Chapter 7

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Transcript Chapter 7

Essentials of Biology
Sylvia S. Mader
Chapter 7
Lecture Outline
Prepared by: Dr. Stephen Ebbs
Southern Illinois University Carbondale
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
7.1 Cellular Respiration
• The ATP molecules that provide energy to
eukaryotic cells are produced during
cellular respiration.
• During cellular respiration, the
mitochondria take in O2 and release CO2.
• Cellular respiration is the reason that
animals breathe.
7.1 Cellular Respiration (cont.)
• Oxidation, the removal of hydrogen atoms
from a molecule, is a central reaction in
cellular respiration.
oxidation
C6H12O6 + 6 O2
6 CO2 + 6 H2O + energy
reduction
7.1 Cellular Respiration (cont.)
• The breakdown of glucose during cellular
respiration releases energy.
• The slow oxidation of glucose in the
mitochondria allows the energy to be
removed slowly and stored as ATP.
7.1 Cellular Respiration (cont.)
Phases of Complete Glucose
Breakdown
• Cellular respiration involves a metabolic
pathway of enzymes assisted by
coenzymes.
• The two coenzymes involved in cellular
respiration, NAD+ and FAD+, receive the
hydrogen atoms removed from glucose.
Phases of Complete Glucose
Breakdown (cont.)
• The complete oxidation of glucose involves four
phases.
– Glycolysis, the splitting of glucose into two 3-carbon
molecules
– The preparatory reaction, which divides each 3carbon molecules into a 2-carbon molecule and CO2
– The citric acid cycle, which produces CO2, NADH,
FADH2, and ATP
– The electron transport chain, which assists in the
production of the largest amount of ATP
Phases of Complete Glucose
Breakdown (cont.)
7.2 Outside the Mitochondria:
Glycolysis
• Glycolysis takes place in the cytoplasm of the
cell.
• During glycolysis, glucose (a 6-carbon molecule)
is broken down to two pyruvate (3-carbon)
molecules.
• Glycolysis is divided into two stages.
– Energy-Investment Steps
– Energy-Harvesting Steps
7.2 Outside the Mitochondria:
Glycolysis (cont.)
Energy-Investment Steps
• Some molecules must be energized
before they can be broke down.
• To facilitate glucose breakdown during
glycolysis, 2 ATP molecules energize
glucose by donating their phosphate
groups.
Energy-Harvesting Steps
• During the energy-harvesting steps, substrates
are oxidized and the hydrogen atoms removed
are used to form NADH.
• This oxidation also produces substrates with
high-energy phosphate groups, which can be
used to synthesize ATP.
• The transfer of a phosphate group from a
molecule to form ATP is called substrate-level
ATP synthesis.
Energy-Harvesting Steps (cont.)
• Glycolysis produces a total of four ATP.
• Since two ATP were used to initiate
glycolysis, the net ATP production from
glycolysis is two ATP.
• The metabolic fate of pyruvate, the
product of glycolysis, depends upon the
presence of oxygen.
Energy-Harvesting Steps (cont.)
7.3 Inside the Mitochondria
• The remaining stages of cellular
respiration occur in the mitochondria.
• These steps require the presence of
oxygen.
• The structural features of the mitochondria
contribute to cellular respiration.
7.3 Inside the Mitochondria
(cont.)
Preparatory Reaction
• The preparatory (prep) reaction of glycolysis,
which occurs twice for each glucose molecule,
produces the substrate that enters the
subsequent citric acid cycle.
• Several events occur in the preparatory reaction.
– Pyruvate is oxidized and releases a molecule of CO2
and a 2-carbon acetyl group.
– NAD+ accepts a hydrogen atom, producing NADH.
– The acetyl group is attached to coenzyme A (CoA) to
form acetyl-CoA.
The Citric Acid Cycle
• The citric acid cycle occurs in the matrix of the
mitochondria.
• Several events occur during the citric acid cycle.
– The acetyl group is oxidized to CO2.
– Both NAD+ and FAD+ accept hydrogen atoms,
forming NADH and FADH respectively.
– Substrate-level ATP synthesis occurs, forming ATP.
• The citric acid cycle turns twice for each glucose
molecule.
The Citric Acid Cycle (cont.)
The Electron Transport Chain
• The electron transport chain is located in the
cristae of the mitochondria.
• The members of the electron transport chain
accept electrons from the hydrogen atoms
accepted by NADH and FADH2.
• As the electrons are passed down the electron
transport chain, energy is released and captured
for ATP production.
The Electron Transport Chain
(cont.)
• At the end of the electron transport chain, the
electrons are donated to oxygen atoms to form
water.
• The number of ATP molecules formed depends
upon the electron donor.
– The electrons from NADH provide energy for the
synthesis of three ATP molecules.
– The electrons from FADH2 provide energy for the
synthesis of two ATP molecules.
The Electron Transport Chain
(cont.)
The Cristae of a Mitochondrion
• The members of the electron transport
chain are imbedded in the cristae of the
mitochondria in a specific pattern.
• As the members of the electron transport
chain accept electrons from NADH and
FADH2, the H+ are pumped into the
intermembrane space.
The Cristae of a Mitochondrion
(cont.)
• This pumping creates an H+ reservoir in
the intermembrane space.
• This reservoir can be released through an
ATP synthase complex to synthesize ATP.
The Cristae of a Mitochondrion
(cont.)
Energy Yield from Glucose
Metabolism
• The complete breakdown of glucose yields
36 ATP molecules.
– Glycolysis provides 2 net ATP.
– The NADH produced by the prep reaction and
the citric acid cycle yield 30 ATP.
– The electron transport chain uses FADH2 to
produce 4 ATP.
Energy Yield from Glucose
Metabolism (cont.)
Alternative Metabolic Pathways
• Cells can breakdown other molecules, such as
lipids and proteins, to yield ATP.
• Lipids can be broken down to produce more
ATP than glucose.
– The glycerol from lipids enters cellular respiration at
glycolysis.
– The fatty acids from lipids can be metabolized into
acetyl groups, which enter the citric acid cycle.
Alternative Metabolic Pathways
(cont.)
• The hydrocarbon backbone of amino acids
can enter cellular respiration at several
points and can be broken down to produce
energy.
• The small molecules produced during
cellular respiration can be used to
synthesize larger molecules.
Alternative Metabolic Pathways
(cont.)
7.4 Fermentation
• Fermentation is the anaerobic breakdown of
glucose, forming 2 ATP and a toxic by-product.
• In animal cells during fermentation, pyruvate
from glycolysis is reduced to lactate, reforming
NAD+.
• Although fermentation produces only 2 ATP
molecules per glucose, it is essential as a quick
source of ATP energy for cells.
7.4 Fermentation (cont.)
• When fermentation occurs in muscles
during vigorous exercise, the lactate builds
up, as does an oxygen deficit.
• The increase in lactate changes the pH,
creating the “burn” associated with
exercise.
7.4 Fermentation (cont.)
Microorganisms and Fermentation
• Bacterial fermentation produces either
lactate or alcohol + CO2.
• Yeast are well known microorganisms that
produce alcohol and CO2 during
fermentation.
– CO2 production is what causes bread to rise.
– Ethanol production is critical for the making of
beer and wine.