Cellular Respiration

By the end of this class you should understand: The major processes that living things use to make energy The relationship between photosynthesis and cellular respiration The key differences between aerobic and anaerobic processes The three steps of eukaryotic cellular respiration

What is needed to make ATP? ADP (nucleic acid) and phosphate – There is plenty of this in the cell already since it gets reused a lot Energy source (carbohydrate, protein, lipid) Oxygen (for aerobic respiration only) – Anaerobic respiration requires no oxygen

Which cells do this? All cells need energy All cells with mitochondria perform complete cellular respiration (aerobic) Cells with no mitochondria (i.e. red blood cells, most prokaryotes) can only perform anaerobic respiration or fermentation

Complete Cellular Respiration C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O + ATP

Technically a Combustion Reaction: C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O + Heat

Photosynthesis in Reverse! Water is split into O 2 to extract electrons Electron transport chain creates proton gradient – Used by ATP synthase ATP and electron carriers are used up absorbing CO 2 making 3-carbon sugar in the Calvin Cycle 3-carbon sugars made into glucose Glucose is broken down with enzymes to make 3-carbon sugar (glycolysis) 3-carbon sugar enters Krebs cycle, is broken down into CO 2 Products of Krebs cycle are ATP and electron carriers Electron carriers power electron transport chain which creates proton gradient – Used by ATP Synthase Electrons are dumped onto O 2 to make water

Fermentation Breakdown of sugar is near- universal to living things Many different chemical pathways available Anaerobic pathways (lacking oxygen) include producing ethanol and lactic acid – How do you think your beer was made? – Yogurt also made this way

Glycolysis Fermentation typically takes place with no oxygen Most eukaryotes (and a few aerobic prokaryotes) use oxygen to complete metabolism of sugar The first step is glycolysis, or breaking down the sugar with enzymes, into pyruvate

Human Fermentation If no oxygen is present, pyruvate buildup in cell can become toxic Pyruvate is instead converted to lactic acid Lactic acid enters bloodstream and creates the “burning” feeling in your muscles

Krebs Cycle The Krebs Cycle is an enzymatic process Aerobic: requires oxygen to keep running – If no oxygen, no electron carriers available Reactant: 1 Acetyl CoA – Pyruvate is converted to Acetyl CoA first Product: 3 CO 2

Krebs Cycle Performed in the mitochondria Produces ATP and high-energy electrons Produces the CO 2 that we breathe out – CO 2 exits cell and dissolves into blood until we breathe it out at the lungs

Electron Transport Chain Electrons are pushed one by one through a transport chain As the electron moves, its energy is used to pump hydrogen ions into a special reservoir – Sort of like using energy to pump water to a lake above a dam As the hydrogen ions are released back, they turn a “water wheel” that makes ATP

Electron Transport Chain Each of these structures pulls a little more tightly on the electron The final recipient of the electron is oxygen, which makes water This means the entire chain is aerobic

Electron Transport Chain The energy in the electron does work to create a gradient of hydrogen ions The hydrogen ions move down their gradient through an ATP Synthase enzyme This enzyme creates ATP when turned by hydrogen ions – This is called chemiosmosis – This step makes a LOT of ATP (overall total for 1 glucose molecule: ~34 ATP)

ATP Synthase

Cellular Respiration Summary

Cellular Respiration Summary: Glucose – is broken down by glycolysis to Pyruvate – which enters the Krebs cycle and becomes CO 2 – which leaves, but the released electrons power the Electron Transport Chain – which makes fat stacks of ATP – oxygen absorbs the electrons to become water

Alternative Energy This is the main sequence of energy for metabolizing glucose – All organisms with mitochondria perform this type of cellular respiration Most organisms have alternatives as well – Humans can convert fat into Acetyl CoA through a process called beta oxidation – One fat molecule can provide hundreds of ATP!