CHAPTER 5 Harvesting Chemical Energy

Chemical Energy and Food All organisms require energy to carry out their life functions. Evolution has produced a number of biochemical processes that organisms use to obtain energy stored in food. Food provides: – Energy for living things and their cells to function How much energy is in food? – Calorie: amount of energy needed to raise the temperature of one gram of water one degree Celsius – Food labels are kilocalories (1,000 calories)

Metabolism Metabolism – all chemical reactions in an organism Composed of 2 parts: 1)Synthesis a)Reactions that require energy b)Use carbon skeletons and energy for cell growth and maintenance c)Example:Photosynthesis!

Metabolism, continued Composed of 2 parts: 2) Decomposition a. Release energy from food b.Produce carbon skeletons c.Example: 6O 2 + C 6 H 12 O 6  6CO 2 + 6H 2 O + Energy Which of the above makes ATP/ energy? Which of the above uses ATP/ energy?

Overview of Cellular Respiration Main Points: – Decomposition reaction – Provides cells with energy they need to function – Each step catalyzed by an enzyme – Releases energy by oxidizing sugars and other organic substances

Two Types of Respiration 1)Aerobic Respiration (which is typically referred to as Cellular Respiration) a.Requires oxygen b.Electrons flow to oxygen c.Raw materials are fats, proteins, and carbohydrates d.Energy is released e.Overall Equation: 2)Anaerobic Respiration a.Occurs without oxygen b.Electrons flow to another acceptor, such as nitrogen or sulfur in bacteria and yeast 6O 2 + C 6 H 12 O 6 6CO 2 + 6H 2 O + ATP Enzymes

The Stages of Aerobic Respiration GlycolysisKrebs CycleElectron Transport Location What goes in? What comes out? ATP formed Cytoplasm Mitochondrial Matrix Mitochondrial Membranes Glucose H2OH2O Pyruvate/ Acetyl CoA O 2, NADH and FADH 2 22 Net34 Pyruvate & NADH CO 2, NADH, & FADH 2

Glycolysis The first stage for both aerobic and anaerobic respiration. Definition: – The anaerobic (does not require O 2 ) process of breaking down glucose into 2 molecules of pyruvic acid – Each step is catalyzed by different enzymes Location in the Cell: – Cytoplasm of the cell

Steps of Glycolysis 1. Glucose is converted into glucose-6- phosphate – Requires the use of 2 ATP, which releases its phosphates 2.Glucose-6-phosphate is rearranged and eventually splits into two 3-C sugar- phosphates 3.Partial oxidation of these 3-C molecules results in … – the formation of pyruvic acid (pyruvate) – the production of ATP – NAD+ is reduced to form NADH, which will be sent to the ETS

Glycolysis Totals Total Energy Made: – To start glycolysis  2 ATP needed – During glycolysis  4 ATP made Net gain: 2 ATP Electron carrier: – 2 NAD + 2 NADH accepts e - – NAD + accepts 4 high energy electrons and forms NADH. NADH holds them until they are passed to other molecules.

The FATE of PYRUVATE The PRESENCE or ABSENCE of OXYGEN in the cell determines the FATE of PYRUVATE. Aerobic (oxygen) LACTATE Enters MITOCHONDRIA Anaerobic (no oxygen) PYRUVATE

Lactic Acid Fermentation Convert NADH and pyruvate into NAD+ and lactate NAD+ cycles back to glycolysis Small amounts of ATP are made. Other types of fermentation: Alcoholic fermentation… – Produces ethyl alcohol and CO 2. – EX: yeast used to make bread Acetic Acid fermentation… – Produces vinegar – EX: bacteria used to make yogurt, cheese, and sour cream

Fermentation cont. Total Energy Output of Fermentation= No new ATP made! (only 2 ATP from glycolysis) This is why we can’t exercise rapidly for long periods of time!

Cellular Respiration (Aerobic!)

The FATE of PYRUVATE The PRESENCE or ABSENCE of OXYGEN in the cell determines the FATE of PYRUVATE. Aerobic (oxygen) LACTATE Enters MITOCHONDRIA Anaerobic (no oxygen) PYRUVATE

Glycolysis Review At the end of glycolysis, there is still a lot of unused energy stored in the 2 molecules of pyruvic acid To access this energy, cells need O 2. Therefore, the final steps in cellular respiration are aerobic because they require O 2

Pyruvate enters the Mitochondria… Produces acetate (acetic acid) Produces NADH from NAD+ CoEnzyme A picks up acetate and forms Acetyl CoA CoA delivers acetate to the Krebs Cycle Also known as the Citric Acid Cycle

The Mitochondria – Cite of ATP synthesis – Compartments in which the Krebs cycle and electron transport chain occurs – Number in cells vary from 10 to 1000s based on activity – Made of 2 membranes: 1.Inner – contains many enzymes, made of more protein than lipids, forms cristae (folds) which increase surface area. 2.Outer – regulates movement of molecules in and out of the mitochondria

Steps of the Kreb’s Cycle An enzyme combines the 2C acetyl group of acetyl CoA with a 4C acid (oxaloacetate), forming a 6 C acid (citric acid) and releasing CoA. Enzymes rearrange the 6C acid and convert it into a 5 C acid (Ketogluterate). These reactions release CO 2 into the atmosphere and harvest electrons to form NADH from NAD+. Enzymes rearrange the 4 C acid two times, forming one molecule of ATP (2) and FADH 2 Finally, enzymes convert the rearranged 4 C acid into oxaloacetate and form a third molecule of NADH. The cycle continues as oxaloacetate enters the beginning.

Pyruvic acid or Pyruvate Acetyl- CoA CO 2 atmosphere Citric acid or Citrate Other molecules electrons CO 2 Captured by NAD+ and FAD To E.T.C H+ 2 ATP

Remember… The CO 2 released is the source of the CO 2 in your breath when you exhale ATP produced directly in the Kreb’s cycle can be used in cellular activities When O 2 is present, the high energy electrons can be used to generate huge amounts of ATP

Steps of the Electron Transport System 1.H atoms are carried by NAD and FAD to the ETS 2.Each system consists of a series of electron carriers, enzymes, and other proteins known as cytochromes which are embedded in the cristae of the mitochondria. 3.H atoms are accepted by the system and separated into electrons and protons. 4.The electron carriers transfer the electrons step by step through the system to a cytochrome. 5.The cytochrome combines the electrons with protons and O 2 forming H 2 O (this step requires oxygen!)

Steps of the Electron Transport System 6.At each step the electrons release free energy, some is used by proton pumps to actively transport protons from the matrix across the cristae to the intermembrane space. 7.A high concentration of protons accumulate causing it to be unstable 8.Protons diffuse back to the matrix of the mitochondria, they pass through the ATP synthase (where ATP is made.) 9.ATP can be transferred out of the mitochondria and used by the cell. e-e- e-e- e-e- e-e- ATP e-e- NADH  NAD + + e - + H + FADH 2  FAD + e - + H + O2O2 H+H+ H2OH2O Exhaled as waste