Cellular Respiration and Fermentation

Chapter 9

Where do organisms get their energy?

• For all organisms, food molecules contain chemical energy that is released when its chemical bonds are broken.

• Heterotrophs need to eat food to obtain energy. How is this different than autotrophs?

• Energy stored in food is expressed in units of calories: the amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius. 1000 calories = 1 kilocalorie, or Calorie.

• fats, proteins, and carbohydrates all store energy• The energy stored in each molecule varies because their

chemical structures, and therefore their energy-storing bonds, differ.

• Carbs and protein: 4 Calories of energy per gram• Fats: 9 Calories of energy per gram

• Cells break down food molecules and use the energy stored in the chemical bonds to produce compounds such as ATP that power the activities of the cell.

• How do cells use energy? 1. Movement

2. Making new parts for the cell3. Repairing cell parts4. Transport of food and wastes

via active transport5. Heat production in warm

blooded animals

How Do We Get Energy From ATP?

By breaking the high- energy bonds between the last two phosphates in ATP

• The foods we eat contain usable energy• If oxygen is available, organisms can break

down food and generate energy by the process of cellular respiration.

Equation:

ATP

• Why doesn’t Earth run out of oxygen?• Where does all the carbon dioxide waste

product go? • As cellular respiration happens, it is balanced

by another process ____________________.

• The energy flows in opposite directions. Photosynthesis “deposits” energy, and cellular respiration “withdraws” energy.

The release of energy by cellular respiration takes place in plants, animals, fungi, protists, and most bacteria.

• There are three stages of cellular respiration – Glycolysis– Krebs Cycle– Electron Transport

Chain

– Where does most cellular respiration take place?

Mitochondria

• Inner Membrane• Outer membrane• Cristae• Matrix

1. Glycolysis

• Glycolysis means “sugar breaking”

• Glucose breaks into 2 molecules of pyruvate.

• Happens in the cytoplasm of the cell

• In the process of glycolysis 2 ATP are produced and 2 NADH are produced.

• NAD+ accepts electrons from the breaking of glucose.

• NADH carries the high-energy electrons to the electron transport chain, where they can be used to produce more ATP

Glucose

NAD+

NADH

ADP

ATP

Pyruvic acid

Although oxygen is required for cellular respiration, glycolysis is anaerobic because it does not require oxygen to function.

2. Krebs Cycle (Citric acid cycle)• Pyruvate enters the mitochondrial matrix

– The inner most compartment of the mitochondria• Pyruvate is broken down into carbon dioxide and other molecules• 2 ATP released • Electron carriers NADH and FADH2 are produced

NAD+

NADH

FAD

FADH2

CO2

High energy electron carriers NADH and FADH2 make their way to the ETC

Cytoplasm Matrix

• The Krebs cycle is aerobic (with the presence of oxygen), a process that requires oxygen. Even though the Krebs cycle does not directly require oxygen, we call it aerobic because it would not run with out the oxygen requiring ETC.

• What is the last step in cellular respiration? Where are we going to get most of the ATP our cells need?

3. The Electron Transport Chain• The ETC occurs in the inner membrane of the

mitochondria NADH FADH2 ETC

• NADH and FADH2 pass their high energy electronsto the ETC

• A total of 32 ATP are made

• After the electrons pass through the ETC, Oxygen takes them and combines with hydrogen to form water.

• Oxygen is the final electron acceptor.

• Without oxygen, the Krebs cycle and the ETC will not function. Why?– What is made in the Krebs cycle?– Why is oxygen a requirement in the ETC?

C6H12O6 + 6O2 6CO2 + 6H2O + ENERGY

• Reactants?• Products?• Where do each of the reactants come from?• Where do each of the products come from?

Note: NADH and FADH2 go to the ETC

Energy Totals

– In the presence of oxygen, the complete breakdown of glucose through cellular respiration results in the production of 36 ATP molecules.

– This represents about 36 percent of the total energy of glucose. The remaining 64 percent is released as heat.

Energy Totals

– The cell can generate ATP from just about any source, even though we’ve modeled it using only glucose. Complex carbohydrates are broken down into simple sugars like glucose. Lipids and proteins can be broken down into molecules that enter the Krebs cycle or glycolysis at one of several places.

Fermentation 9.3• Cellular respiration requires oxygen. The Krebs

cycle and the ETC would not work with out it. • What happens when we hold our breath and dive

under water?• What happens if we can not replace oxygen fast

enough?• What about microorganisms that live in places

where oxygen isn’t available?• How do organisms generate energy when oxygen

is not available?

• Fermentation is a process by which energy can be released from food molecules in the absence of oxygen.

• Anaerobic process that occurs in the cytoplasm

• Two types of fermentation: – Alcoholic Fermentation– Lactic acid fermentation

Alcoholic Fermentation • 1. Alcoholic Fermentation: pyruvate is broken

down to ethanol and in the process it releases CO2

• Yeast and a few other microorganisms use alcoholic fermentation that produces ethyl alcohol and carbon dioxide.

• This process is used to produce alcoholic beverages and causes bread dough to rise.

Holes from release of carbon dioxide

• Ethanol is toxic to yeast and a concentration of about 12% ethanol kills yeast. This is why naturally fermented wine contains about 12% alcohol.

• 2. Lactic Acid Fermentation: In lactic acid fermentation, pyruvate is converted into lactic acid

• Does not give off carbon dioxide

• Humans produce lactic acid when we undergo strenuous exercise

• Prokaryotes (bacteria) produce lactic acid and are used in the production of dairy products.

• Cheese, yogurt, buttermilk, sour cream, pickles, sauerkraut and kimchi are all examples of foods we eat that are produced from lactic acid fermentation.

Energy and Exercise

• Humans have three main sources of ATP: • 1. ATP in the muscles• 2. ATP made by lactic acid fermentation• 3. ATP produced by cellular respiration

Quick Energy– Cells normally contain small amounts of

ATP produced during cellular respiration, enough for a few seconds of intense activity.

– Lactic acid fermentation can supply enough ATP to last about 90 seconds. However, extra oxygen is required to get rid of the lactic acid produced. Following intense exercise, a person will huff and puff for several minutes in order to pay back the built-up “oxygen debt” and clear the lactic acid from the body.

Long-Term Energy– For exercise lasting longer than 90

seconds, cellular respiration is required to continue production of ATP.

– Cellular respiration releases energy more slowly than fermentation does.

– The body stores energy in the form of the carbohydrate glycogen. These glycogen stores are enough to last for 15 to 20 minutes of activity. After that, the body begins to break down other stored molecules, including fats, for energy.

Long-Term Energy

– Hibernating animals like this brown bear rely on stored fat for energy when they sleep through the winter.