Download Ch. 06 Celluar Respiration: Obtaining Energy from Food

Chapter 6
Cellular Respiration: Obtaining
Energy from Food
Biology and Society:
Marathoners versus Sprinters
• It is unusual to find a runner who complete equally well
in both 100m and 1000m races.
• Natural differences in the muscles of these athletes favor
sprinting or long-distance running.
• The muscles that move
our legs contain two main
types of muscle fibers:
Slow-twitch fibers &
Fast-twitch fibers
© Jong B. Lee, Ph.D.
• Slow-twitch fibers (지근): function best in marathons
Generate less power
Last longer
Generate ATP using oxygen
• Fast-twitch fibers (속근): function
best in sprints
Generate more power
Fatigue much more quickly
Can generate ATP without using oxygen
• All human muscles contain both types of fibers but in
different ratios.
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ENERGY FLOW AND CHEMICAL CYCLING
IN THE BIOSPHERE
• Fuel molecules in food represent solar energy
• Animals depend on plants to convert solar energy to
chemical energy
:This chemical energy is in the form of sugars and other
organic molecules. 그 외 clothing, lumber, paper
• Autotrophs (자가 영양 생물): called producers (생산자)
– “Self-feeders”: organisms that make all their own
organic matter from inorganic nutrients
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• Heterotrophs (종속 영양 생물)
– “Other-feeders”
– Humans and other animals that
cannot make organic molecules from
inorganic ones
– Depend on autotrophs for their
organic fuel and material for growth
and repair
– Called consumers (소비자)
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Chemical Cycling Between Photosynthesis and
Cellular Respiration
• The ingredients for photosynthesis are carbon dioxide
and water
– CO2 is obtained from the air by a plant’s leaves
– H2O is obtained from the damp soil by a plant’s roots
• Chloroplasts rearrange the atoms of these ingredients to
produce sugars (glucose) and other organic molecules
– Oxygen gas is a by-product of photosynthesis
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• Both plants and animals perform cellular respiration
– Cellular respiration is a chemical process that
harvests energy from organic molecules
– Cellular respiration occurs in mitochondria
– Cellular respiration uses to convert energy extracted
from organic fuel to another form of chemical energy
called ATP, an energy currency in the cell
• The waste products of cellular respiration, CO2 and H2O,
are used in photosynthesis
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CELLULAR RESPIRATION: AEROBIC HARVEST
OF FOOD ENERGY
• Cellular respiration
– A living version of internal combustion
– The main way that chemical energy is harvested from
food and converted to ATP
– This is an aerobic process—it requires oxygen
– 유기 연료에서 추출한 에너지 → 화학에너지인 ATP
에너지로 전환하기 위해, O2를 필요로 한다.
The Relationship Between Cellular Respiration and
Breathing
Cellular respiration and breathing are closely related
– Cellular respiration
requires a cell to
exchange gases with
its surroundings
– Breathing exchanges
these gases between
the blood and outside
air
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The Overall Equation for Cellular Respiration
The Role of Oxygen in Cellular Respiration
• A common fuel molecule for cellular respiration is glucose
During cellular respiration, hydrogen and its bonding
electrons change partners
– This is the overall equation for what happens to
glucose during cellular respiration
H+ + e-
Glucose
– The series of arrows indicates that cellular
respiration consists of many chemical steps
– The process can produce up to 38 ATP molecules for
each glucose consumed
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Oxygen
Carbon
dioxide
Water
Energy
Hydrogen and its electrons go from sugar to oxygen,
forming water (That hydrogen transfer turns out to
be the key to why oxygen is so vital to the harvest of
energy during cellular respiration)
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Redox Reactions
• Chemical reactions that transfer electrons from one
substance to another are called oxidation-reduction
reactions (산화 환원 반응) : Redox reactions for short
• The loss of electrons (and hydrogens) during a redox
reaction is called oxidation
• The acceptance of electrons (and hydrogens) during a
redox reaction is called reduction
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• Energy is released when hydrogen and its bonding
electrons change partners, from sugar to oxygen.
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A very rapid electron fall
Why does electron transfer to oxygen release energy?
– In redox reactions, oxygen is an “electron grabber”.
– When electrons move from glucose to oxygen, it is
as though they were falling.
