Harvesting Energy:
Harvesting Energy:
Glycolysis and Cellular
Glycolysis and Cellular
Respiration
Respiration
Chapter 8 Chapter 8
Overview of Glucose
Overview of Glucose
Breakdown
Breakdown
The overall equation for the complete The overall equation for the complete breakdown of glucose is:
breakdown of glucose is:
CC66HH1212OO66 + 6O + 6O22 6CO 6CO22 + 6H + 6H22O + ATPO + ATP
The main stages of glucose metabolism are:The main stages of glucose metabolism are:
– GlycolysisGlycolysis
– Cellular respiratioCellular respirationn
Overview of Glucose
Overview of Glucose
Breakdown
Breakdown
GlycolysisGlycolysis– Occurs in the cytosol Occurs in the cytosol
– Does not require oxygenDoes not require oxygen
– Breaks glucose into pyruvateBreaks glucose into pyruvate
– Yields two molecules of ATP per molecule of Yields two molecules of ATP per molecule of glucos
glucosee
Overview of Glucose
Overview of Glucose
Breakdown
Breakdown
If oxygen is absent fermentation occursIf oxygen is absent fermentation occurs
– pyruvate is converted into either lactate, or into pyruvate is converted into either lactate, or into ethanol and CO
ethanol and CO22
If oxygen is present cellular respiration If oxygen is present cellular respiration occur
occurss
Overview of Glucose
Overview of Glucose
Breakdown
Breakdown
Cellular respiration Cellular respiration
– Occurs in Occurs in mitochondriamitochondria (in eukaryotes) (in eukaryotes) – Requires oxygenRequires oxygen
– Breaks down pyruvate into carbon dioxide and Breaks down pyruvate into carbon dioxide and water
water
– Produces an additional 32 or 34 ATP Produces an additional 32 or 34 ATP molecules, depending on the cell typ molecules, depending on the cell typee
Glycolysis
Glycolysis
• Glucose activation phaseGlucose activation phase
– Glucose molecule converted to highly reactive Glucose molecule converted to highly reactive fructose bisphosphate by two enzyme-
fructose bisphosphate by two enzyme- catalyzed reactions, using 2 ATP
catalyzed reactions, using 2 ATPss
Glycolysis
Glycolysis
• Energy harvesting phaseEnergy harvesting phase
– Fructose bisphosphate is split into two three-Fructose bisphosphate is split into two three- carbon molecules of glyceraldehyde 3-
carbon molecules of glyceraldehyde 3- phosphate (G3P)
phosphate (G3P)
– In a series of reactions, each G3P molecule is In a series of reactions, each G3P molecule is converted into a pyruvate, generating two
converted into a pyruvate, generating two
ATPs per conversion, for a total of four ATPs ATPs per conversion, for a total of four ATPs – Because two ATPs were used to activate the Because two ATPs were used to activate the
glucose molecule there is a net gain of two glucose molecule there is a net gain of two ATPs per glucose molecul
ATPs per glucose moleculee
Glycolysis
Glycolysis
1.1. Energy harvesting phase (continued)Energy harvesting phase (continued)
– As each G3P is converted to pyruvate, two As each G3P is converted to pyruvate, two
high-energy electrons and a hydrogen ion are high-energy electrons and a hydrogen ion are added to an “empty” electron-carrier NAD+ to added to an “empty” electron-carrier NAD+ to make the high-energy electron-carrier
make the high-energy electron-carrier molecule NADH
molecule NADH
– Because two G3P molecules are produced per Because two G3P molecules are produced per glucose molecule, two NADH carrier
glucose molecule, two NADH carrier molecules are formed
molecules are formed
Glycolysis
Glycolysis
Summary of glycolysis:Summary of glycolysis:
– Each molecule of glucose is broken down to Each molecule of glucose is broken down to two molecules of pyruvate
two molecules of pyruvate
– A net of two ATP molecules and two NADH A net of two ATP molecules and two NADH (high-energy electron carriers) are forme
(high-energy electron carriers) are formedd
Fermentation
Fermentation
Pyruvate is processed differently under Pyruvate is processed differently under aerobic and anaerobic conditions
aerobic and anaerobic conditions
Under aerobic conditions, the high energy Under aerobic conditions, the high energy electrons in NADH produced in glycolysis electrons in NADH produced in glycolysis are ferried to ATP-generating reactions in are ferried to ATP-generating reactions in the mitochondria, making NAD+ available the mitochondria, making NAD+ available
to recycle in glycolysi to recycle in glycolysiss
Fermentation
Fermentation
Under anaerobic conditions, pyruvate is Under anaerobic conditions, pyruvate is converted into lactate or ethanol, a
converted into lactate or ethanol, a process called fermentation
process called fermentation
Fermentation does not produce more Fermentation does not produce more
ATP, but is necessary to regenerate the ATP, but is necessary to regenerate the
high-energy electron carrier molecule high-energy electron carrier molecule
NAD+, which must be available for NAD+, which must be available for
glycolysis to continu glycolysis to continuee
Fermentation
Fermentation
Some cells ferment pyruvate to form acidsSome cells ferment pyruvate to form acids
Human muscle cells can perform Human muscle cells can perform fermentation
fermentation
– Anaerobic conditions produced when muscles Anaerobic conditions produced when muscles use up O
use up O22 faster than it can be delivered (e.g. faster than it can be delivered (e.g.
