Respiration

1. Respiration Topic 8.1

2. Respiration • In respiration, energy stored in organic food molecules is transferred to adenosine triphosphate (ATP) • ATP is used to run various metabolic processes in the cell • Synthesizing ATP uses a series of oxidation and reduction reactions • Energy lost from the oxidation of food molecules can be absorbed by the reduction reaction to form ATP

3. Oxidation • Typically has a loss of energy • Has a loss of electrons which increases charge • A lot of times facilitated by the gain of oxygen • Also facilitated by the loss of a hydrogen

4. Reduction • Typically has a gain of energy • Has a gain of electrons which reduces charge • A lot of times associated with the loss of an oxygen • Also associated by gain of hydrogen

5. Glycolysis • The first step of all types of cellular respiration • Happens in the cytoplasm of all cells • A 6 carbon molecule of glucose is oxidized into 2, 3 carbon pyruvate molecules coupled with the reduction of ADP to ATP • Broken into several steps

6. Glycolysis cont. Phosphorylation • First stage begins by phos-phorylating glucose into a hexose diphosphate • This step actually uses ATP • The phosphate groups that are added allow a stronger interaction between the hexose and its enzyme

7. Glycolysis cont. Lysis • Hexose diphosphate is broken down into two 3, Carbon triose phosphate molecules • These are intermediate molecules in many biochemical reactions • The phosphate group on each of the triose phosphates allows a stong bond with the next enzyme in the pathway

8. Glycolysis cont. Oxidation and ATP formation • Each triose phosphate (TP) is oxidized to a 3 carbon molecule called pyruvate • Each TP has a hydrogen removed to reduce a NAD+ into a NADH • Each TP also uses the energy in its phosphate bond to phosphoryl-ate 2 ADP into ATP (total of 4 ATP made minus 2 used at beginning for net of 2) • Called substrate level phosphorylation

9. Substrate level phosphorylation • When ATP is produced by a direct transfer of a phosphate group from a substrate molecule to an ADP • This is in contrast to chemiosmotic pumps

10. Mitochondria • Matrix – fluid inside the mitochondria that contains enzymes for Krebs cycle and link reaction • Outer membrane – separates contents from rest of cell and creates a compartment for aerobic respiration • Inner membrane – contains the electron transport chains and ATP synthase, which carry out oxidative phosphorylation

11. Cristae – tubular projections of the inner membrane which increase the surface area for oxidative phosphorylation- the creation of ATP • Space between the inner and outer membranes- protons are pumped into it by the electron transport chain. Because of the small space a high concentration is formed for chemiosmosis

12. Aerobic Respiration Aerobic Respiration is the production of ATP in the presence of Oxygen in the mitochondria Link Reaction • Pyruvate made in glycolysis is absorbed by the mitochondria • Enzymes in the matrix remove hydrogen from the pyruvate (oxidation) • Other enzymes remove a carbon from 3C-pyruvate (decarboxylation)

13. Link reaction cont. • These two steps together are called oxidative decarboxylation • Hydrogen is accepted by NAD+ (reduced) to NADH+H • Carbon that is removed becomes CO2 waste • Remaining two-carbon molecule is an acetyl group which reacts with Co-enzyme A to become acetyl CoA • Acetyl CoA is the start molecule of the Krebs cycle

14. Krebs cycle

15. Krebs Cycle cont. • The product of the link reaction (acetyl CoA) joins the Krebs cycle which takes place in the matrix. 1. Acetyl CoA joins a 4C acceptor compound already in the cycle to form a 6C molecule (citric acid). - Coenzyme A is released to go and bring more pyruvate into the matrix

16. Krebs Cycle cont. 2. 6C compound (citric acid) is oxidatively decarboxylated to a 5C compound - this carbon is given of as CO2 - NAD+ is reduced to NADH + H

17. Krebs Cycle cont. 3. The 5C compound is further oxidized and decarboxylated to make a 4C compound - again C is given off as CO2 - again a NAD+ is reduced to NADH+H

18. Krebs Cycle cont. 4. The remaining steps are the regeneration of the 4C acceptor molecule the will combine with acetly CoA at the beginning of the Krebs cycle - final reduction of an NAD+ to NADH+H - Reduction of a FAD (coenzyme) to FADH2 - ADP reduced to an ATP by substrate level phosphorylation

19. Krebs Cycle Summary One turn of the Krebs Cycle yields • 2 CO2 • 3 NADH+H • 1 FADH2 • 1 ATP (by subtrate level phos.) -Everything above is X2 because there are two molecules of pyruvate from every molecule of glucose - NADH+H and FADH2 will feed into the electron transport chain to make the majority of ATP

20. Electron Transport Chain akaOxidative Phosphorylation • The ETC is a series of electron carriers located in the inner mitochondrial membrane 1. Electron carrying molecules (NADH+H, FADH2) produced in the Krebs cycle move from the matrix to the inner membrane.

21. Electron Transport Chain akaOxidative Phosphorylation cont. 2. NADH+H and FADH2 are oxidized (lose electrons) and the H ions with attached electrons enter the ETC where the reduce (add electrons) a series of reactions.

22. Electron Transport Chain akaOxidative Phosphorylation cont. 3. Some of these reactions separate the H from their electrons. H ions then leave the ETC and enter the inter membrane space 4. The high concentration of H+ ions is used by ATP synthase during chemiosmosis to produce ATP

23. ATP synthesis during Chemiosmosis • As the H+ ions diffuse from the inter-membrane space back to the matrix, ATP synthase uses this force to turn its pumps which phosphorylates ADP to ATP • The coupling of the oxidation reactions in the ETC and mechanism of ATP synthase phosphorylating ATP is oxidative phosphorylation

24. Role of Oxygen in Respiration • Oxygen is the final electron acceptor at the end of the electron transport chain • At the same time it accepts H ions in the matrix to form water (waste product) • If O2 is not available, electrons will stop flowing thru ETC • NADH +H cannot be converted to NAD+ and the link reaction cannot take place for aerobic respiration

25. Electron Transport Chain akaOxidative Phosphorylation

26. Structure Folded inner membrane forming cristae Small space between double membranes Matrix Function Increases surface area for the electron transfer system Allows accumulation of protons Isolates enzymes for Krebs cycle enzymes Structure vs. Function in Mitochondria • Electron micrographs of muscle cells can show adaptations to aerobic respiration • Increased number of Mitochondria • Increased concentration of Krebs cycle enzymes in matrix

27. Structure and Function cont. • Electron micrographs of muscle cells can show adaptions to aerobic respiration • Increased number of Mitochondria • Increased concentration of Krebs cycle enzymes in matrix

28. Acetyl CoA in Metabolism • Acetyl CoA is the start molecule of the Krebs cycle • Carbohydrates are broken down into pyruvate and pyruvate is converted to Acetyl CoA • Fats are broken down into glycerol and fatty acids • Fatty acids are broken into 2C fragments that that are oxidized into Acetyl CoA