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Cellular Respiration
All organisms need energy
Why do we need energy?
To Grow
To Move
To Reproduce
ETC.
Source of Energy
• All living things require energy to maintain homeostasis
• The ultimate source of energy is the SUN
• Autotrophs obtain energy directly from the sun
– plants, algae, and photosynthetic bacteria
• Heterotrophs obtain their energy from food molecules
– animals and human
Photosynthesis and Respiration
• Photosynthesis & respiration provide
energy for life
• Photosynthesis
– uses solar energy to produce
Glucose/O2 from CO2 & H2O
• Cellular respiration
– Uses O2 and makes ATP
Making Energy (ATP)
• Plants cells make ATP during photosynthesis
• Cells of other organisms make ATP by breaking down food
such as carbohydrates, fats and proteins
• ATP later provides energy for cellular work ( breathing,
digestion of food, muscle movement etc. )
Respiration provides energy from
food
Catabolic Pathways and Production of ATP
• The breakdown of organic molecules is an
EXERGONIC reaction
• FERMENTATION is a partial degradation of
sugars that occurs without O2
• AEROBIC respiration uses organic molecules
such as Carbohydrates, Fat, Protein, Nucleic Acid
and O2 ----- yields ATP
• ANAEROBIC respiration uses compounds other
than O2
Anaerobic Processes
• No oxygen is
required for these
processes.
• Includes glycolysis,
the breakdown of
glucose, and
fermentation.
• Some bacteria and
yeast are examples
of anaerobes.
http://www.biol.vt.edu/research/images/C._perfringens_in_mac._jpg.jpg
http://www.utoronto.ca/greenblattlab/images/a/yeast%201.jpg
Cellular Respiration uses oxygen and glucose to produce
Carbon dioxide, water, and ATP.
Glucose
Oxygen gas
Carbon
dioxide
Water
Energy
Breathing and Cell Respiration are related
O2
BREATHING
CO2
Lungs
CO2
Bloodstream
O2
Muscle cells
carrying out
CELLULAR
RESPIRATION
Sugar + O2  ATP + CO2 + H2O
How efficient is cell respiration?
Energy released
from glucose
(as heat and light)
Energy released
from glucose
banked in ATP
Gasoline energy
converted to
movement
About
40%
25%
100%
Burning glucose
in an experiment
“Burning” glucose
in cellular respiration
Burning gasoline
in an auto engine
• Cellular respiration includes both aerobic and
anaerobic respiration but is often used to refer
to aerobic respiration
• Although carbohydrates, fats, and proteins are all
consumed as fuel, it is helpful to trace cellular
respiration with the sugar glucose:
REDOX Reactions
Oxidation and Reduction
• The transfer of electrons during chemical
reactions releases energy stored in organic
molecules
• This released energy is ultimately used to
synthesize ATP
Redox Reactions
• Chemical reactions that transfer electrons between
reactants are called oxidation-reduction reactions, or
redox reactions
• In oxidation, a substance loses electrons, or is
oxidized
• In reduction, a substance gains electrons, or is
reduced (the amount of positive charge is reduced)
Redox reactions
• Oxidation-reduction
• OIL RIG
(adding e- reduces + charge)
• Oxidation is e- loss;
reduction is e- gain
• Reducing agent:
e- donor
• Oxidizing agent:
e- acceptor
becomes oxidized
(loses electron)
becomes reduced
(gains electron)
• The electron donor is called the reducing agent
• The electron receptor is called the oxidizing
agent
• In cellular respiration, glucose is oxidized and
oxygen is reduced.
becomes oxidized
becomes reduced
NAD+ and Electron Transport Chain
• In cellular respiration, glucose and other organic
molecules are broken down in a series of steps
• Electrons from organic compounds are usually
first transferred to NAD+, a coenzyme
• As an electron acceptor, NAD+ functions as an
oxidizing agent during cellular respiration
• Each NADH (the reduced form of NAD+)
represents stored energy that is tapped to
synthesize ATP
Oxidizing agent in respiration
• NAD+ (nicotinamide
adenine dinucleotide)
• Removes electrons from
food (series of reactions)
• NAD + is reduced to
NADH
Enzyme action:
dehydrogenase
• Oxygen is the eventual
electron acceptor
Electron Carriers (shuttle)
• Nicotinamide Adenine Dinucleotide
• (NAD+ →NADH)
• FAD → FADH2
• NADH passes the electrons to the electron
transport chain
• ½ O2 pulls electrons down the chain and forms
water
• The energy yielded is used to regenerate ATP
What is ATP ?
• ATP stands for adenosine triphosphate
• Energy carrying molecule used by cells to fuel their
cellular process
• ATP has
– a nitrogen base adenine
– a 5 carbon sugar ribose
– and 3 phosphate (PO4) groups
How ATP Works?
• Energy is stored in bond
between the 2nd and 3rd
phosphate groups
• When the bond is broken,
energy is released and ADP is formed
• ATP re - forms when ADP binds to a phosphate group
ATP / ADP Cycle
• ATP is constantly used and remade in the cell.
