Cellular Respiration: Cellular Respiration: GlycolysisGlycolysis

Monday September 24Monday September 24thth, 2012, 2012

Review of Oxidation and Review of Oxidation and ReductionReduction

OxidationOxidation: Losing electrons. Called : Losing electrons. Called oxidation because you tend to lose oxidation because you tend to lose electrons to oxygen. Oxygen is electrons to oxygen. Oxygen is electronegative (likes to hog electrons)electronegative (likes to hog electrons)

ReductionReduction: Gaining electrons: Gaining electrons

How do Cells Convert How do Cells Convert Chemical Energy from one Chemical Energy from one Form to Another?Form to Another?

We will be looking at 2 energy-transfer We will be looking at 2 energy-transfer mechanisms:mechanisms:

Substrate-level PhosphorylationSubstrate-level Phosphorylation Oxidative PhosphorylationOxidative Phosphorylation

Substrate-Level Substrate-Level PhosphorylationPhosphorylation

Substrate-level Substrate-level phosphorylationphosphorylation is a type of is a type of metabolism that results in the metabolism that results in the formation and creation of formation and creation of Adenosine Triphosphate Adenosine Triphosphate (ATP)(ATP)

Phosphate group is Phosphate group is transferred to ADP from transferred to ADP from substratesubstrate

Example of Example of phosphoenolpyruvate as phosphoenolpyruvate as substratesubstrate

For each glucose molecule For each glucose molecule created = 4 ATP molecules created = 4 ATP molecules are generated in Glycolysis are generated in Glycolysis (step 1) and 2 in Krebs Cycle (step 1) and 2 in Krebs Cycle (step 3)(step 3)

Oxidative Oxidative PhosphorylationPhosphorylation

As electrons are transferred from one carrier to As electrons are transferred from one carrier to another, energy is released and used to form another, energy is released and used to form ATP. Because oxygen must be present to ATP. Because oxygen must be present to accept the electrons at the end of the ETC, the accept the electrons at the end of the ETC, the process of forming ATP is called process of forming ATP is called oxidative oxidative phosphorylationphosphorylation

Oxidative phosphorylation can produce more Oxidative phosphorylation can produce more ATP molecules per glucose molecule than ATP molecules per glucose molecule than substrate-level phosphorylationsubstrate-level phosphorylation

What you should know What you should know about Glycolysis!about Glycolysis!

Anaerobic process Anaerobic process does not require does not require oxygenoxygen

Takes place in the cytoplasm (the liquid Takes place in the cytoplasm (the liquid stuff that organelles swim around in)stuff that organelles swim around in)

Makes up the first 10 steps of cellular Makes up the first 10 steps of cellular respirationrespiration

Glycolysis! Glycolysis! Splitting Splitting SugarsSugars

Glycolysis is the process of breaking down Glycolysis is the process of breaking down glucoseglucose

Glucose (6-carbon sugar) is split into 2 Glucose (6-carbon sugar) is split into 2 molecules of pyruvic acid (3-carbon sugars)molecules of pyruvic acid (3-carbon sugars)

Catabolic processCatabolic process Results in 2 molecules of ATP, 2 molecules Results in 2 molecules of ATP, 2 molecules

of pyruvic acid, 2 molecules of water and 2 of pyruvic acid, 2 molecules of water and 2 NADH (an enzyme that helps transport NADH (an enzyme that helps transport electrons)electrons)

Two Main Stages of Two Main Stages of Glycolysis:Glycolysis:

Glycolysis 1Glycolysis 1: The activation phase, : The activation phase, which uses ATP molecules; andwhich uses ATP molecules; and

Glycolysis 2Glycolysis 2: Oxidation and : Oxidation and phosphorylation reactions, which not only phosphorylation reactions, which not only reduce glucose to pyruvate but also reduce glucose to pyruvate but also produce ATP moleculesproduce ATP molecules

Glycolysis 1Glycolysis 1 In it’s most simplest form, glucose can be In it’s most simplest form, glucose can be

thought of as a 6-carbon molecule (also thought of as a 6-carbon molecule (also contains some Hydrogen and Oxygen:contains some Hydrogen and Oxygen:

