1 Energy metabolism, enzyme and Cofactors

2 Forms of Energy These forms of energy are important to life: – chemical – radiant (examples: heat, light) – mechanical – electrical Energy can be transformed from one form to another. Chemical energy is the energy contained in the chemical bonds of molecules. Radiant energy travels in waves and is sometimes called electromagnetic energy. An example is visible light. Photosynthesis converts light energy to chemical energy. Energy that is stored is called potential energy.

3 Laws of Thermodynamics 1st law: Energy cannot be created or destroyed. – Energy can be converted from one form to another. The sum of the energy before the conversion is equal to the sum of the energy after the conversion. Example: A light bulb converts electrical energy to light energy and heat energy. Fluorescent bulbs produce more light energy than incandescent bulbs because they produce less heat. 2nd law: Some usable energy dissipates during transformations and is lost. – During changes from one form of energy to another, some usable energy dissipates, usually as heat. The amount of usable energy therefore decreases.

4 Energy is required to form bonds. Atoms or molecules Energy + Energy Larger molecule The energy that was used to form the bonds is now stored in this molecule.

5 Energy is released when bonds are broken. Energy The energy is now released. It may be in a form such as heat or light or it may be transferred to another molecule. Menu

6 ATP (Adenosine Triphosphate) CH N C C C NH 2 N HC N N C C C C O C O P O P O P O CH 2 O O O O - O - O - - H OH H 3 phosphate groups Base (adenine) Ribose

7 A ATP ATP Stores Energy The phosphate bonds are high-energy bonds. A Energy ADP + P i + Energy Breaking the bonds releases the energy.

8 ATP ADP + P i Energy (from glucose or other high-energy compounds) ATP is Recycled ATP (Adenosine Triphosphate) is an energy-rich molecule used to supply the cell with energy. The energy used to produce ATP comes from glucose or other high-energy compounds. ATP is continuously produced and consumed as illustrated below. ADP + P i + Energy  ATP + H 2 O (Note: P i = phosphate group)

ATP ADP + P i Energy Menu ATP ADP ATP Energy release Energy absorbed + P i

10 Catabolic and Anabolic Reactions the breakdown of complex organic compounds to simpler compounds generally release energy and are called catabolic reactions. Anabolic reactions are those that consume energy while synthesizing compounds. ATP produced by catabolic reactions provides the energy for anabolic reactions. Anabolic and catabolic reactions are therefore coupled (they work together) through the use of ATP.

ATPADP + P i Energy Menu An anabolic reaction A catabolic reaction

12 Energy Supplied Energy Released Anabolic Reactions Anabolic reactions consume energy. Substrates (Reactants) Products Menu

13 Energy Supplied Energy Released Catabolic reactions release energy Catabolic Reactions Substrate (Reactant) When bonds are broken, energy is released. Menu

14 Energy Supplied Energy Released Activation Energy Menu spark An example of activation energy is the spark needed to ignite gasoline.

15 Energy Supplied Energy Released Activation energy without enzyme Activation energy with enzyme Enzymes lower the amount of activation energy needed for a reaction. Menu

16 is transferred with electrons Energy is transferred with electrons Oxidized atom Electron is donated Energy is donated Reduced atom Electron is received Energy is received

17 is transferred with electrons Energy is transferred with electrons Oxidized atom Electron is donated Energy is donated Reduced atom Electron is received Energy is received Oxidized atom Electron is donated Energy is donated Reduced atom Electron is received Energy is received

18 is transferred with electrons Energy is transferred with electrons Oxidized atom Electron is donated Energy is donated Reduced atom Electron is received Energy is received Oxidized atom Electron is donated Energy is donated Reduced atom Electron is received Energy is received This atom served as an energy carrier. It picked up an electron from the atom on the left and gave it to the one on the right.

19 Oxidation and Reduction Oxidation is the loss of electrons or hydrogen atoms. Oxidation reactions release energy. Reduction is gain of electrons or hydrogen atoms and is associated with a gain of energy. Oxidation and reduction occur together. When a molecule is oxidized, another must be reduced. These coupled reactions are called oxidation-reduction or redox reactions. Food is highly reduced (has many hydrogens). The chemical pathways in cells that produce energy for the cell oxidize the food (remove hydrogens), producing ATP.

20 Cofactors Many enzymes require a cofactor to assist in the reaction. These "assistants" are nonprotein and may be metal ions such as magnesium (Mg++), potassium (K+), and calcium (Ca++). The cofactors bind to the enzyme and participate in the reaction by removing electrons, protons, or chemical groups from the substrate.

21 Coenzymes Cofactors that are organic molecules are coenzymes. In oxidation-reduction reactions, coenzymes often remove electrons from the substrate and pass them to different enzymes. In this way, coenzymes serve to carry energy in the form of electrons (or hydrogen atoms) from one compound to another.

