Chapter 9: Cellular Respiration and Fermentation

I.Section 9.1: Cellular Respiration: An Overview *You feel weak when you are hungry because food is a source of energy. *Weakness is your body’s way of telling you your energy supplies are low A. Chemical Energy and Food 1. Organisms get the energy they need from food. 2. Energy stored in food is expressed as a calorie.

3. calorie – the amount of energy needed to raise the temperature of 1 gram of water by 1 o Celsius. *Calorie (capital C) – used on food labels; is actually a kilocalorie or 1000 calories 4. Energy molecules: a) fats b) proteins c) carbohydrates *energy stored in each food source differs based on the molecules structure

Energy storage in foods: ex) 1 g of glucose = 3811 calories 1 g of beef triglyceride = 8893 calories 5. General calculations: a) 1 g of carbohydrate = calories (4 Calories) b) 1 g of protein = 4000 calories (4 Calories) c) 1 g of fat = 9000 calories (9 Calories)

*Cells don’t just break food down and release it as heat though; they break the molecules down gradually and use the energy to create ATP.

B. Overview of Cellular Respiration 1. Cellular respiration is the process that releases energy from food when oxygen is present. 2. Chemical Equation:

The cellular respiration process involves many steps; if all the energy was released at once much of it would be lost as heat. 3. Stages of Cellular Respiration: a) glycolysis – only taps into about 10% of the energy b) krebs cycle – generates a small amount of ATP c) electron transport chain – makes the bulk of the ATP

Three stages of Cellular Respiration

4. Oxygen and Energy *oxygen is the end of the ETC for cellular respiration. a) aerobic – the term used to refer to pathways that require oxygen. *Krebs cycle and ETC both require O 2 b) anaerobic – “without air”; process that does not require O 2 *glycolysis occurs without O 2

5. Locations for cell respiration: a) glycolysis – in the cytoplasm b) krebs cycle – in the mitochondrial matrix c) ETC – in the innermembrane of the mitochondria

C. Comparing Photosynthesis and Cell Respiration: PhotosynthesisCell Respiration Uses CO 2 from atmosphereUses O 2 from atmosphere Gives off O 2 Gives off CO 2 Creates ATP to build sugarBreaks sugar to build ATP Occurs plants and organisms w/ chloroplasts; Occurs in both plants and animals; happens anywhere there are mitochondria

The Link between Photosynthesis and Cellular Respiration

II. Section 9.2: The Process of Cellular Respiration A. Glycolysis – The first step 1. Glycolysis – Glyco = “sugar” Lysis = “to cut” *Glycolysis literally means the cutting or breaking up of sugar; occurs when 1 molecule of glucose (6 carbons) is broken into 2 molecules of pyruvic acid (3 carbons each) 2. location - cytoplasm

3. ATP Production: Glycolysis results in a production of 4 ATPs, but it requires 2 ATPs to get it started. Thus you have a net gain of 2 ATPs: uses- 2 ATPs made+4 ATPs net gain = 2 ATPs

Glycolysis

4. NADH Production a) NAD+ - “energy carrier”; nicotinamide dinucleotide. Main job is to pick up electrons released from the glucose. NAD + + e H  NADH b) NADH – carries electrons to the ETC 5. The advantages of Glycolysis a) net gain of 2 ATP molecules b) FAST – get thousands of ATPs in milliseconds c) does NOT require O 2

B. The Krebs Cycle *named after Hans Krebs, British biochemist who figured it all out in 1937 *The purpose of the cycle is to break pyruvic acid down into carbon dioxide, and extract energy. *AKA – The Citric Acid Cycle; because the first molecule made is citric acid.