OOOOOO – GlucoseOOOOOO – Glucose First step in glycolysis: substrate-level First step in glycolysis: substrate-level

phosphorylation phosphorylation when a phosphate when a phosphate group is added to the glucose molecule group is added to the glucose molecule by ATP:by ATP:

OOOOOOOOOOOOOOOO This makes This makes Fructose-6-phosphateFructose-6-phosphate

Glycolysis 1, continued…Glycolysis 1, continued…

Another ATP molecule must Another ATP molecule must phosphorylate the fructose-6-phosphate, phosphorylate the fructose-6-phosphate, producing producing fructose-1,6-diphosphatefructose-1,6-diphosphate

This molecule is split into two This molecule is split into two PGALPGAL (glyceraldehyde-3-phosphate)(glyceraldehyde-3-phosphate)

** Glycolysis 1 uses up two molecules of ** Glycolysis 1 uses up two molecules of ATPATP

Glycolysis 1Glycolysis 1

Glycolysis IIGlycolysis II

Each PGAL is oxidized Each PGAL is oxidized the electrons the electrons that are removed are picked by the that are removed are picked by the coenzyme NAD+coenzyme NAD+

Remember, when these electrons are Remember, when these electrons are picked up, so is a hydrogen ion, thus picked up, so is a hydrogen ion, thus NAD+ is reduced to NADHNAD+ is reduced to NADH

NADH carries the H atom to another NADH carries the H atom to another electron carrier where 2 electrons and a electron carrier where 2 electrons and a hydrogen are removed, once again hydrogen are removed, once again forming NAD+forming NAD+

Glycolysis II, continued…Glycolysis II, continued…

In the meanwhile PGAL that was In the meanwhile PGAL that was oxidized, gets phosphorylated and oxidized, gets phosphorylated and becomes PGAP becomes PGAP 2 molecules of PGAP 2 molecules of PGAP are createdare created

ADP molecules remove the phosphate ADP molecules remove the phosphate groups from PGAP groups from PGAP 2 molecules of 2 molecules of ATP and PGA produced!ATP and PGA produced!

PGA is then oxidized to make two water PGA is then oxidized to make two water molecules and two molecules and two PEPPEP (phosphoenolpyruvate) molecules(phosphoenolpyruvate) molecules

Glycolysis II, continued …Glycolysis II, continued …

Another substrate-level phosphorylation Another substrate-level phosphorylation occurs – 2 ADP molecules remove the occurs – 2 ADP molecules remove the phosphate groups from the PEP phosphate groups from the PEP molecules molecules results in 2 ATP molecules results in 2 ATP molecules and 2 pyruvate moleculesand 2 pyruvate molecules

The energy stored in these ATP can now The energy stored in these ATP can now be used for aerobic cellular respiration in be used for aerobic cellular respiration in mitochondriamitochondria

SummarySummary The process of Glycolysis results in 2 ATP The process of Glycolysis results in 2 ATP

moleculesmolecules We started with 1, 6-carbon molecule of glucoseWe started with 1, 6-carbon molecule of glucose We added 2 phosphorous molecules to Glucose We added 2 phosphorous molecules to Glucose

and converted the Glucose to Fructose and converted the Glucose to Fructose 2 ATP 2 ATP molecules are usedmolecules are used

Enzyme breaks down fructose into 2, 3-carbon Enzyme breaks down fructose into 2, 3-carbon sugar isomerssugar isomers

The 2, 3-carbon sugars were changed by NAD+, The 2, 3-carbon sugars were changed by NAD+, which left us with NAD+ with some H+ electronswhich left us with NAD+ with some H+ electrons

The End Results are:The End Results are: 4 ATP molecules, 2 H2O, 2 pyruvic acids 4 ATP molecules, 2 H2O, 2 pyruvic acids

and 2 NADH moleculesand 2 NADH molecules 2 molecules of ATP were used during the 2 molecules of ATP were used during the

process process 2 ATP molecules result as net2 ATP molecules result as net The 2 pyruvic molecules are either passed The 2 pyruvic molecules are either passed

along and used in the Krebs Cycle to create along and used in the Krebs Cycle to create more ATP or are converted to lactic acidmore ATP or are converted to lactic acid