while sprinting) while sprinting)
– Lactate (lactic acid) produced from pyruvatLactate (lactic acid) produced from pyruvatee
Fermentation
Fermentation
Some microbes ferment pyruvate to other Some microbes ferment pyruvate to other acids (as seen in making of cheese, yogurt, acids (as seen in making of cheese, yogurt,
sour cream) sour cream)
Some microbes perform fermentation Some microbes perform fermentation
exclusively (instead of aerobic respiration) exclusively (instead of aerobic respiration)
Yeast cells perform Yeast cells perform alcoholic fermentatioalcoholic fermentationn
Cellular Respiration
Cellular Respiration
In eukaryotic cells, cellular respiration occurs In eukaryotic cells, cellular respiration occurs within
within mitochondriamitochondria, organelles with two , organelles with two membranes that produce two compartments membranes that produce two compartments – The inner membrane encloses a central The inner membrane encloses a central
compartment containing the fluid
compartment containing the fluid matrixmatrix – The outer membrane surrounds the The outer membrane surrounds the
organelle, producing an
organelle, producing an intermembrane intermembrane spacspacee
Pyruvate Breakdown in
Pyruvate Breakdown in
Mitochondria
Mitochondria
• After glycolysis, pyruvate diffuses into the After glycolysis, pyruvate diffuses into the mitochondrion into the matrix space
mitochondrion into the matrix space
• Pyruvate is split into COPyruvate is split into CO22 and a 2-carbon and a 2-carbon acetyl group, generating 1 NADH per
acetyl group, generating 1 NADH per pyruvat
pyruvatee
Pyruvate Breakdown in
Pyruvate Breakdown in
Mitochondria
Mitochondria
• Acetyl group is carried by a helper Acetyl group is carried by a helper
molecule called Coenzyme A, now called molecule called Coenzyme A, now called
Acetyl CoA Acetyl CoA
• Acetyl CoA enters the Krebs Cycle and is Acetyl CoA enters the Krebs Cycle and is broken down into
broken down into COCO22
Pyruvate Breakdown in
Pyruvate Breakdown in
Mitochondria
Mitochondria
• Electron carriers NADElectron carriers NAD++ and FAD are and FAD are loaded with electrons to produce 3 loaded with electrons to produce 3
NADH & 1 FADH
NADH & 1 FADH22 per Acetyl CoA per Acetyl CoA
6. One ATP also made per Acetyl CoA in 6. One ATP also made per Acetyl CoA in
the Krebs Cycl the Krebs Cyclee
Electron Transport Chain
Electron Transport Chain
Most of the energy in glucose is stored in Most of the energy in glucose is stored in electron carriers NADH and FADH
electron carriers NADH and FADH22
– Only 4 total ATP produced per glucose after Only 4 total ATP produced per glucose after complete breakdown in the Krebs Cycle
complete breakdown in the Krebs Cycle
NADH and FADHNADH and FADH22 deposit electrons into deposit electrons into electron transport chains
electron transport chains in the inner in the inner mitochondrial membrane
mitochondrial membrane
Electrons join with oxygen gas and Electrons join with oxygen gas and hydrogen ions to made H
hydrogen ions to made H22O at the end of O at the end of the ETC
the ETCss
Chemiosmosis
Chemiosmosis
1.1. Energy is released from electrons as they Energy is released from electrons as they are passed down the electron transport
are passed down the electron transport chain
chain
2.2. Released energy used to pump hydrogen Released energy used to pump hydrogen ions across the inner membrane
ions across the inner membrane
– Hydrogen ions accumulate in intermembrane Hydrogen ions accumulate in intermembrane spacspacee
Chemiosmosis
Chemiosmosis
1.1. Hydrogen ions form a concentration Hydrogen ions form a concentration
gradient across the membrane, a form of gradient across the membrane, a form of
stored energy stored energy
• Hydrogen ions flow back into the matrix Hydrogen ions flow back into the matrix through an ATP synthesizing enzyme
through an ATP synthesizing enzyme
– Process is called Process is called chemiosmosichemiosmosiss
Chemiosmosis
Chemiosmosis
• Flow of hydrogen ions provides energy to Flow of hydrogen ions provides energy to link 32-34 molecules of ADP with
link 32-34 molecules of ADP with phosphate, forming 32-34 ATP
phosphate, forming 32-34 ATP
• ATP then diffuses out of mitochondrion ATP then diffuses out of mitochondrion
and used for energy-requiring activities in and used for energy-requiring activities in
the cel the celll
Influence on How Organisms
Influence on How Organisms
Function
Function
Metabolic processes in cells are heavily Metabolic processes in cells are heavily
dependent on ATP generation (cyanide kills dependent on ATP generation (cyanide kills
by preventing this) by preventing this)
Muscle cells switch between fermentation Muscle cells switch between fermentation and aerobic cell respiration depending on O and aerobic cell respiration depending on O22
availabilit availabilityy