Chapter 9: Cellular Respiration Ferguson Revised Spring 2014 to match text wksts 9.1 and 9.2

Chemical Energy and Food We eat because food provides our bodies with energy. Q1?: calorie = amount of energy needed to raise one gram of water one degree Celsius.

There are 1000 calories in 1 Calorie (notice the difference in the capital C) on our food labels the Calories are given. Cells don’t actually “burn” calories from molecules like glucose. Instead, they gradually release the energy.

Overview of Cellular Respiration Process that releases energy by breaking down glucose and other food molecules in the presence of oxygen. 6O 2 + C 6 H 12 O 6  6CO 2 + 6H 2 O + Energy How does this compare to Photosynthesis?? The process we call Cellular Respiration begins with a chemical pathway called glycolysis. Although we know that glucose has 90 times more energy than the ATP molecule (from chapter 8) in the first step of cellular respiration, glycolysis only releases a small amount of that energy.

Overview of Cellular Respiration There are 3 main stages: Each stage captures some chemical energy in the cell, and uses it to produce ATP. ◦ Glycolysis (step that occurs in the cytoplasm) ◦ Krebs Cycle (in mitochondria) ◦ Electron Transport Chain (in mitochondria)

The different stages are important so that our cells get as much energy as possible through the process of cellular respiration.... If there was only one step in the pathway a problem would occur... all of the energy from glucose would be released at once, and most of that energy would be lost in the form of light and heat, instead of being stored in ATP molecules

Glycolysis Process in which one molecule of glucose is broken in half, producing two molecules of pyruvic acid. Occurs in the cytoplasm. The cell starts glycolysis by using the energy from 2 ATP molecules to produce 4 ATP molecules. What is the net gain of ATP?

Glycolysis Uses the electron carrier NAD +, which becomes NADH. Can produce thousands of ATP in seconds Does NOT require oxygen. (Anaerobic)

The function of NAD+ in glycolysis The electron carrier, NAD+ holds a pair of high energy electrons (as NADH) until they can be transferred. In this way it helps pass the energy from glucose to other cell pathways. This helps to produce thousands of ATP molecules in the cell.

Can problems arise in this step? If cells were to generate large amounts of ATP just from glycolysis, then within a few seconds all the NAD+ electron carriers would be filled up with electrons, and the process would stop until they could be moved to a different pathway.

Fermentation A process that releases energy from food molecules in the absence of oxygen. Both types of fermentation regenerate NAD + that can be used in Glycolysis. Fermentation changes NADH back to NAD+ by passing the high energy electrons back to the pyruvic acid.

2 types of fermentation Alcoholic Fermentation Used by yeasts and other microorganisms ◦ Pyruvic Acid + NADH  alcohol + CO 2 + NAD + When yeast is baked the small amt of alcohol produced evaporates in the oven at high temp. Lactic Acid Fermentation – muscle cells, and the bacteria used in dairy products. ◦ Pyruvic Acid + NADH  lactic acid + NAD +

Instead of Fermentation… At the end of Glycolysis, about 90% of the energy in glucose is still unused, locked away in the bonds of pyruvic acid. To release the remaining energy, cells must use oxygen. The next 2 steps of cellular respiration are said to be aerobic.

During rapid exercise your muscle cells produce ATP by lactic acid fermentaion When you need a quick sprint, your muscle cells run out of stored oxygen quickly, and may not have time to go through the entire cellular respiration process so to get a quick energy boost the ATP is used.

At the end of glycolysis 90% of the chemical energy in glucose is still unused. Because the final stages of cellular respiration require oxygen they are considered to be aerobic.

The Krebs Cycle Pyruvic acid is broken down into carbon dioxide in a series of energy- extracting reactions. Begins when a molecule of pyruvic acid enters the mitochondria. After many reactions, the pyruvic acid becomes CO 2, NADH is formed, ATP is formed, and another electron carrier, FADH 2 is formed.

The Krebs Cycle CO 2 is released when we exhale. ATP is used to power the cell’s activities. In the presence of oxygen, the electron carriers NADH and FADH 2 are used to create even greater amounts of ATP.

Electron Transport Chain Uses high-energy electrons from the Krebs cycle to convert ADP to ATP. The chain is composed of a series of proteins throughout the membranes of the mitrochondria. These proteins pump H + ions through the membrane, which powers ATP Synthase to convert ADP to ATP.

Electron Transport Chain

The Totals Glycolysis alone can only produce 2 net ATP. In the presence of oxygen, Cellular Respiration can produce 36 molecules of ATP.

Energy and Exercise Quick Energy ◦ When athletes only need energy for a quick burst (~90 seconds), they resort to the energy from Glycolysis and Lactic Acid Fermentation. Long-Term Energy ◦ When athletes need energy for an extended period of time, cellular respiration is the only way to provide continuous energy.

Comparing Photosynthesis and Cellular Respiration Using an analogy – if photosynthesis is the process that deposits energy in a “saving account” then cellular respiration would be the process that “withdraws” the energy. How are these processes opposite in terms of carbon dioxide? Photosynthesis is the process that removes CO 2 from the atmosphere while cellular respiration puts it back. How are these processes opposite in terms of oxygen? Photosynthesis releases O 2 gas into the atmosphere and cellular respiration uses that oxygen to release energy from food. What else could we compare about the 2 processes?

Comparing Photosynthesis and Cellular Respiration PhotosynthesisCellular Respiration FunctionEnergy captureEnergy release LocationChloroplastsMitochondria ReactantsCO 2 and H 2 OC 6 H 12 O 6 and O 2 ProductsC 6 H 12 O 6 and O 2 CO 2 and H 2 O Equation 6CO H 2 O + energy  C 6 H 12 O 6 + 6O 2 6O 2 + C 6 H 12 O 6  6CO 2 + 6H 2 O + Energy