Cellular Respiration Notes

Energy released from food is measured in calories. A calorie = energy required to raise the temp of 1 gram of water by 1 degree Celsius. A Calorie is equal to a kilocalorie or 1000 calories. Food labels express their energy in Calories.

Cell Respiration is the release of energy from food in the presence of oxygen.

Equation = 6O2 + C6H12O6 6CO2 + 6H20 + energy

There are three stages of cellular respiration, Glycolysis – Krebs Cycle – Electron Transport Chain.

Similar to the Electron Transport Chain observed in Photosynthesis, electrons that move along the membrane power pumps that move Hydrogen ions across a gradient. There is also the requirement of an electron receptor at the end of the chain, in Cellular Respiration, that receptor is Oxygen.

As the cell requires more energy, the demand for oxygen increases as well.

If Oxygen is present, the process or pathway is called aerobic (in air). Kreb’s and ETC are aerobic.

If oxygen is not present, the process is called anaerobic (without air). Glycolysis is technically anaerobic as it occurs without oxygen being present. Fermentation is another anaerobic pathway we will discuss later.

Before we can talk about glycolysis, we need to discuss the structure of a mitochondria.

The Mitochondria contains its own DNA (scientists believe it was once a prokaryote before eukaryotic cells engulfed the prokaryote and took advantage of its energy producing capabilities)

It carries out its own protein synthesis from its own DNA coding.

Glycolisis occurs in the cytoplasm of the cell, Krebs occurs in the matrix of the mitochondria and the electron transport chain functions along the innermembrane and intermembrane space.

GlycolisisLiterally means “sugar-breaking”Requires multiple enzymes and chemical reactions to transform the glucose molecule. It also requires the input of 2 ATP molecules.THE BANK

ATP Invested

ATP OUT

Net ATP

NADH FADH2 CO2 H20

Glycolysis 2 4 2 2Kreb’s CycleETCFermentation

Glycolysis turns one 6-Carbon Atom molecule of Glucose into 2, 3-carbon atom molecules of Pyruvic Acid. The entire reaction costs the cell two molecules of ATP but produces 4 molecuels of ATP for a net gain of 2 and Oxidizes NAD+ into NADH.

NAD+ and FAD in glycolysis and the krebs cycle are the same as what molecules we just learned about in Photosynthesis? What is their job?

Glycolysis has two main advantages, it is fast, REALLY fast, and it occurs without oxygen. Thousands of ATP molecules can be created in a matter of milliseconds.

KREBS CYCLE

Krebs cycle, also known as the citric acid cycle, occurs in the matrix of the mitochondria. As pyruvic acid moves into the matrix, one atom of carbon is lost to CO2, this same reaction yields on molecule of NADH. This 2-carbon atom is known as acetic acid. This molecule bonds with a compound called coenzyme A creating a molecule called acetyl-CoA. This molecule then enters the Krebs Cycle, binding with a 4-carbon atom molecule already present resulting in a 6-carbon atom molecule known as citric acid. 2 carbon atoms leave citric acid resulting in 2 more CO2 molecules being produced as well as two more molecules of NADH. The remaining 4 carbon-atom molecule goes through a process of realignment resulting in the production of 1 molecule of ATP, one more molecule of NADH and one molecule of FADH2.

The 4-carbon atom molecule that remains in the cycle is then prepared to receive another molecule of Acetyl-CoA (formed from Pyruvic acid) and start the process over.

THE BANKATP ATP Net NADH FADH2 CO2 H20

Invested OUT ATPGlycolysis 2 4 2 2Kreb’s Cycle 2 2 8 2 6ETCFermentation

Electron Transport Chain

Similar to the ETC in Photosynthesis, the ETC in the Mitochondria uses energy from the electrons, carried by NADH and FADH2 to pump hydrogen ions across a membrane. In this case the ions are pumped into the intermembrane space. ATP synthase is found at the end of the ETC and functions the exact same as we just learned; as hydrogen ions move through it, the turbine spins, powering the formation of ATP. The difference is ATP synthase releases the ATP into the Matrix of the Mitochondria (back into the area where work is being done)The final destination for the electrons that move along the ETC is oxygen. Oxygen molecules receive these low-energy electrons and a hydrogen ion forming water. In other words, water is a waste product of cell respiration. If oxygen is not present, meaning the electrons have nothing accepting them at the end of the chain, the electron transport chain cannot function and the process shuts down.

THE BANKATP Invested

ATP OUT

Net ATP

NADH FADH2 CO2 H20

Glycolysis 2 4 2 2Kreb’s Cycle 2 2 8 2 6ETC 32 32 6Fermentation

The carrier NADH from glycolysis results in the production of 2 ATP molecules in ETCThe carrier NADH from Krebs results in the production of 3 ATP molecules in ETCThe carrier FADH2 from Krebs results in the production of 2 ATP molecules in ETC

In the presence of oxygen, 36 molecules of ATP are produced.Without oxygen, and only considering glycolysis, only 2 molecules of ATP are produced.