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