Cellular Respiration: ATP and Glycolysis IB HL Biology 1 Topic Statements 3.7 and 8.1 Adapted from L. Ferguson and J. Naftzinger

Cell Respiration- controlled release of energy from organic compounds in cells to form ATP 3.7.1

Why cell respiration? Cells require a constant source of energy to perform various tasks Movement Transport Division

Energy and Cells All living cells need a continual supply of energy This energy is used for a wide range of processes including active transport and protein synthesis Most of these processes require energy in the form of ATP (adenosine triphosphate) ATP is a chemical substance that can diffuse to any part of the cell and release energy

Summary Equation C6H12O6 + O2  CO2 + H2O + ATP The summary equation for cellular respiration is: C6H12O6 + O2  CO2 + H2O + Glucose + oxygen  carbon dioxide + water + ATP ATP

Key players in this process Glucose: source of fuel NAD+/FAD: electron carriers Differences between NAD and FAD Enzymes: mediate entire process Mitochondria: site of aerobic respiration ATP: principal end product Protons/Electrons: sources of potential energy Oxygen: final electron acceptor

NAD+ and FAD carry electrons or hydrogens oxidation = when a molecule loses electrons reduction = when a molecule gains electrons some molecules are used as an electron shuttle: moving electrons from one part of the process to another NAD+ and FAD carry electrons or hydrogens (NADH and FADH2)

NAD+: an electron carrier In order for electrons to be passed from one compound to another, an electron carrier is needed NAD+ is reduced to NADH when picking up electrons It is oxidized back to NAD+ when losing them

HOW OXIDATION REDUCTION 8.1.1 Forms of oxidation and reduction. In respiration the oxidation of organic compounds is coupled to the reduction of ADP to ATP. The oxidation of ATP is then coupled to biological processes such as muscle contraction of protein synthesis. OXIDATION HOW REDUCTION Loss of electrons NAD+ and FAD pick up oxygen, lose hydrogens, and gain e- from glucose and drop them off at the ETC where they add a little energy to move H+ ions which all are picked up by oxygen Gain of electrons Gain of oxygen Loss of oxygen Loss of hydrogen Gain of hydrogen Results in many C-O bonds Results in many C-H bonds Results in a compound with lower potential energy Results in a compound with higher potential energy

Redox Reactions Reduction: reducing overall positive charge by gaining electrons Oxidation: loss of electrons OIL RIG Oxidation Is Loss of e- and addition of oxygen Reduction Is Gain of e- and loss of oxygen Redox reactions produce energy change Reduction absorbs energy (endergonic) Oxidation releases energy (exergonic)

Why many REDOX Reactions? Combustion of glucose  many reactions (enzymes) The alternative in one simple reaction… D’oh ! KaBoOM !!

Where do the electrons come from? Remember all those hydrogen atoms that make up glucose? Hydrogens are found in fats, too. Hydrogen = 1e-, so here, H = e-

Respiration is a controlled release of energy It’s a highly exergonic, but well-controlled process Mediated by enzymes, electron carriers Otherwise, it would be like an explosion Not compatible with life!

Every cell produces its own ATP, by a process called cell respiration In cell respiration, organic compounds such as glucose or fat are carefully broken down Energy from them is used to make ATP Cell respiration is defined as controlled release of energy, in the form of ATP, from organic compounds in cells Cell respiration can be aerobic or anaerobic. Aerobic cell respiration involves the use of oxygen and anaerobic cell respiration does not

Phosphorylation Addition of a phosphate group to a molecule; ex. Adding PO4 to ADP to form ATP Occurs in two ways Substrate level phosphorylation Oxidative phosphorylation

Substrate-level phosphorylation An enzyme transfers a phosphate group from a substrate to ADP Making ATP with an enzyme Ineffective in generating large amounts of ATP Occurs during glycolysis; addition of PO4 to glucose and ATP is made when pyruvate loses PO4 to ADP

