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Cellular Respiration: Glycolysis

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1 Cellular Respiration: Glycolysis
Monday September 24th, 2012

2 Review of Oxidation and Reduction
Oxidation: Losing electrons. Called oxidation because you tend to lose electrons to oxygen. Oxygen is electronegative (likes to hog electrons) Reduction: Gaining electrons

3 How do Cells Convert Chemical Energy from one Form to Another?
We will be looking at 2 energy-transfer mechanisms: Substrate-level Phosphorylation Oxidative Phosphorylation

4 Substrate-Level Phosphorylation
Substrate-level phosphorylation is a type of metabolism that results in the formation and creation of Adenosine Triphosphate (ATP) Phosphate group is transferred to ADP from substrate Example of phosphoenolpyruvate as substrate For each glucose molecule created = 4 ATP molecules are generated in Glycolysis (step 1) and 2 in Krebs Cycle (step 3)

5 Oxidative Phosphorylation
As electrons are transferred from one carrier to another, energy is released and used to form ATP. Because oxygen must be present to accept the electrons at the end of the ETC, the process of forming ATP is called oxidative phosphorylation Oxidative phosphorylation can produce more ATP molecules per glucose molecule than substrate-level phosphorylation


7 What you should know about Glycolysis!
Anaerobic process  does not require oxygen Takes place in the cytoplasm (the liquid stuff that organelles swim around in) Makes up the first 10 steps of cellular respiration

8 Glycolysis!  Splitting Sugars
Glycolysis is the process of breaking down glucose Glucose (6-carbon sugar) is split into 2 molecules of pyruvic acid (3-carbon sugars) Catabolic process Results in 2 molecules of ATP, 2 molecules of pyruvic acid, 2 molecules of water and 2 NADH (an enzyme that helps transport electrons)

9 Two Main Stages of Glycolysis:
Glycolysis 1: The activation phase, which uses ATP molecules; and Glycolysis 2: Oxidation and phosphorylation reactions, which not only reduce glucose to pyruvate but also produce ATP molecules

10 Glycolysis 1 In it’s most simplest form, glucose can be thought of as a 6-carbon molecule (also contains some Hydrogen and Oxygen: OOOOOO – Glucose First step in glycolysis: substrate-level phosphorylation  when a phosphate group is added to the glucose molecule by ATP: OOOOOOOO This makes Fructose-6-phosphate

11 Glycolysis 1, continued…
Another ATP molecule must phosphorylate the fructose-6-phosphate, producing fructose-1,6-diphosphate This molecule is split into two PGAL (glyceraldehyde-3-phosphate) ** Glycolysis 1 uses up two molecules of ATP

12 Glycolysis 1

13 Glycolysis II Each PGAL is oxidized  the electrons that are removed are picked by the coenzyme NAD+ Remember, when these electrons are picked up, so is a hydrogen ion, thus NAD+ is reduced to NADH NADH carries the H atom to another electron carrier where 2 electrons and a hydrogen are removed, once again forming NAD+

14 Glycolysis II, continued…
In the meanwhile PGAL that was oxidized, gets phosphorylated and becomes PGAP  2 molecules of PGAP are created ADP molecules remove the phosphate groups from PGAP  2 molecules of ATP and PGA produced! PGA is then oxidized to make two water molecules and two PEP (phosphoenolpyruvate) molecules

15 Glycolysis II, continued …
Another substrate-level phosphorylation occurs – 2 ADP molecules remove the phosphate groups from the PEP molecules  results in 2 ATP molecules and 2 pyruvate molecules The energy stored in these ATP can now be used for aerobic cellular respiration in mitochondria


17 Summary The process of Glycolysis results in 2 ATP molecules
We started with 1, 6-carbon molecule of glucose We added 2 phosphorous molecules to Glucose and converted the Glucose to Fructose  2 ATP molecules are used Enzyme breaks down fructose into 2, 3-carbon sugar isomers The 2, 3-carbon sugars were changed by NAD+, which left us with NAD+ with some H+ electrons

18 The End Results are: 4 ATP molecules, 2 H2O, 2 pyruvic acids and 2 NADH molecules 2 molecules of ATP were used during the process  2 ATP molecules result as net The 2 pyruvic molecules are either passed along and used in the Krebs Cycle to create more ATP or are converted to lactic acid

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