• Energy is released or stored by breaking or making
a phosphate bond.
http://www.columbia.edu/cu/biology/courses/c2005/purves6/figure06-09.jpg
Stages of Cellular Respiration
•THREE stages:
• GLYCOLYSIS (happens in the cytoplasm)
• KREBS CYCLE or CITRIC ACID CYCLE (happens in
the inner compartments of mitochondria)
• ELECTRON TRANSPORT CHAIN or ETC ( in the
inner membrane of mitochondria)
• Summary:
C6H12O6 + 6 O2  6 CO2 + 6H2O + ATP
Steps of Glycolysis
• Energy - requiring steps
– 2 ATP added to glucose (6C) molecule to energize it
– glucose split to 2 PGAL (3C) or G3P
• Energy - releasing steps
– each PGAL splits into pyruvate (3C) molecules
– producing ATP and NADH
Fig. 9-6-1
Electrons
carried
via NADH
Glycolysis
Pyruvate
Glucose
Cytosol
ATP
Substrate-level
phosphorylation
Fig. 9-6-2
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolysis
Pyruvate
Glucose
Mitochondrion
Cytosol
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Fig. 9-6-3
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolysis
Pyruvate
Glucose
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Mitochondrion
Cytosol
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation
• The process that generates most of the ATP is
called the oxidative phosphorylation because it
is powered by redox reactions
• It generates nearly 90% of the ATP
• A smaller amount of ATP is formed in glycolysis
and in the citric acid cycle by substrate-level
phosphorylation
Enzyme
Enzyme
ADP
P
Substrate
+
Product
ATP
An Overview of Cellular Respiration
Glycolysis
• The first stage of cellular respiration & fermentation
• Occurs in the cytoplasm of the cell
• Anaerobic ( O2 is not required)
• Breaks down glucose (6 Carbon) molecule into two pyruvic
acid or pyruvate (3 Carbon) molecules
• It takes 2 ATP to jump – start the reactions
Steps of Glycolysis
• Energy - requiring steps
– 2 ATP added to glucose (6C) molecule to energize it
– glucose split to 2 PGAL (3C) or G3P
• Energy - releasing steps
– each PGAL splits into pyruvate (3C) molecules
– producing ATP and NADH
End Product of Glycolysis
• Makes 4 ATP (2 ATP
used up, net yield is 2 ATP)
• 2 NADH & 2 molecules
• of pyruvate (pyruvic acid)
• If O2 is available to the cell - pyruvate moves into
mitochondria
End Products of Glycolysis
• Makes 4 ATP (2 ATP
used up, net yield is 2 ATP)
• 2 NADH & 2 molecules
• of pyruvate (pyruvic acid)
• If O2 is available to the cell - pyruvate moves into
mitochondria
NEEDS
RELEASES
2 ATP
2adp + 2p
1 GLUCOSE
2 PYRUVATE
2 NAD
2 NADh
4 ADP+4P
4 ATP
Mitochondria
• A large organelle with double
membrane
– inner fold is called cristae
– central cavity known as matrix
• Site of aerobic cellular respiration
– energy stored in glucose is used to make ATP
PREP REACTION (between glycolysis and
citric acid cycle)
• Occurs in the inner compartment of the
mitochondrion.
• 2 - Three carbon pyruvic acid is converted to
2 - Two carbon, acetyl CoA
2 CO2
2 NADH
Prep Reaction
• Pyruvic acid from glycolysis in mitochondria
– reacts with coenzyme A, to form acetyl coenzyme (2C)
– in the process CO2 and NADH are also produced
Krebs Cycle (Citric Acid Cycle)
• Occurs in the in the inner membrane of mitochondria
• Named after the biochemist Hans Krebs
• Kreb’s Cycle is also known as the Citric acid Cycle
• Requires 2 cycles in order to completely oxidize one
molecule of glucose (2 acetyl CoA)
• Over all there are five intermediate chemical steps
Krebs Cycle (Citric Acid Cycle)
Results of Krebs Cycle
• Each turn of the cycle makes:
– 1 ATP, 3 NADH, 1 FADH2, and 2CO2
• 2 turns ( one for each pyruvate) makes:
– 2 ATP, 6 NADH, 2 FADH2, and 4CO2
• CO2 is a waste product that diffuses out of the cells
• NADH & FADH2 move to the electron transport chain (ETC)
The Krebs Cycle
Needs
RELEASES
2 FAD
2 FADH2
6 NAD
6 NADH
Pyruvate
CO2
2ADP + 2P
2ATP
Electron Transport Chain
• Happens in the inner membrane
• Accepts electron from NADH and FADH2
• Electrons provide energy for active transport
of H+ from inner compartment to outer
compartment forming a membrane potential.
• H+ then pass down a concentration
gradient providing energy for ATP synthase
to attach a phosphate atom to ADP → ATP
• Terminal electron acceptor is oxygen; thus
H2O is a by-product.
•Total 32 ATP are produced.
