Chapter 7Cellular Respiration

Section 7.1

Glycolysis and Fermentation

• All cells break down complex organic compounds into simpler molecules

• As the compounds are broken down, cells release energy

• Some of the energy is used to make ATP from ADP

Harvesting Chemical Energy

• ATP is the main energy currency of cells

• Cellular respiration- the complex process in which cells make ATP by breaking down organic compounds

Cellular Respiration

• Begins with glycolysis

• Glycolysis yields a small amount of ATP

• Two possible pathways depending on the presence or absence of oxygen

Aerobic vs. Anaerobic

• Aerobic: oxygen is present (pathway will lead to aerobic respiration)

• Anaerobic: oxygen is absent (pathway leads to fermentation)

Glycolysis

• Takes place in the cytosol of the cell

• Involves four main steps

• One 6-Carbon molecule of glucose is oxidized to produce two three-Carbon molecules of pyruvic acid

• Two ATP molecules are used in step 1

• Four ATP molecules are produced in step 4

• Glycolysis has a net yield of 2 ATP

Fermentation

• Occurs in the absence of oxygen

• Converts pyruvic acid into other compounds

• These pathways regenerate NAD+

Lactic Acid Fermentation

• An enzyme converts pyruvic acid into another 3-carbon compound called lactic acid

• Two hydrogen atoms are transferred to pyruvic acid

Uses of Lactic Acid

• Microorganisms are used for lactic acid fermentation in cheese and yogurt

• Also occurs in muscle cells during strenuous exercise (muscle cells use up oxygen faster than it can be delivered)

Alcoholic Fermentation

• Plant cells and unicellular organisms, such as yeast, convert pyruvic acid into ethyl alcohol

• Used in bread, wine, beer, etc.

Energy Yield

• Energy is measured in units of kilocalories (kcal)

• One kilocalorie equals 1000 calories (cal)

• Oxidation of a standard amount of glucose releases 686 kcal

Efficiency of Glycolysis

• Efficiency of = energy required to make ATP glycolysis energy released by oxidation of glucose

= 2 X 12 kcal X 100% 686 kcal = 3.5%

• Anaerobic pathways probably evolved very early in the history of life on Earth

• For more than a billion years, this was the only pathway available for harvesting chemical energy

• The first organisms to use anaerobic pathways were bacteria

• Larger organisms have greater energy requirements that cannot be met by only anaerobic pathways

• Must use aerobic respiration

Chapter 7

Section 7.2

Aerobic Respiration

• Produces 20 times as much ATP as produced by glycolysis alone

• Has two major stages: the Krebs cycle and the electron transport chain

Energy Yield• Maximum of 38 ATP molecules can be produced

from 1 molecule of glucose

• Efficiency = Energy required to make ATP Energy released by oxidation of glucose

= 38 X 12 kcal X 100% = 66% 686 kcal

• Aerobic respiration is nearly 20 times more efficient than glycolysis alone

• Glucose glycolysis pyruvic acid acetyl CoA Krebs cycle

Summarizing Cellular Respiration

• C6H12O6 + 6O2 6 CO2 + 6H2O + energy

• Cellular respiration provides ATP that all cells need to support the activities of life

• Also provides carbon skeletons that can be built up into larger molecules

• Cells need specific organic compounds to build macromolecules