therefore, the reaction proceeds much more rapidly. Chapter 1

How do cells control chemical reactions? Enzymes are very specific a. Specificity is based on shape of enzyme and substrate

How do cells control chemical reactions? Biology: Life on Earth (Audesirk) How do cells control chemical reactions? 4. Most enzymes function as parts of complex, regulated biochemical pathways Syncope – fainting Oligomenorrhea – infrequently light & abnormal menstrual cycles Chapter 1

Enzyme activity is regulated How do cells control chemical reactions? Enzyme activity is regulated

Biology: Life on Earth (Audesirk) Figure: 06.11 Title: Enzyme regulation by allosteric regulation and competitive inhibition Caption: (a) Many enzymes have an active site and an allosteric regulatory site on different parts of the molecule. (b) When enzymes are inhibited by allosteric regulation, binding by a regulator molecule alters the active site so the enzyme is less compatible with its substrate. (c) During competitive inhibition, a molecule somewhat similar to the substrate fits into the active site and blocks entry of the substrate. Chapter 1

Lipitor and cholesterol

Biology: Life on Earth (Audesirk) Enzyme activation Figure: 06.11 Title: Enzyme regulation by allosteric regulation and competitive inhibition Caption: (a) Many enzymes have an active site and an allosteric regulatory site on different parts of the molecule. (b) When enzymes are inhibited by allosteric regulation, binding by a regulator molecule alters the active site so the enzyme is less compatible with its substrate. (c) During competitive inhibition, a molecule somewhat similar to the substrate fits into the active site and blocks entry of the substrate. Chapter 1

Rate of catalyzed chemical reactions Environmental factors influence the “rate” of enzyme activity pH, temperature

Rate of catalyzed chemical reactions Environmental factors influence the “rate” of enzyme activity Concentration of enzymes, substrates, activation factors, inhibition factors

Most enzymes are proteins Mutation and loss of enzyme function Why do mutated enzymes result in biochemical disorders? -Lysosomal diseases

Which of these statements regarding enzymes is FALSE? Enzymes are proteins that function as biological catalysts. Enzymes display specificity for certain molecules to which they attach. Enzymes provide energy for the reactions they catalyze. The activity of enzymes can be regulated by factors in their environment. An enzyme may be used many times over for a specific reaction.

The hydrolysis of sucrose to glucose and fructose occurs spontaneously in human cells. However, if you dissolve sucrose in water and keep the solution overnight at room temperature, there is no detectable conversion to glucose and fructose. Why? The energy of the reactant is higher than the energy of the products. The energy of the products is higher than the energy of the reactant. The activation energy of the reaction increases. The reaction is endergonic. The reaction requires a catalyst.

Cellular methionine (an amino acid) concentrations are regulated by feedback inhibition. Which enzyme is most likely the target of feedback inhibition in methionine synthesis? 1) AK 2) DS 3) HSDH 4) HSP 5) CS HSP