Oxidative phosphorylation Refers to phosphorylation that occurs due to redox reactions transferring electrons from food to oxygen Occurs in electron transport chains in mitochondrion Makes ATP using energy derived redox reactions

Three stages of cell respiration Stage 1: Glycolysis (energy investment) Some ATP is made, some is used Stage 2: Krebs Cycle (oxidation of pyruvate) Generation of CO2 Stage 3: Oxidative Phosphorylation -ETC Generation of most ATP

Three stages of respiration

The Use of Glucose in Respiration Glucose is often the organic compound that is used in cell respiration During Glycolysis, chemical reactions in the cytoplasm break down glucose into a simpler organic compound called pyruvate In these reactions, a small amount of ATP is made using energy released from glucose Glucose is a 6 carbon monosaccharide molecule. Pyruvate is a 3 carbon molecule. http://www.johnkyrk.com/glycolysis.html

Summary of glycolysis: Location: Cytoplasm of all cells Outline: Oxidation of Glucose (6 carbons) to two Pyruvate (3 carbon compound) is coupled to the reduction of ADP to ATP In the following models the hydrogen and oxygen are not shown. The models show the number of carbons in each molecule not the structural formula. Summary of glycolysis: Remember in the examination you will come across the names of the molecules and stages rather than these model diagrams. So make sure you learn the terminology. Glycolysis takes place in the cytoplasm of the cell. It does not require oxygen. The hexose sugar (glucose) is converted into two 3C atoms compounds called pyruvate. Two ATP are consumed but four are produced making a net gain of 2 ATP Two NADH + H+ are produced which will yield more ATP when they are transferred to the mitochondria and oxidative phosphorylation. Yield: 2 Pyruvate + 2 ATP + 2NADH + 2H+

PHOSPHORYLATION The first stage actually begins by phosphorylating glucose to a hexose diphosphate. The phosphate groups allow a stronger interaction between the hexose and its enzyme.

LYSIS This stage involves the breaking of the hexose diphosphate into two triose phosphate molecules. The triose phosphate is an intermediate in many biochemical reactions. The phosphate group allows the sugar to form stronger interaction with the next enzyme in the pathway.

OXIDATION/ATP FORMATION This is the main oxidative stage of glycolysis which results in the formation of ATP and NADH + H+ Each Triose phosphate (TP) is oxidized to a 3 carbon molecule called Pyruvate Each TP has hydrogen removed (oxidation) to reduce one NAD+ to NADH Each TP adds a phosphate to Adenosine Diphosphate reducing this to ATP (substrate level phosphorylation) Note that each Triose phosphate releases enough energy for the formation of two ATP

Energy In: 2 ATP Energy Out: 4 ATP NET 2 ATP Steps – A fuel molecule is energized, using ATP. Glucose 1 3 Step 1 Glucose-6-phosphate 2 Fructose-6-phosphate Energy In: 2 ATP 3 Fructose-1,6-diphosphate Step A six-carbon intermediate splits into two three-carbon intermediates. 4 4 Glyceraldehyde-3-phosphate (G3P) 5 Step A redox reaction generates NADH. 5 1,3-Diphosphoglyceric acid (2 molecules) 6 Steps – ATP and pyruvic acid are produced. 3-Phosphoglyceric acid (2 molecules) Energy Out: 4 ATP 6 9 7 2-Phosphoglyceric acid (2 molecules) 8 2-Phosphoglyceric acid (2 molecules) NET 2 ATP 9 Pyruvic acid (2 molecules per glucose molecule)

Glycolysis Animations McGraw Hill animation Glycoysis movie

The Evolutionary Significance of Glycolysis Glycolysis occurs in nearly all organisms Glycolysis probably evolved in ancient prokaryotes before there was oxygen in the atmosphere

Glycolysis General Outline No Oxygen Anaerobic Oxygen Aerobic Glucose Glycolysis No Oxygen Anaerobic Oxygen Aerobic Pyruvic Acid Transition Reaction Fermentation Krebs Cycle ETS 4 ATP Net 2 ATP 36 ATP