2016
Chapter 9: Cellular Respiration
From Topic 2.1 Understanding:
• Anabolism is the synthesis of complex molecules from simpler molecules including the formation of macromolecules from monomers by condensation reactions.
• Catabolism is the breakdown of complex molecules into simpler molecules including the hydrolysis of macromolecules into monomers.
From Topic 2.8
Essential idea: Cell respiration supplies energy for the functions of life.
Nature of science: Assessing the ethics of scientific research—the use of invertebrates in respirometer experiments has ethical implications (4.5). Skill: Analysis of results from experiments involving measurement of
respiration rates in germinating seeds or invertebrates using a respirometer.
Understandings:
• Cell respiration is the controlled release of energy from organic compounds to produce ATP.
• ATP from cell respiration is immediately available as a source of energy in the cell.
• Anaerobic cell respiration gives a small yield of ATP from glucose.
• Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose.
Applications and skills:
• Application: Use of anaerobic cell respiration in yeasts to produce ethanol and carbon dioxide in baking.
• Application: Lactate production in humans when anaerobic respiration is used to maximize the power of muscle contractions.
Guidance:
• Details of the metabolic pathways of cell respiration are not needed but the substrates and final waste products should be known.
• There are many simple respirometers which could be used. Students are expected to know that an alkali is used to absorb CO2, so reductions in volume are due to oxygen use. Temperature should be kept constant to avoid volume changes due to temperature fluctuations.
Aim 8: The ethics of the use of animals in experiments could be discussed in relation to respirometer experiments. Large-scale use of food plants for biofuels and the resulting impact on food prices has ethical implications.
From Topic 8.2
Nature of science: Paradigm shift—the chemiosmotic theory led to a paradigm shift in the field of bioenergetics (2.3)
Understandings:
• Cell respiration involves the oxidation and reduction of electron carriers.
• Phosphorylation of molecules makes them less stable.
• Energy released by oxidation reactions is carried to the cristae of the mitochondria by reduced NAD and FAD.
• The structure of the mitochondrion is adapted to the function it performs.
• In glycolysis, glucose is converted to pyruvate in the cytoplasm. • Glycolysis gives a small net gain of ATP without the use of oxygen.
• In aerobic cell respiration pyruvate is decarboxylated and oxidized, and converted into acetyl compound and attached to coenzyme A to form acetyl coenzyme A in the link reaction. • In the Krebs cycle, the oxidation of acetyl groups is coupled to the reduction of hydrogen carriers, liberating carbon dioxide. • Transfer of electrons between carriers in the electron transport chain in the membrane of the cristae is coupled to proton
pumping.
• In chemiosmosis protons diffuse through ATP synthase to generate ATP.
Chapter 9: Cellular Respiration
From Topic 8.2
Guidance:
• The names of the intermediate compounds in gylcolysis and the Krebs cycle are not required.
Applications and skills:
• Application: Electron tomography used to produce images of active mitochondria.
• Skill: Analysis of diagrams of the pathways of aerobic respiration to deduce where decarboxylation and oxidation
reactions occur.
Introduction
•
Catabolism:
breaking of
large molecules to smaller
molecules, as a result it
releases stored energy
•
C
6
H
12
O
6
+ 6O
2
6 CO
2
+
6 H
2
O + energy (ATP) and
heat
•
Efficiency
•
Cell @ 40%
•
Car @ 20%
How Energy is Transferred
Cell respiration involves the oxidation and reduction of electron carriers. Energy released by oxidation reactions is carried to the cristae of the mitochondria by reduced NAD and FAD.
•
Energy is transferred in the form of electrons
•
Electrons are transferred through hydrogens (it is the
mechanism for electron transfer)
•
Some energy is stored as phosphate bonds in ATP
•
Hydrogen carriers (NAD+) shuttle electrons in
oxidation-reduction reactions
•
LEO-GER:
- Loss of e- is oxidation
- Gain of e- is reduction.
Electron Carriers: NADH and FADH
2
FADH
2
Generating Energy in the form of ATP
• Phosphorylation of molecules makes them less stable
•
There are two ways for ATP synthesis:
-
Oxidative Phosphorylation
: uses energy from a series
of redox reactions that occurs in the electron transport chain
to produce ATP
-
Substrate Level Phosphorylation
: when an enzyme
Fuel For Respiration
Cell respiration supplies energy for the functions of life. Cell respiration is the controlled release of energy from organic compounds to produce ATP. • ATP from cell respiration is immediately available as a source of energy in the cell.
•
Food is the source of energy (digestion)
Other Sources of “Fuel”
•
Glucose is the best fuel
•
Polysaccharides are broken to release glucose
•
Proteins can be broken down to be Amino acids and then
converted to intermediate products that are broken down
in Krebs.
•
Lipids are broken down to glycerol (to Glycolysis) and fatty
Stages of Cellular Respiration
In glycolysis, glucose is converted to pyruvate in the cytoplasm.• Glycolysis gives a small net gain of ATP without the use of oxygen• In the Krebs cycle, the oxidation of acetyl groups is coupled to the reduction of hydrogen carriers, liberating carbon dioxide. In chemiosmosis protons diffuse through ATP synthase to generate ATP.
