BISC 101 Lecture Notes - Lecture 11: Citric Acid Cycle, Acetyl-Coa, Oxidative Phosphorylation

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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
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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
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