Cellular Respiration Michael Kinney What is cellular respiration

Cellular Respiration Michael Kinney

What is cellular respiration? n Cellular respiration is the process by which energy is released from food to ATP.

Getting Food n Organisms need a way to collect the energy they need to live. They can either make that food themselves, or get it from another source.

Making your own food Organisms that make their own food are called autotrophs. n Auto-= self n -troph= feeder n Autotrophs get their food from photosynthesis. n

If I can’t make my own food Organisms that can’t make their own food are called heterotrophs. n Hetero-= different, other n -troph= feeders n

How do I get energy from the foods I eat? n Carbohydrates, like sugar molecules, have their chemical bonds broken by enzymes so that these large molecules, like glucose, are broken down into smaller molecules. This is known as digestion. n Fats and proteins can be broken down as well when carbohydrates are in insufficient amounts.

So where does this energy come into play? n After digestion occurs, other enzymes will come in and break the C-H bonds of our smaller molecules. n This is known as catabolism.

To review glucose Glucose is a six carbon sugar, it can exist in either a linear form while in a solution, or in a ring shape when in a solid form. n One molecule of glucose contains 6 carbon, 6 oxygen, and 12 hydrogen atoms. n

What powers the cell? n The cell uses ATP as a form of “energy currency” which the cell gets from performing respiration. n This ATP is used to perform all kinds of functions in the cell or organism.

So how do I break down the glucose? n The bonds of those hydrogen – carbon links need to be broken to release the energy bound inside of them. n Cells harvest the energy of bonds from electrons to produce more ATP. n This less energized electron that is paired with a proton is paired with some other molecule* – *depends on type of respiration.

*And that some other molecule would be? ? ? * The reaction that will occur depends on the molecule that accepts this hydrogen atom. n When oxygen accepts the hydrogen atom, this is known as aerobic respiration. n When something other than oxygen accepts the hydrogen, this is known as anaerobic respiration. n – When an organic molecule accepts the hydrogen atom, this is called fermentation.

Our equation for respiration n The general equation for respiration is as follows: n C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O + energy (ATP or heat)

Glycolysis is the place where all respiration begins. n All living things can undergo glycolysis. n

Glycolysis n Glycolysis begins by taking glucose and using two ATP to bind a phosphate group from each to our glucose. n Then our six carbon sugar diphosphate is split into 2 three carbon sugar phosphates.

Glycolysis n After that, the 2 three carbon sugar phosphates will, in a series of energy harvesting reactions, will each be converted into a pyruvate (3 carbon sugar). n During this time, an electron and two protons will be used to convert two NAD+ to NADH and 4 ATP are formed.

At the end of glycolysis n 4 ATP made minus 2 ATP that were needed to start the reaction = 2 net ATP. n 2 NADH are created n 2 three carbon sugars are made.

Aerobic Respiration

Aerobic Respiration n Takes place inside the mitochondria. n This step is referred to as oxidation of pyruvate. n After glycolysis, in the presence of oxygen, a molecule of carbon dioxide is cleaved off of the pyruvate. A pair of hydrogens will be picked up by NAD+ and more NADH will be created.

Mitochondria Anatomy

n What is left is a 2 carbon acetyl group, that will be coupled with a coenzyme labeled coenzyme A. n These two molecules coupled together are referred to as Acetyl-Co. A.

What Acetyl-Co. A is used for. Acetyl Co. A is used to begin making ATP in the Krebs cycle (citric acid cycle) or for lipid synthesis. n Animals store energy in these lipids as fat reserves. n

The Krebs Cycle n 1. When the Krebs cycle uses the 2 carbons of Acetyl-Co. A and binds them with a 4 carbon starting material. n 2. The new 6 carbon molecule is oxidized and decarboxylated (meaning a CO 2 group is removed) and more NAD+ is converted to NADH. n 3. The new 5 carbon molecule is oxidized and decarboxylated even further, and an ATP is created.

n 4. This new four carbon molecule is further oxidized (hydrogen is being removed) and more NADH and 2 FADH 2 (another electron carrier) are being produced. n 5. The energy harnessed from the NADH will be used in an electron transport chain*. – *ETC is also found in photosynthesis (light rxns)

Oxidative Phosphorylation: Electron Transport Chain n The hydrogen will pass through the series of membranes in the electron transport chain. n As the hydrogen is passed down the electron transport chain, the energy given off is used to create ATP. n This is chemiosmosis. n Oxygen accepts the electrons transported by the ETC. When it does, water is generated.

The net gain of Aerobic respiration n The overall theoretical gain of ATP from aerobic respiration is 36 ATP. – 2 ATP from glycolysis – 30 ATP from the NADH molecules – 4 from FADH 2 n At the end of the electron transport chain, oxygen receives our electron (remember it is coupled with a proton) and water is created.

Anaerobic respiration

Anaerobic Respiration n Anaerobic respiration occurs when oxygen is not our electron receptor at the end of the ETC. n The final electron receptor will be something other than oxygen. The process that is undergone is referred to as fermentation. n Both aerobic and anaerobic respiration start out with glycolysis.

Anaerobic Respiration: Ethanol fermentation In yeast, the electron receptor that takes NADH’s electron is pyruvate, the end product of glycolysis. n The end product of this type of fermentation is ethanol, which is actually toxic to yeast. n 2 ATP is gained (from glycolysis) n

Anaerobic Respiration: Lactic Acid Fermentation n n After glycolysis, the final receptor in animal cells is again, pyruvate. A compound called lactase dehydrogenase will remove the electron from NADH and move the electron back to pyruvate, creating lactic acid. If too much lactic acid builds up in the muscles, muscle function can be impaired. 2 ATP is gained.