Chapter 9: Cellular Respiration

Chemical Energy and Food

A calorie is the energy required to raise 1g of water 1˚C– 1g of glucose releases 3811

calories 1 Calorie (capital “C”) on

food labels is actually a kilocalorie (1000 calories)– 1g of glucose releases

3.811 Calories

Using Chemical Energy

Plants and animals both use glucose for metabolic fuel

Glucose is not directly usable– Must be converted into ATP

first

Cellular Respiration Overview

Converts glucose into ATP Occurs in both plants and

animals Cellular Respiration

Reaction:– C6H12O6 + 6O2 → 6CO2 + 6H2O

Opposite of photosynthesis- 6CO2 + 6H2O → C6H12O6 + 6O2

Glycolysis

Series of reactions which break a 6-carbon glucose molecule into two 3-carbon molecules called pyruvic acid (a.k.a. pyruvate)

Occurs in the cytoplasm

Glucose

to electron transport chain

2 Pyruvate2 G3P

Glycolysis

Process is ancient – all organisms from simple bacteria to humans perform

it the same way Yields 2 ATP and 2 NADH per glucose molecule

Glucose

to electron transport chain

2 Pyruvate2 G3P

Glycolysis

Overview: Glucose is converted

into 2 pyruvic acid molecules– A.K.A. pyruvate

Pyruvic acid is a reactant in the Krebs Cycle

Glycolysis

Step 1: The cell invests 2 ATP

to convert glucose 2 G3P

Glycolysis

Step 2: 4 ATP molecules are

produced from the conversion of 2 G3P 2 pyruvic acid

2 NADH molecules are produced– Used in E.T.C.

Glycolysis

Aerobic Cellular Respiration

Oxygen required = aerobic 2 more sets of reactions which occur in a

specialized organelles called mitochondria1. The Krebs Cycle

2. The Electron Transport Chain

The Krebs Cycle

AKA The Citric Acid Cycle Completes the breakdown of glucose

– Carbon and oxygen atoms end up in CO2 and H2O, respectively

Produces only 2 more ATP – but produces electron carriers NADH and FADH2

which move to the 3rd stage (The Electron Transport Chain)

The Krebs Cycle

Citric Acid Production

The Krebs Cycle

Products (per glucose): 6 CO2

2 ATP 8 NADH 2 FADH2

to E.T.C.

http://upload.wikimedia.org/wikipedia/commons/0/0b/Citric_acid_cycle_with_aconitate_2.svg

Electron Transport Chain

Powered by electron carriers from the Kreb’s Cycle

Produces a total of 32 ATP Water is formed when oxygen combines with

protons

The Electron Transport Chain

Electron Transport

Hydrogen Ion Movement

ATP Production

ATP synthase

H+ Diffusion

Intermembrane

Space

Inner Membrane

Mitochondrial Matrix

H+ Active Transport

Energy Tally

36 ATP for aerobic vs. 2 ATP for anaerobic

– Glycolysis 2 ATP

– Krebs 2 ATP

– Electron Transport Chain 32 ATP 36 ATP

Anaerobic organisms can’t be too energetic but are important for global recycling of carbon

Anaerobic Cellular Respiration

Also called fermentation Some organisms thrive in environments with little or no

oxygen– Marshes, bogs, digestive tracts, sewage treatment tanks, etc.

No oxygen used = anaerobic Results in no more ATP

– The final steps in these pathways serve ONLY to regenerate NAD+ so it can keep glycolysis running

End products such as ethanol and CO2 (yeast in beer/bread) or lactic acid (muscle cells)

Fermentation Overview

Alcoholic Fermentation

Used by yeasts and other microorganisms Produces carbon dioxide and ethanol Used to make bread and alcoholic drinks (beer, wine,

etc.)

Lactic Acid Fermentation

Used by both unicellular and multicellular organisms Lactic acid buildup in muscles causes a burning sensation Used in the production of sour cream, cheese, yogurt, and

many other foods & beverages

Glucose Pyruvic Acid Lactic Acid

Fermentation Overview