Respiration
• Cellular respiration is the process by which
cells transfer chemical energy from sugar
molecules to ATP molecules.
• As this happens cells release CO2 and use
up O2
• Respiration can be AEROBIC or ANAEROBIC
Breathing supplies oxygen to our cells and
removes carbon dioxide
– Breathing provides for the exchange of O2 and CO2
Between an organism and its environment
O2
CO2
Breathing
Lungs
CO2
Bloodstream
O2
Muscle cells carrying out
Cellular Respiration
Glucose + O2
Figure 6.2
CO2 + H2O + ATP
The human body uses energy from ATP for all its activities.
– ATP powers almost all cellular and body activities
.
CELLULAR RESPIRATION
• Cellular respiration is an energy- releasing
process. It produces ATP
• ATP is the universal energy source
Making ATP
• Plants make ATP during photosynthesis
• Cells of all organisms make ATP by
breaking down carbohydrates, fats, and
protein
– The energy in an ATP molecule
• Lies in the bonds between its phosphate groups
Adenosine
Adenosine diphosphate
Triphosphate
Phosphate
groups
P
Adenine
P
P
H2O
P
Hydrolysis
Ribose
ATP
Figure 5.4A
ADP
P +
P +
Energy
REDOX REACTIONS
– The loss of electrons is called oxidation.
– The addition of electrons is called reduction
Overview of Aerobic Respiration
C6H12O6 + 6O2  6CO2 + 6H2O +ATP
glucose
oxygen
carbon
dioxide
water
– When glucose is converted to carbon dioxide
•
It loses hydrogen atoms, which are added to
oxygen, producing water
Loss of hydrogen atoms
(oxidation)
C6H12O6 +
6 O2
6 CO2
Glucose
6 H2O
+ Energy
(ATP)
Gain of hydrogen atoms
(reduction)
Figure 6.5A
+
STAGES OF CELLULAR RESPIRATION
Overview: Cellular respiration occurs in three
main stages
1. Glycolysis
2. Krebs Cycle or Citric Acid Cycle
3. Electron Transport Chain or Phosphorylation
– Stage 1:
Glycolysis
– No oxygen needed. It is universal
•
•
Occurs in the cytoplasm
Breaks down glucose into pyruvate, producing
a small amount of ATP (2)
GLYCOLYSIS
• Where?: In the cytosol of all cells.
Both aerobic and anaerobic respiration begin with glycolysis.
• What happens?: The cell harvests energy by oxidizing glucose
to pyruvate.
• One molecule of glucose (6 carbons) is converted to two
pyruvate molecules (3 carbons) through a series of 10 reactions
mediated by enzymes.
• Result:
2 pyruvate molecules (each with a 3 carbon backbone)
2 NADH molecules. Carrier that picks up hydrogens
stripped from glucose.
2 ATP molecules. 4 are made but cells use 2 to start
glycolysis so net gain is 2
An overview of cellular respiration
Preparatory steps to enter the Krebs cycle
• The 2 pyruvate molecules enter the mitochondrion
and an enzyme strips one carbon from each
pyruvate.
• This two carbon molecule is picked up by Coenzyme A in preparation for the Krebs cycle.
• This is acetyl CoA. This is what enters the Krebs
cycle:
C-C-CoA (oxaloacetate)
Stage 2 :
The citric acid cycle or Krebs cycle
•
•
•
•
Takes place in the mitochondria
Completes the breakdown of glucose (catabolism),
producing a small amount of ATP (2ATP)
Pyruvate is broken down to carbon dioxide
More coenzymes are reduced .Supplies the third
stage of cellular respiration with electrons (hydrogen
carriers such as NADH)
KREBS CYCLE or citric
acid cycle
• This cycle involves a series of 8 steps forming and
rearranging. Each time it releases CO2 and NADH
carries hydrogen to the last step.
6 CO2 are given off as waste (this is the most oxidized
form of Carbon)
In total:
6 CO2
6 NADH are produced and
2 FADH and only
2 ATP
An overview of cellular respiration
Stage 3:
Oxidative phosphorylation or electron transport
chain
•
•
•
Occurs in the mitochondria (inner membrane)
Uses the energy released by “falling” electrons to
pump H+ across a membrane
Harnesses the energy of the H+ gradient through
chemiosmosis, producing ATP
Chemiosmosis
Chemiosmosis is an energy coupling mechanism that uses
energy stored on H+
Chemiosmosis is the coupling of the REDUX reactions of
the electron transport chain to ATP synthesis
– NADH passes electrons to an electron transport
chain
– As electrons “fall” from carrier to carrier and finally
to O2
•
Energy is released in small quantities
NADH
NAD
+
H
+
ATP
2e

+
Controlled
release of
energy for
synthesis
of ATP

2 H
+
2e
1
2
H2O
Figure 6.5C
O2
ELECTRON TRANSPORT CHAIN
• Electron transport systems are embedded (protein
molecules) in inner mitochondrial membranes (cristae)
• NADH and FADH2 give up electrons that they
picked up in earlier stages to electron transport
system
• Electrons are transported through the system
• The final electron acceptor is oxygen. The
hydrogen combines with the oxygen to form water
Electron transport chain
H+
H+
H+
H+
+
.
