Cell Respiration

Cellular Respiration To perform their many tasks cells require transfusions of energy from outside sources To perform their many tasks cells require transfusions of energy from outside sources Energy enters ecosystems as sunlight, the energy source for plants and other photosynthetic organisms Energy enters ecosystems as sunlight, the energy source for plants and other photosynthetic organisms Animals obtain energy by eating plants or by eating organisms that eat plants Animals obtain energy by eating plants or by eating organisms that eat plants

Cellular Respiration During cellular respiration organic compounds are broken down using oxygen as a reactant During cellular respiration organic compounds are broken down using oxygen as a reactant Organic compounds + oxygencarbon dioxide + water + energy

Cellular Respiration Respiration is a stepwise redox (reduction/oxidation) reaction Respiration is a stepwise redox (reduction/oxidation) reaction Recall: a redox reaction is a transfer of one or more electrons from one reactant to another Recall: a redox reaction is a transfer of one or more electrons from one reactant to another C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + energy Cellular Respiration: Na + Cl 2 NaCl reduction oxidation reduction

Cellular Respiration Energy is not liberated all at once (explosion!) Energy is not liberated all at once (explosion!) jJVc0 jJVc0 jJVc0 jJVc0

Glucose is broken down gradually Glucose is broken down gradually Hydrogen atoms and electrons are stripped from glucose and are passed to a coenzyme called nicotinamide adenine dinucleotide (NADH) Hydrogen atoms and electrons are stripped from glucose and are passed to a coenzyme called nicotinamide adenine dinucleotide (NADH) Eventually electrons are passed to oxygen in a series of steps called the electron transport chain Eventually electrons are passed to oxygen in a series of steps called the electron transport chain

NAD + is an oxidizing agent C OH + NAD + C O + NADH Oxidized form Reduced form

Four Stages of Respiration 1) Glycolysis (cytoplasm) 2) Pyruvate oxidation (mitochondria) 3) Krebs cycle (citric acid cycle) 4) Oxidative phosphorylation

The first stage of respiration Glycolysis - Lysis of sugar

Respiration

Glycolysis splits one molecule of glucose into two smaller molecules of pyruvate

Glycolysis is the first stage of respiration! Glycolysis splits one molecule of glucose into two smaller molecules of pyruvate Glucose is a hexose (6-carbon) molecule

Glycolysis is the first stage of respiration! Glycolysis splits one molecule of glucose into two smaller molecules of pyruvate Glucose is a hexose (6-carbon) molecule Pyruvate is a triose (3-carbon) molecule

Glycolysis takes place in the cytoplasm of cells.

- it’s the first step for both aerobic and anaerobic respiration

Glycolysis 2 ADP

Overall Reaction of Glycolysis

Glucose Glucose 2 x pyruvate 2 x pyruvate

There are TWO STAGES of GLYCOLYSIS – Phosphorylation and Oxidation

Stage One – Phosphorylation: Investment Phase animations/glycolysis.html

Stage One - Phosphorylation 1-3. Glucose is phosphorylated by adding 2 phosphates from 2 molecules of ATP to give first glucose-6-phosphate and finally a fructose 1,6-bisphosphate.

Stage One - Phosphorylation 4,5. The fructose 1,6-bisphosphate is split using water (hydrolysis) to glyceraldehyde-3-phosphate (G3P)

Glyceraldehyde 3- phosphate (G3P)

What’s the point? Glucose can now no longer leave the cell!!!! Glucose can now no longer leave the cell!!!!

Molecules produced are much more reactive! Molecules produced are much more reactive! Glyceraldehyde 3- phosphate

Stage Two – Oxidation (pay-off)

Stage Two - Oxidation The G3P is oxidized (loses electrons), and phosphorylated, forming two molecules of pyruvate.

Stage Two - Oxidation 6 cont... Coenzyme NAD + collects the hydrogen ions, forming 2 reduced NAD (NADH + H + )

Stage Two - Oxidation 6. Coenzyme NAD + collects the hydrogen ions, forming 2 reduced NAD (NADH + H + ) A coenzyme is a helper molecule that carries chemical groups or ions, e.g. NAD + removes H + and carries it to other molecules.

The 2 molecules of reduced NADH go to the electron transport chain (ETC), part 4 of respiration.

Stage Two - Oxidation 4 ATP are produced, but 2 were used up at the beginning, so there’s a net gain of 2 ATP.

Glucose Glucose 2 x pyruvate 2 x pyruvate

CHOICES: aerobic or not? - if aerobic, pyruvate will travel to mitochondria

Mitochondria  Found in nearly all eukaryotic cells  In animal cells they are oval  Cristae increase surface area and are the site of electron transport  The matrix is like the cytoplasm of cells where enzymatic reactions take place

Reaction 2. Pyruvate Oxidation Second reaction of cellular respiration

Aerobic = Occurs in the presence of oxygen Pyruvate produced in the cytosol is transported to the mitochondrial matrix Pyruvate is converted to acetyl-CoA while NAD+ is reduced to NADH

Link Reaction – 2 nd stage of respiration

One carbon atom is removed from pyruvate in the form of CO 2. The remaining 2-carbon molecule combines with coenzyme A to produce acetyl coenzyme A (acetyl CoA). Another oxidation reaction happens when NAD + collects more hydrogen ions. This forms reduced NAD (NADH + H + ).

No ATP is produced in this reaction.

The Link reaction happens Twice for every Glucose Molecule

Link Reaction – 2 nd stage of respiration The Link reaction happens Twice for every Glucose Molecule So for every glucose molecule used in glycolysis, two pyruvate and two acetyl CoA molecules are made.

So for each glucose molecule:

Two molecules of acetyl CoA go into Krebs cycle (part 3 of respiration)

So for each glucose molecule: Two molecules of acetyl CoA go into Krebs cycle (part 3 of respiration)

So for each glucose molecule: Two molecules of acetyl CoA go into Krebs cycle (part 3 of respiration) Two carbon dioxide molecules are released as a waste product of respiration

So for each glucose molecule: Two molecules of acetyl CoA go into Krebs cycle (part 3 of respiration) Two carbon dioxide molecules are released as a waste product of respiration Two molecules of reduced NAD are formed and go into the electron transport chain (part 4 of respiration)

So for each glucose molecule: Two molecules of acetyl CoA go into Krebs cycle (part 3 of respiration) Two carbon dioxide molecules are released as a waste product of respiration Two molecules of reduced NAD are formed and go into the electron transport chain (part 4 of respiration)