1.Citric Acid Production *location – mitochondrial matrix a) Step 1 – pyruvic acid enters the mitochondria. b) Acetyl CoA formation – one carbon from the pyruvic acid is removed and leaves as CO 2. Coenzyme A is then added on c) citric acid – the 2 carbons from the Acetyl CoA are added to a 4 carbon molecule producing the 6 carbon molecule citric acid

Acetyl CoA Formation

2. Energy Extraction a) Citric acid loses a carbon as CO 2, this produces: 1) a 5 carbon molecule 2) energy that gets picked up by NAD + b) 5 carbon molecule loses a carbon, this produces: 1) a 4 carbon molecule 2) energy that gets picked up by NAD + c) the 4 carbon molecule is recycled back into the starting molecule creating ATP and FADH 2 along the way

The Krebs / Citric Acid Cycle

d) Summary: *For each pyruvic acid that enters the Krebs cycle, the following are produced: 1) 3 NADH 2) 1 ATP 3) 1 FADH 2 *up to this point we have made a total of 3 ATP

C. Electron Transport and ATP Synthesis *the electron transport chain uses the high energy electrons from glycolysis and the krebs cycle to convert ADP  ATP 1. Electron Transport *located in innermembrane of mitochondria a) NADH drops off electrons at beginning of chain b) FADH 2 drops its electrons off a little further down the chain c) energy from electrons is used to pump H + from the mitochondrial matrix to the intermembrane space; this creates a gradient so that there is a high amount of H + in the space, and low in the matrix

d) O 2 – oxygen is the final electron acceptor at the end of the ETC; it picks up the electrons, combines them with H + which then leaves the body as H 2 O. *this is why our bodies need oxygen! So the electrons have somewhere to go, NOT so we can “breathe”

2. ATP Production a) H + ions want to go from high  low b) in order to do so they must go through a protein channel; “facilitated diffusion” c) ATP Synthase – as H + go through the ATP Synthase tunnel, it spins and hooks together ADP + P  ATP

D. The Totals a) glycolysis = 2 ATP b) Krebs Cycle = 2 ATP (1 for each pyruvic acid) c) ETC = 32 ATP = 32 ATP overall tally = 36 ATP

*What about other food??? 1)Complex carbs are turned into glucose 2)Lipids and Proteins are broken down into molecules that can enter either glycolysis or the krebs cycle *We get about 36% efficiency from glucose: 36% of the energy is turned into ATP 64% is lost as heat

III. Section 9.3 Fermentation *what happens when O 2 is NOT available? A. Fermentation *during glycolysis ATP is made and NAD + picks up electrons and becomes NADH; as long as O 2 is available in the ETC the NAD + can drop off the energized electrons and come back to glycolysis to pick up more electrons. But if no O 2 is present then NADH cannot unload the energized electrons and the process is stuck… *Fermentation releases energy from food to make ATP when O 2 is not available.

*2 types of Fermentation: 1. Alcoholic a) who does it – yeast and some other types of microorganisms b) how: pyruvic acid + NADH  alcohol + CO 2 + NAD + *in this case the NADH uses its electrons to convert pyruvic acid into alcohol, thus the NADH can become NAD + again and is free to do glycolysis and generate 2 more ATP molecules.

Alcoholic Fermentation c) What is it used for: 1) brewing beer and other alcoholic beverages 2) yeast uses this to cause dough to rise; the CO 2 is what creates the spongy pockets in the bread

2. Lactic Acid a) who does it – most organisms such as humans and certain bacteria b) how: Pyruvic acid + NADH  lactic acid + NAD + *NADH uses its electrons to turn pyruvic acid into lactic acid, thus NADH  NAD + and can be used glycolysis again to make ATP.

Lactic Acid Fermentation c) What is it used for: 1) to make food and beverages like cheese, yogurt, buttermilk, and sour cream 2) humans utilize this process during anaerobic exercises

B. Energy and Exercise *humans have 3 main sources of ATP: 1) ATP already in muscles 2) ATP made via lactic acid fermentation (no O 2 ) 3) ATP produced by cell respiration (O 2 present) 1. Quick Energy a) ATP already stored in cells from cell respiration is used up quickly in exercise b) once this ATP is used up, the body begins lactic acid fermentation, but it only supplies enough ATP to last about 90 seconds, this leads to lactic acid building up in the muscle cells; this is why we can’t do anaerobic exercises for long periods.

2. Long-term energy a) for exercises lasting longer than 90 seconds we must use cellular respiration to get our ATP b) cellular respiration releases energy more slowly than fermentation c) energy is stored in muscles and liver cells in the form of glycogen; glycogen stores give enough energy for about minutes of exercise; after 20 minutes the body must tap into other food molecules, such as stored lipids