Electron Transport Chain
• electrons from NADH and FADH2 are passed to
many electron transport enzymes which form an
electron transport chain
• at the end of the chain, an enzyme combines electrons
from the chain, H+ (hydrogen ions) from the cell, and
O2 (oxygen) to make H2O (water).
• oxygen is the final electron accepter and is needed to
obtain energy from NADH and FADH2
Electron Transport chain
Occurs on the CRISTAE of
the mitochondria
The Electron Transport
chain
Needs
Releases
2 FADH2
FAD
10 NADH
NAD
O2
H2O
ADP + P
Up to 34 ATP
ATP Formation
• the mitochondria accepts electrons, while some
enzymes pump hydrogen ions outside the inner
membrane
• movement of hydrogen ions is what powers
the making of ATP
• the movement of a pair of electrons down the
electron transport chain produces enough
energy to make 3 ATP molecules from ADP
ATP Formation
• the more H ions on the outside makes the
outside more positively charged than the inside
• the difference in the charges gives the energy
needed to make ATP from ADP
• the mitochondrion membrane lets the enzymes
pump ions out, but won’t let them come back
in
Electron Transport Chain
Electron Transfer Phosphorylation
• Electron transfer sets up H+ ion gradients
• H+ concentration gradient provides energy to make ATP
from ADP and Pi
• Making ATP by adding Pi to ADP is called phosphorylation
• Each time one electron passes to oxygen (O2)
– 3 ATP are produced for each NADH
– 2 ATP are produced for each FADH2
Electron Transport Chain
• Cytochromes carry electron
carrier molecules (NADH &
FADH2) down to oxygen
• Chemiosmosis: energy
coupling mechanism
ATP Synthase
• A channel protein in the inner mitochondrial membrane
• Allows H+ to diffuse down their concentration gradient,
back into the inner compartment
• This flow of H+ drives the formation of ATP from ADP &
unbound phosphate (Pi)
– oxidative phosphorylation
Final ATP Tally
Stage
NADH
Glycolysis
2
Pyruvic
acid
conversion
2
Krebs cycle
6
ETC
FADH2
2
2
10
2
32-34
Loss due to
active
transport
Total ATP
ATP Yield
-2


36-38
Summary of Energy Harvest
Phosphorylation in Animal Cells
• In cytoplasm (1)
• In mitochondria
(2, 3 & 4)
Other Food Pathways
1. Carbohydrates
2. Lipids
3. Proteins
Anaerobic Respiration
Using Glycolysis → 2 ATP
1. Lactic Acid Fermentation Glucose → Pyruvic Acid → Lactic Acid
– During periods of strenuous exercise, lactic acid may build up
in muscles causing cramping.
– By bacteria in food production…sour cream, yogurt,
sauerkraut, pickles, kimchee
2. Ethanol Fermentation
Glucose → Pyruvic Acid → Acetaldehyde →
Ethanol
By yeast in ethanol production of beer and wine.
CO2 produced causes bread to rise
Related metabolic processes
• Fermentation:
• 1. Alcohol: From
pyruvate to ethanol
• 2. Lactic acid: From
pyruvate to lactate
• Facultative anaerobes
(yeast/bacteria)
Two types of Fermentation
• Alcoholic Fermentation
– in yeast
• Lactic acid Fermentation
– in some bacteria and animal cell
• Steps that follow glycolysis serve only to regenerate NAD+
Fermentation
• Anaerobic extraction of energy from organic molecules
– does not require oxygen
• Takes place only in cytoplasm
• Yields only 2 ATP
• Do not break down glucose completely to CO2 and water
• The ultimate electron acceptor is an organic molecule
and not oxygen
Lactic Acid Fermentation
• Carried out by certain bacteria and animal cell
• Certain bacteria utilized in food production (sour cream,
yogurt, pickles)
Alcoholic Fermentation
• Utilized by yeast in the absence of oxygen
• CO2 produced by fermentation allows bread to rise
• Ethanol utilized in production of beer and wine
Anaerobic respiration
Glucose
Glycolysis
2 Pyruvic acid
Alcohol + CO2
Lactic acid
Chemiosmosis
• Energy released creates a proton gradient across the
mitochondrial membrane
• Proton gradient stores potential energy that can be used
to phosphorylate ADP
• Process is driven by a proton gradient (ATP synthesis
proceeds as protons diffuse back across the membrane)
Metabolism
Catabolic Processes
• Energy releasing
reactions
• Breakdown of large
molecules to small
molecules
• Ingested food is the
source of molecules
Anabolic Processes
• Energy requiring
reactions
• Join small molecules to
form large molecules
• Synthesize molecules
essential to life
How Important is Oxygen??
• without oxygen, electron transport can happen,
but the Krebs Cycle will stop, and ATP
production will also stop
• if our bodies don’t get enough oxygen, then
they’ll try to work from the oxygen from
glycolysis
• oxygen has a major role in the mitochondria of
a cell
Comparison
• photosynthesis and respiration can be thought
of as opposite reactions
• photosynthesis gives energy, respiration takes
energy
• respiration and photosynthesis’ equations are
reverse of each other
• the products of photosynthesis are the reactants
for the breaking down of glucose