H
H+
Protein
complex
H+
Electron
carrier
Intermembrane
space
H+
H+
ATP
synthase
Inner
mitochondrial
membrane
FADH2
Electron
flow
NADH
FAD
NAD+
+
H
1
O + 2 H+
2 2
+
Mitochondrial
matrix
H
H+
Electron Transport Chain
OXIDATIVE PHOSPHORYLATION
Figure 6.10
H2O
ADP
+
P
ATP
H+
Chemiosmosis
HOW MUCH TOTAL ATP(ENERGY) WAS
PRODUCED?
• Glycolysis
2 ATP formed by substrate-level phosphorylation
• Krebs cycle and preparatory reactions
2 ATP formed by substrate-level phosphorylation
• Electron transport phosphorylation
32-34 ATP formed
2+2+34=38
Most ATP production occurs by oxidative
phosphorylation or electron transport chain
WHY OXYGEN?
• Electron transport phosphorylation requires
the presence of oxygen
• Oxygen withdraws spent electrons from the
electron transport system, then combines
with H+ to form water
Web site tutorials to check:
• http://www.sp.uconn.edu/~terry/Comm
on/respiration.html
• http://www2.nl.edu/jste/electron_trans
port_system.htm
• http://www.wisconline.com/objects/MBY2604/MBY2604.s
wf
An overview of cellular respiration
An overview of cellular respiration
Animation: Cell Respiration Overview
How efficient is cellular respiration?
• Only about 40% efficient.
In other words, a call can harvest about 40% of the
energy stored in glucose.
• Most energy is released as heat
Evolution of cellular respiration
• When life originated, atmosphere had little oxygen
• Earliest organisms used anaerobic pathways
• Later, photosynthesis increased atmospheric
oxygen
• Cells arose that used oxygen as final acceptor in
electron transport (without oxygen to act as the final
hydrogen acceptor the cells will die)
Fermentation
• Fermentation allows some cells to produce
ATP without oxygen.
• This is Anaerobic respiration
ANAEROBIC RESPIRATION
Fermentation is an anaerobic alternative
to cellular respiration
• Do not use oxygen
• Produce less ATP( 2) than aerobic pathways
• Two types. One produces alcohol and the
other lactic acid as waste products
– Fermentation pathways
– Anaerobic electron transport
Fermentation
– Under anaerobic conditions, many kinds of cells
can use glycolysis alone to produce small amounts of ATP
• Begin with glycolysis
• Do not break glucose down completely to carbon
dioxide and water
• Yield only the 2 ATP from glycolysis
• Steps that follow glycolysis serve only to regenerate
NAD+
Yeast
• Single-celled fungi
• Carry out alcoholic fermentation
• Saccharomyces cerevisiae
– Baker’s yeast
– Carbon dioxide makes bread dough rise
• Saccharomyces ellipsoideus
– Used to make beer and wine
Our muscle cells…
• In the absence of oxygen our muscles can
carry out fermentation, but the pyruvate
from glycolysis is turned into lactic acid
instead of alcohol
– In alcohol fermentation
•
2
NAD+
NADH is oxidized to NAD+ while converting
pyruvate to CO2 and ethanol
2 NADH
2 NADH
2
NAD+
GLYCOLYSIS
2 ADP + 2 P
Glucose
2
2
ATP
2 Pyruvate
CO2 released
2 Ethanol
Figure 6.13B
Figure 6.13C
More details…
Two stages of glycolysis
• Energy-requiring steps
– ATP energy activates glucose and its six-carbon
derivatives
• Energy-releasing steps
– The products of the first part are split into
three-carbon pyruvate molecules
– ATP and NADH form
•Glycolysis harvests chemical energy by
oxidizing glucose to pyruvate
– In glycolysis, ATP is used to prime a glucose
molecule
•
Which is split into two molecules of pyruvate
2
NAD+
2
NADH
+ 2
H+
Glucose
2 Pyruvate
2 ADP
Figure 6.7A
+2
P
2
ATP
– In the first phase of glycolysis
•
ATP is used to energize a glucose molecule,
which is then split in two
Steps 1 – 3 A fuel molecule is energized,
using ATP.