– Instead of gravity, it is the attraction of electrons to
oxygen that causes the “fall” and energy release
during cellular respiration
– This “fall” of electrons releases energy during
cellular respiration
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• A very rapid electron fall
generates an explosive release
of energy in the form of heat
and light.
ex) A reaction between
hydrogen gas and oxygen gas
• The flame represents energy
released as heat and light
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NADH and Electron Transport Chains
The first stop is an electron acceptor called NAD+
Cellular respiration is a more
controlled “fall” of electrons:
• The transfer of electrons from organic fuel to NAD+
(nicotinamide adenine dinucleotide) reduces it to NADH
Instead of liberating food
energy in a burst of flame,
cellular respiration unlocks
chemical energy in smaller
amounts that cells can put to
productive use
• The rest of the path consists of
The path that electrons take
on their way down from
glucose to oxygen involves
many steps.
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The Metabolic Pathway of Cellular Respiration
• Cellular respiration is an example of a metabolic
pathway: a series of chemical reactions in cells
• A specific enzyme catalyzes each reaction in a
metabolic pathway
•
All of the reactions involved in cellular respiration can
be grouped into three main stages
an electron transport chain
: This chain involves a series of
Redox reactions
• This electron transport chain lead ultimately to the
production of large amounts of ATP
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A Road Map for Cellular Respiration
Cytosol
Mitochondrion
High-energy
electrons
carried
mainly by
NADH
High-energy
electrons
carried
by NADH
Glycolysis
Glucose
2
Pyruvic
acid
Krebs
Cycle
Electron
Transport
1. Glycolysis (해당과정) in cytoplasm
2. The Krebs cycle in mitochondria matrix
3. Electron transport in mitochondria inner membrane
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Stage 1: Glycolysis (해당과정)
• A molecule of glucose is split into two molecules of
pyruvic acid in cytosol (but not mitochondria)
cf) pyruvic acid (피브루산) formula: CH3-C-COOH
• Meanings of this metabolism (생화학적인 의미)
- These molecules then donate high energy electrons to
NAD+, forming NADH (Generate two NADH
molecules per glucose)
- Generate two ATP molecules: by substrate-level of
phosphorylation (기질수준의 인산화 과정에 의해서)
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Substrate level of phosphorylation
Glycolysis makes some ATP directly when enzymes
transfer phosphate groups from fuel molecules to ADP
(substrate level of phosphorylation , 기질수준 의 인산화 )
Enzyme
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Stage 2: The Krebs Cycle (= The citric acid cycle)
• The Krebs cycle completes the breakdown of sugar This
cycle completes the breakdown of sugar produce CO2
• Generate three NADH and one FADH2 (function as
electron donor for electron transfer system)
• Generate two ATP molecules
(by substrate level of phosphorylation)
이 과정에 참여하는 효소들은 mitochondria 내부의 액체에
존재한다. 즉, mitochondria matrix에서 수행됨.
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Krebs cycle
• In the citric acid cycle, pyruvic acid from glycolysis is
first “prepped” into a usable form, Acetyl CoA.
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Stage 3: Electron Transport
• Electron transport (전자전달) releases the energy your
cells need to make the most of their ATP
• The molecules of
electron transport chains
are built into the inner
membranes of
mitochondria (electron
transport chain을 구성하는
단백질과 그 밖에 분자들은
mitochondria의 내막에 존재)
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• The entire electron transport chain functions as a
chemical machine that uses energy released by the “fall”
of electrons to pump hydrogen ions across the inner
mitochondrial membrane
• The energy stored by electron transport behaves
something like the electron reservoir of water behind a
dam
• The membrane, analogous to the dam, temporarily
restrains the H+ ions.
• By pumping H+ ions,
electron transport chains
store potential energy
by making the ions more
concentrated on one side
of the membrane than on the other (these H+ ions store
potential energy)
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• There is a tendency for the H+ ions to gush back to
where they are less concentrated, just as there is a
tendency for water to flow downhill.
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• When the hydrogen ions flow back through the
membrane, they release energy
Space between
membranes
H
H
Electron
carrier
H
H
H
H
H
H
H
H
H
Protein
complex
– The ions flow through ATP synthase. This action spin
a component of the ATP synthase and activate
catalytic action. ATP synthase takes the energy from
this flow and synthesizes ATP
H
H
Inner
mitochondrial
membrane
FADH2
Electron
flow
Matrix
H
1
2
NADH
H
FAD
– ATP synthase는 ADP 분자에 Phosphate-group을
부착시켜 ATP를 재 발생시킨다.
