Cellular Respiration .

What is Cellular Respiration???A Famous scientist once said “Cellular Respiration is

in my opinion, the most important biochemical reaction in Heterotrophic systems”

Me (Just now)Cellular Respiration is the mechanism in which we

derive energy from what we eat. All Heterotrophs use cellular respiration to obtain

energy.Most Autotrophs use photosynthesis to obtain

energy.Cellular respiration is the inverse of photosynthesis.

Photosynthesis vs. Cellular Respiration Photosynthesis

Cellular Respiration

Cellular Respiration

The process of Cellular Respiration occurs in 3-4 steps.

1) Glycolysis

2) Krebs Cycle

3) Eletron Transport Chain

1) Glycolysis Gluc- comes from the Greek word meaning Sweet. Cose- we put at the end of words to signify Sugars. Lyses- means to break down. This process occurs in the cell’s Cytoplasm. Glycolysis- is the process in which one molecule of glucose (a 6 carbon compound) is broken in

half, producing two molecules of pyruvic acid (a 3-carbon compound) , 2 ATPs and 2 NADH bi products.

This is an Anaerobic Process (no oxygen required) this means glycolysis can provide energy to the cell when oxygen is not available.

Even though glycolysis is an energy-releasing process,the cell needs to put in a little energy to get things going. At the pathway's beginning, 2 molecules of ATP are used up.

Although the cell puts 2 ATP molecules to get glycolysis going, when glycolysis is complete, 4 ATP molecules have been produced. This gives the cell a net gain of 2 ATP molecules.

Catalyzed reactions produce NADH. NADH holds the electrons until they can be transferred to other molecules. By doing this, NAD+ helps to pass energy from glucose to other pathways in the cell.

Problems with GlycolysisAlthough the energy production from glycolysis

is small, 2 Net ATP’s are formed (used 2 ATP’s and generated 4) and 2 NADH, the process is so fast that cells can produce thousands of ATP molecules in just a few milliseconds.

However, when a cell generates large amounts of ATP from glycolysis, it runs into a problem. In just a few seconds, all of the cell's available NAD+ molecules are filled up with electrons. Without NAD+, the cell cannot keep glycolysis going, and ATP production stops.

2) Kreb’s Cycle The Krebs cycle is named after Hans Krebs,

the British biochemist who demonstrated its existence in 1937.

To extract the rest of the energy stored in electrons from glycolysis, the cell turns to one of the world's most powerful electron acceptors ---

Oxygen!!! Oxygen is required for the final steps of

cellular respiration. Because the pathways of cellular respiration require oxygen, they are said to be aerobic.

This process occurs in the matrix of mitochondria.

Kreb’s Cycle preparationPyruvic Acid Oxidation

As we remember from glycolysis glucose was lysed to make 2 pyruvic acid molecules.

Each pyruvic acid molecules is oxidized meaning 1 carbon is taken away.

This makes a 2 carbon molecules called Acetyl CoA. This process also reduces NAD+ to NADH

All of this is catalysed by Enzymes !! Proteins that bring things together in the right way so they can react.

At the end of pyruvic acid oxidation 1 NADH is Produced

Once Acetyl CoA and NADH are produced the Kreb’s Cycle can begin!

Remember before Kreb’s cycle pyruvate is oxidized and forms 2 carbon Acetyl CoA and produces 1 NADH.

Next Acetyl CoA merges with a 4 carbon molecule to form 6 carbon Citric Acid.

2 Carbon molecule + 4 carbon molecule = 6 carbon Citric Acid.

1 carbon is sliced off and 1 NAD+ is reduced to NADH.

Now we are left with a 5 carbon molecule and again a carbon molecule is sliced off.

During this process 1 ATP and 1 NADH are produced.

Tada!!! We are back to a 4 Carbon Molecule :D

1 FADH and 1 NADH are produced and the Krebs Cycle starts all over again.

Le’s add them up!1 NADHFrom Pyruvate Oxidation3 NADH1 ATP 1 FADH2

From Krebs (x 2 for each Pyruvic acid)FADH and NADH are converted to ATP later in the Electron Transport Chain

What is happening to the Carbon???

It becomes CO2 when it attaches to oxygen then they leave your system as you exhale. Every time the Krebs cycle runs you generate 3 molecules of CO2 for each pyruvate.

Electron Transport ChainThe Krebs cycle generates high-energy compounds (10NADH and 2

FADH2 )that are passed to. The electrons are then passed from those carriers to the Electron Transport Chain.

The electron transport chain- uses the high-energy electrons from the Krebs cycle to convert ADP into ATP.

In Eukaryotes, the electron transport chain is composed of a series of carrier proteins located in the inner membrane of the Mitochondrion.

In prokaryotes, the same chain are in the Cell Membrane.On average the ETC produces 3 molecules of ATP from each molecule of

NADH (30 ATP) and 1 molecule of ATP from each FADH (2 ATP) produced in the Kreb’s Cycle.

Every time a pair of high-energy electrons moves down the electron transport chain, the energy is used to move H+ ions across the membrane. These ions then rush back across the membrane, producing enough force to spin the ATP synthase and generate enormous amounts of ATP.

So lets count...2 ATP

2 NADH From Glycolysis

+

2 NADH From Oxidation of Pyruvate

+

6 NADH

2 ATP

2 FADH From Krebs

Electron Transport System (Converts NADH and FADH to ATP)

10 NADH x 3 = 30 ATPs

2 FADH x 2 = 4 ATPs

4 ATP

________________________

38 ATPs Total!!!