1. Cell Respiration Mitochondria, scanning electron microscope (SEM) by Dr. David Furness

2. Life Requires Energy Living cells require energy from outside sources Organisms may get this energy from the sun, by consuming other organisms, or from heat and chemicals released by the earth.

3. Energy enters most ecosystems from the sun. Producers, such as green plants and algae, use that energy to generate polysaccharides like cellulose and starch from carbon dioxide.

4. Consumers ingest and release energy locked in those molecules through the process of cell respiration. – A food web shows the flow of that energy.

5. In biology, consumers are also referred to as heterotrophs. – From the Greek hetero- meaning “different”, and -troph meaning “nutrition.” Producers are referred to as autotrophs. – From the Greek auto- meaning “self”, and –troph meaning “nutrition”.

6. Potential and Kinetic Energy Polysaccharides, proteins, and lipids all contain a great deal of stored, or potential energy. – This energy is not useful to the cell unless it can be converted to kinetic energy in a controlled manner and used to create some kind of cellular motion.

7. ATP The molecule most utilized by cells to perform work is adenosine tri-phosphate, or ATP. – This molecule is sometimes called the “energy currency” of the cell.

8. ATP is an especially useful molecule for cells because its potential energy can be quickly and easily released by removing a phosphate group (PO 4 ) and generating ADP, or adenosine di- phosphate. – The phosphate group can also be re-added to the molecule later, making it like a tiny rechargeable battery.

9. The conversions between incoming light energy, macromolecules, and ATP all occur within two organelles in eukaryotes: – The chloroplast (production of polysaccharides by photosynthesis). – The mitochondria (release of ATP by cell respiration).

10. Glycolysis The first part of cell respiration, called glycolysis, occurs within the cytosol outside of the mitochondria. – Glycolysis translates to “splitting of sugar.”

11. The first part of glycolysis, called the investment phase, uses 2 ATP molecules are needed to split one molecule of glucose (a 6-carbon monosaccharide) into two molecules of pyruvate, a 3-carbon molecule.

12. The second part, the payoff phase, results in the production of 4 molecules of ATP and 2 molecules of NADH as the pyruvate is converted to pyruvic acid. Glycolysis also generates a molecule of NADH. – NADH is a carrier molecule that, in eukaryotes, transports a hydrogen ion (H+) and an electron (e-) for use later on in cell respiration.

13. In summary, these changes occur during glycolysis: – 1 Glucose → 2 Pyruvic Acid –4 ADP → 4 ATP –2 NAD+ → 2 NADH

14. Glycolysis produces ATP very quickly, which is an advantage when the energy demands of the cell suddenly increase. Glycolysis is anaerobic, meaning it does not require oxygen. – Some prokaryotes rely heavily on glycolysis, as they lack mitochondria needed to perform the rest of cell respiration. – Eukaryotes will also use glycolysis in situations where oxygen levels are insufficient. The process of generating ATP primarily from glycolysis is called anaerobic fermentation.

15. Fermentation Glycolysis is can only proceed as long as there is sufficient NAD+ present. Different organisms have evolved different ways of replenishing NAD+ from NADH: – Alcoholic fermentation converts the pyruvic acid to ethyl alcohol and carbon dioxide. – Lactic acid fermentation converts the pyruvic acid to lactic acid.

16. Eukaryotic yeast and some types of prokaryotic bacteria use alcoholic fermentation. – This process is used to produce alcoholic beverages and causes bread dough to rise.used to produce alcoholic beverages

17. Multicellular organisms, including humans, carry out fermentation using a chemical reaction that converts pyruvic acid to lactic acid. – This most often occurs when the muscles aren’t receiving sufficient oxygen.muscles aren’t receiving sufficient oxygen – The decrease in pH irritates muscle fibers and causes temporary soreness.

18. Movement to Mitochondria Before the next stage can begin, pyruvic acid must first be transported inside the mitochondria. Pyruvic acid is combined with an enzyme called Coenzyme A. – This enzyme helps with the transportation of pyruvic acid into the mitochondria.

19. Pyruvic acid + Coenzyme A makes Acetyl CoA, which moves into the mitochondria. One more molecule of NADH is produced. This also releases one molecule of CO2 as a waste product.

20. Citric Acid Cycle Acetyl-CoA from glycolysis enters the matrix, the innermost compartment of the mitochondrion. – Once inside, the Coenzyme A is released back to the cytosol.

21. The 2-carbon molecule of acetate that entered from glycolysis joins up with another 4- carbon molecule already present. This forms citric acid, and begins the citric acid cycle portion of cell respiration.

22. Citric acid (6-carbon molecule) proceeds through a series of steps that convert it back to the original 4- carbon molecule. – The two extra carbons are released as carbon dioxide.

23. Energy released by the breaking and rearranging of carbon bonds during this process is captured in the forms of ATP, NADH, and FADH 2. – FADH 2 has the same purpose as NADH – to transport high-energy electrons and H+ ions.

24. For each turn of the cycle, the following are generated: – 1 ATP molecule – 3 NADH molecules – 1 FADH 2 molecule

25. Citric Acid Cycle Summary Remember! Each molecule of glucose results in 2 molecules of pyruvic acid, which enter the citric acid cycle. Between acetyl-CoA formation and the citric acid cycle, the products are: – 6 CO 2 molecules, – 2 ATP molecules, – 8 NADH molecules, – 2 FADH 2 molecules.

26. Electron Transport Chain The electron transport chain occurs in the inner membrane of the mitochondria. – This part of cell respiration utilizes all of the molecules of NADH and FADH 2 that were generated in glycolysis and the citric acid cycle.

27. NADH and FADH 2 release the electrons and H+ ions they were carrying. – The electrons are passed along a chain of proteins. – The energy from these electrons is used to transport some of the H+ ions into the intermembrane space of the mitochondria.

28. When the electrons reach the end of the chain of proteins, they join up with the rest of the H + ions and oxygen to form water (H 2 O).

29. This creates a “reservoir” of H + ions in the intermembrane space of the mitochondria.

30. Chemiosmosis H+ then moves back across the membrane, into the inner fluid, passing through a channel protein called ATP Synthase. The power of this natural diffusion of H+ ions is used to convert ADP molecules into ATP molecules. – The process, called chemiosmosis, is analogous to how electricity is generated in a hydroelectric dam.

31. Total ATP Production 32 molecules of ATP are generated in chemiosmosis. – This combines with the 2 ATP produced in the citric acid cycle, and the 2 produced in glycolysis. The net result of cell respiration is about 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 36 total ATP – The remainder is lost as waste heat.

32. Other Energy Sources Carbohydrates are not the only source of energy taken in by consumer organisms. Proteins are digested into amino acids, triglycerides are digested into glycerol and fatty acids. – Each is able to enter cell respiration at some point.

33. Cell Respiration and Evolution Glycolysis occurs in nearly all organisms, so it probably evolved in ancient prokaryotes before there was oxygen in the atmosphere. The endosymbiosis theory states that the mitochondria of eukaryotes at one point was an independent species of prokaryotic bacteria that was absorbed by a eukaryotic cell through endocytosis.

34. Origin of Mitochondria Mitochondria are unlike any other organelle in that they only originate from other mitochondria. – The mitochondria present in each of your cells all originated from the ones in the egg cell provided by your mother. – Sperm only provide DNA.

35. Unlike other organelles, mitochondria also have their own tiny circular DNA, similar to that seen in modern bacteria.