Notes – Aerobic respiration - Krebs Cycle Biology
Aerobic respiration – Krebs cycle
Objectives - SWBAT
Describe the major events of aerobic respiration
Describe the 1 and 2 phases of aerobic respiration
st nd
Terms to remember:
Reduction – the addition of electrons to an atom or ion
Oxidation – the loss of an electron from an atom or ion
Aerobic respiration – the breakdown of pyruvate in the presence of oxygen
Occurs inside mitochondria
ATP produced in two pathways – Krebs cycle and electron transport chain (see Figure 6.12)
st
1 step of aerobic respiration
Pyruvate (3-carbon) binds to coenzyme A (CoA)
one carbon in form of CO2 released
two carbon molecule called acetyl-CoA formed
molecule of NAD+ reduced to become NADH
NAD+ = nicotinamide adenine dinucleotide
Pyruvate + NAD+ + CoA ----- Acetyl-CoA + NADH + CO2
high-energy electrons contained in reduced NADH and FADH2 later used to convert ADP to ATP
in the electron transport chain
CO2 diffuses from the cell and eventually expelled through breathing
nd
acetyl-CoA enters 2 phase of aerobic respiration – Krebs Cycle
Krebs Cycle (2nd step of aerobic respiration)
nd
series of oxidation reactions that make up the 2 phase of aerobic respiration
named after discoverer – Hans Krebs
also called citric acid cycle because first reaction forms the 6-carbon compound citric acid
see Figure 6.13
Overall cycle
Acetyl-Co binds to a 4 -carbon compound present in mitochondria produces citric acid
Citric acid passes through series of oxidation reactions that free electrons and remove 2 carbons;
released carbon units with oxygen and diffuse from mitochondria as CO 2
Remaining 4 -carbon molecule eventually binds with another acetyl-CoA, starting the cycle all over
again
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Notes – Aerobic respiration - Krebs Cycle Biology
Freed electrons reduce 3 molecules of NAD+ to NADH and one molecule of FAD to FADH2
FAD = flavin adenine dinucleotide
FAD and NAD+ are electron-carriers
FAD = flavin adenine dinucleotide
High-energy electrons contained in reduced carriers NADH and FADH2 are used to generate ATP
in the electron transport chain (the next step of aerobic respiration)
Yields – one glucose yields:
4 ATP
10 NADH
2 FADH2
Aerobic respiration - net 36 molecules of ATP maximum
(includes - glycolysis, Krebs cycle, electron transport chain)
Each molecule of glucose produces 2 aceytl-CoA
Therefore, one molecule of glucose provide reactants (acetyl-CoA) for two turns of the Krebs cycle
– one turn for each molecule of acetyl-CoA
Questions
Compare the roles of NADH, FADH2 and ATP in aerobic respiration. How are they similar? How are
they different?
All are involved in the release or transfer of energy.
NADH and FADH2 transfer energy in the form of high-energy hydrogens. Energy in ATP is
released when phosphate bonds break.
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