NAD
H
O2  2 H
H2O
ADP  P
H
Electron transport chain
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H
ATP
H
ATP synthase
– Some of deadliest poisons (CO and HCN) do their
damage by disrupting electron transport (blocking the
transfer of electrons to oxygen
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The Versatility of Cellular Respiration
• Cellular respiration (versatile metabolic furnace) can
“burn” other kinds of molecules besides glucose
– Diverse types of carbohydrates
– Fats
– Proteins
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Adding Up the ATP from Cellular Respiration
ATP 생성 상황
A summary of ATP yield during cellular respiration
Glucose  2 pyruvic acid + 2 ATP + 2 NADH
2 pyruvic
acid  6 CO2 + 6 H2O + 2 ATP + 8 NADH + 2 FADH2
10 NADH x 3 ATP/NADH = 30 ATP
2 FADH2 x 2 ATP/FADH2 = 4 ATP
4 ATP + 30 ATP + 4 ATP = 38 ATP
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FERMENTATION: ANAEROBIC HARVEST OF
FOOD ENERGY
• Some of your cells can actually work for short periods
without oxygen
– For example, muscle cells can produce ATP under
anaerobic conditions
• Fermentation (발효): The anaerobic harvest of food
energy
Fermentation in Human Muscle Cells
• Human muscle cells can make ATP with and without
oxygen
– If you start to run because you’re late for class your
muscle forced to work under anaerobic conditions.
– They have enough ATP to support activities such as
quick sprinting for about 5 seconds
– A secondary supply of energy
(creatine phosphate) can keep muscle
cells going for another 10 seconds
– To keep running, your muscles must
generate ATP by the anaerobic process of fermentation
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• Glycolysis is the metabolic pathway that provides ATP
during fermentation
– To harvest food energy during glycolysis, NAD+ (not
NADH) must be present as an electron acceptor
– This is no problem under aerobic condition, because
the cell regenerates its NAD+ when NADH drops its
electron cargo down electron transport chains to O2
– However, this productive recycling of NAD+ cannot
occur under anaerobic conditions because there is no
O2 to accept the electron
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– Instead, NADH disposes of (처분하다) electrons by
adding them to pyruvic acid produced by glycolysis
– 즉, 해결책: Pyruvic acid is reduced by NADH,
producing NAD+, which keeps glycolysis going
• Glycolysis produces just two ATPs
– Is not efficient compared with 38 ATPs under the
aerobic condition
– Your cells have to consume more glucose fuel
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• Lactic acid (젖산) as a by-product after fermentation in
muscle cells
– A temporary accumulation of lactic acid in muscle cells
contributes to the soreness or burning you feel after
exhausting run
– The lactic acid eventually transported in the blood from
muscles to the liver, where liver cells convert it back to
pyruvic acid
– Oxygen debt: O2 that metabolic pathway requires after
you’ve stopped vigorous activity (you breathe hard even
after stopping exercise). The extra oxygen is used to
generate glucose from lactic acid (gluconeogenesis)
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Fermentation in Microorganisms
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Fermentation in Microorganisms
• Yeast (효모), a microscopic fungus
• Various types of microorganisms perform fermentation
– Fermentation products: cheese, sour cream, yogurt
(주로 젖산 때문에 이러한 맛이 발생)
– Yeast cells are capable of both cellular respiration
and fermentation but a slightly different type of
fermentation
– 그 밖에 soy source (soybean), pickle cucumbers,
pepperoni, salami 등이 있다.
– This pathway (=alcohol fermentation) produces CO2
and ethyl alcohol
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• The food industry uses yeast to produce various food
products
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EVOLUTION CONNECTION:
LIFE ON AN ANAEROBIC EARTH
• 산소의 사용능력에 따라 생물체의 분류
- Facultative anaerobe: an organism that harvest food
energy by either cellular respiration or fermentation
- Obligate anaerobe: 산소 접촉 시 사망, 깊은 토양 속
미생물, 캔 속의 미생물, 늪지대에 사는 미생물
- Obligate aerobe: 산소를 절대적으로 필요로 하는 생명체
Ancient bacteria probably used glycolysis to make ATP
long before oxygen was present in Earth’s atmosphere
– Glycolysis is a metabolic heirloom from the earliest
cells that continues to function today in the harvest of
food energy
– Krebs cycle & electron transport chain은 산소가
존재하는 aerobic condition에서만 작동하지만
glycolysis는 aerobic 과 anaerobic condition에서 모두
작동할 수 있다. 그러므로 아마도 고대의 bacteria들은
지구의 대기에 산소가 없을 때 glycolysis를 사용하여 ATP를
만들었을 것으로 추정한다.
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