22 Coenzymes Coenzymes are organic cofactors that are not protein. They bind to the enzyme and also participate in the reaction by carrying electrons or hydrogen atoms. Enzyme Coenzyme

23 Vitamins are Coenzymes VitaminCoenzyme Name B 3 (Niacin)NAD + B 2 (riboflavin)FAD B 1 (thiamine)Thiamine pyrophosphate B 5 (Pantothenic acid)Coenzyme A (CoA) B 12 Cobamide coenzymes

24 Electron Carriers Some coenzymes are electron carriers function in photosynthesis and cellular respiration. Three major electron carriers are listed below. Respiration – NAD + – FAD Photosynthesis – NADP +

NAD + (Nicotinamide Adenine Dinucleotide) Organic Molecule + NAD + NAD + + 2H  NADH + H + NAD + functions in cellular respiration by carrying two electrons. With two electrons, it becomes NADH. NAD + oxidizes its substrate by removing two hydrogen atoms. One of the hydrogen atoms bonds to the NAD +. The electron from the other hydrogen atom remains with the NADH molecule but the proton (H + ) is released. NAD + + 2H  NADH + H + NADH can donate two electrons (one of them is a hydrogen atom) to another molecule. Menu Oxidized Organic Molecule +

26 NAD + + 2H  NADH + H + NADH + H + NAD + Energy + 2H Energy + 2H

27 NADP + + 2H  NADPH + H + NADPH + H + NADP + Energy + 2H Energy + 2H

28 NADP + (Nicotinamide Adenine Dinucleotide Phosphate) NADP + + 2H  NADPH + H + NADP + is similar to NAD + in that it can carry two electrons, one of them in a hydrogen atom, the other one comes from a hydrogen that is released as a hydrogen ion. (Click here to review NAD +.)Click here to review NAD +. Electrons carried by NADPH in photosynthesis are ultimately used to reduce CO 2 to carbohydrate.

29 Phosphorylation ATP is synthesized from ADP + P i. The process of synthesizing ATP is called phosphorylation. Two kinds of phosphorylation are illustrated on the next several slides. – Substrate-Level Phosphorylation – Chemiosmotic Phosphorylation

30 Substrate-Level Phosphorylation ADP High-energy molecule A high-energy molecule (substrate) is used to transfer a phosphate group to ADP to form ATP.

31 Substrate-Level Phosphorylation ADP High-energy molecule A high-energy molecule (substrate) is used to transfer a phosphate group to ADP to form ATP. This bond will be broken, releasing energy.

32 Substrate-Level Phosphorylation ADP High-energy molecule A high-energy molecule (substrate) is used to transfer a phosphate group to ADP to form ATP. The energy released will be used to bond the phosphate group to ADP, forming ATP.

33 Substrate-Level Phosphorylation A high-energy molecule (substrate) is used to transfer a phosphate group to ADP to form ATP. Enzyme An enzyme is needed. ADP High-energy molecule

34 Substrate-Level Phosphorylation Enzyme

35 Substrate-Level Phosphorylation Low-energy moleculeATP The energy has been transferred from the high- energy molecule to ADP to produce ATP.

36 Mitochondrion Structure Cristae Matrix Intermembrane Space This drawing shows a mitochondrion cut lengthwise to reveal its internal membrane.

H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Outside Intermembrane Space Matrix This drawing shows a close-up of a section of a mitochondrion. Matrix (inside) Chemiosmotic Phosphorylation Menu

00 H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Outside Intermembrane Space Matrix Matrix (inside) Menu Pumps within the membrane moves hydrogen ions from the matrix to the intermembrane space creating a concentration gradient. H+H+ H+H+ H+H+ This process requires energy -- cellular respiration.

H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Outside Intermembrane Space Matrix Matrix (inside) Menu Chemiosmotic Phosphorylation A high concentration of hydrogen ions in the intermembrane space creates a gradient for diffusion of H+ back to the matrix.

H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Outside Intermembrane Space Matrix Matrix (inside) Menu the hydrogen ions pass through this protein (called ATP synthase) as they return to the matrix down the diffusion gradient. Chemiosmotic Phosphorylation

H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ATP ADP + P i H+H+ Outside Intermembrane Space ATP synthase produces ATP by phosphorylating ADP. The energy needed to produce ATP comes from hydrogen ions forcing their way into the matrix as they pass through the ATP synthase. Matrix (inside) Menu Chemiosmotic Phosphorylation

42 Chemiosmotic Phosphorylation Chemiosmotic phosphorylation is used by the mitochondrion to produce ATP. The energy needed to initially pump H + ions into the intermembrane space comes from glucose. The entire process is called cellular respiration. The chloroplast also produces ATP by chemiosmotic phosphorylation. The energy needed to produce ATP comes from sunlight.

43 Chloroplast Structure The chloroplast is surrounded by a double membrane. Molecules that absorb light energy (photosynthetic pigments) are located on disk-shaped structures called thylakoids. The interior portion is the stroma. Thylakoids Double membrane Stroma

44 H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ A Thylakoid In order to synthesize ATP, hydrogen ions must first be pumped into the thylakoid. This process requires energy. A concentration gradient of hydrogen ions is established. The chemical gradient can be used as an energy source for producing ATP.

45 H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ADP + P i ATP Chemiosmotic Phosphorylation ATP synthase produces ATP by phosphorylating ADP. The energy comes from hydrogen ions forcing their way into the stroma as they pass through the ATP synthase hydrogen ions force through this protein (ATP synthase) as they return to the stroma.

46 Phosphorylation We have just discussed two different forms of phosphorylation: – Substrate-level phosphorylation – Chemiosmotic phosphorylation We saw that chemiosmotic phosphorylation occurred in both the mitochondria (during cellular respiration) and in the chloroplast (during photosynthesis). These two processes are sometimes given separate names: – Oxidative phosphorylation (in mitochondria) – Photophosphorylation (in chloroplast)

Chemiosmosis : Chloroplasts vs. Mitochondria Similarities Similarities: In both organelles Redox reactions of electron transport chains generate a H+ gradient across a membrane Involves ATP synthase which uses this proton-motive force to make ATP Difference Difference: use different sources of energy to accomplish this (proton gradient). Chloroplasts use light energy (photophosphorylation) and mitochondria use the chemical energy in organic molecules (oxidative phosphorylation).