Glucose
ATP
PREPARATORY PHASE
(energy investment)
Step
1
ADP
P
Glucose-6-phosphate
P
Fructose-6-phosphate
P
Fructose-1,6-diphosphate
2
ATP
3
ADP
P
Step 4 A six-carbon intermediate splits
into two three-carbon intermediates.
Figure 6.7C
4
– In the second phase of glycolysis
•
ATP, NADH, and pyruvate are formed
P
Step 5 A redox reaction generates
6
9
NADH.
NAD
P
+
5
+
5
P 6 NADH
+H+
P
P
NADH
+H+
P
Steps 6 – 9 ATP and pyruvate
are produced.
NAD
Glyceraldehyde-3-phosphate
(G3P)
ADP
P
6
P 1,3-Diphosphoglycerate
ADP
6
ATP
7
6
ATP
P
P
7
P
8
8
H2O
7
P 3-Phosphoglycerate
7
8
2-Phosphoglycerate
8
H2O
P
P
9
ADP
Phosphoenolpyruvate
(PEP) 9
ADP
9
ATP
ENERGY PAYOFF PHASE
9
ATP
Pyruvate
Net Energy Yield from Glycolysis
Energy requiring steps:
2 ATP invested
Energy releasing steps:
2 NADH formed
4 ATP formed
Glycolysis net yield is 2 ATP and 2 NADH
Preparatory reactions before the Krebs cycle
• Preparatory reactions
– Pyruvate is oxidized into two-carbon acetyl units and
carbon dioxide
– NAD+ is reduced
pyruvate + coenzyme A + NAD+
acetyl-CoA + NADH + CO2
• One of the carbons from pyruvate is released in CO2
• Two carbons are attached to coenzyme A and continue
on to the Krebs cycle
Pyruvate is gets ready for the citric acid cycle
– Prior to the citric acid cycle
•
Enzymes process pyruvate, releasing CO2 and
producing NADH and acetyl CoA
NAD+
NADH
CoA
2
Pyruvate
Acetyl CoA
(acetyl coenzyme A)
1
Figure 6.8
+ H+
CO2
3
Coenzyme A
Krebs cycle
– The acetyl units are oxidized to carbon dioxide
– NAD+ and FAD are reduced
Products:
•
•
•
•
•
Coenzyme A
2 CO2
3 NADH
FADH2
ATP
The citric acid cycle (Krebs)completes the oxidation
of organic fuel (glucose), generating many NADH and
FADH2 molecules
– In the citric acid cycle
•
The two-carbon acetyl part of acetyl CoA is oxidized
Acetyl CoA
CoA
CoA
CITRIC ACID CYCLE
2 CO2
3 NAD+
FADH2
3 NADH
FAD
+
3 H+
ATP
Figure 6.9A
ADP + P
Krebs Cycle or Citric Acid Cycle
For each turn of the Krebs cycle
•
Two CO2 molecules are released (All of the
carbon molecules in pyruvate end up in carbon dioxide)
• Three NADH and one FADH2
(Coenzymes are
reduced, they pick up electrons and hydrogen)
• One molecule of ATP is formed for each
turn so the net yield of ATP for the Krebs
or Citric Acid cycle is 2 ATP molecules.
What happened to co-enzymes (NAD and FAD) during the
first two stages?
Co-enzymes were reduced (gained electrons)
• Glycolysis
• Preparatory
reactions
• Krebs cycle
2 NADH
2 FADH2 + 6 NADH
• Total
2 FADH2 + 10 NADH
2 NADH
Most ATP production occurs by oxidative
phosphorylation or electron transport chain
– Electrons from NADH and FADH2
•
Travel down the electron transport chain to oxygen,
which picks up H+ to form water
– Energy released by the redox reactions
•
Is used to pump H+ into the space between the
mitochondrial membranes
ELECTRON TRANSPORT CHAIN OR
PHOSPHORYLATION
• Takes place in the mitochondria
• Coenzymes deliver electrons to electron
transport systems
• Electron transport sets up H+ ion gradients
• Flow of H+ down gradients powers ATP
formation
• The net yield from oxidative
phosphorilation is 32 to 34 ATP molecules
Making ATP : Chemiosmotic model
– In chemiosmosis, the H+ diffuses back through the
inner membrane through ATP synthase complexes
•
Driving the synthesis of ATP
H+
H+
H+
H+
+
.