.
•
There are three main stages:
•
Glycolysis
•
Krebs Cycle (Citric Acid Cycle)
Glycolysis
In glycolysis, glucose is converted to pyruvate in the cytoplasm. • Glycolysis gives a small net gain of ATP without the use of oxygen.
•
Glycolysis: “splitting of
sugar” occurs in the
cytosol
-
Must invest 2 ATP’s first
-
Produces 4 ATP’s at the
end, but a net gain of 2
ATP’s
-
Followed by “prep”
step, when acetyl CoA
turns to pyruvate
Glycolysis
• In glycolysis, glucose is converted to pyruvate in the cytoplasm. • Glycolysis gives a small net gain of ATP without the use of oxygen.
“Prep” Step
In aerobic cell respiration pyruvate is decarboxylated and oxidized, and converted into acetyl compound and attached to coenzyme A to form acetyl coenzyme A in the link reaction.
•
“Prep” Step: this is not the official name! but we can’t find a
better name for it. Hahah…
-
The conversion of pyruvate to acetyl CoA before entering the Citric Acid
Cycle (aka Krebs/tricarboxylic acid cycle (TCA))
-
Produces two NADH (since there’s two pyruvates that enter and two
“Prep” Step
In aerobic cell respiration pyruvate is decarboxylated and oxidized, and converted into acetyl compound and attached to coenzyme A to form acetyl coenzyme A in the link reaction.
•
“Prep” Step: this is not the official name! but we can’t find a
better name for it. Hahah…
-
The conversion of pyruvate to acetyl CoA before entering the Citric Acid
Cycle (aka Krebs/tricarboxylic acid cycle (TCA))
-
Produces two NADH (since there’s two pyruvates that enter and two
Citric Acid Cycle
•
Citric Acid Cycle
:
- Occurs in the
mitochondrial matrix
- For each Acetyl CoA, 3
Electron Transport Chain and Chemiosmosis
Transfer of electrons between carriers in the electron transport chain in the membrane of the cristae is coupled to proton pumping.
•
Occurs in the inner membrane of the mitochondria between the matrix and the intermembrane
space
•
Transport is carried out by a series of membrane proteins
•
Some carry just electrons, while others take protons with electrons (H+ and e-)
Electron Transport Chain and Chemiosmosis
In chemiosmosis protons diffuse through ATP synthase to generate ATP.
•
Chemiosmosis:
when energy in the form of H+ ions
gradient across a membrane is used to make ATP
Total Energy Yield
Cell respiration is the controlled release of energy from organic compounds to produce ATP.• ATP from cell respiration is immediately available as a source of energy in the cell.
•
A review of Cellular Respiration
Fermentation
• Lactate production in humans when anaerobic respiration is used to maximize the power of muscle contraction • Anaerobic cell respiration gives a small yield of ATP from glucose Use of anaerobic cell respiration in yeasts to produce ethanol and carbon dioxide in baking
•
Fermentation
: w/o O
2
Krebs and ETC cannot occur
- It is an extension of glycolysis in anaerobic conditions
- Can produce ATP by substrate level phosphorylation only
- needs to replenish the NAD+ as an e- carrier to keep it going
•
There are two types:
Fermentation
Use of anaerobic cell respiration in yeasts to produce ethanol and carbon dioxide in baking. Lactate production in humans when anaerobic respiration is used to maximize the power of muscle contractions.
•
Lactic Fermentation
: this causes the pain you feel after
you exercise too much; also used in making cheese and
yogurt
•
Alcoholic Fermentation:
this is used for brewing ,
• Anabolism is the synthesis of complex molecules from simpler molecules including the formation of macromolecules from monomers by condensation reactions.
Nature of science: Assessing the ethics of scientific research—the use of invertebrates in respirometer experiments has ethical implications (4.5).
Skill: Analysis of results from experiments involving measurement of respiration rates in germinating seeds or invertebrates using a respirometer.
• Details of the metabolic pathways of cell respiration are not needed but the substrates and final waste products should be known.
• There are many simple respirometers which could be used. Students are expected to know that an alkali is used to absorb CO2, so reductions in volume are due to oxygen use. Temperature should be kept constant to avoid volume changes due to
temperature fluctuations.
The ethics of the use of animals in experiments could be discussed in relation to respirometer experiments. Large-scale use of food plants for biofuels and the resulting impact on food prices has ethical implications.
Paradigm shift—the chemiosmotic theory led to a paradigm shift in the field of bioenergetics (2.3) • Phosphorylation of molecules makes them less stable.
• Energy released by oxidation reactions is carried to the cristae of the mitochondria by reduced NAD and FAD. • The structure of the mitochondrion is adapted to the function it performs.
• Transfer of electrons between carriers in the electron transport chain in the membrane of the cristae is coupled to proton pumping.
• Oxygen is needed to bind with the free protons
