BISC 101 Lecture Notes - Lecture 11: Citric Acid Cycle, Acetyl-Coa, Oxidative Phosphorylation
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13 Jul 2015
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BSC 101 – Lecture 11 – Cellular Respiration
Life is Work
•Living cells require energy from outside sources
•Some animals, such as the giant panda, obtain energy by eating plans, and
some animals feed on other organisms that eat plants
•Energy flows into an ecosystem as sunlight and leaves as heat
•Photosynthesis: Generates O2 and organic molecules, which are used in cellular
respiration
•Cells use chemical energy stored in organic molecule to regenerate ATP which
powers work
•Glucose is used to produce ATP through either cellular respiration or
fermentation
•Cellular respiration is much more efficient than fermentation
Catabolic Pathways Yield Energy (ATP) By Oxidizing Organic Fuels
•Cellular Respiration: Set of metabolic reactions and processes that take place in
the cells of organisms to convert biochemical energy from nutrients into ATP, and
then release waste products
oSet of catabolic reactions
oExergonic = Spontaneous and favorable
oMore energy in the reactants than products
•Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful
to trace cellular respiration with the sugar glucose
C6H12O6 + 6O2 6CO2 + 6H20 + Energy (ATP + Heat)
Redox Reactions: Oxidation and Reduction
•The transfer of electrons during chemical reactions releases energy stored in
organic molecules
•Oxidation – Reduction Reactions or Redox Reactions: Chemical reactions that
transfer electrons between reactions
•Oxidation: A substance loses electrons and is oxidized
•Reduction: A substance gains electrons and is reduced
Ex: Na + Cl Na+ + Cl-
oNa becomes oxidized as it loses an electron
oCl becomes reduced as it gains an electron
•Chemists definition of redox reaction refers to molecules losing or gaining
electrons
oOIL RIG: Oxidation Is Losing, Reduction is Gaining
oLEO says GER: Losing Electrons is Oxidation, Gain of Electrons is
Reduction
•In addition, biologists use this concept with respect to molecules losing or gaining
hydrogen atoms
•Reducing Agent: The electron (or H atom) donor; oxidized
•Oxidizing Agent: The electron (or H atom) receptor or receiver; reduced
Oxidation of Organic Fuel Molecules During Cellular Respiration
•During cellular respiration, the fuel (such as glucose) is oxidized, and O2 is
reduced
C6H12O6 + 6O2 6CO2 + 6H2O + Energy
•Glucose is the reducing agent
oIt is oxidized or undergoing oxidation
•Oxygen is the oxidizing agent
oIt is reduced or undergoing reduction
•In cellular respiration, glucose and other organic molecules are broken down in a
series of steps
The Stages of Cellular Respiration
•Cellular respiration has three stages
1. Glycolysis: Breaks down one molecule of glucose into two molecules of pyruvate
acid
•Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
•Pyruvate: Three – carbon molecule
•Involves a series of 10 enzyme – catalyzed reactions
•Besides 2 pyruvate, net products also include 2 ATP, 2 NADH, and 2H+
•ATP is not produced, it is only used here
•NAD+ : Co – enzyme that accepts electrons in order to become NADH
•NADH can give up its electrons to become NAD+
•Glycolysis occurs in cytoplasm or cytosol of eukaryotes
2. Citric Acid Cycle: Completes the breakdown of glucose
•The pyruvate produced by glycolysis is transported from the cytosol (cytoplasm)
into the mitochondria
•Pyruvate enters into the inner layer of the mitochondria by moving through a
membrane protein called the pyruvate carrier
•Active transport – requires energy
•The citric acid cycle completes the energy – yielding oxidation of organic
molecules
•Inside the mitochondrion, pyruvate reacts with a compound called coenzyme A
(CoA)
•Pyruvate reacts with CoA to produce acetyl CoA
•Before the citric acid cycle can begin, pyruvate must be converted to acetyl co –
enzyme (acetyl CoA), which links the cycle to glycolysis
oGlucose broken down into 2 molecules after glycolysis, so this means
that 2CO2, 2NADH, and 2 Acetyl CoA are produced