Cellular Respiration
Chapter 8.3
Main Idea
Living organisms obtain energy by breaking
down organic molecules during cellular
respiration
Real-World Connection
• Monarch butterflies must constantly
feed on nectar from flowers to
provide energy to sustain themselves
during their winter migration to parts
of Mexico and California each year.
• Similarly, humans and other living
organisms need reliable food sources
to supply energy to survive and grow.
Cellular Respiration
• The function of cellular respiration is to
harvest electrons from carbon compounds,
such as glucose, and use that energy to make
ATP.
• ATP is used to provide energy for cells to do
work.
CHEMICAL EQUATION
C6H12O6 + 6O2  6CO2 + 6H2O + Energy
(notice this equations is the opposite of
photosynthesis…weird!)
SING ALONG TIME
• Sugar Sugar
Cellular Respiration (CR)
• CR occurs in two main parts:
Glycolysis and aerobic respiration
• Glycolysis is an anaerobic process,
which means it does not require
oxygen
• Aerobic respiration includes
the Krebs cycle and electron
transport chain, which does
require oxygen
Glycolysis
• Glucose (sugar) is broken down in the
cytoplasm through the process of glycolysis
• Glucose (6 carbon compound) is broken down
into 2 pyruvate (3 carbon compound)
molecules
• For every glycolysis reaction 4 molecules of
ATP are produced, but there is only a net yield
of 2
• Because glycolysis begins with the input of 2
molecules of ATP
• 4 total ATP- 2 ATP @ input= net yield of 2 ATP
Krebs Cycle
• Glycolysis has a net result of 2 ATP and 2
pyruvate molecules.
• Most of the energy from the glucose is still
contained in the pyruvate
• In the presences of oxygen, pyruvate is
transported to the mitochondria and is
eventually converted to carbon dioxide
• The Krebs cycle is also known as the Tricarboxylic acid (TCA) cycle and the citric acid
cycle.
Steps of the Krebs Cycle
• Pyruvate joins with a co-enzyme called acetyl
CoA
• Acetyl CoA binds with citric acid
• Citric acid breaks down into 2 molecules of
carbon dioxide and 1 ATP
• Finally, acetyl CoA and citric acid are
generated and the cycle continues
• Recall that two molecules of pyruvate are
formed during glycolysis, resulting in how
many turns of the Krebs cycle?????
• AND THE ANSWER IS…………
• The net yield of the Krebs cycle is 2 ATP, 8
NADH, and 2 FADH2
Electron Transport
• Electron transport is the final step in the
breakdown of glucose
• High-energy electrons and hydrogen ions from
NADA and FADH2 produced in the Krebs cycle
are used to convert ADP to ATP
• NADH and FADH2 release electrons, the
energy carriers are converted to NAD+ and
FAD, and H+ ions are released into the
mitochondria
• H+ ions diffuse down their concentration
gradient back across the membrane through
ATP synthase molecules
• Oxygen is the final electron acceptor in the
electron transport chain
• The electron transport chain produces 24 ATP
Overall ATP Production
• One molecule of glucose yields 36 ATP in
eukaryotes (what are eukaryotes??)
• One molecule of glucose yields 38 ATP in
prokaryotes (what are prokayotes??)
Anaerobic Respiration
• The anaerobic pathway that follows glycolysis
is fermentation
• There are 2 main types of fermentation
– Lactic acid fermentation
– Alcohol fermentation
Lactic Acid Fermentation
• Enzymes convert the pyruvate made during
glycolysis to lactic acid
• Skeletal muscle produces lactic acid when the
body cannot supply enough oxygen, such as
during strenuous exercise
• Lactic acid build up results in fatigued
and sore muscles
• Lactic acid also is produced by several
micro-organisms that often are used to
produce many foods, including cheese,
yogurt, and sour cream
Alcohol Fermentation
• Alcohol fermentation occurs in yeast and
some bacteria
• During fermentation, pyruvate is converted to
ethyl alcohol and carbon dioxide