H
H+
Protein
complex
H+
Electron
carrier
Intermembrane
space
H+
H+
ATP
synthase
Inner
mitochondrial
membrane
FADH2
Electron
flow
NADH
FAD
NAD+
+
H
1
O + 2 H+
2 2
+
Mitochondrial
matrix
H
H+
Electron Transport Chain
OXIDATIVE PHOSPHORYLATION
Figure 6.10
H2O
ADP
+
P
ATP
H+
Chemiosmosis
Certain poisons interrupt critical events in
cellular respiration
– Various poisons
•
•
•
Block the movement of electrons
Block the flow of H+ through ATP synthase
Allow H+ to leak through the membrane
Cyanide,
carbon monoxide
Rotenone
H+
H+
H+
Oligomycin
H+
H+
H+
H+ H+ H+
ATP
Synthase
DNP
FAD
FADH2
1 O2 + 2 H+
2
NAD+
NADH
H+
H+
H2O
ADP + P
ATP
+
H
Electron Transport Chain
Figure 6.11
Chemiosmosis
•Review: Each molecule of glucose yields many
molecules of ATP
– Oxidative phosphorylation, using electron transport
and chemiosmosis
•
Produces up to 38 ATP molecules for each glucose
molecule that enters cellular respiration
Electron shuttle
across membrane
Cytoplasm
Mitochondrion
2 NADH
2 NADH
(or 2 FADH2)
2 NADH
GLYCOLYSIS
2
Glucose
Pyruvate
2 Acetyl
CoA
+ 2 ATP
by substrate-level
phosphorylation
CITRIC ACID
CYCLE
+ 2 ATP
by substrate-level
phosphorylation
Maximum per glucose:
Figure 6.12
6 NADH
About
38 ATP
2 FADH2
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
+ about 34 ATP
by oxidative phosphorylation
Anaerobic Electron Transport
• Carried out by certain bacteria
• Electron transport system is in bacterial
plasma membrane
• Final electron acceptor is compound from
environment (such as nitrate), NOT oxygen
• ATP yield is almost as good as from aerobic
respiration
INTERCONNECTIONS BETWEEN
MOLECULAR BREAKDOWN AND
SYNTHESIS
• Cells use many kinds of organic molecules
as fuel for cellular respiration
– Carbohydrates, fats, and proteins can all fuel
cellular respiration
•
When they are converted to molecules that enter
glycolysis or the citric acid cycle
Food, such as
peanuts
Carbohydrates
Fats
Sugars
Glycerol
Proteins
Fatty acids
Amino acids
Amino
groups
Glucose
G3P
Pyruvate
Acetyl
CoA
GLYCOLYSIS
ATP
Figure 6.14
CITRIC
ACID
CYCLE
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
How is energy obtained from proteins?
• Proteins are broken down to amino acids
• Amino acids are broken apart
• Amino group is removed, ammonia forms, is
converted to urea and excreted
• Carbon backbones can enter the Krebs cycle
How do we get energy from fats?
• Most stored fats are triglycerides
• Triglycerides are broken down to glycerol and
fatty acids
• Glycerol is converted to PGAL, an intermediate of
glycolysis
• Fatty acids are broken down and converted to
acetyl-CoA, which enters Krebs cycle
LE 9-19
Proteins
Carbohydrates
Amino
acids
Sugars
Glycerol Fatty
acids
Glycolysis
Glucose
Glyceraldehyde-3- P
NH3
Fats
Pyruvate
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation
• Food molecules provide raw materials for
biosynthesis
– Cells use some food molecules and intermediates from
glycolysis and the citric acid cycle as raw materials
– This process of biosynthesis
•
Consumes ATP
ATP needed to drive biosynthesis
ATP
CITRIC
ACID
CYCLE
GLUCOSE SYNTHESIS
Acetyl
CoA
Pyruvate
G3P
Glucose
Amino
groups
Amino acids
Proteins
Fatty
acids
Glycerol
Fats
Cells, tissues, organisms
Figure 6.15
Sugars
Carbohydrates
• The fuel for respiration ultimately comes from
photosynthesis
– All organisms
•
Can harvest energy from organic molecules
– Plants, but not animals
•
Can also make these molecules from inorganic sources by the
process of photosynthesis
Figure 6.16
Electrons “fall” from organic molecules to
oxygen during cellular respiration
• In cellular respiration, glucose and other fuels are
oxidized, releasing energy.
• In the summary equation of cellular respiration:
C6H12O6 + 6O2  6CO2 + 6H2O+ ATP
• Glucose is oxidized (loses electrons), oxygen is
reduced ( gains electrons)
• Cellular respiration does not oxidize glucose in a
single step that transfers all the hydrogen in the
fuel to oxygen at one time.
glucose is broken down gradually in a series of
steps, each catalyzed by a specific enzyme